To see the other types of publications on this topic, follow the link: Net pressure ratio.
Journal articles on the topic 'Net pressure ratio'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 journal articles for your research on the topic 'Net pressure ratio.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse journal articles on a wide variety of disciplines and organise your bibliography correctly.
1
Zivic, Marija, Antun Galovic, and Zdravko Virag. "Detailed analysis of the effect of the turbine and compressor isentropic efficiency on the thermal and exergy efficiency of a Brayton cycle." Thermal Science 18, no. 3 (2014): 843–52. http://dx.doi.org/10.2298/tsci1403843z.
Full textAbstract:
Energy and exergy analysis of a Brayton cycle with an ideal gas is given. The irreversibility of the adiabatic processes in turbine and compressor is taken into account through their isentropic efficiencies. The net work per cycle, the thermal efficiency and the two exergy efficiencies are expressed as functions of the four dimensionless variables: the isentropic efficiencies of turbine and compressor, the pressure ratio, and the temperature ratio. It is shown that the maximal values of the net work per cycle, the thermal and the exergy efficiency are achieved when the isentropic efficiencies and temperature ratio are as high as possible, while the different values of pressure ratio that maximize the net work per cycle, the thermal and the exergy efficiencies exist. These pressure ratios increase with the increase of the temperature ratio and the isentropic efficiency of compressor and turbine. The increase of the turbine isentropic efficiency has a greater impact on the increase of the net work per cycle and the thermal efficiency of a Brayton cycle than the same increase of compressor isentropic efficiency. Finally, two goal functions are proposed for thermodynamic optimization of a Brayton cycle for given values of the temperature ratio and the compressor and turbine isentropic efficiencies. The first maximizes the sum of the net work per cycle and thermal efficiency while the second the net work per cycle and exergy efficiency. In both cases the optimal pressure ratio is closer to the pressure ratio that maximizes the net work per cycle.
2
Srisiriwat, Nawadee. "Energy Analysis of Hydrogen Production from Methanol under Atmospheric Pressure and Supercritical Water Conditions." Advanced Materials Research 1119 (July 2015): 548–53. http://dx.doi.org/10.4028/www.scientific.net/amr.1119.548.
Full textAbstract:
The energy analysis of hydrogen production from the methanol reforming and oxidation under atmospheric (ATM) pressure and supercritical water (SCW) conditions was performed. The equilibrium hydrogen was investigated by the minimization of the Gibbs free energy based on Peng-Robinson equation of state for high pressure and ideal gas equation for atmospheric pressure. An objective of this study was to obtain the optimum operating conditions to maximize the net hydrogen yield, defined as the hydrogen yield taking into account also the methanol consumed by combustion to generate heat. This was done by investigating the effect of operating parameters over the following ranges: temperatures between 773 and 1273 K, pressures between 0.1 and 25.0 MPa, water-to-methanol (H2O:MeOH) ratios between 1 and 5, and oxygen-to-methanol (O2:MeOH) ratios between 0 and 1.05. At ATM pressure, it was found that the equilibrium hydrogen yield increases with increasing H2O:MeOH ratio but the peak of equilibrium H2yield is at 973 K for higher H2O:MeOH ratio than 1:1. Additionally, the total heat load increases significantly as the reaction temperature and the water amount increase. Therefore, the optimum net H2yield is at the H2O:MeOH ratio of 2:1 and the reaction temperature at 973 K. Under SCW conditions, an increase of temperature and water amount in the system constantly increases the equilibrium H2yield. It means that the high H2O:MeOH ratio and temperature are required in SCW. The presence of oxygen in hydrogen production was investigated that an increase of O2:MeOH ratio constantly decreases the H2yield and also the net H2yield for reaction at ATM pressure whereas under SCW conditions, the equilibrium H2yield and the net H2yield increase with increasing oxygen up to 0.42 and 0.84, respectively.
3
Liu, Zhengnan, Rui Zhang, Zhaojing Liu, and Yuming Zhang. "Experimental Study on Swelling Behavior and Its Anisotropic Evaluation of Unsaturated Expansive Soil." Advances in Materials Science and Engineering 2021 (May 25, 2021): 1–13. http://dx.doi.org/10.1155/2021/6937240.
Full textAbstract:
Evaluation of swelling behavior is important for designing structures in expansive soils areas, especially for highway that the swelling pressure generated upon pavement and retaining structures in both vertical and horizontal directions due to infiltration. In this study, modification was made on unsaturated consolidation oedometer to provide synchronized measurement of vertical swelling strain (VSS) and lateral pressure (LP) of expansive soil under constant net normal stress and controlled matric suction. Vertical swelling (VS) test and lateral swelling (LS) test were conducted to investigate the anisotropic swelling behavior. The influence of mean net stress and net stress ratio on VSS was investigated, and the anisotropic swelling behavior of unsaturated expansive soil was characterized using anisotropic swelling ratio. The results show that the VSS nonlinearly decreased as the mean net stress increased and increased as the net stress ratio increased. The expansive soil would rapidly enter the passive state due to lateral swelling pressure under relatively low surcharge, with major principal axis rotating from vertical direction to lateral direction, which advances the possibility of passive failure for light retaining structures. The anisotropic swelling behavior objectively exists and varies with matric suction and net normal stress, which should not be ignored for engineering application.
4
Cheon, Dong-Jin, Yong-Chul Kim, Jong-Ho Lee, and Sung-Won Yoon. "Experimental Investigation of Wind Pressure Characteristics for Cladding of Dome Roofs." Materials 14, no. 18 (September 13, 2021): 5266. http://dx.doi.org/10.3390/ma14185266.
Full textAbstract:
Cladding for dome roofs is often made of membrane materials that are light and easy to install. Due to these characteristics, wind damage to dome roof cladding is very common. In particular, open or retractable dome roofs are prone to wind damage because of inadequacies in wind load calculations. In this study, the wind pressure characteristics of a dome with a central opening were investigated. Wind tunnel tests were performed, and the pressure distribution was investigated by analyzing external and internal pressure coefficients. Based on the experimental results, the peak net pressure coefficients for the cladding design of a dome roof with a central opening were proposed. For the external peak pressure coefficients, the values of leeward regions were similar despite height–span ratios and turbulence intensity values. For the internal peak pressure coefficients, negative pressure was dominant, and the coefficients were not significantly affected by changes in height–span ratio. This tendency locally increased the negative peak net pressure, in which the load acts in the upward direction, and relatively significantly increased the positive peak net pressure, in which the load acts in the downward direction.
5
Demers, Denis, and Serge Leroueil. "Evaluation of preconsolidation pressure and the overconsolidation ratio from piezocone tests of clay deposits in Quebec." Canadian Geotechnical Journal 39, no. 1 (February 1, 2002): 174–92. http://dx.doi.org/10.1139/t01-071.
Full textAbstract:
The preconsolidation pressure and overconsolidation ratio profiles are the most important factors related to the mechanical behaviour of clay deposits. They are interpreted on the basis of a limited number of laboratory tests, but the near-continuous information provided by the piezocone can allow local data to be extrapolated to an entire site. Numerous methods have been proposed for relating piezocone data to preconsolidation pressure and the overconsolidation ratio, but their validity is still uncertain. In this paper, nine methods are compared on the basis of data collected on 31 sensitive clay sites in Quebec whose preconsolidation pressure profiles are well known. Each method is briefly presented and the most promising are identified. The simplest method, which directly relates preconsolidation pressure to net tip resistance, also appears to be the most effective.Key words: clay, preconsolidation pressure, overconsolidation ratio, piezocone, correlations.
6
Houlden, D., M. Li, and S. Portman. "Importance of ventricle-to-brain ratio (VBR) and volume of CSF drainage in the treatment of very low pressure hydrocephalus." Canadian Journal of Neurological Sciences / Journal Canadien des Sciences Neurologiques 42, S1 (May 2015): S43. http://dx.doi.org/10.1017/cjn.2015.194.
Full textAbstract:
Introduction: Low pressure hydrocephalus is a known complication of prolonged hydrocephalus sometimes treatable with continued low-pressure drainage at subatmospheric pressures. Clarke et. al. and Filipidis et. al. have reported poor outcomes when treating very low pressure hydrocephalus (VLPH). We present 4 cases of very low pressure hydrocephalus (VLPH) following transnasal endoscopic resection of suprasellar lesions and hypothesize that poor prognostic cases can be identified thereby avoiding prolonged futile treatments. Methods: We performed a retrospective chart review of 4 cases of VLPH and tried to identify metrics contributing to successful treatment. We examined the Pearson correlations between Glasgow Coma Scale and ventricle-to-brain ratio (VBR); volume of CSF drained; net fluids; and serum sodium, urea, and creatinine. Results: Our investigation reveals that Glasgow Coma Score is positively correlated with increased CSF drainage and negatively correlated with increased ventricle-to-brain ratio. The most important determinant of good outcome is brain compliance as measured by the brain’s ability to maintain a good GCS score in the face of wide ranges in ventricle-to-brain ratio (VBR). Conclusion: We propose that futile prolonged subatmospheric drainage be avoided by declining treatment in patients who have ventriculitis and patients who have a narrow range of ventricle-to-brain ratio (VBR) concurrent with a good neurological examination.
7
Weng, Ding Wei, Qun Lei, Zi Yi Guo, and Yong Luo. "A New Method of Fracture Designing to Elevate SRV in Natural Fractured Sandstone Reservoir." Applied Mechanics and Materials 275-277 (January 2013): 1471–75. http://dx.doi.org/10.4028/www.scientific.net/amm.275-277.1471.
Full textAbstract:
This paper firstly analyze the relationship between the fracture net pressure and the sand to fluid ratio (SOR), and the conclusion is that the high SOR could accumulate high net pressure to make the natural fractures open in natural fractured sandstone reservoir. Then relationship between the cumulative oil production and opening the natural fractures is analyzed by means of reservoir numerical simulation, and the conclusion is that the cumulative oil production increased apparently as the area of opening natural fractures increasing. Based on the analyses, a new method of optimizing fracture conductivity to elevate the stimulating reservoir volume (SRV) was formed: firstly, evaluate the stress field and calculate the critical net pressure of the natural fractures opening; secondly, determine the average proppant concentration according the relationship between the net pressure and proppant concentration; thirdly, calculate the fracture conductivity according to the proppant concentration; at last, optimize the fracture length. There are two key works: one is acquiring the accurate principal stress combining the indoor experiment and field test; the other one is acquiring accurate conductivity of proppant, and long term conductivity experiments are recommended.
8
Gao, You, De’an Sun, and Annan Zhou. "Hydromechanical behaviour of unsaturated soil with different specimen preparations." Canadian Geotechnical Journal 53, no. 6 (June 2016): 909–17. http://dx.doi.org/10.1139/cgj-2015-0381.
Full textAbstract:
The effect of different specimen preparation methods (compaction, reconstitution) on the hydromechanical behaviour and microstructure of soil was studied through a series of soil-water retention tests, triaxial tests, and mercury intrusion porosimetry (MIP) tests on an unsaturated clayey silt. Key findings from this experimental study include the following. (i) The air-entry value of the reconstituted specimen is higher than that of the compacted specimen with the same initial void ratio. (ii) The reconstituted specimen exhibits a unimodal pore-size distribution and the compacted specimen exhibits a bimodal pore-size distribution, according to results of the MIP tests. (iii) The soil-water characteristic curves and residual gravimetric water content of compacted and reconstituted specimens are almost the same in the high suction range. (iv) The void ratio of a reconstituted specimen decreases sharply with increasing suction value under an isotropic net stress (such as 20 kPa), while the void ratio of a compacted specimen shows a small change for the same suction change process. (v) Under the same net confining pressure, the shear strength of both compacted and reconstituted specimens increases with the suction increase. The shear strength of the reconstituted specimen is higher than that of the compacted specimen with the same density under the same suction and net confining pressure.
9
Lin, Xinxing, Chonghui Chen, Aofang Yu, Likun Yin, and Wen Su. "Performance Comparison of Advanced Transcritical Power Cycles with High-Temperature Working Fluids for the Engine Waste Heat Recovery." Energies 14, no. 18 (September 17, 2021): 5886. http://dx.doi.org/10.3390/en14185886.
Full textAbstract:
To efficiently recover the waste heat of mobile engine, two advanced transcritical power cycles, namely split cycle and dual pressure cycle, are employed, based on the recuperative cycle. Performances of the two cycles are analyzed and compared through the development of thermodynamic models. Under given gas conditions, seven high-temperature working fluids, namely propane, butane, isobutane, pentane, isopentane, neopentane, and cyclopentane, are selected for the two cycles. At the design system parameters, the highest work 48.71 kW, is obtained by the split cycle with butane. For most of fluids, the split cycle has a higher work than the dual pressure cycle. Furthermore, with the increase of turbine inlet pressure, net work of the split cycle goes up firstly and then decreases, while the work of dual pressure cycle increases slowly. For the split cycle, there exists a split ratio to get the maximum network. However, for the dual pressure cycle, the larger the evaporation temperature, the higher the net work. On this basis, system parameters are optimized by genetic algorithm to maximize net work. The results indicate that the highest work 49.96 kW of split cycle is obtained by pentane. For the considered fluids, except cyclopentane, split cycle always has a higher work than dual pressure cycle. Due to the higher net work and fewer system components, split cycle is recommended for the engine waste heat recovery.
10
Zhang, W., L. Chen, and F. Sun. "Performance optimization for an open-cycle gas turbine power plant with a refrigeration cycle for compressor inlet air cooling. Part 2: Power and efficiency optimization." Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 223, no. 5 (May 14, 2009): 515–22. http://dx.doi.org/10.1243/09576509jpe727.
Full textAbstract:
The power and efficiency of the open cycle gas turbine power plant with a refrigeration cycle for compressor inlet air cooling with pressure drop irreversibilities are optimized based on the model established using finite time thermodynamics in Part 1 of this article by adjusting the mass flowrate (or the distribution of pressure losses along the flow path). It is shown that there are optimal air mass flowrates (or the distribution of pressure losses along the flow path) that maximize the net power output, and the maximum has additional maximum with respect to the compressor overall pressure ratio. When optimization is performed with the constraints of the fixed fuel flow and the plant size, the net power output and the thermal conversion efficiency of the cycle can be maximized again by properly allocating the fixed flow area among the compressor inlet and the power turbine outlet. The numerical examples show the effects of design parameters on the power output and heat conversion efficiency. The net power output and the thermal conversion efficiency are improved by using the refrigeration cycle for compressor air inlet cooling.
11
Caron, Olivier, Thierry Gélat, Patrice Rougier, and Jean-Pierre Blanchi. "A Comparative Analysis of the Center of Gravity and Center of Pressure Trajectory Path Lengths in Standing Posture: An Estimation of Active Stiffness." Journal of Applied Biomechanics 16, no. 3 (August 2000): 234–47. http://dx.doi.org/10.1123/jab.16.3.234.
Full textAbstract:
The center of foot pressure (CP) motions, representing the net neuromuscular control, was compared to the center of gravity (CG) motions, representing the net performance. The comparison focused on the trajectory path length parameter along the mediolateral and antero-posterior axes because these two variables depend on amplitude versus frequency relationship. This relationship was used to evaluate the CG motions based on the CP motions. Seven subjects stood still on a force plate with eyes open and eyes closed. The results showed that the ratio of (CP – CG)/CP trajectory path length was personal for each subject. These results suggest different levels of passive (ligaments, elastic properties) and active (reflex activity) stiffness. For some subjects, this ratio was significantly lower for the eyes open condition than for the eyes closed condition, indicating a decrease of the active stiffness for the eyes open condition. Therefore, a CG – CP comparative analysis appeared helpful in understanding the control of balance and necessary to quantify the subjects’ net performance.
12
Saikaew, Charnnarong. "Factors Influencing Hardness of a Coating Material for Coating a Machine Component." Key Engineering Materials 821 (September 2019): 294–300. http://dx.doi.org/10.4028/www.scientific.net/kem.821.294.
Full textAbstract:
This work investigated the influences of DC current, pressure and N2 to Ar gas flow rate on hardness of a TiN hard coating material for coating a fishing net-weaving machine component of a fishing net-weaving machine, namely upper hook. The target of this study was to maximize the hardness of TiN coated upper hook in order to maximize the corresponding wear resistance. Three process factors including DC current, operating pressure and N2 to Ar flow rate ratio were simultaneously investigated using the factorial design with replicates at the center point of the three factors method. Analysis of variance was used to investigate the effect of the three factors on the hardness of the TiN coated upper hook and the contour plots based on empirical model were plotted to obtain an appropriate operating condition of the statistically significant process factors with maximizing hardness value leading to the wear resistance of the upper hook. The results showed that the operating pressure and the N2 to Ar flow rate ratio and interaction among the three process factors significantly affected the average hardness at the level of significance of 0.05. Finally, an appropriate operating condition of the significant process factors was obtained at the higher levels of the operating pressure and the N2 to Ar flow rate ratio.
13
Woodward, J. B. "Optimal Second-Law Efficiency for a Brayton Cycle With an Internal Heat Source." Journal of Energy Resources Technology 117, no. 4 (December 1, 1995): 343–48. http://dx.doi.org/10.1115/1.2835433.
Full textAbstract:
Net work of an endoreversible Brayton cycle and its second-law efficiency are examined for a heat source (hot air) that is initially at a temperature typical of adiabatic and stoichiometric combustion. That temperature is taken to be well above maximum cycle temperature. When heat is transferred to the cycle via a heat exchanger, maximum work per unit of heat source mass and per unit of heat source availability (second-law efficiency) are found to occur at a cycle pressure ratio that differs from the pressure ratio for maximum cycle first-law efficiency. When the heat source is internal, i.e., a fraction of the cycle working fluid, maximum work per unit of heat source mass is found to occur at the pressure ratio found for the external source; on the other hand, maximum work per unit of heat source availability is found to occur at the highest possible cycle pressure ratio, which is the same point at which cycle first-law efficiency is a maximum.
14
Marler, Thomas E., Michael V. Mickelbart, and Roland Quitugua. "Papaya Ringspot Virus Influences Net Gas Exchange of Papaya Leaves." HortScience 28, no. 4 (April 1993): 322–24. http://dx.doi.org/10.21273/hortsci.28.4.322.
Full textAbstract:
Leaves of container-grown papaya (Carica papaya L.) plants were inoculated with papaya ringspot virus (PRV) to determine its influence on dark respiration and photosynthesis. Photosynthetic capacity, apparent quantum yield, ratio of variable to maximum fluorescence from dark-adapted leaves, and photosynthetic CO2-use efficiency were reduced by PRV infection. Internal CO2 partial pressure at ambient external CO2 was not affected, but leaf dark respiration was increased by PRV infection. These results suggest that reduced growth, yield, and fruit quality common in PRV-infected papaya plants is caused, at least partially, by reduced photosynthesis and increased respiration.
15
Espinosa, Luis F., and Petros Lappas. "Mathematical Modelling Comparison of a Reciprocating, a Szorenyi Rotary, and a Wankel Rotary Engine." Nonlinear Engineering 8, no. 1 (January 28, 2019): 389–96. http://dx.doi.org/10.1515/nleng-2017-0082.
Full textAbstract:
Abstract This paper provides an explanation of the geometry, design, and operational principles for the three engines; having special emphasis in the Szorenyi rotary engine which has a deforming rhombus revolving inside a mathematically defined stator. A basic ideal mathematical simulation of those engines were performed, assuming the Otto cycle for the three engines. Also, it assumes the volumetric efficiency of 100%, a wide-open throttle (WOT), no knock nor any mechanical or thermal losses. This simulation focuses on how the fuel burns during combustion, creating pressure and thus, net work. A comparison in pressure traces and cycle performance is made. The study concludes analysing and comparing the ignition advance; finding the best advance for each engine thus the net work between the three engines during one working cycle. Finally, this paper analyses how the different volume change ratio for the combustion chamber of the Szorenyi, Wankel and the reciprocating engine have an effect in the pressure, net work and thermal efficiency generated inside the chamber during combustion for every working cycle.
16
Perez Fontan, J. J., G. P. Heldt, and G. A. Gregory. "Mean airway pressure and mean alveolar pressure during high-frequency jet ventilation in rabbits." Journal of Applied Physiology 61, no. 2 (August 1, 1986): 456–63. http://dx.doi.org/10.1152/jappl.1986.61.2.456.
Full textAbstract:
Mean airway pressure underestimates mean alveolar pressure during high-frequency oscillatory ventilation. We hypothesized that high inspiratory flows characteristic of high-frequency jet ventilation may generate greater inspiratory than expiratory pressure losses in the airways, thereby causing mean airway pressure to overestimate, rather than underestimate, mean alveolar pressure. To test this hypothesis, we ventilated anesthetized paralyzed rabbits with a jet ventilator at frequencies of 5, 10, and 15 Hz, constant inspiratory-to-expiratory time ratio of 0.5 and mean airway pressures of 5 and 10 cmH2O. We measured mean total airway pressure in the trachea with a modified Pitot probe, and we estimated mean alveolar pressure as the mean pressure corresponding in the static pressure-volume relationship to the mean volume of the respiratory system measured with a jacket plethysmograph. We found that mean airway pressure was similar to mean alveolar pressure at frequencies of 5 and 10 Hz but overestimated it by 1.1 and 1.4 cmH2O at mean airway pressures of 5 and 10 cmH2O, respectively, when frequency was increased to 15 Hz. We attribute this finding primarily to the combined effect of nonlinear pressure frictional losses in the airways and higher inspiratory than expiratory flows. Despite the nonlinearity of the pressure-flow relationship, inspiratory and expiratory net pressure losses decreased with respect to mean inspiratory and expiratory flows at the higher rates, suggesting rate dependence of flow distribution. Redistribution of tidal volume to a shunt airway compliance is thought to occur at high frequencies.(ABSTRACT TRUNCATED AT 250 WORDS)
17
Srisattayakul, Parinya, Charnnarong Saikaew, Anurat Wisitsoraat, and Naphatara Intanon. "Effects of Sputtering Coating Factors on Elastic Modulus of MoN Coatings." Advanced Materials Research 896 (February 2014): 249–52. http://dx.doi.org/10.4028/www.scientific.net/amr.896.249.
Full textAbstract:
Surface quality of an upper hook, an important fishing net-weaving machine component manufactured from stainless steel, was improved by systematically investigating the effects of sputtering coating factors using experimental design. Three factors of MoN coating on upper hooks including DC current, operating pressure, and Ar/N2 ratio were studied and optimized for maximum elastic modulus. It was found that the three coating factors affected the elastic modulus of the MoN coating on upper hooks. In addition, the optimal operating condition for MoN coating that produced a maximum elastic modulus was obtained at DC current of 0.35 A, operating pressure of 0.01 mbar, and Ar/N2 ratio of 1.5.
18
Singhal, Sonal, Sandra L. Houston, and William N. Houston. "Swell pressure, matric suction, and matric suction equivalent for undisturbed expansive clays." Canadian Geotechnical Journal 52, no. 3 (March 2015): 356–66. http://dx.doi.org/10.1139/cgj-2014-0159.
Full textAbstract:
Methods of computation for soil heave based on an “equivalent” net normal stress path approach often have built-in assumptions regarding the relationship between in situ matric suction, overburden stress, and swell pressure. The term “matric suction equivalent” has been previously defined as the difference between in situ state of stress projected on the net normal stress plane (represented by swell pressure) and overburden stress. Correlations between matric suction, overburden stress, and swell pressure for matric suction values in excess of the air-entry value have not been well studied and are explored here for expansive soils. Filter paper (in-contact) and constant volume swell pressure tests were performed on undisturbed tube samples of expansive soils taken from Arizona, Colorado, and Texas. In general, the ratio of the matric suction equivalent to the matric suction decreases with increasing soil suction. An empirical relationship was established in which the matric suction equivalent was found to be proportional to the logarithm of the matric suction for in situ matric suctions greater than a certain value, termed as the “intercept matric suction”. A correlation between the intercept matric suction and the soil’s plasticity index (PI) was found for the clays of this study. The developed correlations represent a method for obtaining approximate estimates of in situ matric suction for expansive soils from PI and swell pressure data. Implications of the study findings for the use of an equivalent net normal stress approach for estimation of soil heave are explored.
19
Viskovic, Alberto. "Mode Pressure Coefficient Maps as an Alternative to Mean Pressure Coefficient Maps for Non-Gaussian Processes: Hyperbolic Paraboloid Roofs as Cases of Study." Computation 6, no. 4 (December 12, 2018): 64. http://dx.doi.org/10.3390/computation6040064.
Full textAbstract:
Wind tunnel experiments are necessary for geometries that are not investigated by codes or that are not generally and parametrically investigated by literature. One example is the hyperbolic parabolic shape mostly used for cable net roofs, for which codes do not provide pressure coefficients and literature only gives mean, maxima, and minima pressure coefficient maps. However, most of pressure series acquired in wind tunnels on the roof are not Gaussian processes and, for this reason, the mean values are not precisely representative of the process. The paper investigates the ratio between mean and mode of pressure coefficient series acquired in wind tunnels on buildings covered with hyperbolic paraboloid roofs with square plans. Mode pressure coefficient maps are given as an addition to traditional pressure coefficient maps.
20
Mallick, K., A. Jarvis, G. Wohlfahrt, G. Kiely, T. Hirano, A. Miyata, S. Yamamoto, and L. Hoffmann. "Components of near-surface energy balance derived from satellite soundings – Part 2: Latent heat flux." Biogeosciences Discussions 11, no. 6 (June 4, 2014): 8085–113. http://dx.doi.org/10.5194/bgd-11-8085-2014.
Full textAbstract:
Abstract. This paper introduces a relatively simple method for recovering global fields of latent heat flux. The method focuses on specifying Bowen ratio estimates through exploiting air temperature and vapour pressure measurements obtained from infra-red soundings of the AIRS (Atmospheric Infrared Sounder) sensor onboard the NASA-Aqua platform. Through combining these Bowen ratio retrievals with satellite surface net available energy data we have specified estimates of global surface latent heat flux at the 1° by 1° scale. These estimates were evaluated against data from 30 terrestrial tower flux sites covering a broad spectrum of biomes. Taking monthly average 13:30 h data for 2003, this revealed a relatively good agreement between the satellite and tower measurements of latent heat flux, with a pooled root mean square deviation of 79 W m−2, and no significant bias. However, this success partly arose as a product of the under specification of the AIRS Bowen ratio compensating for the under specification of the AIRS net available energy.
21
Govinda Rao, B., Y. Datta Bharadwaz, Chukka Virajitha, and V. Dharma Rao. "Effect of injection parameters on the performance and emission characteristics of a variable compression ratio diesel engine with plastic oil blends – An experimental study." Energy & Environment 29, no. 4 (January 29, 2018): 492–510. http://dx.doi.org/10.1177/0958305x17753208.
Full textAbstract:
Due to the depleting fossil fuel reserves and increasing environmental concerns, researchers have been studying the effect of adding different types of oils to diesel and more recently plastic oil. The present paper is an experimental study of the effect of compression ratio and injection parameters such as injection pressures and injection timing on the performance and emission characteristics of a variable compression ratio diesel engine fuelled with blends of plastic oil. Various proportions of ethanol and diesel are blended with plastic oils for the preparation of test fuels. It is observed from the experimental study that P90D5E5 blend gives the highest brake thermal efficiency yielding an increase of 16% and 38% compared with pure diesel and pure plastic oil, respectively. Smoke emissions are found to be the lowest for P90D5E5 than diesel and P100. Brake-specific fuel consumption, carbon monoxide and smoke values are reduced for all blends with an increase in injection timing, pressure and compression ratio. Combustion analysis of the blends indicates higher values of cylinder pressures and net heat release rates for P90D5E5 and P100, respectively.
22
Crane, R. I. "A critical analysis of the thermodynamic advantages of reheat in gas turbines." Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 212, no. 2 (March 1, 1998): 81–87. http://dx.doi.org/10.1243/0957650981536600.
Full textAbstract:
Apparently conflicting ideas on the effects of reheat on gas turbine performance can be obtained when comparing thermodynamics textbook treatments with recent literature on the new generation of reheat machines. These are resolved through the use of models with varying degrees of realism. The models are built with ‘live mathematics’ software which makes it straightforward to incorporate additional irreversibilities and less-simplified gas property relationships, and can be more effective than algebraic analyses for demonstrating the effect of cycle parameters. It is shown how the sign of the change in overall efficiency due to reheat depends on pressure and temperature ratios and on compressor and turbine efficiencies, and why a high compressor pressure ratio is beneficial. The trade-off between gains in specific net work and efficiency, by selection of the reheating pressure, is illustrated, the current relevance of the value that maximizes net work, traditionally termed ‘optimum’, is questioned and it is demonstrated that an exhaust temperature suitable for combined cycle operation requires a higher reheating pressure. Further results show how fuel consumption and gross power are divided between high- and low-pressure combustors and turbines respectively.
23
Liu, Xiaoqiang, Zhanqing Qu, Tiankui Guo, Dongying Wang, Qizhong Tian, and Wei Lv. "A new chart of hydraulic fracture height prediction based on fluid–solid coupling equations and rock fracture mechanics." Royal Society Open Science 5, no. 10 (October 2018): 180600. http://dx.doi.org/10.1098/rsos.180600.
Full textAbstract:
The conventional method to predict hydraulic fracture height depends on linear elastic mechanics, and the typical Gulrajani–Nolte chart fails to reflect fracture height when the net pressure in the fracture is too high. Based on fluid–solid coupling equations and rock fracture mechanics, a new chart is obtained by the ABAQUS extended finite-element method. Compared with the Gulrajani–Nolte chart, this new chart shows that longitudinal propagation of hydraulic fracture is still finite when the net pressure in the fracture is higher than in situ stress difference between reservoir and restraining barrier. The barrier has a significant shielding effect on the longitudinal propagation of hydraulic fracture, and there is a threshold for an injection rate of fracturing fluid to ensure hydraulic fracture propagates in the barrier. Fracture height decreases with the increase of in situ stress difference. When the ratio of net pressure to in situ stress difference is less than 0.56, the propagation of hydraulic fracture is completely restricted in the reservoir. Hydraulic fracturing parameters in Well Shen52 and Well Shen55 are optimized by using the new chart. Array acoustic wave logging shows that the actual fracture height is at an average error within 14.3% of the theoretical value, which proves the accuracy of the new chart for field application.
24
Selvan, P. T., and G. S. Goteti. "Performance, Emission and Combustion Characteristics of VCR CRDI Diesel Engine Fuelled with n-butanol Blends." International Journal of Automotive and Mechanical Engineering 16, no. 3 (October 3, 2019): 6825–43. http://dx.doi.org/10.15282/ijame.16.3.2019.01.0513.
Full textAbstract:
This research work indicates the analysis conducted to investigate the performance, exhaust emission and combustion characteristics of a VCR diesel engine fuelled with nbutanol blends at a rated speed of 1500 rpm with 300 bar injection pressure at compression ratios of 16, 18 and 20. The test fuel was prepared by adding n-butanol 10% (NB10) and 20% (NB20) to diesel by volume. The combustion characteristics investigated were; rise in-cylinder pressures, net heat release rate, cumulative heat release rate and mass fraction of fuel burned at all loads using three compression ratios. The emission and performance study also conducted. The higher heat release rates, increased cylinder pressures were observed for both the blends compared to diesel. Increased brake thermal efficiency observed at higher compression ratio for NB20 blend. It had also been observed that the emissions of CO2, HC and NOx were increased for both the blends, while CO emissions decreased in trend with an increase in compression ratio and blend strength.
25
Houlden, Danielle, Dmitriy Khodorskiy, Sandra Miller-Portman, and Maria Li. "Importance of Frontal Horn Ratio and Optimal CSF Drainage in the Treatment of Very Low-Pressure Hydrocephalus." Journal of Neurological Surgery Part B: Skull Base 79, no. 04 (December 11, 2017): 379–85. http://dx.doi.org/10.1055/s-0037-1609033.
Full textAbstract:
Introduction Unlike low-pressure hydrocephalus, very low pressure hydrocephalus (VLPH) is a rarely reported clinical entity previously described to be associated with poor outcomes and to be possibly refractory to treatment with continued cerebrospinal fluid (CSF) drainage at subatmospheric pressures.1, 2 We present four cases of VLPH following resection of suprasellar lesions and hypothesize that untreatable patients can be identified early, thereby avoiding futile prolonged external ventricular drainage in ICU. Methods We performed a retrospective chart review of four cases of VLPH encountered between 2007 and 2015 in two different institutions and practices and tried to identify factors contributing to successful treatment. We hypothesized that normalization of frontal horn ratio (FHR), optimization of volume of CSF drained, and avoidance of fluid shifts would contribute to improved Glasgow Coma Score (GCS). We examined fluid shifts by studying net fluids shifts and serum levels of sodium, urea, and creatinine. We used Pearson and Spearman correlations to identify measures that would correlate with improved GCS. Results Our study reveals that improving GCS is positively correlated with decreased FHR and increased CSF drainage within an optimal range. The most important determinant of good outcome is retention of brain viscoelasticity as evidenced by restoration and maintenance of good GCS score despite fluctuations in FHR. Conclusion Futile prolonged subatmospheric drainage can be avoided by declining to continue treatment in patients who have permanently altered brain compliance secondary to unsealed CSF leaks, irremediable ventriculitis, and who are therefore unable to sustain an improved neurologic examination.
26
Maqableh, A. M., S. A. Ammourah, A. F. Khadrawi, M. A. Al-Nimr, and A. C. Benim. "Hydrodynamics behaviour of a fluid flow in micro-venturi." Canadian Journal of Physics 90, no. 1 (January 2012): 83–89. http://dx.doi.org/10.1139/p11-145.
Full textAbstract:
Hydrodynamic behaviour of a fluid flow in micro-venturi is investigated numerically taking into account the effect of the Knudsen number (Kn), diameter ratio (β), and Reynolds number (Re). It is found that the velocity jump in the throat of the venturi increases with increasing Re. The axial velocity takes its maximum values at the narrowest section, and these values increase with decreasing Kn. Also, it is found that the dimensionless pressure distribution and the net pressure loss increase as Kn decreases while pressure attains its maximum values at the entrance section. On the other hand, it is observed that increasing Kn and decreasing β cause the discharge coefficient to decrease.
27
Macdonald, S. Ellen, and Victor J. Lieffers. "Photosynthesis, water relations, and foliar nitrogen of Piceamariana and Larixlaricina from drained and undrained peatlands." Canadian Journal of Forest Research 20, no. 7 (July 1, 1990): 995–1000. http://dx.doi.org/10.1139/x90-133.
Full textAbstract:
Rates of net assimilation and related ecophysiological parameters were measured three times during the 1988 growing season on a total of 80 black spruce (Piceamariana (Mill.) B.S.P.) and 80 tamarack (Larixlaricina (Du Roi) K. Koch) trees from two peatland locations, each with paired drained and undrained plots. Ditching for drainage was completed in March 1984. There was no evidence of improved water relations in trees on the drained plots. The initial effect of drainage was the improvement of nitrogen relations. This, in turn, was associated with higher rates of net assimilation. In general, trees in the drained plots were characterized by higher rates of net assimilation, water-use efficiency, mesophyll conductance to CO2, a lower ratio of intercellular to ambient partial pressure of CO2, and higher foliar nitrogen content. For tamarack, the drainage effect was only significant at one location, which was described as the poorer site. For both species, measures of net assimilation and foliar nitrogen were positively correlated with leader growth.
28
Nishimura, Tomoyoshi, Yasunari Hirabayashi, Delwyn G. Fredlund, and Julian K.-M. Gan. "Influence of stress history on the strength parameters of an unsaturated statically compacted soil." Canadian Geotechnical Journal 36, no. 2 (September 25, 1999): 251–61. http://dx.doi.org/10.1139/t98-098.
Full textAbstract:
Unsaturated soils are generally near the ground surface and are commonly overconsolidated due to environmental effects. The stress state variables for an unsaturated, in situ profile consist of the net total stress, (σ - ua), and matric suction, (ua - uw), where σ is the total stress (in three directions), ua is the pore-air pressure, and uw is the pore-water pressure. These stress state variables control the behavior of the unsaturated soil. A total stress ratio, TSR, was used in this study as a measure of the stress history. The total stress ratio is defined as the ratio of the compaction pressure to the current confining pressure. Shear tests were conducted using a modified direct shear apparatus on a statically compacted unsaturated soil subjected to various total stress ratios with controlled matric suction. The shear strength parameters (i.e., ϕ', ϕb, and c') for an unsaturated soil were measured using the modified direct shear apparatus. The total stress ratio influences the shear strength parameter ϕb of a compacted soil. The shear strength parameter ϕb decreases with matric suction regardless of the loading history. For a compacted soil with a total stress ratio of 1.0, ϕb was higher than that for the soil tested at a total stress ratio greater than 1.0, regardless of increase in matric suction, and was shown to be influenced by loading history.Key words: unsaturated soil, shear strength, stress history, compacted soil, direct shear test, matric suction.
29
Устинов and Vladimir Ustinov. "Experimental study of forest soil resistance to cone penetration." Forestry Engineering Journal 6, no. 3 (October 10, 2016): 188–96. http://dx.doi.org/10.12737/21698.
Full textAbstract:
This article informs us about testing the theoretical dependence to calculate cone index re-garding the soil deformation module. Common methods of calculation tractive performance of wheeled mover do not allow to analyze the influence of the geometric parameters of wheeled mover,inner tire pressure, slip ratio, wheel load, as well as the physical and mechanical properties of forest soil on rolling resistance, net thrust and drawbar pull coefficient in complex.
30
Kim, Kyoung Hoon, Se Woong Kim, and Hyung Jong Ko. "A Thermodynamic Analysis of Cogeneration System in Parallel Circuit Based on Organic Rankine Cycle." Advanced Materials Research 505 (April 2012): 534–38. http://dx.doi.org/10.4028/www.scientific.net/amr.505.534.
Full textAbstract:
The combined heat and power generation system using Organic Rankine Cycle (ORC) has become a promising technology for efficient conversion of low-grade heat source to useful form of energy. In this study thermodynamic performance is investigated for a cogeneration system which consists of ORC power plant and an additional process heater as a parallel circuit. Nine different kinds of fluids of R143a, R22, R134a, R152a, R123, R113, isobutene, butane, and isopentane are considered as a working fluid of ORC. The effects of system parameters such as turbine inlet pressure, source temperature, and process heat load on the system performance including ratio of mass flow rates, net work production, and the first and second law efficiencies of thermodynamics for each fluid. Results show that there exists an optimal turbine inlet pressure to yield maximum net work. The selection of the working fluid for the combined system which assumes the maximum second-law efficiency is dependent on the source temperature level.
31
Mao, Xiao Fei. "The Application of Regression Analysis in the Characteristics Research of Adjustment to Flue Gas Temperature at Furnace Outlet of CFB Boiler." Advanced Materials Research 518-523 (May 2012): 2247–53. http://dx.doi.org/10.4028/www.scientific.net/amr.518-523.2247.
Full textAbstract:
A type of HG-1025/18.64-L.PM41 circulating fluidized bed boiler (CFB) has been put into production since 2009, a lot of significant experiences have been accumulated by the equipment improvement and operation exploration. To further understand the adjustment characteristics of flue gas temperature at furnace outlet, the operation data of 30 operating conditions have been measured, and also the method of regression analysis is applied to research and analyze the correlative factors composed of boiler load rate, ash content as received basis, volatile content as received basis, net calorific value as received basis, particle diameter of feeding coal, bed pressure, primary air ratio, upper secondary air ratio, lower secondary air ratio and oxygen content at furnace outlet.
32
Kempski, Philipp, Eliot Quataert, Jonathan Squire, and Matthew W. Kunz. "Shearing-box simulations of MRI-driven turbulence in weakly collisional accretion discs." Monthly Notices of the Royal Astronomical Society 486, no. 3 (May 3, 2019): 4013–29. http://dx.doi.org/10.1093/mnras/stz1111.
Full textAbstract:
ABSTRACT We present a systematic shearing-box investigation of magnetorotational instability (MRI)-driven turbulence in a weakly collisional plasma by including the effects of an anisotropic pressure stress, i.e. anisotropic (Braginskii) viscosity. We constrain the pressure anisotropy (Δp) to lie within the stability bounds that would be otherwise imposed by kinetic microinstabilities. We explore a broad region of parameter space by considering different Reynolds numbers and magnetic-field configurations, including net vertical flux, net toroidal-vertical flux, and zero net flux. Remarkably, we find that the level of turbulence and angular-momentum transport are not greatly affected by large anisotropic viscosities: the Maxwell and Reynolds stresses do not differ much from the MHD result. Angular-momentum transport in Braginskii MHD still depends strongly on isotropic dissipation, e.g. the isotropic magnetic Prandtl number, even when the anisotropic viscosity is orders of magnitude larger than the isotropic diffusivities. Braginskii viscosity nevertheless changes the flow structure, rearranging the turbulence to largely counter the parallel rate of strain from the background shear. We also show that the volume-averaged pressure anisotropy and anisotropic viscous transport decrease with increasing isotropic Reynolds number (Re); e.g. in simulations with net vertical field, the ratio of anisotropic to Maxwell stress (αA/αM) decreases from ∼0.5 to ∼0.1 as we move from Re ∼ 103 to Re ∼ 104, while 〈4$\pi$Δp/B2〉 → 0. Anisotropic transport may thus become negligible at high Re. Anisotropic viscosity nevertheless becomes the dominant source of heating at large Re, accounting for ${\gtrsim } 50 {{\ \rm per\ cent}}$ of the plasma heating. We conclude by briefly discussing the implications of our results for radiatively inefficient accretion flows on to black holes.
33
Cho, Soo Yong, Jin Han Kim, and Chae Sil Kim. "Design of Compressor Impeller Using Evolutionary Optimization Technique." Applied Mechanics and Materials 271-272 (December 2012): 833–37. http://dx.doi.org/10.4028/www.scientific.net/amm.271-272.833.
Full textAbstract:
Configuration design on an impeller using to the centrifugal compressor of turbocharger was conducted to improve its performance. Impeller shape was adjusted by changing its meridional contours and blade profile. Total nine design variables were chosen with constraints. ANN (Artificial Neural Net) was adopted as a main optimization algorithm with PSO (Particle Swarm Optimization) in order to reduce the optimization time. This ANN was learned and trained with the design variable sets which were obtained using DOE (Design of Experiment). This ANN was continuously improved its accuracy for each generation of which population was one hundred. New design variable set in each generation was selected using a non-gradient based method of PSO in order to obtain the global optimized result. After 7th generation, the difference of efficiency and pressure ratio predicted by ANN and CFD (Computational Fluid Dynamics) was less than 0.6%. From more than 1,200 design variable sets, a pareto of efficiency versus pressure ratio was obtained and an optimized result was selected based on the multi-objective function. On this optimized impeller, the efficiency and pressure ratio were improved by 1% and 9.3%, respectively.
34
Mallick, K., A. Jarvis, G. Wohlfahrt, G. Kiely, T. Hirano, A. Miyata, S. Yamamoto, and L. Hoffmann. "Components of near-surface energy balance derived from satellite soundings – Part 2: Noontime latent heat flux." Biogeosciences 11, no. 24 (December 22, 2014): 7369–82. http://dx.doi.org/10.5194/bg-11-7369-2014.
Full textAbstract:
Abstract. This paper introduces a relatively simple method for recovering global fields of latent heat flux. The method focuses on specifying Bowen ratio estimates through exploiting air temperature and vapour pressure measurements obtained from infrared soundings of the AIRS (Atmospheric Infrared Sounder) sensor onboard NASA's Aqua platform. Through combining these Bowen ratio retrievals with satellite surface net available energy data, we have specified estimates of global noontime surface latent heat flux at the 1°×1° scale. These estimates were provisionally evaluated against data from 30 terrestrial tower flux sites covering a broad spectrum of biomes. Taking monthly average 13:30 data for 2003, this revealed promising agreement between the satellite and tower measurements of latent heat flux, with a pooled root-mean-square deviation of 79 W m−2, and no significant bias. However, this success partly arose as a product of the underspecification of the AIRS Bowen ratio compensating for the underspecification of the AIRS net available energy, suggesting further refinement of the approach is required. The error analysis suggested that the landscape level variability in enhanced vegetation index (EVI) and land surface temperature contributed significantly to the statistical metric of the predicted latent heat fluxes.
35
Tao, Zhigang, Tongxing Zhang, Daoyong Zhu, Weili Gong, and Manchao He. "Physical Modeling Test on Deformation and Failure of Rock Slope with New Support System." Advances in Civil Engineering 2020 (June 29, 2020): 1–18. http://dx.doi.org/10.1155/2020/8825220.
Full textAbstract:
In order to explore the monitoring and control method of rock slope, indoor physical model testing of collapse control and monitoring were carried out with the example of a rock slope collapse area project in Jietai Temple in Beijing, China, as the prototype. Based on the similarity theory, in this study, a new structural support with Negative Poisson’s Ratio bolt and flexible anchored net was utilized to reinforce the rock slope. Following a graded loading sequence, the collapse failure characteristics and the overall control effect of energy absorption reinforcement measures were explored. The experimental results demonstrated that the entire process of slope collapse presented four distinct stages of failure: fracture generation, fracture propagation, partial collapse, and overall collapse. The full-field displacement nephogram and the displacement monitoring point of the collapse area indicated that the large deformation and failure of the collapsed surrounding rock were effectively controlled, while the Negative Poisson’s Ratio bolt and the flexible anchored net had good reinforcement effects. The experimental stress record presented that the change of pressure curve was an apparent regularity in the entire process of slope collapse, which reflects the change state of internal force of surrounding rock; it includes the function of monitoring of slope collapse. It was indicated that the Negative Poisson’s Ratio bolt along with the large-deformation flexible anchored net had good reinforcement monitoring effect on the rock slope collapse disaster.
36
Leśny, Jacek, and Monika Panfil. "A gap filling method for active surface heat balance structure." ITM Web of Conferences 23 (2018): 00023. http://dx.doi.org/10.1051/itmconf/20182300023.
Full textAbstract:
The paper describes gap filling procedures for active surface heat balance structure data recorded for fields of rape, maize, spring and winter wheat and an apple orchard. The balance components were determined based on the Bowen ratio requiring direct measurements of net radiation, soil heat flux, temperature and water vapour pressure profiles. The latter is used to determine vertical gradients and the Bowen ratio, with sensible and latent heat fluxes calculated from the heat balance equation. Missing data are filled in from regression dependencies between individual balance components at various measurement sites. The regression data set comprised results recorded over 24 h, before the gap in measurements and after 24 h. Multiple regressions were determined from a 48-h measurement set. Regression was applied to establish missing values of net radiation (Rn), soil heat flux (G) and latent heat (LE), while sensible heat was calculated from the active surface heat balance equation. Relatively the greatest differences were found for latent heat and soil fluxes, with both estimated values deviating by 13% from the measured daily average, for net radiation the relative difference was 10% and for sensible heat – 6%. This method successfully filled gaps in measured heat balance data from April to September.
37
Leddin, D. J. "Characterization of small intestinal water, sodium, and potassium transport and morphology in the pig." Canadian Journal of Physiology and Pharmacology 70, no. 1 (January 1, 1992): 113–15. http://dx.doi.org/10.1139/y92-016.
Full textAbstract:
The suitability of the young pig for studies of intestinal transport was investigated by determination of net water, sodium, and potassium absorption, and morphometry in jejunum and ileum. Active net absorption was seen in both jejunum and ileum. There was no difference in absorption between segments and there was a good correlation between water and electrolyte transport. Heart rate, arterial pressure, and absorption were constant with time. Villus height and width were similar to those of human, but crypt depth was greater, and the ratio of villus height to crypt depth less. The mucosa was partially permeable to polyethylene glycol 4000 and this marker is not suitable for studies of transport in young pigs.Key words: pig, intestinal transport, morphology, polyethylene glycol.
38
Gaspar, Stefan, Jan Pasko, and Dusan Knezo. "The Influence of the Tablet Height and Plunger Pressing Velocity on the Final Porosity of Die Casting." Materials Science Forum 916 (March 2018): 244–48. http://dx.doi.org/10.4028/www.scientific.net/msf.916.244.
Full textAbstract:
With a pressure die casting process, one of the important factors affecting the quality of castings represented by porosity is plunger pressing velocity determines the regime die cavity filling and correct determination of dose mass of a molten metal required for one casting cycle. The mass is given by a total of the net mass of a casting, overflows, a gate system and a metal rest inside a filling chamber (the tablet height). As a rule, the tablet height represents the largest mass ratio regarding the waste metal. A correct determination of the tablet height is important from both economical and qualitative aspect of a pressure die casting process.
39
Feng, Yee Chang. "A Clean Energy Generation System of In-Tandem Combinations Each of Heat Pump, Compressor and Turbine in Wind Tunnel." Applied Mechanics and Materials 705 (December 2014): 289–94. http://dx.doi.org/10.4028/www.scientific.net/amm.705.289.
Full textAbstract:
This is a series of in-tandem combinations each of heat pump, air compressor, and air turbine disposed in a wind tunnel, working together to generate clean/renewable electricity. The air compressor, located at downstream of the preceding air turbine, extracts air from this turbine thus reduces its backpressure and causes pressure drop at the turbine exit. Turbine output work Wtb is proportional to temperature difference (T3-T4) of turbine inlet/outlet air, which varies exponentially with turbine outlet/inlet air pressure ratio P4/P3 in adiabatic process as below: Wtb = MCp (T3-T4) = MCpT3{1-P4/P3(1-1/k)} as T4=T3(P4/P3)(1-1/k) where, M=mass flow rate of air; Cp&Cv=constant pressure/volume specific heat capacities of air; k= Cp/Cv=1.4. An ASME paper [1] verifies that a suction blower put at turbine exit reducing back pressure of 200 mbar can increase turbine inlet/outlet air pressure ratio P3/P4by 25%. Therefore, Wtb becomes more than those turbines without such blowers as (T3-T4) becomes larger, thus this unique Clean Energy Generation System of Heat Pumps, Compressors, and Turbines (HPCT system) achieves producing net useful electric power. In HPCT system, each air compressor works efficiently to reduce air pressure at preceding turbine outlet, as it extracts more air from the turbine than the blower mentioned in the ASME paper, because compressors have higher compression ratio than blowers. Thus, such feature gives higher turbine pressure ratio to each combination of HPCT system than those turbines without blowers (or compressors) to reduce back pressure at turbine exit. Therefore, HPCT system of higher turbine air pressure ratio P3/P4 achieves producing more turbine output work, as air temperature at turbine exit simultaneously drops more when P3/P4 becomes larger. Heat pump is an efficient device to move heat from low-temperature source to high-temperature sink, and geothermal heat source is preferable as it provides steady and warmer heat energy. This “moved” heat is used to heat up the air in wind tunnel to offset the energy extracted by turbine from HPCT system. Also, HPCT system is fully thermally insulated, thus theoretically being of zero heat loss, as it works adiabatically. P-V&T-S curves and performance of each combination of HPCT system working cycle are studied to compare it with actual gas turbine cycle and ideal Brayton cycle. Working examples of HPCT system are presented to simulate practical applications of HPCT system, and find out virtual net useful output work and energy efficiency. HPCT system is a “COLD” Engine of Zero Carbon Emission, works under moderate energy efficiency and with higher energy density than most existing renewable energy generation systems. More importantly, it is a simply designed system using only conventional knowledge, and can be made by the existing technology under the least investment risk.
40
Yu, Wan, Qichao Gong, Dan Gao, Gang Wang, Huashan Su, and Xiang Li. "Thermodynamic Analysis of Supercritical Carbon Dioxide Cycle for Internal Combustion Engine Waste Heat Recovery." Processes 8, no. 2 (February 12, 2020): 216. http://dx.doi.org/10.3390/pr8020216.
Full textAbstract:
Waste heat recovery of the internal combustion engine (ICE) has attracted much attention, and the supercritical carbon dioxide (S-CO2) cycle was considered as a promising technology. In this paper, a comparison of four S-CO2 cycles for waste heat recovery from the ICE was presented. Improving the exhaust heat recovery ratio and cycle thermal efficiency were significant to the net output power. A discussion about four different cycles with different design parameters was conducted, along with a thermodynamic performance. The results showed that choosing an appropriate inlet pressure of the compressor could achieve the maximum exhaust heat recovery ratio, and the pressure increased with the rising of the turbine inlet pressure and compressor inlet temperature. The maximum exhaust heat recovery ratio for recuperation and pre-compression of the S-CO2 cycle were achieved at 7.65 Mpa and 5.8 MPa, respectively. For the split-flow recompression cycle, thermal efficiency first increased with the increasing of the split ratio (SR), then decreased with a further increase of the SR, but the exhaust heat recovery ratio showed a sustained downward trend with the increase of the SR. For the split-flow expansion cycle, the optimal SR was 0.43 when the thermal efficiency and exhaust heat recovery ratio achieved the maximum. The highest recovery ratio was 24.75% for the split-flow expansion cycle when the total output power, which is the sum of the ICE power output and turbine mechanical power output, increased 15.3%. The thermal performance of the split-flow expansion cycle was the best compared to the other three cycles.
41
Lechowicz, Zbigniew, Masaharu Fukue, Simon Rabarijoely, and Maria Sulewska. "Evaluation of the Undrained Shear Strength of Organic Soils from a Dilatometer Test Using Artificial Neural Networks." Applied Sciences 8, no. 8 (August 17, 2018): 1395. http://dx.doi.org/10.3390/app8081395.
Full textAbstract:
The undrained shear strength of organic soils can be evaluated based on measurements obtained from the dilatometer test using single- and multi-factor empirical correlations presented in the literature. However, the empirical methods may sometimes show relatively high values of maximum relative error. Therefore, a method for evaluating the undrained shear strength of organic soils using artificial neural networks based on data obtained from a dilatometer test and organic soil properties is presented in this study. The presented neural network, with an architecture of 5-4-1, predicts the normalized undrained shear strength based on five independent variables: the normalized net value of a corrected first pressure reading (po − uo)/σ′v, the normalized net value of a corrected second pressure reading (p1 − uo)/σ′v, the organic content Iom, the void ratio e, and the stress history indictor (oc or nc). The neural model presented in this study provided a more reliable prediction of the undrained shear strength in comparison to the empirical methods, with a maximum relative error of ±10%.
42
Rubiano Berna, Jorge Enrique, Christer Sandberg, Mark Martinez, and James Olson. "Theoretical analysis of LC-refining – pressure screening systems in TMP." Nordic Pulp & Paper Research Journal 34, no. 1 (March 26, 2019): 46–58. http://dx.doi.org/10.1515/npprj-2018-0040.
Full textAbstract:
Abstract LC refining of mechanical pulps has proven to save energy in the production of TMP pulps. However, the specific role of LC refining as part of a TMP system has not been thoroughly studied since it is difficult to conceive any particular system at industrial-scales and impractical at pilot-scales. In this study, pressure screening and LC refining models that describe fibre length distributions, together with correlations to predict refining power were used to model three basic refining systems. From the simulation results, the impact of important variables such as reject ratio, refiner gap and refining net-power was studied. Performance curves of length-weighed average fibre length were generated from simulation results and were used to assess each system behaviour and also to make comparisons between systems. Data from an industrial scale TMP mill sub-system was gathered and compared to simulation results showing relative errors between 0–18 % on the predicted variables.
43
Parker, Anthony P. "Autofrettage of Open-End Tubes—Pressures, Stresses, Strains, and Code Comparisons." Journal of Pressure Vessel Technology 123, no. 3 (November 24, 2000): 271–81. http://dx.doi.org/10.1115/1.1359209.
Full textAbstract:
Autofrettage is used to introduce advantageous residual stresses into pressure vessels. The Bauschinger effect can produce less compressive residual hoop stresses near the bore than are predicted by “ideal” autofrettage solutions. A recently developed numerical analysis procedure is adopted and extended. The ratio of calculated autofrettage pressure (numerical)/ideal autofrettage pressure (Tresca criterion and plane stress) is calculated and verified against available solutions. The case of open-end conditions based upon von Mises and engineering plane strain (constant axial strain with zero net axial force) is examined in detail. The ratio in this case varies between unity and 2/3, but exhibits very significant variations from the plane stress case when the diameter ratio of the tube exceeds 1.8. Results are within 0.5 percent of available analytical, numerical, and experimental results. A simple numerical fit allows all autofrettage pressures to be replicated to within 0.5 percent. The true plane strain pressure ratio is examined and shown to be inappropriate in modeling engineering plane strain. A number of residual hoop and axial stress profiles is presented for radius ratio 2.0. Calculated pressures are used to determine residual hoop stress values for tube diameter ratios from 1.1 to 3.0 for the full range of percentage overstrain levels. These comparisons indicate that Bauschinger effect is evident when the ratio autofrettage radius/bore radius exceeds 1.2, irrespective of diameter ratio. To assist designers the important values of residual hoop stress at the bore are summarized in a composite plot and a numerical fit is provided. The accuracy of the current ASME code using pressure criteria is assessed. The code is shown to be generally and modestly conservative. A design procedure is proposed which appears capable of extending code validity beyond 40 percent overstrain (the limit of the current code) and of eliminating the small nonconservatism at very low overstrain. Hoop strain values are calculated at both the bore and outside diameter of a tube of radius ratio 2 at the peak of the autofrettage cycle using von Mises criterion with open-end, closed-end, and plane strain conditions. These are compared with available solutions; general agreement is demonstrated, with agreement within 2 percent with an accepted simple formula in the case of open ends. ASME code predictions of percentage overstrain based upon strains at the peak of the autofrettage cycle are generally within 6 percent of numerical predictions. This is in turn produces an agreement within approximately 3 percent in residual bore hoop stress calculation. This discrepancy is generally conservative, becoming non-conservative only at overstrain levels exceeding 80 percent. Strain during removal of autofrettage pressure, in the presence of Bauschinger effect, is also calculated. This shows that the difference in strain during the unloading phase is up to 8 percent (ID) and 6.3 percent (OD) compared with the predictions of elastic unloading. These latter results show similar agreement with the ASME code as in the peak-strain analysis and permit correction of estimates of percentage overstrain based upon permanent bore enlargement.
44
Ju, Xin Yao, Feng Jiao Wang, Yi Kun Liu, and Ling Zhe Cai. "Application on Expert System to Predict the Effect of Fracturing Measures." Advanced Materials Research 616-618 (December 2012): 1033–37. http://dx.doi.org/10.4028/www.scientific.net/amr.616-618.1033.
Full textAbstract:
Hydraulic fracturing is one of the main stimulations, however, it is effected by various factors. This paper considers the influence of net thickness, permeability, flow pressure, water cut, injector—producer distance, cumulative injection-production ratio, sand input intensity, pad fluid volume, sand ratio. Applying the expert system to establish the predictive knowledge base, dividing various effect factors into four grades, and giving the different membership functions according to different grade. The 76% prediction results of established expert system are the same as actual results, and 20.5% are close to the actual results. The results show that the established expert system has the guidance action on the layer selection of fracturing and the fracturing design.
45
Möller, Heinrich, Pfarelo Daswa, and Gonasagren Govender. "The Mechanical Properties of Rheo-High Pressure Die Cast Al-Mg-Si-(Cu) 6xxx Series Alloys." Solid State Phenomena 217-218 (September 2014): 61–66. http://dx.doi.org/10.4028/www.scientific.net/ssp.217-218.61.
Full textAbstract:
Near-net shape casting of wrought aluminium alloys has proven to be difficult due to a tendency towards hot tearing during cooling. Rheo-high pressure die casting (R-HPDC), has been shown to be an effective method of producing near-net shape wrought aluminium alloy castings. Limited information is available regarding the mechanical properties of age-hardenable wrought Al-castings produced by semi-solid metal forming. The purpose of this study is to investigate the effects of chemical composition and natural pre-ageing on the hardness and mechanical properties of rheo-HPDC 6xxx series Al-Mg-Si-(Cu) alloys in the T6 temper condition. The effects of the addition of Cu, as well as the (Mg+Si) content and Mg:Si ratio of the alloys are quantified. Alloys that are included are Cu-free 6004 and 6082, as well as Cu-containing 6013, 6111 and 6066. It is shown that the addition of Cu and excess Si result in higher hardness and strength. Natural pre-ageing has a significant effect (positive for 6004 and negative for the others) on the T6 properties. Good strength values can be achieved, but ductility is dependent on factors such as hot tearing during casting and incipient melting during solution heat treatment.
46
Islam, Tanvirul, and Jayantha Kodikara. "Interpretation of the loading–wetting behaviour of compacted soils within the “MPK” framework. Part I: Static compaction." Canadian Geotechnical Journal 53, no. 5 (May 2016): 783–805. http://dx.doi.org/10.1139/cgj-2014-0316.
Full textAbstract:
Depending on the state paths, loading–wetting of compacted unsaturated soils can exhibit complex volumetric behaviour, such as swelling, collapse, collapse followed by swelling, swelling followed by collapse, and swelling pressure development. Microscopically, these behaviours arise from complex interactions among applied stresses, air–water pressure deficit or suction at the water menisci, moisture content or degree of saturation in the voids, and the nature of the micro- and macrosoil aggregates of compacted soils that depend on the level of suction. While significant advances have been made in modelling hydromechanical behaviour of compacted unsaturated soils taking these interactions into account, input parameter determination requires advanced testing equipment and the testing processes can be very time-consuming. In 2012, a relatively simple and practical framework within the void ratio – moisture ratio (water volume / solid volume) – net stress space (referred to as the MPK framework) has been proposed by Kodikara to explain–predict these state paths. A desirable feature of this framework is that it identifies a direct link between the well-known compaction curve and the compacted soil constitutive behaviour. This paper presents a comprehensive series of tests on statically compacted soils, the results of which are in close agreement with this framework. Two soil types, namely lightly reactive kaolin and more reactive clay (referred to as Merri Creek soil), were used in the testing. The soils were prepared with different moisture contents from the dry state and statically compacted at constant water content to obtain void ratio – moisture ratio – net stress constitutive surfaces, as well as soil specimens for state path tests. The state path test results of yielding under loading, collapse under wetting, swelling pressure development, and change in yield pressure due to wetting are explained within this framework. In addition, some published data on a silty soil mixture were also analysed, highlighting that the framework is valid, regardless of the degree of reactivity of the soil. Suction was not measured in the authors’ experiments, as it was not required to explain the above state paths according to this framework. However, it is recognised that suction is the conjugate state variable to the moisture content. Therefore, in future experiments, suction will be measured and its role will be fully explained within the framework, adding more generality.
47
Childs, D. W., and Chang-Ho Kim. "Analysis and Testing for Rotordynamic Coefficients of Turbulent Annular Seals With Different, Directionally-Homogeneous Surface-Roughness Treatment for Rotor and Stator Elements." Journal of Tribology 107, no. 3 (July 1, 1985): 296–305. http://dx.doi.org/10.1115/1.3261054.
Full textAbstract:
A combined analytical-computational method is developed to calculate the transient pressure field and dynamic coefficients for high-pressure annular seal configurations which may be used in interstage and neck-ring seals of multistage centrifugal pumps. The solution procedure applies to constant-clearance or convergent-tapered geometries which may have different (but directionally-homogeneous) surface-roughness treatments on the stator or rotor seal elements. It applies in particular so-called “damper-seals” which employ smooth rotors and deliberately-roughened stator elements to enhance rotor stability. Hirs’ turbulent lubrication equations are modified slightly to account for different surface-roughness conditions on the rotor and stator. A perturbation analysis is employed in the eccentricity ratio to develop zeroth and first order perturbation equations. The zeroth-order equations define both the leakage and the development of circumferential flow due to shear forces at the rotor and stator surfaces. The first-order equations define perturbations in the pressure and axial and circumferential velocity fields due to small relative motion between the seal rotor and stator. The solution applies for small motion about a centered position and does not employ linearization with respect to either the taper angle or the degree of swirl, i.e., the difference between the circumferential velocity at the given axial position and the asymptotic circumferential-velocity solution. Test results for four different surface-roughness confirm the predicted net damping increase for “damper seals.” A round-hole-pattern stator yielded the highest net damping and lowest leakage of all seals tested. The seals are substantially stiffer than predicted, but the theory does an adequate job of predicting net damping.
48
Abdul Rasheed, Mohammed Iqbal, Bert Rietman, Hendrikus Antonius Visser, and Remko Akkerman. "A Parametric Study on Compression Molding of Reference Parts with Integrated Features Using Carbon Composite Production Waste." Key Engineering Materials 651-653 (July 2015): 458–63. http://dx.doi.org/10.4028/www.scientific.net/kem.651-653.458.
Full textAbstract:
Compression molding of near net-shaped rib-stiffened plates has been performed for a parametric investigation on the filling behavior of chopped woven flake reinforcements. The experimental investigation showed that different aspect ratios of ribs can be filled completely within the tested maximum ratio of flake size to rib opening width of 6.25 and a maximum consolidation pressure of 15 bar. However, defects such as voids, non-impregnated regions and fiber matrix separation may arise depending on the combination of parameters and a mechanical jamming effect caused by the woven architecture of the flakes. A tendency for a limiting consolidation pressure is observed based on the fiber matrix separation. The ability to re-use thermoplastic prepreg cutting waste has been demonstrated.
49
Scepi, N., G. Lesur, G. Dubus, and M. Flock. "Turbulent and wind-driven accretion in dwarf novae threaded by a large-scale magnetic field." Astronomy & Astrophysics 620 (November 29, 2018): A49. http://dx.doi.org/10.1051/0004-6361/201833921.
Full textAbstract:
Dwarf novae (DNe) are accreting white dwarfs that show eruptions caused by a thermal-viscous instability in the accretion disk. The outburst timescales constrain α, the ratio of the viscous stress to the thermal pressure, which phenomenologically connects to the mechanism of angular momentum transport. The eruptive state has α ≈ 0.1 while the quiescent state has α ≈ 0.03. Turbulent transport that is due to the magneto-rotational instability (MRI) is generally considered to be the source of angular momentum transport in DNe. The presence of a large-scale poloidal field threading the disk is known to enhance MRI-driven transport. Here, we perform 3D local magnetohydrodynamic (MHD) shearing-box simulations including vertical stratification, radiative transfer, and a net constant vertical magnetic flux to investigate how transport changes between the outburst and quiescent states of DNe. We find that a net vertical constant magnetic field, as could be provided by the white dwarf or by its stellar companion, provides a higher α in quiescence than in outburst, in opposition to what is expected. Including resistivity quenches MRI turbulence in quiescence, suppressing transport, unless the magnetic field is high enough, which again leads to α ≈ 0.1. A major difference between simulations with a net poloidal flux and simulations without a net flux is that angular momentum transport in the former is shared between turbulent radial transport and wind-driven vertical transport. We find that wind-driven transport dominates in quiescence even for moderately low magnetic fields ∼1 G. This can have a great impact on observational signatures since wind-driven transport does not heat the disk. Furthermore, wind transport cannot be reduced to an α prescription. We provide fits to the dependence of α with β, the ratio of thermal to magnetic pressure, and Teff, the effective temperature of the disk, as well as a prescription for the wind torque as a function of β that is in agreement with both local and global simulations. We conclude that the evolution of the thermal-viscous instability, and its consequences on the outburst cycles of CVs, needs to be thoroughly revised to take into account that most of the accretion energy may be carried away by a wind instead of being locally dissipated.
50
Kozhevnikov, Evgenii, Evgenii Riabokon, and Mikhail Turbakov. "A Model of Reservoir Permeability Evolution during Oil Production." Energies 14, no. 9 (May 8, 2021): 2695. http://dx.doi.org/10.3390/en14092695.
Full textAbstract:
In this paper, we present a mathematical model to predict the evolution of rock permeability depending on effective pressure during oil production. The model is based on the use of the results of well testing data from wells operating in the oil fields of the Perm–Solikamsk region in the north of the Volgo Ural oil and gas province. Dependences of the change in flow characteristics in the reservoir on the effective pressure were established. We performed a comparative assessment using permeability and effective pressure data that were normalized to dimensionless forms of k/ko and P/Po. The factors and their influence on the nature of the change in permeability from the reservoir pressure were determined. Depending on the type of rock, its composition, initial permeability, and bedding conditions, we determined the limits of variation of the constants in empirical equations describing the change in the permeability of rocks from the effective pressure. The mathematical model we developed enables the prediction of the change in permeability of rocks during oil production from reservoirs on the basis of reservoir properties such as initial permeability, initial reservoir pressure, average bedding depth, net-to-gross ratio, and initial effective rock pressure.