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Jablonská, Jana, and Milada Kozubková. "Diagnostics of Resistance Coefficients and Cavitation of Flow Control Valve." Applied Mechanics and Materials 752-753 (April 2015): 980–87. http://dx.doi.org/10.4028/www.scientific.net/amm.752-753.980.
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The paper deals with the determination of characteristic as dependence of the valve pressure drop on the flow rate, flow characteristic and cavitation conditions in case of water flow in the flow control valve. Emphasis is put on the utilization of simple, available relationships and measuring for identification of the basic valve coefficients, e.g. loss coefficient, flow rate coefficient and cavitation factor. These coefficients are used for designing of pipe circuits. In this paper there is defined methodology for determining those coefficients and is applied to the modified cone of flow control valve for verification the linear flow characteristic. It is necessary to consider the fact that in various countries the modifications of coefficients are preferred and it is therefore necessary to specify them.
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Yu, Y. H., and W. W. Blessing. "Cutaneous vasoconstriction in conscious rabbits during alerting responses detected by hippocampal theta-rhythm." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 272, no. 1 (January 1, 1997): R208—R216. http://dx.doi.org/10.1152/ajpregu.1997.272.1.r208.
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We determined whether alerting stimuli cause cutaneous vasoconstriction in conscious rabbits. We compared ear blood flow with renal, mesenteric, and femoral flows at rest and in response to nonnoxious alerting stimuli, which induced theta-rhythm (4-9 Hz) in the simultaneously recorded hippocampal electroencephalogram (EEG). theta-Inducing stimuli (e.g., whistles and fur touches) reduced ear flow by 95 +/- 6%, commencing 1-2 s after the EEG change and lasting 45 s. Renal flow did not significantly change with alerting stimuli, mesenteric and femoral flows slightly decreased, arterial pressure transiently rose (+10 +/- 3 mmHg), and heart rate fell (+43 +/- 9 beats/min). At rest, the coefficient of variation for ear flow (62 +/- 6%) was greater than for other flows (P < 0.01). Phentolamine (1 mg/kg iv) reduced this coefficient to 29 +/- 4% (P < 0.01). Our study demonstrates that alerting responses in conscious rabbits are associated with selective cutaneous vasoconstriction, without increase in flow to skeletal muscle.
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George, S. C., A. L. Babb, and M. P. Hlastala. "Dynamics of soluble gas exchange in the airways. III. Single-exhalation breathing maneuver." Journal of Applied Physiology 75, no. 6 (December 1, 1993): 2439–49. http://dx.doi.org/10.1152/jappl.1993.75.6.2439.
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The exchange characteristics of a highly soluble gas with the pulmonary airways during a single-exhalation maneuver were analyzed using a mathematical model previously described by our group (M. E. Tsu et al. Ann. Biomed. Eng. 16: 547–571, 1988). The model integrates the simultaneous exchange of water, heat, and a soluble gas with the pulmonary airways. The purpose of this paper is to provide experimental data for model validation. Exhaled ethyl alcohol concentration profiles of human subjects were measured with an Intoxilyzer 5000 and were plotted against exhaled volume measured with a wedge spirometer. Each subject performed a series of breathing maneuvers in which exhalation flow rate was the only variable. Phase III has a positive slope (0.047 +/- 0.0089 mol alcohol in air.mol alcohol in alveolus-1.l-1) that is statistically independent (P > 0.05) of flow rate. Reducing the molecular diffusion coefficient of alcohol in the nonperfused tissue layer improves the fit of the model to the experimental data. The optimal diffusion coefficient of alcohol for all subjects was 12 +/- 5.3 (SD) x 10(-7) cm2/s, which is 8% of the diffusion coefficient of alcohol in water (1.6 x 10(-5) cm2/s). We concluded that the experimental data showing a positive slope of the exhaled alcohol profile are consistent with a reduced diffusivity of alcohol in the respiratory mucosa. The reduced diffusion coefficient enhances reabsorption of alcohol by the airways on exhalation and creates a positive phase III slope.
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Loukam, Imed, Bachir Achour, and Lakhdar Djemili. "Chezy’s resistance coefficient in an egg-shaped conduit." Journal of Water and Land Development 37, no. 1 (June 1, 2018): 87–96. http://dx.doi.org/10.2478/jwld-2018-0028.
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Abstract When calculating uniform flows in open conduits and channels, Chezy’s resistance coefficient is not a problem data and its value is arbitrarily chosen. Such major disadvantage is met in all the geometric profiles of conduits and channels. Knowing the value of this coefficient is essential to both the design of the channel and normal depth calculation. The main objective of our research work is to focus upon the identification of the resistance coefficient relationship. On the basis of the rough model method (RMM) for the calculation of conduits and channels, a general explicit relation of the resistance coefficient in turbulent flow is established with different geometric profiles, particularly the egg-shaped conduit. Chezy’s resistance coefficient depends strongly on the filling rate, the discharge, the longitudinal slope, the absolute roughness of the internal walls of the conduit and the kinematic viscosity of the liquid. Moreover, in this work, a simplified method is presented to determine Chezy’s resistance coefficient with a limited number of data, namely the discharge, the slope of the conduit, the absolute roughness and the kinematic viscosity. Last but not least, after studying the variation of Chezy’s resistance coefficient as a function of the filling rate, an equally explicit expression is given for the easy calculation of this coefficient when its maximum value is reached. Examples of calculation are suggested in order to show how the Chezy’s coefficient can be calculated in the egg-shaped conduit.
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Rup, Kazimierz, Lukasz Malinowski, and Piotr Sarna. "Indirect measurement of the flow rate based upon a solution of an inverse coefficient problem." International Journal of Numerical Methods for Heat & Fluid Flow 28, no. 1 (January 2, 2018): 92–102. http://dx.doi.org/10.1108/hff-10-2016-0405.
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Purpose The purpose of this paper is to extend the possibilities of using the earlier developed indirect method of fluid flow rate measurement in circular pipes to the square-section channels with elbows installed. Design/methodology/approach The idea of the method is based on selecting such a value of the Reynolds number assumed as a coefficient in fluid flow equations, which fulfills with set accuracy the condition of equality between the measured and computed pressure difference at the end points of the secant of the elbow arch. The numerical calculus takes into consideration the exact geometry of the flow space and the measured temperature of the fluid, on the basis of which its thermo–physical properties are determined. To implement the proposed method in practice, a special test stand was built. The numerical computations were carried out using the software package FLUENT. Findings The results of calculations were compared with corresponding results of measurements achieved on the stand, as well as those found in the literature. The comparative analysis of the obtained numerical and experimental results shows a high grade of consistence. Practical implications The discussed elbow flow meter, implementing the extended indirect measuring method, can be applied to determine the flow rate of gases, as well as liquids and suspensions. Originality/value The indirect method used to measure the volumetric flow rate of the fluid is characterized by high accuracy and repeatability. The high accuracy is possible because of a very realistic mathematical model of the complex flow in the curved duct. The indirect method eliminates the necessity of frequent calibration of the flow meter. The discussed extended indirect measuring method can be applied to determine the flow rate of gases as well as liquids and suspensions. The fluid flow rate measurement based on the method considered in this paper can be particularly useful in newly designed as well as already operated ducts.
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Chen, Kang Ping, and Di Shen. "Drainage flow of a viscous compressible fluid from a small capillary with a sealed end." Journal of Fluid Mechanics 839 (February 2, 2018): 621–43. http://dx.doi.org/10.1017/jfm.2018.56.
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Volumetric expansion driven drainage flow of a viscous compressible fluid from a small capillary with a sealed end is studied in the low Mach number limit using the linearized compressible Navier–Stokes equations with no-slip condition. Density relaxation, oscillation and decay as well as the velocity field are investigated in detail. It is shown that fluid drainage is controlled by the slow decay of the standing acoustic wave inside the capillary; and the acoustic wave retards the density diffusion by reducing the diffusion coefficient of the density envelope equation by one half. Remarkably the no-slip flow exhibits a slip-like mass flow rate. The period-averaged mass flow rate at the exit (drainage rate) is found proportional to the fluid’s kinematic viscosity via the density diffusion coefficient and the average drainage speed is independent of the capillary radius. These findings are valid for arbitrarily small capillaries as long as the continuum assumption holds and they are in stark contrast to the classical lubrication based theory. Generalization to a capillary with a sound absorbing end is achieved by a simple model. The reported results offer new insights to the nature of slow viscous compressible flows in very small capillaries.
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Jalal M. Jalil, Jalal M. Jalil. "CFD Simulation for a Road Vehicle Cabin." journal of King Abdulaziz University Engineering Sciences 18, no. 2 (January 1, 2007): 129–48. http://dx.doi.org/10.4197/eng.18-2.7.
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A numerical study of a two-dimensional, turbulent, recirculating flow within a passenger car cabin is presented. The study is based on the solution of the elliptic partial differential equations representing conservation of mass, momentum, temperature, turbulence energy and its dissipation rate in finite volume form. Algebraic expressions for the turbulent viscosity and diffusion coefficients are calculated using the two-equation model(k − ε). Different parameters are considered to illustrate their influences on the flow filed and temperature distribution inside car cabin. These parameters include number and location of the air conditioning systems inlets inside car cabin, different air temperatures at the inlets, different air velocities at the inlets, different solar intensity during day-time for a certain day of the year, different diffuse solar radiation (variation in the kind of car glass). Generally, the results indicate some of negative effects such as development of zones of low air circulation. Also it is found that the number of inlets inside car cabin play an important role in determining car air conditioning system efficiency. Moreover, the air temperature and velocity at inlets play an important role in determining cabin climate. The results are used to enhance the understating of the airflow fields within a road vehicle passenger cabin.
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Manley, Harold J., Darcie L. Bridwell, Rowland J. Elwell, and George R. Bailie. "Influence of Peritoneal Dialysate Flow Rate on the Pharmacokinetics of Cefazolin." Peritoneal Dialysis International: Journal of the International Society for Peritoneal Dialysis 23, no. 5 (September 2003): 469–74. http://dx.doi.org/10.1177/089686080302300512.
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Objective To determine the impact of dialysate flow rate (DFR) on cefazolin pharmacokinetics (PK) in peritoneal dialysis (PD) patients. Methods A meta-analysis of published reports, identified by MEDLINE search (1966-2002) and other sources, containing information on cefazolin PK data in PD patients was conducted. Data were analyzed based upon low DFR (≤ 5.50 mL/minute) or high DFR (> 5.50 mL/minute). Data available were from North American (NA) ( n = 45) and Singaporean ( n = 10) patients. Complete data sets were available for 33 patients (CDS patients). Data were analyzed with respect to data origin and data set completeness: all patients (ALL), NA, and CDS. Analysis of log-transformed cefazolin PK data was performed to determine coefficient of determination ( r2) between DFR and cefazolin elimination rate constant (kel), clearance total (ClT), and clearance peritoneal (ClPD). Clearance total data were extrapolated to DFR observed in continuous flow PD. Results Published literature provided data on 55 PD patients (12 high DFR, 43 low DFR). Regardless of data origin (ALL, NA, or CDS), a prominent coefficient of determination ( p < 0.0001) existed between DFR and all cefazolin PK data except ClPD. The p value for DFR correlation to ClPD was 0.953, 0.011, and 0.036 for ALL, NA, and CDS patients, respectively. Cefazolin ClT and ClPD increased at higher DFRs. Conclusion These findings demonstrate that an increased DFR leads to an increased rate of cefazolin clearance in NA PD patients. The impact of Asian descent on cefazolin ClPD warrants further investigation. Clinicians dosing cefazolin in PD patients using a higher DFR than that used to determine cefazolin PK should use increased doses or prescribe lower/comparable DFRs. Data are not yet available for patients prescribed very high DFRs ( e.g., continuous flow PD); extrapolation of our results demonstrates significant influences on clearance and risk for underdosing.
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HAMZAH, ESAH, ALI OURDJINI, MUBARAK ALI, PARVEZ AKHTER, MOHD RADZI HJ. MOHD TOFF, and MANSOR ABDUL HAMID. "INFLUENCE OF NITROGEN FLOW RATE ON FRICTION COEFFICIENT AND SURFACE ROUGHNESS OF TiN COATINGS DEPOSITED ON TOOL STEEL USING ARC METHOD." Surface Review and Letters 14, no. 05 (October 2007): 1007–13. http://dx.doi.org/10.1142/s0218625x07010408.
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In the present study, the effect of various N 2 gas flow rates on friction coefficient and surface roughness of TiN -coated D2 tool steel was examined by a commercially available cathodic arc physical vapor deposition (CAPVD) technique. A Pin-on-Disc test was carried out to study the Coefficient of friction (COF) versus sliding distance. A surface roughness tester measured the surface roughness parameters. The minimum values for the COF and surface roughness were recorded at a N 2 gas flow rate of 200 sccm. The increase in the COF and surface roughness at a N 2 gas flow rate of 100 sccm was mainly attributed to an increase in both size and number of titanium particles, whereas the increase at 300 sccm was attributed to a larger number of growth defects generated during the coating process. These ideas make it possible to optimize the coating properties as a function of N 2 gas flow rate for specific applications, e.g. cutting tools for automobiles, aircraft, and various mechanical parts.
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Wan, Stephen, Jason Leong, Te Ba, Arthur Lim, and Chang Wei Kang. "Numerical Characterization of the Performance of Fluid Pumps Based on a Wankel Geometry." Journal of Fluids 2014 (September 30, 2014): 1–7. http://dx.doi.org/10.1155/2014/241010.
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The performance of fluid pumps based on Wankel-type geometry, taking the shape of a double-lobed limaçon, is characterized. To the authors’ knowledge, this is the first time such an attempt has been made. To this end, numerous simulations for three different pump sizes were carried out and the results were understood in terms of the usual scaling coefficients. The results show that such pumps operate as low efficiency (<30%) valveless positive displacements pumps, with pump flow-rate noticeably falling at the onset of internal leakage. Also, for such pumps, the mechanical efficiency varies linearly with the head coefficient, and, within the onset of internal leakage, the capacity coefficient holds steady even across pump efficiency. Simulation of the flow field reveals a structure rich in three-dimensional vortices even in the laminar regime, including Taylor-like counterrotating vortex pairs, pointing towards the utility of these pumps in microfluidic applications. Given the planar geometry of such pumps, their applications as microreactors and micromixers are recommended.
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Yang, WuGang, ZhenCai Yang, KaiGe Wen, ZhaoHui Yang, and YuWen Zhang. "Numerical investigation on the gas entrainment rate on ventilated supercavity body." Journal of Computational Multiphase Flows 8, no. 4 (November 22, 2016): 169–77. http://dx.doi.org/10.1177/1757482x16654021.
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The supercavitation technique provides a means of significantly increasing the velocity of an underwater vehicle. This technique involves essentially the creation of stable supercavity shape. The method of artificial ventilation is most effective for generating and dominating the supercavity. This paper focuses on the numerical simulation of flow field around three-dimensional body. The method is based on the multiphase computational fluid dynamics model combined with the turbulence model and the full cavity model. The fundamental similarity parameters of ventilated supercavity flows that include cavitation number, Froude number Fr, entrainment rate CQ, and drag coefficient Cx are all investigated numerically in the case of steady flow and gravity field. We discuss the following simulations results in three parts: (1) the variations of the cavitation number and the supercavity’s relative diameter with entrainment rate; (2) the drag coefficient versus the cavitation number; and (3) deformation of supercavity axis caused by gravitational effect for three different fixed three Froude numbers. In the full paper, we give the comparison results of the drag reduction ratio among numerical simulation and experiment conducted in hydrodynamic tunnel and towing tank, respectively. We summarize our discussion of gravitational effect on the axis deformation of supercavity as follows: in the case of smaller Froude number, the inclination of the cavity axis increases monotonously with increasing horizontal length and reaches its maximal value at the end of supercavity; this deformation can be almost completely negligible when the Froude number Fr is larger than 7.0. The comparisons with the experimental data in the hydrodynamic tunnel and the towing tank indicate that the present method is effective for predicting the flows around ventilated supercavity; that the numerical results is in good agreement with the experimental ones and that the maximal value of the drag reduction ratio can be expected to reach the value of 90% compared with that of the condition of non-cavitation.
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Nearing, Mark A., Viktor O. Polyakov, Mary H. Nichols, Mariano Hernandez, Li Li, Ying Zhao, and Gerardo Armendariz. "Slope–velocity equilibrium and evolution of surface roughness on a stony hillslope." Hydrology and Earth System Sciences 21, no. 6 (June 30, 2017): 3221–29. http://dx.doi.org/10.5194/hess-21-3221-2017.
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Abstract. Slope–velocity equilibrium is hypothesized as a state that evolves naturally over time due to the interaction between overland flow and surface morphology, wherein steeper areas develop a relative increase in physical and hydraulic roughness such that flow velocity is a unique function of overland flow rate independent of slope gradient. This study tests this hypothesis under controlled conditions. Artificial rainfall was applied to 2 m by 6 m plots at 5, 12, and 20 % slope gradients. A series of simulations were made with two replications for each treatment with measurements of runoff rate, velocity, rock cover, and surface roughness. Velocities measured at the end of each experiment were a unique function of discharge rates, independent of slope gradient or rainfall intensity. Physical surface roughness was greater at steeper slopes. The data clearly showed that there was no unique hydraulic coefficient for a given slope, surface condition, or rainfall rate, with hydraulic roughness greater at steeper slopes and lower intensities. This study supports the hypothesis of slope–velocity equilibrium, implying that use of hydraulic equations, such as Chezy and Manning, in hillslope-scale runoff models is problematic because the coefficients vary with both slope and rainfall intensity.
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Bandhauer, Todd M., Akhil Agarwal, and Srinivas Garimella. "Measurement and Modeling of Condensation Heat Transfer Coefficients in Circular Microchannels." Journal of Heat Transfer 128, no. 10 (March 7, 2006): 1050–59. http://dx.doi.org/10.1115/1.2345427.
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A model for predicting heat transfer during condensation of refrigerant R134a in horizontal microchannels is presented. The thermal amplification technique is used to measure condensation heat transfer coefficients accurately over small increments of refrigerant quality across the vapor-liquid dome (0<x<1). A combination of a high flow rate closed loop primary coolant and a low flow rate open loop secondary coolant ensures the accurate measurement of the small heat duties in these microchannels and the deduction of condensation heat transfer coefficients from measured UA values. Measurements were conducted for three circular microchannels (0.506<Dh<1.524mm) over the mass flux range 150<G<750kg∕m2s. Results from previous work by the authors on condensation flow mechanisms in microchannel geometries were used to interpret the results based on the applicable flow regimes. The heat transfer model is based on the approach originally developed by Traviss, D. P., Rohsenow, W. M., and Baron, A. B., 1973, “Forced-Convection Condensation Inside Tubes: A Heat Transfer Equation For Condenser Design,” ASHRAE Trans., 79(1), pp. 157–165 and Moser, K. W., Webb, R. L., and Na, B., 1998, “A New Equivalent Reynolds Number Model for Condensation in Smooth Tubes,” ASME, J. Heat Transfer, 120(2), pp. 410–417. The multiple-flow-regime model of Garimella, S., Agarwal, A., and Killion, J. D., 2005, “Condensation Pressure Drop in Circular Microchannels,” Heat Transfer Eng., 26(3), pp. 1–8 for predicting condensation pressure drops in microchannels is used to predict the pertinent interfacial shear stresses required in this heat transfer model. The resulting heat transfer model predicts 86% of the data within ±20%.
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Huang, Weidong, and David B. Bogy. "The Effect of the Accommodation Coefficient on Slider Air Bearing Simulation." Journal of Tribology 122, no. 2 (June 8, 1999): 427–35. http://dx.doi.org/10.1115/1.555384.
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In solving the slider air bearing problem, both the Molecular Gas-film Lubrication (MGL) model and the Direct Simulation Monte Carlo (DSMC) model require the accommodation coefficient as input. The accommodation coefficient represents the fraction of the air molecules that interact with solid boundaries in a diffusive manner. In general, the value 1 is used for the accommodation coefficient, which represents a fully diffusive reflection. However, in magnetic hard disk drives, the disk and slider surfaces are becoming ever smoother with different kinds of lubrication on the disk, while the temperature is becoming higher due to the faster spindle speed. Under these conditions the unit value of the accommodation coefficient may no longer be suitable. In order to understand the effect of the accommodation coefficient on the slider’s flying parameters, we used Kang’s new database for the Poiseuille flow rate Qp and Couette flow rate Qc to solve the modified Reynolds equation for two groups of sliders, e.g., negative and positive pressure sliders (“negative” refers to sliders with subambient pressure zones). The results show that, in general, the smaller the accommodation coefficient, the lower the flying height and pitch angle. Positive pressure sliders are more sensitive to the accommodation coefficient than are negative pressure sliders. The typical discrepancy in flying height is around 10%. Also, it is shown that for positive pressure sliders the lower the flying height, the larger the discrepancy percentage. [S0742-4787(00)00402-1]
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Batista, Rafael Oliveira, Rubens Alves de Oliveira, Maria Elidayane da Cunha, Rutilene Rodrigues da Cunha, Jeane Cruz Portela, and Marcelo Tavares Gurgel. "Flow rate variation and biological agents that obstruct drippers of swine effluent." Comunicata Scientiae 9, no. 2 (August 1, 2018): 125–32. http://dx.doi.org/10.14295/cs.v9i2.2658.
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Emitter clogging is the major problem of drip irrigation systems operating with wastewater. The objective of this study was to evaluate the alteration of the flow rate variation coefficient (FVC) and to identify the biological agents that cause obstruction in drip units operating with swine effluent and public water supply. The experiment was set up in a split-plot scheme, with the times of application of swine effluent and public water supply in the main plots and dripper types in the secondary parcels, evaluating times of FVC in the tertiary parcels, using a completely randomized design (CRD) with three repetitions. The FVC of the drip subunits was calculated on every 40 hours as well as the microscopic analysis of the biological agents of clogging, until 160 h. At the end of the tests, biofilm samples were collected in each drip unit to identify the groups of predominant bacteria. The results indicated that the FVC was effective in detecting the clogging of the emitters, evidencing that the construction characteristics and the times of application of swine effluent and of the public water supply interfere in this process. Microscopic analyzes of the biofilm indicated that the main biological agents that caused obstruction were algae, bacteria, fungi and protozoa.
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Shin, Chang-Hwan, Ju-Yong Park, and Wang-Kee In. "Pressure loss coefficient and flow rate of side hole in a lower end plug for dual-cooled annular nuclear fuel." Nuclear Engineering and Design 265 (December 2013): 375–82. http://dx.doi.org/10.1016/j.nucengdes.2013.06.033.
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Andrzejczyk, Rafal, Tomasz Muszynski, and Przemysław Kozak. "Experimental investigation on straight and u-bend double tube heat exchanger with active and passive enhancement methods." MATEC Web of Conferences 240 (2018): 02001. http://dx.doi.org/10.1051/matecconf/201824002001.
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Authors in this work want to demonstrate the possibility to increase the heat transfer efficiency by using simple wire coil inserts to create turbulent flow in the boundary layer as well as air blowing into the annulus of the pipe. In the study, Wilson plot approach was applied in order to estimate heat transfer coefficients for all heat exchanger (HX) configurations. The study focuses on experimental values of heat transfer coefficient (HTC) and pressure drops. The primary objectives of the work are to: I. Provide an experimental comprehensive database for HTC and pressure drops; II. Analysis effect of different flow conditions e.g. water mass flow rate, the void fraction on heat transfer and hydraulic performance of tested elements. III. Compare influences of both passive and active methods at the efficiency of simple heat exchangers constructions; IV. Validation experimental results with selected experimental models from the open literature.
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Dong, Chenhao, Rongguo Ma, Yujie Yin, Borui Shi, Wanting Zhang, and Yidan Zhang. "Traffic Conflict Analysis of Motor Vehicles and Nonmotor Vehicles Based on Improved Cellular Automata." Mathematical Problems in Engineering 2020 (January 31, 2020): 1–11. http://dx.doi.org/10.1155/2020/2529816.
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In recent years, with the rapid development of China’s logistics industry and urban service industry, electric bicycles have gradually become an important means of transportation in cities due to their flexibility, green technology, and low operating costs. Because electric bicycles travel though motor vehicle lanes and nonmotor vehicle lanes, the conflict between motor and nonmotor vehicles has become increasingly prominent, and the safety situation is not optimistic. However, most theories and models of mixed traffic flow are based on motor vehicles and bicycles and few involve electric bicycles. To explore the traffic safety situation in an urban mixed traffic environment, this paper first uses cellular automata (CA) to establish a three-strand mixed traffic flow model of motor vehicles, electric bicycles, and bicycles and verifies the reliability of the model by using a MATLAB simulation based on the actual survey data. Then, using the technology of traffic conflicts and the conflict rate as the index to evaluate the traffic safety situation, the change in the conflict rate with different road occupancies and different proportional coefficients of motor vehicles is studied. In the end, the conflict rate is compared between the mixed traffic flow and the setting of a physical isolation divider, which provides some suggestions on when to set a physical isolation divider to separate motor vehicles from nonmotor vehicles. The results show that in a mixed traffic environment, the conflict rate first increases and then decreases with increasing road occupancy and reaches a peak when the road occupancy is 0.6. In addition, in mixed traffic environments, the conflict rate increases with an increasing proportional coefficient of the motor vehicle. When the road occupancy rate is within the range of [0.6, 0.9] or when the proportional coefficient of motor vehicle is between [0.8, 0.9], a physical isolation divider can be set to separate motor vehicles and nonmotor vehicles from the space to improve traffic safety.
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Masuki, Shizue, John H. Eisenach, Frank A. Dinenno, and Michael J. Joyner. "Reduced forearm α1-adrenergic vasoconstriction is associated with enhanced heart rate fluctuations in humans." Journal of Applied Physiology 100, no. 3 (March 2006): 792–99. http://dx.doi.org/10.1152/japplphysiol.00586.2005.
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In the present study, we assessed whether heart rate (HR) or arterial pressure fluctuations are enhanced in healthy young humans with reduced α-adrenergic vasoconstrictor responses and, if so, whether this occurs for both α1- and α2-adrenergic receptor-mediated vasoconstriction. Arterial pressure (brachial artery catheter) and HR (ECG) were monitored continuously, and α1- and α2-adrenergic responsiveness was determined by assessing the effects of brachial artery infusions of phenylephrine (α1-adrenergic agonist) and dexmedetomidine (α2-adrenergic agonist), respectively, on forearm blood flow (strain gauge plethysmography). α1-Adrenergic responsiveness varied markedly among the subjects ( n = 20) and was inversely correlated with coefficient of variation for HR ( R2 = 0.37, P < 0.01), whereas the responsiveness was not correlated with the coefficient of variation for either systolic or diastolic arterial pressure. α1-Adrenergic responsiveness was inversely and more strongly correlated with baroreflex sensitivity ( R2 = 0.62, P < 0.0001), determined from beat-to-beat changes in HR and systolic arterial pressure, than the coefficient of variation for HR. On the other hand, α2-adrenergic responsiveness was not correlated with any of the parameters determined above. These results suggest that, in healthy young subjects, the enhanced HR response to changes in systolic pressure helps maintain the stability of arterial blood pressure when α1-adrenergic responsiveness is reduced.
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Sajadi Bami, Yasamin, Jahangir Porhemmat, Hossein Sedghi, and Navid Jalalkamali. "Performance Evaluation of Mike Nam Rainfall-Runoff (R-R) Model in Daily Flow Simulation (Case Study: Gonbad Catchment in Hamedan)." Journal of Applied Engineering Sciences 10, no. 1 (May 1, 2020): 1–6. http://dx.doi.org/10.2478/jaes-2020-0001.
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AbstractNowadays, many hydrological rainfall-runoff (R-R) models, both distributed and lumped, have been developed to simulate the catchment. However, selecting the right model to simulate a specific catchment has always been a challenge. A proper understanding of the model and its advantages and limitations is essential for selecting the appropriate model for the purpose of the study. To this end, several studies have been carried out to evaluate the performance of hydrological models for specific areas (mountainous, marshy and so on). This study was conducted aimed at evaluating the performance of MIKE11 NAM lumped conceptual hydrological rainfall-runoff model in simulation of daily flow rate in Gonbad catchment. The NAM model was calibrated and validated using flow rate data of three hydrometric stations of the Gonbad catchment. The model performance was evaluated using Percent bias (PBIAS) and the coefficient of determination or Nash-Sutcliffe coefficient. A Nash Sutcliffe efficiency (NSE) of 0.80, 0.89 and 080 were obtained during calibration, whereas, for the validation period, NSE of 0.81, 0.87 and 0.71 were obtained for Nemooneh sub catchment, Shahed sub catchment and Gonbad catchment respectively. Percent bias of -0.6, 1.5 and 6.3 were achieved for calibration, while -2.7, 7.6 and -4.2 were acquired during validation for Nemooneh sub catchment, Shahed sub catchment and Gonbad catchment respectively. Based on the results, the MIKE 11 NAM lumped conceptual model was capable of simulating daily mean flow rate and mean flow volume.
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Saini, Anju, V. K. Katiyar, and Pratibha. "Effects of first-order chemical reactions on the dispersion coefficient associated with laminar flow through the lungs." International Journal of Biomathematics 07, no. 02 (March 2014): 1450021. http://dx.doi.org/10.1142/s1793524514500211.
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This paper aims to look into the determination of effective area-average concentration and dispersion coefficient associated with unsteady flow through a small-diameter tube where a solute undergoes first-order chemical reaction both within the fluid and at the boundary. The reaction consists of a reversible component due to phase exchange between the flowing fluid and the wall layer, and an irreversible component due to absorption into the wall. To understand the dispersion, the governing equations along with the reactive boundary conditions are solved numerically using the Finite Difference Method. The resultant equation shows how the dispersion coefficient is influenced by the first-order chemical reaction. The effects of various dimensionless parameters e.g. Da (the Damkohler number), α (phase partitioning number) and Γ (dimensionless absorption number) on dispersion are discussed. One of the results exposes that the dispersion coefficient may approach its steady-state limit in a short time at a high value of Damkohler number (say Da ≥ 10) and a small but nonzero value of absorption rate (say Γ ≤ 0.5).
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Wang, Wen. "Change in Properties of the Glycocalyx Affects the Shear Rate and Stress Distribution on Endothelial Cells." Journal of Biomechanical Engineering 129, no. 3 (November 4, 2006): 324–29. http://dx.doi.org/10.1115/1.2720909.
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The endothelial glycocalyx mediates interactions between the blood flow and the endothelium. This study aims to evaluate, quantitatively, effects of structural change of the glycocalyx on stress distribution and shear rate on endothelial cells. In the study, the endothelial glycocalyx is modeled as a surface layer of fiber matrix and when exposed to laminar shear flow, the matrix deforms. Fluid velocity and stress distribution inside the matrix and on cell membranes are studied based on a binary mixture theory. Parameters, such as the height and porosity of the matrix and the drag coefficient between fluid and matrix fibrils, are based on available data and estimation from experiments. Simple theoretical solutions are achieved for fluid velocity and stress distribution in the surface matrix. Degradation of the matrix, e.g., by enzyme digestion, is represented by reductions in the volume fraction of fibrils, height, and drag coefficient. From a force balance, total stress on endothelial surface remains constant regardless of structural alteration of the glycocalyx. However, the stress that is transmitted to endothelial cells by direct “pulling” of fiber branches of the glycocalyx is reduced significantly. Fluid shear rate at the cell membrane, on the other hand, increases. The study gives quantitative insight into the effect of the structural change of the glycocalyx on the shear rate and pulling stress on the endothelium. Results can be used to interpret experiments on effects of the glycocalyx in shear induced endothelial responses.
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Roushangar, Kiyoumars, Mohammad Taghi Alami, Jalal Shiri, and Mahdi Majedi Asl. "Determining discharge coefficient of labyrinth and arced labyrinth weirs using support vector machine." Hydrology Research 49, no. 3 (March 3, 2017): 924–38. http://dx.doi.org/10.2166/nh.2017.214.
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Abstract A labyrinth weir is a linear weir folded in plan-view which increases the crest length and the flow rate for a given channel width and an upstream flow depth. The present study aimed at determining discharge coefficients of labyrinth and arced labyrinth weirs using support vector machine (SVM)-based models. A total of 527 laboratory test data of four types of weirs, namely, Normal and Inverted orientation Labyrinth Weirs in flume (NLW, ILW) and Arced Labyrinth Weirs with and without nappe Breakers in reservoir (ALW, ALWB), were captured from the published literature and utilized to feed the SVM-based models. The obtained results revealed the capability of the SVM-based models in determining discharge coefficients. The results showed that the SVM-based model of arced labyrinth weir (ALW) produced the most accurate results when three dimensionless parameters, e.g. (HT/P) head water ratio, (α/θ) angle ratio and (Lc/W) magnification ratio, were introduced as input parameters (Root mean square error [RMSE]= 0.013 and R2 = 0.970 for the test stage). Nonetheless, sensitivity analysis showed that Froude number and head water ratio are the most influential parameters on discharge coefficients of the labyrinth and arced labyrinth weirs, respectively.
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Duran, Deniz, Celalettin Karadogan, and Izzet Ozdemir. "On the Importance of Thermo-Mechanical Modelling of the Double Cup Extrusion Test." Advanced Materials Research 966-967 (June 2014): 311–22. http://dx.doi.org/10.4028/www.scientific.net/amr.966-967.311.
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Finding the correct friction coefficient for the simulation of bulk metal forming processes is crucial. The practical approach nowadays for this objective is to conduct a friction sensitive process-test and the corresponding numerical simulation in order to reveal the friction coefficient. The Double Cup Extrusion Test (DCET) is one of the widely used friction tests for bulk metal forming. Although, there is a large body of literature on DCETs, there are still important aspects which have not been addressed yet. Motivated by this fact, this study emphasizes and demonstrates the importance of thermo-mechanical modelling to evaluate the DCET for the characterization of friction coefficients even for cold forging processes. To this end, thermo-mechanical material characterization covering necessary temperature and strain rate spectrum is conducted and used in the thermo-mechanically coupled finite element analysis (FEA) of the DCET. These findings are compared with the results of single flow curve based purely mechanical FEA in terms of cup height ratios as well as force-displacement curves for two different press speeds.
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Zhang, Jingtao, Haipeng Zhang, Donghee Lee, Sangjin Ryu, and Seunghee Kim. "Study on the effect of pore-scale heterogeneity and flow rate during repetitive two-phase fluid flow in microfluidic porous media." Petroleum Geoscience 27, no. 2 (January 26, 2021): petgeo2020–062. http://dx.doi.org/10.1144/petgeo2020-062.
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Various energy recovery, storage, conversion and environmental operations may involve repetitive fluid injection and thus, cyclic drainage–imbibition processes. We conducted an experimental study for which polydimethylsiloxane (PDMS)-based micromodels were fabricated with three different levels of pore-space heterogeneity (coefficient of variation, where COV = 0, 0.25 and 0.5) to represent consolidated and/or partially consolidated sandstones. A total of 10 injection-withdrawal cycles were applied to each micromodel at two different flow rates (0.01 and 0.1 ml min−1). The experimental results were analysed in terms of flow morphology, sweep efficiency, residual saturation, the connection of fluids and the pressure gradient. The pattern of the invasion and displacement of the non-wetting fluid converged more readily in the homogeneous model (COV = 0) as the repetitive drainage–imbibition process continued. The overall sweep efficiency converged between 0.4 and 0.6 at all tested flow rates, regardless of different flow rates and COV in this study. In contrast, the effective sweep efficiency was observed to increase with higher COV at the lower flow rate, while that trend became reversed at the higher flow rate. Similarly, the residual saturation of the non-wetting fluid was largest at COV = 0 for the lower flow rate, but it was the opposite for the higher flow-rate case. However, the Minkowski functionals for the boundary length and connectedness of the non-wetting fluid remained quite constant during repetitive fluid flow. Implications of the study results for porous media-compressed air energy storage (PM-CAES) are discussed as a complementary analysis at the end of this paper.Supplementary material: Figures showing the distribution of water (Fig. S1) and oil (Fig. S2) at the end of each drainage and imbibition step in different microfluidic pore-network models are available at https://doi.org/10.6084/m9.figshare.c.5276814Thematic collection: This article is part of the Energy Geoscience Series available at: https://www.lyellcollection.org/cc/energy-geoscience-series
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VILLANUEVA, PIA, MARIA A. FERNÁNDEZ, ZULEMA DE BARBIERI, and HERNÁN PALOMINO. "CONSANGUINITY ON ROBINSON CRUSOE ISLAND, AN ISOLATED CHILEAN POPULATION." Journal of Biosocial Science 46, no. 4 (August 12, 2013): 546–55. http://dx.doi.org/10.1017/s0021932013000436.
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SummaryThe population of Robinson Crusoe Island is estimated at 633 inhabitants. The current population has a common origin from the first eight families who colonized the island at the end of the 19th century. The objective of this study was to determine the rates of consanguinity, the average coefficients of inbreeding, the types of consanguineous marriages and the inbreeding evolution between 1900 and 2000 on the island. All marriages registered on the island, from the last colonization until 2000 (417 in total), were included in the analysis. In addition, extended genealogies were obtained. The consanguinity rate was 14.9% and the average coefficient of inbreeding (α) 54.05×10–4. The most frequent type of consanguineous marriages was between second cousins, followed by first cousins. The average value of the first/second cousin ratio was 1.11. The population of Robinson Crusoe Island has a high rate of inbreeding. The unique characteristic of the island – its small current population, originating from just a few families, with small rate of gene flow – could explain the observed high and increasing consanguinity.
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Karn, Ashish, Roger E. A. Arndt, and Jiarong Hong. "An experimental investigation into supercavity closure mechanisms." Journal of Fluid Mechanics 789 (January 19, 2016): 259–84. http://dx.doi.org/10.1017/jfm.2015.680.
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Substantial discrepancy in the conditions for attainment of different closure modes of a ventilated supercavity has existed widely in the published literature. In this study, supercavity closure is investigated with an objective to understand the physical mechanisms determining closure formation and transition between different closure modes and to reconcile the observations from prior studies under various flow settings. The experiments are conducted in a closed-wall recirculating water tunnel to image ventilated supercavity closure using high speed and high-resolution photography and simultaneously measure pressure inside the cavity. The flow conditions are varied systematically to cover a broad range of water velocity, ventilation flow rate and cavitator size, which correspond to different Froude numbers, air entrainment coefficients and blockage ratios, respectively. In addition to the classical closure modes reported in the literature (e.g. re-entrant jet, twin vortex, quad vortex, etc.), the study has revealed a number of new closure modes that occur during the transition between classical modes, or under very specific flow conditions. Closure maps are constructed to depict the flow regimes, i.e. the range of Froude number and air entrainment coefficient, for various closure modes at different blockage ratios. From the closure map at each blockage ratio, a critical ventilation flow rate, below which the supercavity collapses into foamy cavity upon reduction of Froude number, is identified. The air entrainment coefficients corresponding to such critical ventilation rate are found to be independent of blockage ratio. It has been observed that in the process of generating a supercavity by increasing ventilation flow rate, the cavitation number gradually reduces to a minimum value and stays fixed upon further increments in the ventilation rate. Once a supercavity is formed, the ventilation rate can be decreased to a much lower value with no change in cavitation number while still maintaining a supercavity. This process is accompanied by a change in closure modes, which generally goes from twin vortex, to quad vortex, and then to re-entrant jet. In addition, the blockage effect is shown to play an important role in promoting the occurrence of twin-vortex closure modes. Subsequently, a physical framework governing the variation of different closure modes is proposed, and is used to explain mode transition upon the change of flow conditions, including the blockage effect. This framework is further extended to shed light on the occurrence of closure modes for ventilated supercavitation experiments across different types of flow facilities, the natural supercavity closure and the pulsating supercavity reported in the literature. Finally, in combination with a recent numerical study, our research discusses the role of the internal flow physics on the observed features during supercavity formation and closure-mode transition, paving the way for future investigations in this direction.
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Guo, Biao, Chang Chun Ge, Yi Xu, Qiu Yan Lu, and Sui Cai Zhang. "Flow and Densification Behaviors of Sintered P/F-10C50 Steel under Hot Compression." Materials Science Forum 849 (March 2016): 811–18. http://dx.doi.org/10.4028/www.scientific.net/msf.849.811.
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The hot deformation and densification behaviors of sintered P/F-10C50 steel were investigated by hot compression tests on Gleeble-1500 thermal mechanical simulator at the temperature ranging from 900 °C to 1000 °C and the strain rate ranging from 0.1 s-1 to 10 s-1. The flow and densification characteristics of the tested specimens at different deformation temperatures and strain rates were studied. The flow stress of the sintered steel persistently increases until the end of the test as the result of matrix and geometric work hardening. The higher deformation temperature and strain rate are conductive to the healing of the pores and promote the densification of the sintered steel, while the higher deformation temperature and lower strain rate impede the densification. The constitutive equation of the sintered steel is established by the means of stepwise regression. The flow stresses predicted by the established constitutive equation are in good agreement with the experimental values, and the correlation coefficient (R) and the average absolute relative error (AARE) are 0.9931 and 3.52%, respectively. These results demonstrate the hot deformation behaviors of the sintered P/F-10C50 steel are excellently predicted by the established constitutive equation.
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Vemula, Rajesh, A. J. Chamkha, and Mallesh M. P. "Nanofluid flow past an impulsively started vertical plate with variable surface temperature." International Journal of Numerical Methods for Heat & Fluid Flow 26, no. 1 (January 4, 2016): 328–47. http://dx.doi.org/10.1108/hff-07-2014-0209.
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Purpose – The purpose of this paper is to focus on the numerical modelling of transient natural convection flow of an incompressible viscous nanofluid past an impulsively started semi-infinite vertical plate with variable surface temperature. Design/methodology/approach – The problem is governed by the coupled non-linear partial differential equations with appropriate boundary conditions. A robust, well-tested, Crank-Nicolson type of implicit finite-difference method, which is unconditionally stable and convergent, is used to solve the governing non-linear set of partial differential equations. Findings – The local and average values of the skin-friction coefficient (viscous drag) and the average Nusselt number (the rate of heat transfer) decreased, while the local Nusselt number increased for all nanofluids, namely, aluminium oxide-water, copper-water, titanium oxide-water and silver-water with an increase in the temperature exponent m. Selecting aluminium oxide as the dispersing nanoparticles leads to the maximum average Nusselt number (the rate of heat transfer), while choosing silver as the dispersing nanoparticles leads to the minimum local Nusselt number compared to the other nanofluids for all values of the temperature exponent m. Also, choosing silver as the dispersing nanoparticles leads to the minimum skin-friction coefficient (viscous drag), while selecting aluminium oxide as the dispersing nanoparticles leads to the maximum skin-friction coefficient (viscous drag) for all values of the temperature exponent m. Research limitations/implications – The Brinkman model for dynamic viscosity and Maxwell-Garnett model for thermal conductivity are employed. The governing boundary layer equations are written according to The Tiwari-Das nanofluid model. A range of nanofluids containing nanoparticles of aluminium oxide, copper, titanium oxide and silver with nanoparticle volume fraction range less than or equal to 0.04 are considered. Practical implications – The present simulations are relevant to nanomaterials thermal flow processing in the chemical engineering and metallurgy industries. This study also provides an important benchmark for further simulations of nanofluid dynamic transport phenomena of relevance to materials processing, with alternative computational algorithms (e.g. finite element methods). Originality/value – This paper is relatively original and illustrates the influence of variable surface temperature on transient natural convection flow of a viscous incompressible nanofluid and heat transfer from an impulsively started semi-infinite vertical plate.
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Fatela, Pedro, Goncalo V. Mendonca, António Prieto Veloso, Janne Avela, and Pedro Mil-Homens. "Blood Flow Restriction Alters Motor Unit Behavior During Resistance Exercise." International Journal of Sports Medicine 40, no. 09 (July 10, 2019): 555–62. http://dx.doi.org/10.1055/a-0888-8816.
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AbstractWe aimed to determine whether blood flow restriction (BFR) alters the characteristics of individual motor units during low-intensity (LI) exercise. Eight men (26.0±3.8 yrs) performed 5 sets of 15 knee extensions at 20% of one-repetition maximum (with and without BFR). Maximal isometric voluntary contractions (MVC) were performed before and after exercise to quantify force decrement. Submaximal isometric voluntary contractions were additionally performed for 18 s, matching trapezoidal target-force trajectories at 40% pre-MVC. EMG activity was recorded from the vastus lateralis muscle. Then, signals were decomposed to extract motor unit recruitment threshold, firing rates and action potential amplitudes (MUAP). Force decrement was only seen after LI BFR exercise (–20.5%; p<0.05). LI BFR exercise also induced greater decrements in the linear slope coefficient of the regression lines between motor unit recruitment threshold and firing rate (BFR: –165.1±120.4 vs. non-BFR: –44.4±33.1%, p<0.05). Finally, there was a notable shift towards higher values of firing rate and MUAP amplitude post-LI BFR exercise. Taken together, our data indicate that LI BFR exercise increases the activity of motor units with higher MUAP amplitude. They also indicate that motor units with similar MUAP amplitudes become activated at higher firing rates post-LI BFR exercise.
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Kravchuk, O. "TO THE HYDRAULIC CALCULATION OF PRESSURE DRAINAGE PIPELINES, OPERATING IN DISTRIBUTION REGIME." Municipal economy of cities 3, no. 163 (June 29, 2021): 68–74. http://dx.doi.org/10.33042/2522-1809-2021-3-163-68-74.
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A system of two differential equations which describes the movement of fluid in a pipe with a variable flow rate and the conditions for the fluid outflow through the walls of drainage pipelines into the surrounding soil is considered. It is reasoned that the second term in the original equation, which takes into account energy losses associated with a flow rate variation along the length, can be neglected without a substantial error. The considered system is reduced to dimensionless form by introducing original variables. The coefficient of collecting drainage pipeline resistance «ζl» and the generalized parameter «A», which take into account the structural and hydraulic characteristics of the considered flow, are two main parameters used in the analysis. The concept of an infinitely long drainage pipeline (a pipeline with an infinite walls filtration capacity) is introduced in the article. Also it is noted that such pipeline will have a maximum throughput comparing to pipes of the same diameter but limited length. Quite simple and practical calculated dependencies for the determination of the nature of flow rate variation and pressure drop along the length of the pipeline were received on the basis of the conducted analysis. Important characteristics of pressure distribution pipelines were calculated on the basis of offered formulas. Corresponding graphical dependencies were built for visibility. In particular, graphs of the flow rate variation at the end of the distributor, depending on the design and filtration characteristics of the «soil-drain» system, are presented. Graph that shows the dependence of the variation in the flow rate distribution unevenness along the length of the drainage pipe at various hydraulic conductivity values of the surrounding soil is important for understanding the drainage pipelines particularity. The necessity to take into account the nature of the flow rate connection unevenness along the length for obtaining reliable results for real drainage pipelines calculation is demonstrated.
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Fischer Filho, João A., Vinicius M. R. de Oliveira, Alexandre B. Dalri, and José R. Zanini. "Performance of pressure-compensating emitters using treated sewage effluent for irrigation." Revista Brasileira de Engenharia Agrícola e Ambiental 20, no. 10 (October 2016): 869–73. http://dx.doi.org/10.1590/1807-1929/agriambi.v20n10p869-873.
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ABSTRACT This study aimed to evaluate the flow variation of pressure-compensating emitters using treated sewage effluent (TSE). A drip irrigation system with four types of pressure-compensating emitters (G1 - Naan Dan Jain Model Top Drip, G2 - Naan Dan Jain Model Naan PC, G3 - Drip-Plan, G4 - Naan Dan Jain Model Naan Amnon) was installed with TSE from the sewage treatment station, filtered through a disc filter (120 mesh). Seven evaluations of flow rate of the drippers were performed (0, 100, 200, 300, 400, 500 and 600 h of operation) operating at 100 kPa. The experimental design was completely randomized in a 4 x 7 factorial arrangement (4 models and 7 times) with four replicates and Tukey test to compare the means. The relative flow rate (Qr), flow rate coefficient of variation (CVQ) and degree of clogging (DC) were determined. It was found that the models of emitters were not much susceptible to clogging during the operation of the system. The G4 model showed better performance compared with the others, presenting mean Qr of 99.92%, CVQ of 2.69% and DC of 1.19% at the end of the experiment. The results revealed that emitters are affected by the time of use of TSE.
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Flagiello, Domenico, Arianna Parisi, Amedeo Lancia, and Francesco Di Natale. "A Review on Gas-Liquid Mass Transfer Coefficients in Packed-Bed Columns." ChemEngineering 5, no. 3 (August 2, 2021): 43. http://dx.doi.org/10.3390/chemengineering5030043.
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This review provides a thorough analysis of the most famous mass transfer models for random and structured packed-bed columns used in absorption/stripping and distillation processes, providing a detailed description of the equations to calculate the mass transfer parameters, i.e., gas-side coefficient per unit surface ky [kmol·m−2·s−1], liquid-side coefficient per unit surface kx [kmol·m−2·s−1], interfacial packing area ae [m2·m−3], which constitute the ingredients to assess the mass transfer rate of packed-bed columns. The models have been reported in the original form provided by the authors together with the geometric and model fitting parameters published in several papers to allow their adaptation to packings different from those covered in the original papers. Although the work is focused on a collection of carefully described and ready-to-use equations, we have tried to underline the criticalities behind these models, which mostly rely on the assessment of fluid-dynamics parameters such as liquid film thickness, liquid hold-up and interfacial area, or the real liquid paths or any mal-distributions flow. To this end, the paper reviewed novel experimental and simulation approaches aimed to better describe the gas-liquid multiphase flow dynamics in packed-bed column, e.g., by using optical technologies (tomography) or CFD simulations. While the results of these studies may not be easily extended to full-scale columns, the improved estimation of the main fluid-dynamic parameters will provide a more accurate modelling correlation of liquid-gas mass transfer phenomena in packed columns.
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Sun, Qi Guo, Yue Fei Wang, Ying Wang, Peng Niu, and Xiong Shi Wang. "Numerical Study on Rolling Bearing Temperature Field under the Oil-Air Lubrication." Applied Mechanics and Materials 487 (January 2014): 580–84. http://dx.doi.org/10.4028/www.scientific.net/amm.487.580.
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Speed of rolling bearing and flow rate of air have important influences on the bearing’s working temperature under the oil-air lubrication mode. Based on basic principle of lubrication, one of the heat productivity equations of deep groove ball bearing is selected to calculate the heat value of bearing’s cavity. The bearing’s temperature field is simulated by Fluent at different rotational speeds and air flow rates. Results of the simulation show that the highest temperatures of bearing have a quantitative relationship with the bearing’s rotational speeds. The relationships between the velocity of inlet and heat transfer coefficient, viscosity of the lubricant and the heating of bearing are analyzed in the end of this paper.
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Mesri, Gholamreza, and Tao-Wei Feng. "Constant rate of strain consolidation testing of soft clays and fibrous peats." Canadian Geotechnical Journal 56, no. 10 (October 2019): 1526–33. http://dx.doi.org/10.1139/cgj-2018-0259.
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The constant rate of strain (CRS) oedometer test, using an imposed vertical strain rate [Formula: see text] equal to 10 times the end-of-primary (EOP) vertical strain rate [Formula: see text], requiring a test duration of about 2 days produces reliable information on both the e versus log[Formula: see text] relation and e versus logkv relation of soft clays and fibrous peats. An empirical correction for the strain rate effect on preconsolidation pressure leads to the EOP e versus log[Formula: see text] relation and EOP [Formula: see text]. The imposed vertical strain rate [Formula: see text] produces excess pore-water pressures at the impervious bottom of the specimen, corresponding to [Formula: see text] values in the range of 3%–15% and allows, use of the Darcy flow equation, a reliable calculation of the coefficient of permeability. Compressibility and permeability data are from CRS and incremental loading (IL) oedometer tests on specimen quality designation (SQD) A samples of seven soft clays and two fibrous peats are presented in this paper.
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Pons, M., and Ph Grenier. "Experimental Data on a Solar-Powered Ice Maker Using Activated Carbon and Methanol Adsorption Pair." Journal of Solar Energy Engineering 109, no. 4 (November 1, 1987): 303–10. http://dx.doi.org/10.1115/1.3268222.
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The solar-powered ice maker has been described in a previous article [1]. The present article draws conclusions from experiments conducted on this prototype. Some specific effects appear: the end of desorption is delayed, a chimney effect takes place between collectors, and heat transfers within the collectors are pointed out. The experimental heat balances of each component are analyzed. First, the effective thermal loss coefficients of collectors are calculated in every configuration; their efficiencies lies betweeen 30 and 40 percent. But the nightly cooling is not as efficient as expected. Secondly, the heat transfer coefficient of condensers is very low. Thirdly, the evaporator is efficient and variations of evaporated flow-rate are presented. Supercooling is observed. Finally, the measured Net Solar C.O.P. is 0.12 when Qi is 22 MJ/m2 (a nice summer day in Paris) and 0.10 when Qi is 19 MJ/m2. In conclusion, major improvements are proposed.
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Hagoort, Jacques. "An Improved Model for Estimating Flow Impairment by Perforation Damage." SPE Journal 12, no. 02 (June 1, 2007): 235–44. http://dx.doi.org/10.2118/98137-pa.
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Summary In this work, we present two simple formulas for the skin of a perforated well caused by perforation damage: one for the reduction in permeability, and one for the increase in non-Darcy flow coefficient (beta factor). They are based on the inflow performance of a single perforation obtained by means of a prolate-spheroidal flow model. This model rigorously accounts for the flow convergence toward a perforation, especially near the tip of the perforation. It provides a more realistic description of the inflow than a radial flow model, the basis for the existing skin formulas proposed by McLeod (1983). In the case of perforations with a large aspect ratio and a thin damaged zone, the formula for the skin due to permeability reduction reduces to McLeod's formula. The formula for the non-Darcy skin yields a significantly larger skin than predicted by the radial flow model, up to a factor 1.4 for large aspect ratios. Finally, we demonstrate that perforated wells are much more liable to non-Darcy flow than openhole wells, in particular if the perforations are severely damaged. Introduction Oil and gas wells are commonly completed with production casing cemented in place and perforated to enable fluids to enter the wellbore. The perforations are created by perforating guns and have the form of straight elongated and circular holes that stick into the formation perpendicular to the wall of the wellbore. The perforation holes are surrounded by a damaged zone of crushed and compacted rock. Typically, a perforation has a diameter of approximately a quarter-in., a length of a few up to more than a dozen inches and a crushed zone thickness of up to 1 in. It has been long recognized that perforation damage may drastically impair the flow efficiency of a perforated well. Not only is this caused by a lower permeability in the crushed zone, but also by a higher inertial resistance coefficient (non-Darcy flow coefficient), which is particularly important for prolific, high-rate gas wells. Customarily, the inflow performance of a perforated well is described by the radial openhole inflow formula, in which the effect of the perforations (e.g. geometry, shot density, phasing, and perforation damage) is included as a pseudo skin (Bell et al. 1995). The current model for estimating the Darcy and non-Darcy skins due to perforation damage was proposed by McLeod(1983). In this model the perforation is represented by an open circular cylinder surrounded by a concentric crushed zone of reduced permeability and enhanced non-Darcy flow coefficient, and the inflow into this cylinder is assumed to be radial, perpendicular to its axis.
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Harris, S. L., T. Stephenson, and P. Pearce. "Aeration investigation of biological aerated filters using off-gas analysis." Water Science and Technology 34, no. 3-4 (August 1, 1996): 307–14. http://dx.doi.org/10.2166/wst.1996.0445.
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The bulk of the operating costs for biological aerated filters are associated with aeration, accordingly, any efficiency improvements which may be made to this aspect of the process could result in significant savings operationally. This study used off-gas analysis to determine the effects on oxygen transfer efficiency of variations to the air flow and substrate loading rates to two pilot scale granular media biological aerated filters (BAFs) treating primary settled sewage. The columns provided a good representation of full scale units, providing up to 99% ammonia reduction. Incremental increases in the mass transfer coefficient (KLa) were observed, as reported elsewhere and attributed to direct interfacial transfer between the bubbles and the biofilm. The OTE varied with flow rate but was far more sensitive at the lower end of the experimental range, rising sharply for air flow rates below 5 to 10 m/h. Increasing the organic loading rate also improved the OTE. The use of fine bubble diffusers did not improve the OTE, however, probably as a result of the packing media used.
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James Chinaka, Ehiem. "Viscosity and biodiesel characteristics of wild Canarium schweinfurthii Engl. fruit oil." Research in Agricultural Engineering 64, No. 4 (December 31, 2018): 169–75. http://dx.doi.org/10.17221/99/2017-rae.
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The viscosity of two varieties of Canarium schweinfurthiiEngl. fruits oil (large and long) were studied at four different temperatures (30, 40, 50 and 60<sup>o</sup>C) and three shear rates (7.91, 15.82 and 39.54 s<sup>–1</sup>). SurgiFriend Medical (model NDJ-5S) viscometer was used to carry out the study. Biodiesel characteristics of the oil were also investigated. The results showed that variety had no effect (P < 0.05) on the viscosity of Canarium schweinfurthii Engl. fruit while temperature had especially at 50<sup>o</sup>C and above. The shear rate of 15.82 s<sup>–1 </sup>(12 rps) gave the lowest oil viscosity for both varieties. The oil from large fruit had the best temperature stability, low percentage viscosity (6.33%) variation and least activation energy (796.51 J·mol<sup>–1</sup>·K<sup>–1</sup>) while long variety had best biodiesel characteristic for safe handling. Temperature had no significant (P < 0.05) effect on the consistency coefficient (C) and flow behaviour index (n) of both varieties of Canarium schweinfurthii Engl. fruits oil. Besides, oil from both fruit varieties is Newtonian fluids.
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IZUMI, NORIHIRO, and GARY PARKER. "Linear stability analysis of channel inception: downstream-driven theory." Journal of Fluid Mechanics 419 (September 25, 2000): 239–62. http://dx.doi.org/10.1017/s0022112000001427.
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A linear stability analysis of incipient channellization on hillslopes is performed using the shallow-water equations and a description of the erosion of a cohesive bed. The base state consists of a laterally uniform Froude-subcritical sheet flow down a smooth, downward-concave hillslope profile. The downstream boundary condition consists of the imposition of a Froude number of unity. The process of channellization is thus driven from the downstream end. The flow and bed profiles describe a base state that migrates at constant, slow speed in the upstream direction due to bed erosion. Transverse perturbations corresponding to a succession of parallel incipient channels are introduced. It is found that these perturbations grow in time, so describing incipient channellization, only when the characteristic spacing between incipient channels is on the order of 6–100 times the Froude-critical depth divided by the resistance coefficient. The characteristic wavelength associated with maximum perturbation growth rate is found to scale as 10 times the Froude-critical depth divided by the resistance coefficient. Evaluating the friction coefficient as on the order of 0.01, an estimate of incipient channel spacing on the order of 1000 times the Froude-critical depth is obtained. The analysis reveals that downstream-driven channellization becomes more difficult as (a) the critical shear stress required to erode the bed becomes so large that it approaches the Froude-critical shear stress reached at the downstream boundary and (b) the Froude number of the subcritical equilibrium flow attained far upstream approaches unity. Alternative mechanisms must be invoked to explain channellization on slopes high enough to maintain Froude-supercritical sheet flow.
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Bastic, Jelena, Dejan Skala, and Slavica Ivanovic. "Determination of the diffusion coefficient of some highly toxic organic substances by using a diffusion tube CA Hemijska industrija." Chemical Industry 57, no. 1 (2003): 9–14. http://dx.doi.org/10.2298/hemind0301009b.
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The determination of specific characteristics of materials commonly used in the preparation of cloths for the protection of the human body, lungs and other human organs, based on the principles of the effective adsorption of highly toxic organic vapors initially requires the development of specific and reliable techniques for the preparation of a gas stream with the relevant highly toxic organic substances. The dynamic method, one of the techniques commonly used for material characterization, is based on the procedure of determining the concentration of different substances in the gas stream at the inlet and after passing through a specific thin layer of the adsorption material (outlet). Therefore, the generation of a gas phase containing highly toxic organic substances in a defined quantity during a specific time interval, is the requirement that must previously be fulfilled before using the dynamic method for testing specific materials for protection of the human body. Usually, a dynamic method of determining the quality of cloths prepared with specific adsorbents requires a relatively low volumetric flow rate of the gas phase containing the test substance which may be achieved by using a diffusion tube (DT) as the standard equipment for the generation of test substances. A very wide range of concentrations of the test substances in a specific gas phase (inert, air) can be obtained by varying the working conditions (temperature, pressure, gas flow rate) and the geometrical size of the diffusion tube, taking into account that the concentration of toxic substances, is determined as the ratio of their diffusion rate and from the DT and the carrier gas flow rate. The diffusion rate of the test substances from the DT is caused by the concentration gradient between the partial pressure of the saturated vapor at one end of the DT capillary and the partial pressure at the outlet of the diffusion tube according to Fick's law. The mass rate of the generated test substances from the DT is constant for constant conditions (temperature and pressure) in the reservoir of the DT On the basis of a detailed theoretical calculation such a rate (R) may be defined by the equation: R = 16.624 DM(P/T)(A/L)log [P/(P- pv)l, mg/min where: D - the diffusion coefficient, cm/s; M - the molar mass of the test substance, g/mol; P - the pressure in the DT kPa; pv - the vapor pressure of the test substance, kPa; A - the cross sectional area of the capillary of the DT cm2: L - the length of the capillary of the DT cm; T - the temperature, K. A procedure for the constant isothermal vapor generation of hydrogen cyanide (HCN) and 2-bromo-2-chloro-1,1,1-trifluoroethane (halotane) into air by a using diffusion tube is described. The DT was placed into a thermostat 0.5?C) and the diffusion rates of the substance were measured during some time interval and the above equation was used for the determination of the diffusion coefficient. The obtained data were correlated with the calculated ones on the basis of an empirical correlation from the literature. The relative differences in the experimentally determined and theoretically calculated values of the diffusion coefficient for hydrogen cyanide at different temperature (19-23.2?C) were 26-31 % and for halotane (26-45?C) 8-14%.
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Lestari, Retno A. S., Wahyudi B. Sediawan, and Sarto. "Sulphide removal from liquid using biofilm on packed bed of salak fruit seeds." MATEC Web of Conferences 154 (2018): 01031. http://dx.doi.org/10.1051/matecconf/201815401031.
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2This study focused on the removal of sulphide from liquid solution using biofilm on packed bed of salak fruit seeds. Bio-filter operation of 444 hours consists of 6 phases of operation. Each phase lasted for approximately 72 hours to 82 hours and run at various inlet concentration and flow rate. The highest removal efficiency is 92.01%, at the end of phase 7 at the inlet concentration of 60 ppm and the flow rate of 30 mL min-1. Mathematic model of sulphide removal was proposed to describe the operation of bio-filter. The model proposed can be applied to describe the removal of sulphide liquid using bio-filter in packed bed. The simulation results the value of the parameters in process. The value of the rate maximum specific growth is 4.15E-8 s-1, Saturation constant is 9.1E-8 g cm-3, mass transfer coefficient of liquid is 0.5 cm s-1, Henry’s constant is 0.007, and mass of microorganisms growth to mass of sulphide consumed is 30. The value of the rate maximum specific growth in early process is 0.00000004 s-1.
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Watson, P. D., and M. B. Wolf. "Transport parameter estimation from lymph measurements and the Patlak equation." American Journal of Physiology-Heart and Circulatory Physiology 262, no. 1 (January 1, 1992): H293—H298. http://dx.doi.org/10.1152/ajpheart.1992.262.1.h293.
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Two methods of estimating protein transport parameters for plasma-to-lymph transport data are presented. Both use IBM-compatible computers to obtain least-squares parameters for the solvent drag reflection coefficient and the permeability-surface area product using the Patlak equation. A matrix search approach is described, and the speed and convenience of this are compared with a commercially available gradient method. The results from both of these methods were different from those of a method reported by Reed, Townsley, and Taylor [Am. J. Physiol. 257 (Heart Circ. Physiol. 26): H1037-H1041, 1989]. It is shown that the Reed et al. method contains a systematic error. It is also shown that diffusion always plays an important role for transmembrane transport at the exit end of a membrane channel under all conditions of lymph flow rate and that the statement that diffusion becomes zero at high lymph flow rate depends on a mathematical definition of diffusion.
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Gerke, H. H., J. Dusek, and T. Vogel. "Mass transfer effects in 2-D dual-permeability modeling of field preferential bromide leaching with drain effluent." Hydrology and Earth System Sciences Discussions 8, no. 3 (June 22, 2011): 5917–67. http://dx.doi.org/10.5194/hessd-8-5917-2011.
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Abstract. Subsurface drained experimental fields are frequently used for studying preferential flow (PF) in structured soils. Considering two-dimensional (2-D) transport towards the drain, however, the relevance of mass transfer coefficients, apparently reflecting small-scale soil structural properties, for the water and solute balances of the entire drained field is largely unknown. This paper reviews and analyzes effects of mass transfer reductions on Br− leaching for a subsurface drained experimental field using a numerical 2-D dual-permeability model (2D-DPERM). The sensitivity of the "diffusive" mass transfer component on bromide (Br−) leaching patterns is discussed. Flow and transport is simulated in a 2-D vertical cross-section using parameters, boundary conditions (BC), and data of a Br− tracer irrigation experiment on a subsurface drained field (5000 m2 area) at Bokhorst (Germany), where soils have developed from glacial till sediments. The 2D-DPERM simulation scenarios assume realistic irrigation and rainfall rates, and Br-application in the soil matrix (SM) domain. The mass transfer reduction controls preferential tracer movement and can be related to physical and chemical properties at the interface between flow path and soil matrix in structured soil. A reduced solute mass transfer rate coefficient allows a better match of the Br− mass flow observed in the tile drain discharge. The results suggest that coefficients of water and solute transfer between PF and SM domains have a clear impact on Br− effluent from the drain. Amount and composition of the drain effluent is analyzed as a highly complex interrelation between temporally and spatially variable mass transfer in the 2-D vertical flow domain that depends on varying "advective" and "diffusive" transfer components, the spatial distribution of residual tracer concentrations, and the lateral flow fields in both domains from plots of the whole subsurface drained field. The local-scale soil structural effects (e.g., such as macropore wall coatings), here conceptualized as changes in mass transfer coefficients, can have a clear effect on leaching at the plot and field-scales.
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Kelkar, M. G. "Estimation of Turbulence Coefficient Based on Field Observations." SPE Reservoir Evaluation & Engineering 3, no. 02 (April 1, 2000): 160–64. http://dx.doi.org/10.2118/62488-pa.
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Summary Isochronal testing is commonly used to evaluate the performance of gas wells. This paper proposes a new technique to estimate the value of the turbulence coefficient based on isochronal tests. The proposed method is easy to apply and evaluate. Further, the method also provides a value of bg under stabilized conditions which can be used to predict the performance of gas wells under stabilized conditions. The proposed method is validated using field data under a variety of operating conditions. The values of the turbulence coefficient based on the field data can differ significantly compared to the literature correlations. This further shows the importance of obtaining appropriate reservoir parameters based on the field rather than the laboratory data. Introduction The use of isochronal or modified isochronal testing is well established in the gas industry. These tests are common for gas wells which take a long time to reach a stabilized rate. A common example would be a low permeability, fractured reservoir. Instead of testing these wells until a stabilized rate is reached, the wells are tested for a fixed period of time and the bottomhole pressure is measured. For isochronal testing, the well is then shut in until it reaches a stabilized pressure and the procedure is repeated for a different rate. For modified isochronal testing, the well is shut in for a fixed period of time, and the shut-in pressure is measured at the end of that period. The procedure is then repeated at other rates. By repeating this procedure for different time intervals, we can gather information about rate vs. pressure drop in the formation for these time intervals. Ultimately, using this information, our goal is to establish an appropriate rate vs. pressure drop relationship under stabilized conditions. Two procedures are commonly used to establish the equation for rate vs. pressure drop. An empirical method states that q g = C ( p ￣ 2 − p w f 2 ) n . ( 1 ) We can write a simpler equation in terms of pseudo-real pressures as q g = C [ m ( p ￣ ) − m ( p w f ) ] n . ( 2 ) Under transient conditions, the value of C is not constant. Instead, we can write Eq. 2 as q g = C ( t ) [ m ( p ￣ ) − m ( p w f ) ] n , ( 3 ) where C(t) represents a term which is a function of isochronal interval t. In the literature, methods are proposed to estimate the value of C corresponding to the stabilized rate based on the transient state information ?C(t) For example, Hinchman et al.1 propose that 1/C(t)1/n be plotted as a function of log t, and the line be extrapolated until t is equal to the time it takes to reach the stabilized state period. In their method, they assume that n is constant, where n is an inverse of slope when log[m(p¯)−m(pwf)] is plotted as a function of qg. Although we get different straight lines corresponding to different t, the authors assume that the slopes are approximately constant. Another commonly used approach in analyzing isochronal tests is to use an equation, m ( p ￣ ) − m ( p w f ) = a g q g + b g q g 2 . ( 4 ) A similar equation can also be written in terms of pressure squared terms. Eq. 4 is derived starting from Forchheimer's equation. Under transient conditions, we can rewrite Eq. 4 as m ( p ￣ ) − m ( p w f ) = a g ( t ) q g + b g q g 2 , ( 5 ) where ag(t) is a function of isochronal interval, and bg is assumed to be constant. A commonly used technique is to plot ag(t) vs. log (t) and extrapolate ag(t) corresponding to a value of t which represents the time required to reach a stabilized rate.2–4 In using both Eqs. 3 and 5, we have assumed that the contribution due to the non-Darcy effect is not affected during the transient conditions. For example, in applying Eq. 3, we assume that n is constant during the transient period, and in applying Eq. 5, we assume that bg is constant during the transient period. Both n and bg represent the relative contributions of the non-Darcy flow. n will approach 0.5 as the non-Darcy effect becomes dominant, and bg becomes larger as the non-Darcy effect becomes significant. However, by assuming that n and bg are constant during the transient periods, we are ignoring the changes in the relative contributions due to the Darcy and non-Darcy terms. In this article, we extend the previous analysis to account for changes in the non-Darcy term during the transient period. Further, by proper analysis, we propose a method to estimate the value of the turbulence coefficient based on the evaluation of the transient period data. Approach In our approach, instead of using the empirical equation (Eq. 3), we will begin with Forchheimer's equation, where the pressure gradient in a radial reservoir is calculated by ∂ p ∂ r = μ g k v + β ρ g v 2 . ( 6 ) The permeability (k) of the reservoir may be established based on well test data or core information. The turbulence coefficient is difficult to estimate. Although literature correlations5,6 exist to calculate the value of ? based on the laboratory experiments, field evidence7 indicates that the ? values in the field are significantly greater than the laboratory experiments.
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Shourehdeli, Shaban Alyari, Kamran Mobini, and Ali Asakereh. "Numerical Investigation of the Effects of Primary Nozzle Diverging Portion on Performance of the Supersonic Ejector of an Ejector Refrigeration Cycle." International Journal of Air-Conditioning and Refrigeration 27, no. 03 (September 2019): 1950030. http://dx.doi.org/10.1142/s2010132519500305.
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A supersonic ejector with desirable performance characteristics reduces the energy consumption rate of an ejector refrigeration system and increases its coefficient of performance (COP). In this paper, the effects of using different primary nozzles on the performance of a supersonic ejector of an ejector refrigeration system have been numerically studied, while the working fluid is steam. To this end, conical, Rao and parallel-flow primary nozzles with identical converging portions and equal exit area to throat area ratios have been tested. The diverging portion curves for the parallel-flow and Rao nozzles were derived using the method of characteristics. Using the Rao nozzle, the critical entrainment ratio and the critical back pressure were increased compared to the conical nozzle by 6.3% and 2.08%, respectively. It was also found that the physics of the internal flow of the ejector was changed by changing the diverging curve of the primary nozzle.
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Tang, S. L., R. A. Antonia, L. Djenidi, and Y. Zhou. "Transport equation for the isotropic turbulent energy dissipation rate in the far-wake of a circular cylinder." Journal of Fluid Mechanics 784 (October 30, 2015): 109–29. http://dx.doi.org/10.1017/jfm.2015.597.
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The transport equation for the isotropic turbulent energy dissipation rate $\overline{{\it\epsilon}}_{iso}$ along the centreline in the far-wake of a circular cylinder is derived by applying the limit at small separations to the two-point energy budget equation. It is found that the imbalance between the production and the destruction of $\overline{{\it\epsilon}}_{iso}$, respectively due to vortex stretching and viscosity, is governed by both the streamwise advection and the lateral turbulent diffusion (the former contributes more to the budget than the latter). This imbalance differs intrinsically from that in other flows, e.g. grid turbulence and the flow along the centreline of a fully developed channel, where either the streamwise advection or the lateral turbulent diffusion of $\overline{{\it\epsilon}}_{iso}$ governs the imbalance. More importantly, the different types of imbalance represent different constraints on the relation between the skewness of the longitudinal velocity derivative $S$ and the destruction coefficient of enstrophy $G$. This results in a non-universal approach of $S$ towards a constant value as the Taylor microscale Reynolds number $R_{{\it\lambda}}$ increases. For the present flow, the magnitude of $S$ decreases initially ($R_{{\it\lambda}}\leqslant 40$) before increasing ($R_{{\it\lambda}}>40$) towards this constant value. The constancy of $S$ at large $R_{{\it\lambda}}$ violates the modified similarity hypothesis introduced by Kolmogorov (J. Fluid Mech., vol. 13, 1962, pp. 82–85) but is consistent with the original similarity hypotheses (Kolmogorov, Dokl. Akad. Nauk SSSR, vol. 30, 1941b, pp. 299–303 (see also 1991 Proc. R. Soc. Lond. A, vol. 434, pp. 9–13)) ($K41$), and, more importantly, with the almost completely self-preserving nature of the plane far-wake.
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Zhang, Weijie, Jianping Yuan, Qiaorui Si, and Yanxia Fu. "Investigating the In-Flow Characteristics of Multi-Operation Conditions of Cross-Flow Fan in Air Conditioning Systems." Processes 7, no. 12 (December 15, 2019): 959. http://dx.doi.org/10.3390/pr7120959.
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Cross-flow fans are widely used in numerous applications such as low-pressure ventilation, household appliances, laser instruments, and air-conditioning equipment. Cross-flow fans have superior characteristics, including simple structure, small size, stable airflow, high dynamic pressure coefficient, and low noise. In the present study, numerical simulation and experimental research were carried out to study the unique secondary flow and eccentric vortex flow characteristics of the internal flow field in multi-operating conditions. To this end the vorticity and the circumferential pressure distribution in the air duct are obtained based on the performed experiments and the correlation between spectral characteristics of multiple operating conditions and the inflow state is established. The obtained results show that when the area of the airflow passage decreases while the area of the eccentric vortex area gradually increases, then the airflow of the cross-flow fan decreases, the outlet expands, and the flow pattern uniformity reduces. It was found that wakes form in the vicinity of the blade and the tail of the volute tongue, which generate pressure pulsation, and aerodynamic noise. The pressure distribution along the inner circumference shows that the total minimum pressure appears in the eccentric vortex near the volute tongue and the volute returns near the zone. Moreover, it was found that the total pressure near the eccentric vortex is significantly smaller than that of the main flow zone. As the flow rate decreases, the pressure pulsation amplitude of the eccentric vortex region significantly increases, while the static and total pressure pulsation amplitudes are gradually increased. Close to the eccentric vortex on the inner side of the blade in the volute tongue area, total pressure is low, total pressure on the outside of the blade is not affected, and pressure difference between the inner and outer sides is large. When the flow rate of the cross-flow fan is 0.4 Qd, there is no obvious peak at the harmonic frequency of the blade passage frequency. This shows that the aerodynamic noise is caused by the main unstable flow.
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Heshmat, H., and D. Brewe. "Performance of Powder-Lubricated Journal Bearings With MoS2 Powder: Experimental Study of Thermal Phenomena." Journal of Tribology 117, no. 3 (July 1, 1995): 506–12. http://dx.doi.org/10.1115/1.2831282.
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Powder-lubricated, quasi-hydrodynamic journal bearings assist in controlling wear and hold promise for integration in outer space systems/mechanisms and in other hostile-environment applications where the use of conventional lubricants is impractical. Described herein are the thermal phenomena and an assessment of the thermal stability, heat generation and dissipation characteristics of slider-type, powder-lubricated bearings. Powder lubricant films provide lift and separate bearing surfaces and cause side leakage. The reduction in friction coefficient and, consequently, in the heat generated in the bearings, drastically reduces wear of the tribomaterials. Further, bearing side leakage carries away most of the heat generated by shear, reducing the heat to the critical bearing surfaces. Also presented are the thermohydrodynamic effects of powder lubrication (MoS2) on bearing performance criteria, e.g., temperature and friction coefficient as a function of speed and load, including the effect of powder flow rate on bearing performance and wear.
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Kravchuk, O. A. "PARTICULARITIES OF HYDRAULIC CALCULATION OF COLLECTING PREASSURE DRAINAGE PIPELINES." Bulletin of Odessa State Academy of Civil Engineering and Architecture, no. 83 (June 4, 2021): 130–38. http://dx.doi.org/10.31650/2415-377x-2021-83-130-138.
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A system of two differential equations, which describes the fluid motion in a pipe with a variable flow rate and the conditions for fluid entry through the drainage pipelines walls from the surrounding soil, is considered. It is shown that for the studied case the second term in the original equation can be neglected without a significant error. The system is reduced to a dimensionless form by introducing the original variables. The solution of this equations system is given in a dimensionless form. Two main parameters are used in the analysis: the coefficient of collecting drainage pipeline resistance "ζl" and the generalized parameter "A", which takes into account the structural and hydraulic characteristics of the considered flow. Also, the concept of an infinitely long drainage pipeline or, which is the same, a pipeline with an infinite walls filtration capacity of the drainage pipeline is introduced in the article. It is noted that such pipeline will have a maximum throughput compared to pipes of the same diameter but limited length. Sufficiently simple and convenient calculated dependencies for the determination of the nature of flow rate variation and pressure drop along the length of the pipeline were obtained on the basis of the conducted analysis. Series of calculations of important characteristics for such pipes were carried out on the basis of offered formulas. Corresponding graphical dependencies were built for visibility. In particular, graphs of the flow rate variations at the end of the collector, depending on the design and filtration characteristics of the “soil-drain” system, are presented. Graph, that shows the dependence of the change in the flow rate connection unevenness along the length of the drainage pipeline at various hydraulic conductivity values of the surrounding soil, is important for understanding the drainage pipes particularity. The necessity to take into account the nature of the flow rate connection unevenness along the length for obtaining reliable results when calculating real drainage pipelines is shown in the article.