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Letteratura scientifica selezionata sul tema "Pulsating fluid-flow"

Autore: Grafiati

Pubblicato: 4 giugno 2021

Ultima modifica: 4 febbraio 2022

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Articoli di riviste sul tema "Pulsating fluid-flow"

1

Craciunescu, Oana I., e Scott T. Clegg. "Pulsatile Blood Flow Effects on Temperature Distribution and Heat Transfer in Rigid Vessels". Journal of Biomechanical Engineering 123, n. 5 (16 maggio 2001): 500–505. http://dx.doi.org/10.1115/1.1392318.

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The effect of blood velocity pulsations on bioheat transfer is studied. A simple model of a straight rigid blood vessel with unsteady periodic flow is considered. A numerical solution that considers the fully coupled Navier–Stokes and energy equations is used for the simulations. The influence of the pulsation rate on the temperature distribution and energy transport is studied for four typical vessel sizes: aorta, large arteries, terminal arterial branches, and arterioles. The results show that: the pulsating axial velocity produces a pulsating temperature distribution; reversal of flow occurs in the aorta and in large vessels, which produces significant time variation in the temperature profile. Change of the pulsation rate yields a change of the energy transport between the vessel wall and fluid for the large vessels. For the thermally important terminal arteries (0.04–1 mm), velocity pulsations have a small influence on temperature distribution and on the energy transport out of the vessels (8 percent for the Womersley number corresponding to a normal heart rate). Given that there is a small difference between the time-averaged unsteady heat fiux due to a pulsating blood velocity and an assumed nonpulsating blood velocity, it is reasonable to assume a nonpulsating blood velocity for the purposes of estimating bioheat transfer.

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2

Haibullina, A. I., N. X. Zinnatullin e V. K. Ilyin. "Improving heat exchanger efficiency using the pulsed method of cleaning". Power engineering: research, equipment, technology 22, n. 1 (30 aprile 2020): 49–57. http://dx.doi.org/10.30724/1998-9903-2020-22-1-49-57.

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The fouling of heat exchange equipment leads to serious economic losses in many industries, therefore to find a method to reduce deposits on heat transfer surfaces remains an actual task. In this paper, a practical solution is proposed for the implementation of a pulsating cleaning method of oil coolers as an example. The influence of pulsations on cleaning of the external surface of the heat exchanger is studied by computer modeling with Ansys Fluent. The fluid flow was described by the Navier-Stokes equation, particle motion and their interaction was described by the discrete element method (DEM). In the study, a staggered tube bundle was considered. The pulse frequency 0,3125 Hz, the amplitude referred to the diameter of tube is 35, the Reynolds number 100, the duty cycle of the pulsations 0,25. Oil was chosen as the medium. Evaluation of the pulsating cleaning method was carried out on the basis of the analysis of the mechanics of particle collisions on the surface of the central cylinder in the beam, with stationary and pulsating flow. It was found that the pulsating flow helps to reduce deposits in the front of the cylinder and is not effective in the back. An analysis of the mechanics of particle impact on the heat exchange surface showed that this pulsation mode is more effective for removing plastic deposits.

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Komilova, Kh M. "Numerical modeling of vibration fatigue of viscoelastic pipelines conveying pulsating fluid flow". International Journal of Modeling, Simulation, and Scientific Computing 11, n. 03 (giugno 2020): 2050024. http://dx.doi.org/10.1142/s1793962320500245.

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The effect of investigation results on viscoelastic properties of the material and bases on vibration fatigue of a pipeline conveying pulsating fluid flow is given in the paper. A mathematical model of viscoelastic pipeline vibrations based on the theory of beams was developed when a pulsating fluid flows through it. A computational algorithm has been developed to solve vibration problems of composite pipelines conveying pulsating fluid. Stability and amplitude-time characteristics of vibrations of composite pipelines conveying pulsating fluid were studied at wide range of parameters variation of deformable systems and fluid flow.

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4

Xu, Duo, Sascha Warnecke, Baofang Song, Xingyu Ma e Björn Hof. "Transition to turbulence in pulsating pipe flow". Journal of Fluid Mechanics 831 (13 ottobre 2017): 418–32. http://dx.doi.org/10.1017/jfm.2017.620.

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Fluid flows in nature and applications are frequently subject to periodic velocity modulations. Surprisingly, even for the generic case of flow through a straight pipe, there is little consensus regarding the influence of pulsation on the transition threshold to turbulence: while most studies predict a monotonically increasing threshold with pulsation frequency (i.e. Womersley number, $\unicode[STIX]{x1D6FC}$), others observe a decreasing threshold for identical parameters and only observe an increasing threshold at low $\unicode[STIX]{x1D6FC}$. In the present study we apply recent advances in the understanding of transition in steady shear flows to pulsating pipe flow. For moderate pulsation amplitudes we find that the first instability encountered is subcritical (i.e. requiring finite amplitude disturbances) and gives rise to localized patches of turbulence (‘puffs’) analogous to steady pipe flow. By monitoring the impact of pulsation on the lifetime of turbulence we map the onset of turbulence in parameter space. Transition in pulsatile flow can be separated into three regimes. At small Womersley numbers the dynamics is dominated by the decay turbulence suffers during the slower part of the cycle and hence transition is delayed significantly. As shown in this regime thresholds closely agree with estimates based on a quasi-steady flow assumption only taking puff decay rates into account. The transition point predicted in the zero $\unicode[STIX]{x1D6FC}$ limit equals to the critical point for steady pipe flow offset by the oscillation Reynolds number (i.e. the dimensionless oscillation amplitude). In the high frequency limit on the other hand, puff lifetimes are identical to those in steady pipe flow and hence the transition threshold appears to be unaffected by flow pulsation. In the intermediate frequency regime the transition threshold sharply drops (with increasing $\unicode[STIX]{x1D6FC}$) from the decay dominated (quasi-steady) threshold to the steady pipe flow level.

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KAMIYAMA, Shinichi, Kazuo KOIKE e Yuichi IKEDA. "Pulsating pipe-flow characteristics of magnetic fluid." Transactions of the Japan Society of Mechanical Engineers Series B 54, n. 508 (1988): 3331–37. http://dx.doi.org/10.1299/kikaib.54.3331.

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Li, Guo Neng. "Numerical Simulation of Characteristics of Cross-Flow Heat Transfer in Pulsating Flow". Advanced Materials Research 187 (febbraio 2011): 242–46. http://dx.doi.org/10.4028/www.scientific.net/amr.187.242.

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In order to investigate the characteristics of heat transfer in oscillating flow, the computational fluid dynamics method was employed to study the effects of pulsating flow on the heat transfer process in a cross-flow heat exchange pipe, and to analyze the underling mechanism which controls the improvement of heat transfer in pulsating flow through the distribution of temperature. Several pulsating frequencies (f=0, 5, 10, 50, 100, 150 Hz) and a wide range of pulsating amplitudes (inlet velocity u=2.0+Asin(2πft) m/s, A=0, 2, 5, 10, 15, 20 m/s) were explored to find out the best pulsating parameters for heat transfer. Results showed that pulsating flow with a low pulsating frequency (the magnitude of ~101 Hz) should be selected to obtain large heat transfer coefficient, and that pulsating flow with larger pulsating amplitude results in greater heat transfer coefficient. On the other hand, results revealed that only a limited length of the cross-flow exchange pipe was affected by the pulsating flow compared to the whole length, and that the affected length is longer with lower pulsating frequency and larger pulsating amplitude.

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Zhou, Y., Z. Liu e A. Golyanin. "Study on the Effect of Diaphragm Booster on the Pulsed Heat Transfer of Cooling System". Bulletin of Science and Practice 6, n. 4 (15 aprile 2020): 214–22. http://dx.doi.org/10.33619/2414-2948/53/25.

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This paper has developed a diesel engine cylinder liner and cooling water heat exchange enhancement device, including diesel engine cylinder liner, cylinder liner water cooler, hydraulic accumulator, check valve, diaphragm booster, centrifugal water pump, pulse valve and Conical tube. As well as the pulsating circulation system and booster system composed of equipment. The device heats the heat generated by the diesel engine cylinder liner in a pulsating circulation system through a cylinder circulator in a pulsating circulation system to exchange heat with the external low-temperature seawater. By controlling the opening and closing of the pulsating valve in the pulsating circulation system, fluid is generated in the pipe. Pulsing and hydraulically impacting the diaphragm booster connected near the pulsation valve pipeline, the fluid at the outlet of the diaphragm booster is subjected to hydraulic shock and circulates in a closed booster circuit connected to the diaphragm booster and passes through the cone during the flow. The shaped tube accelerates the fluid to return to the diaphragm supercharger, and the kinetic energy of the fluid is converted into the pressure in the pulsating heat exchange system by impacting the elastic diaphragm of the diaphragm supercharger, so that the pulsating speed is increased. The present invention is to increase the pulsating velocity of the diaphragm. Based on the design of the compressor drive, it improves energy efficiency, avoids the use of high-power water pumps, and saves equipment construction and daily operation.

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Liu, Qian, Jiu Yang Yu, Wei Lin, Li Jun Liu, Wen Hao Yang, Yi Wen Chen e Si Hao Nie. "Numerical Analysis on Characteristics of Heat Transfer of Pulsating Flow around the Vibrating Tube". Advanced Materials Research 516-517 (maggio 2012): 935–40. http://dx.doi.org/10.4028/www.scientific.net/amr.516-517.935.

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Fluid flow and heat transfer characteristics of pulsating flow around the vibrating tube was numerically investigated by the dynamic meshing technique of FLUENT. The results showed the combined action of pulsating flow and vibration enhances the coefficient of heat transfer, and the surface heat transfer coefficient of vibrating tube increases with the increment of the tube vibration amplitude, frequency and pulsating flow amplitude, and pulsating flow frequency has less affected. The main reason that pulsating flow enhances heat transfer is the secondary flow, generated by the combined effect of pulsating flow and tube vibration, enhances momentum and energy transfer.

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Hoseinzadeh, S., S. M. Taheri Otaghsara, M. H. Zakeri Khatir e P. S. Heyns. "Numerical investigation of thermal pulsating alumina/water nanofluid flow over three different cross-sectional channel". International Journal of Numerical Methods for Heat & Fluid Flow 30, n. 7 (4 novembre 2019): 3721–35. http://dx.doi.org/10.1108/hff-09-2019-0671.

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Purpose The purpose of this study is to investigate the pulsating flow in a three-dimensional channel. Channel flow is laminar and turbulent. After validation, the effect of different channel cross-sectional geometries (circular, hexagonal and triangular) with the pulsating flow are investigated. For this purpose, the alumina nanofluid was considered as a working fluid with different volume percentages (0 per cent [pure water], 3 per cent and 5 per cent). Design/methodology/approach In this study, the pulsatile flow was investigated in a three-dimensional channel. Channel flow is laminar and turbulent. Findings The results show that the fluid temperature decreases by increasing the volume percentage of particles of Al2O3; this is because of the fact that the input energy through the wall boundary is a constant value and indicates that with increasing the volume percentage, the fluid can save more energy at a constant temperature. And by adding Al2O3 nanofluid, thermal performance improves in channels, but it should be considered that the use of nanofluid causes a pressure drop in the channel. Originality/value Alumina/water nanofluid with the pulsating flow was investigated and compared in three different cross-sectional channel geometries (circular, hexagonal and triangular). The effect of different volume percentages (0 per cent [pure water], 3 per cent and 5 per cent) of Al2O3 nanofluid on temperature, velocity and pressure are studied.

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Dzelzitis, Egils, e Sandra Sidenko. "The Human Comfort Level in an Energy-Saving Simulation Model of Office Building". E3S Web of Conferences 172 (2020): 06009. http://dx.doi.org/10.1051/e3sconf/202017206009.

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Currently high attention is drawn to the studies of the influence of pulsating flow to the heat transfer. Such unsteady flows can be created artificially or may appear during the operation of the thermal energy equipment. The purpose of this work is to perform numerical studies of the pulsating fluid flow effect supplied to a panel heating radiator on its heat output; and to determine the effect of pulsations of heat output on a human comfort level as well. Numerical modeling was prepared with CAD/CFD/HVAC complex of SolidWorks/FlowSimulation software. Where the complete system of Navier-Stokes equations and the energy equation were solved using the k-ε turbulence model in a non-stationary formulation of the problem. Results of the numerical calculations showed that the periodic pulsating flow of the fluid in the heating radiator during operation, in comparison with the stationary mode, leads to increasing and decreasing in the thermal power of the radiator. But at the same time, with an average estimate, the thermal power with pulsations of the fluid’s flow increases for about 10-15% comparing with a stationary mode. Model of the office room in the considered operating mode is not comfortable; this conclusion is based on such criteria as operating temperature, PMV, PPD, identified in the numerical calculations process.

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Tesi sul tema "Pulsating fluid-flow"

1

Cao, Teng. "Pulsating flow effects on turbocharger turbine performance". Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708901.

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2

Alnujaie, Ali H. "Flow-induced Vibration of Double Wall Carbon Nanotubes Conveying Pulsating Fluid". University of Akron / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=akron1555409894074253.

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Kranenbarg, Jelle. "Techniques to inject pulsating momentum". Thesis, Luleå tekniska universitet, Strömningslära och experimentell mekanik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-79097.

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Hydro power plants are an essential part of the infrastructure in Sweden as they stand for a large amount of the produced electricity and are used to regulate supply and demand on the electricity grid. Other renewable energy sources, such as wind and solar power, have become more popular as they contribute to a fossil free society. However, wind and solar power are intermittent energy sources causing the demand for regulating power on the grid to increase. Hydro power turbines are designed to operate at a certain design point with a specific flow rate. The plants are operated away from the design point when used to regulate the supply and demand of electricity. This can cause a specific flow phenomenon to arise in the draft tube at part load conditions called a Rotating Vortex Rope (RVR) which causes dangerous pressure fluctuation able to damage blades and bearings. A solution to mitigate a RVR is to inject pulsating momentum into the draft tube by using an actuator operating at a certain frequency. A literature study was conducted and three techniques were numerically simulated using ANSYS Workbench 19.0 R3; a fluidic oscillator, a piston actuator and a synthetic jet actuator. A dynamic mesh was used to simulate the movement of the piston actuator and diaphragm of the synthetic actuator whilst the mesh of the fluidic oscillator was stationary. The relative errors of the three numerical models were all below 3 %. All devices showed promising results and could potentially be used to mitigate a RVR because they all have the ability to produce high energy jets. The fluidic oscillator had an external supply of water, whereas the other two did not, which means that it could inject the largest mass flow. The piston actuator required a driving motor to move the piston. The diaphragm of the synthetic jet actuator was moved by a Piezoelectric element. Advantages of the fluidic oscillator are that it has no moving parts, in contrary to the two other devices, it can directly be connected to the penstock or draft tube to obtain the required water supply and it is easy to install. It will most likely also be smaller compared to the other two for the same mass flow rate. It does however not generate a pulsating jet, but rather an oscillating jet. The other two devices generate pulsating jets, but have problems with low pressure areas during the intake stroke which can cause cavitation problems. These areas cause the formation of vortex rings close to the outlet. Simulations showed that a coned piston together with a coned cylinder outlet could decrease losses by almost 16 % compared to a normal piston and cylinder. It also decreased the risk for cavitation and the required force to move the piston. Otherwise, a shorter stroke length for a constant cylinder diameter or a longer stroke length for a constant volume displacement also decreased the risk for cavitation and required force. The gasket between the piston and cylinder is a potential risk for leakage. A solution to avoid critical low pressure areas is to install an auxiliary fluid inlet or valve which opens at a certain pressure for the piston actuator as well as the synthetic jet actuator. This will also allow larger mass flow rates and a higher injected momentum. Both devices are more complicated to install and require likely more maintenance compared to the fluidic oscillator. However, there exist many possible design options for the piston actuator. The design of the synthetic jet is more limited because of the diaphragm. The amplitude of the diaphragm also has a direct effect on the pressure levels. The losses increased proportional to the mass flow to the power of three which suggests that it is better to install many small actuators instead of a few large ones.

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Yamin, A. K. M. "Pulsating flow studies in a planar wide-angled diffuser upstream of automotive catalyst monoliths". Thesis, Coventry University, 2012. http://curve.coventry.ac.uk/open/items/e82aae35-8737-48e2-b73d-4758a88f5e1a/1.

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Automotive catalytic converters are used extensively in the automotive industry to reduce toxic pollutants from vehicle exhausts. The flow across automotive exhaust catalysts is distributed by a sudden expansion and has a significant effect on their conversion efficiency. The exhaust gas is pulsating and flow distribution is a function of engine operating condition, namely speed (frequency), load (flow rate) and pressure loss across the monolith. The aims of this study are to provide insight into the development of the pulsating flow field within the diffuser under isothermal conditions and to assess the steady-state computational fluid dynamics (CFD) predictions of flow maldistribution at high Reynolds numbers. Flow measurements were made across an automotive catalyst monolith situated downstream of a planar wide-angled diffuser in the presence of pulsating flow. Cycle-resolved Particle Image Velocimetry (PIV) measurements were made in the diffuser and hot wire anemometry (HWA) downstream of the monoliths. The ratio of pulse period to residence time within the diffuser (J factor) characterises the flow distribution. During acceleration the flow remained attached to the diffuser walls for some distance before separating near the diffuser inlet later in the cycle. Two cases with J ~ 3.5 resulted in very similar flow fields with the flow able to reattach downstream of the separation bubbles. With J = 6.8 separation occurred earlier with the flow field resembling, at the time of deceleration, the steady flow field. Increasing J from 3.5 to 6.8 resulted in greater flow maldistribution within the monoliths; steady flow producing the highest maldistribution in all cases for the same Re. The oblique entry pressure loss of monoliths were measured using a one-dimensional steady flow rig over a range of approach Reynolds number (200 < Rea < 4090) and angles of incidence (0o < α < 70o). Losses increased with α and Re at low mass flow rates but were independent of Re at high flow rates being 20% higher than the transverse dynamic pressure. The flow distribution across axisymmetric ceramic 400 cpsi and perforated 600 cpsi monoliths were modelled using CFD and the porous medium approach. This requires knowledge of the axial and transverse monolith resistances; the latter being only applicable to the radially open structure. The axial resistances were measured by presenting uniform flow to the front face of the monolith. The transverse resistances were deduced by best matching CFD predictions to measurements of the radial flow profiles obtained downstream of the monolith when presented with non-uniform flow at its front face. CFD predictions of the flow maldistibution were performed by adding the oblique entry pressure loss to the axial resistance to simulate the monolith losses. The critical angle approach was used to improve the predictions, i.e. the oblique entry loss was limited such that the losses were assumed constant above a fixed critical angle, αc. The result showed that the perforated 600 cpsi monolith requires the entrance effect to be restricted above αc = 81o, while the losses were assumed constant above αc = 85o for the ceramic 400 cpsi monolith. This might be due to the separation bubble at the monolith entrance being restricted by the smaller hydraulic diameter of the perforated monolith thus limiting the oblique entry loss at the lower incidence angle.

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Fajardo, Peña Pablo. "Methodology for the Numerical Characterization of a Radial Turbine under Steady and Pulsating Flow". Doctoral thesis, Universitat Politècnica de València, 2012. http://hdl.handle.net/10251/16878.

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The increasing use of turbochargers is leading to an outstanding research to understand the internal flow in turbomachines. In this frame, computational fluid dynamics (CFD) is one of the tools that can be applied to contribute to the analysis of the fluid-dynamic processes occurring in a turbine. The objective of this thesis is the development of a methodology for performing simulations of radial turbomachinery optimizing the available computational resources. This methodology is used for the characterization of a vaned-nozzle turbine under steady and pulsating flow conditions. An important effort has been devoted in adjusting the case configuration to maximize the accuracy achievable with a certain computational cost. Concerning the cell size, a local mesh independence analysis is proposed as a procedure to optimize the distribution of cells in the domain, thus allowing to use a finer mesh in the most suitable places. Particularly important in turbomachinery simulations is the influence of the approach for simulating rotor motion. In this thesis two models have been compared: multiple reference frame and sliding mesh. The differences obtained using both methods were found to be significant in off-design regions. Steady flow CFD results have been validated against global measurements taken on a gas-stand. The modeling of a turbine, installed either on a turbocharger test rig or an engine, requires the calculation of the flow in the ducts composing the system. Those ducts could be simulated assuming a one-dimensional (1D) approximation, and thus reducing the computational cost. In this frame of ideas, two CFD boundary conditions have been developed. The first one allows performing coupled 1D-3D simulations, communicating the flow variables from each domain through the boundary. The second boundary condition is based in a new formulation for a stand-alone anechoic end, which intends to represent the flow behavior of an infinite duct. Finally, the turbine was simulat
Fajardo Peña, P. (2012). Methodology for the Numerical Characterization of a Radial Turbine under Steady and Pulsating Flow [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/16878
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Saracoglu, Bayindir Huseyin. "Turbine Base Pressure Active Control Through Trailing Edge Blowing". Wright State University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=wright1346428842.

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7

Scanlon, Thomas J. "Vortex shedding flowmeter pulsating flow CFD studies". Thesis, University of Strathclyde, 1992. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=21339.

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The computational analysis of vortex shedding flow is presented, using the commercially available computational fluid dynamics(CFD) software package PHOENICS. In this analysis it is shown how the use of the conventional PHOENICS default first-order hybrid-upwind convective differencing scheme provides an excellent example of the effects of multidimensional false diffusion. These effects are substantially reduced with the introduction of an alternative scheme, SUCCA ( Skew Upwind Corner Convection Algorithm), for the modelling of convective transport in 2D and 3D analyses; resulting in the promotion of continuous vortex shedding for the 2D model. The mechanism of pulsating flow influence on the vortex shedding process has also been simulated. The results show that a complex transient phenomenon such as vortex shedding can be analysed using the PHOENICS code but only with the implementation of an alternative convection algorithm. The results also demonstrate the SUCCA scheme's ability to accurately represent convective transport and hence substantially reduce the effects of multidimensional false diffusion in numerical flow analyses.

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8

Psimas, Michael J. "Experimental and numerical investigation of heat and mass transfer due to pulse combustor jet impingement". Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/33863.

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Under certain circumstances pulse combustors have been shown to improve both heat transfer and drying rate when compared to steady flow impingement. Despite this potential, there have been few investigations into the use of pulse combustor driven impingement jets for industrial drying applications. The research presented here utilized experimental and numerical techniques to study the heat transfer characteristics of these types of oscillating jets when impinging on solid surfaces and the heat and mass transfer when drying porous media. The numerical methods were extensively validated using laboratory heat flux and drying data, as well as correlations from literature. As a result, the numerical techniques and methods that were developed and employed in this work were found to be well suited for the current application. It was found that the pulsating flows yielded elevated heat and mass transfer compared to similar steady flow jets. However, the numerical simulations were used to analyze not just the heat flux or drying, but also the details of the fluid flow in the impingement zone that resulted in said heat and mass transport. It was found that the key mechanisms of the enhanced transfer were the vortices produced by the oscillating flow. The characteristics of these vortices such as the size, strength, location, duration, and temperature, determined the extent of the improvement. The effects of five parameters were studied: the velocity amplitude ratio, oscillation frequency, the time-averaged bulk fluid velocity at the tailpipe exit, the hydraulic diameter of the tailpipe, and the impingement surface velocity. Analysis of the resulting fluid flow revealed three distinct flow types as characterized by the vortices in the impingement zone, each with unique heat transfer characteristics. These flow types were: a single strong vortex that dissipated before the start of the next oscillation cycle, a single persistent vortex that remained relatively strong at the end of the cycle, and a strong primary vortex coupled with a short-lived, weaker secondary vortex. It was found that the range over which each flow type was observed could be classified into distinct flow regimes. The secondary vortex and persistent vortex regimes were found to enhance heat transfer. Subsequently, transition criteria dividing these regimes were formed based on dimensionless parameters. The critical dimensionless parameters appeared to be the Strouhal number, a modified Strouhal number, the Reynolds number, the velocity amplitude ratio, and the H/Dh ratio. Further study would be required to determine if these parameters offer similar significance for other configurations.

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Hausner, Alejo. "Non-linear effects in pulsating pipe flow". Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=61228.

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The present thesis considers the phenomenon of flow-rate enhancement of polymer solutions in a pipe due to pulsating pressure gradients. It presents an historical review of the problem. The unexplained experimental dependence of enhancement on pulsation frequency reported by Barnes et al is examined, as are later theoretical attempts to reproduce their results. We find that the results can be reproduced only by omitting the important inertial term. The Modified Moment Method is applied to the problem. The results confirm the predictions of other models. The enhancement is of second order in the pulsation amplitude, exhibits a maximum when the pressure gradient is varied, and declines with increasing pulsation frequency. An expansion in powers of the pulsation amplitude gives a satisfactory approximation. Less power is consumed at the same rate of flow if the pressure gradient is constant and not pulsated.

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Reyes, Belmonte Miguel Ángel. "Contribution to the Experimental Characterization and 1-D Modelling of Turbochargers for IC Engines". Doctoral thesis, Universitat Politècnica de València, 2014. http://hdl.handle.net/10251/34777.

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At the end of the 19th Century, the invention of the Internal Combustion Engine (ICE) marked the beginning of our current lifestyle. Soon after the first ICE patent, the importance of increasing air pressure upstream the engine cylinders was revealed. At the beginning of the 20th Century turbo-machinery developments (which had started time before), met the ICE what represented the beginning of turbocharged engines. Since that time, the working principle has not fundamentally changed. Nevertheless, stringent emissions standards and oil depletion have motivated engine developments; among them, turbocharging coupled with downsized engines has emerged as the most feasible way to increase specific power while reducing fuel consumption. Turbocharging has been traditionally a complex problem due to the high rotational speeds, high temperature differences between working fluids (exhaust gases, compressed air, lubricating oil and cooling liquid) and pulsating flow conditions. To improve current computational models, a new procedure for turbochargers characterization and modelling has been presented in this Thesis. That model divides turbocharger modelling complex problem into several sub-models for each of the nonrecurring phenomenon; i.e. heat transfer phenomena, friction losses and acoustic non-linear models for compressor and turbine. A series of ad-hoc experiments have been designed to aid identifying and isolating each phenomenon from the others. Each chapter of this Thesis has been dedicated to analyse that complex problem proposing different sub-models. First of all, an exhaustive literature review of the existing turbocharger models has been performed. Then a turbocharger 1-D internal Heat Transfer Model (HTM) has been developed. Later geometrical models for compressor and turbine have been proposed to account for acoustic effects. A physically based methodology to extrapolate turbine performance maps has been developed too. That model improves turbocharged engine prediction since turbine instantaneous behaviour moves far from the narrow operative range provided in manufacturer maps. Once each separated model has been developed and validated, a series of tests considering all phenomena combined have been performed. Those tests have been designed to check model accuracy under likely operative conditions. The main contributions of this Thesis are the development of a 1-D heat transfer model to account for internal heat fluxes of automotive turbochargers; the development of a physically-based turbine extrapolation methodology; the several tests campaigns that have been necessary to study each phenomenon isolated from others and the integration of experiments and models in a comprehensive characterization procedure designed to provide 1-D predictive turbocharger models for ICE calculation.
Reyes Belmonte, MÁ. (2013). Contribution to the Experimental Characterization and 1-D Modelling of Turbochargers for IC Engines [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/34777
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Più fonti

Libri sul tema "Pulsating fluid-flow"

1

The physics of pulsatile flow. New York: AIP Press, 2000.

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2

Low re multiple-time-scale turbulence model and calculations of steady and pulsating shear layers. [Washington, DC]: National Aeronautics and Space Administration, 1992.

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United States. National Aeronautics and Space Administration., a cura di. Low re multiple-time-scale turbulence model and calculations of steady and pulsating shear layers. [Washington, DC]: National Aeronautics and Space Administration, 1992.

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United States. National Aeronautics and Space Administration., a cura di. Low re multiple-time-scale turbulence model and calculations of steady and pulsating shear layers. [Washington, DC]: National Aeronautics and Space Administration, 1992.

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5

Flowinduced Pulsation And Vibration In Hydroelectric Machinery Engineers Guidebook For Planning Design And Troubleshooting. Springer, 2012.

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Shinbrot, Troy. Biomedical Fluid Dynamics. Oxford University Press, 2019. http://dx.doi.org/10.1093/oso/9780198812586.001.0001.

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Abstract (sommario):

This book provides an overview of fundamental methods and advanced topics associated with complex, especially biological, fluids. The contents are taken from a graduate level course taught to biomedical engineers, many of whom are math averse. Consequently the book is organized around gentle historical foundations and illustrative tabletop experiments to make for accessible reading. The book begins with derivations of fundamental equations, defined in the simplest terms possible, and adds embellishments one at a time to build toward the analysis of complex fluid dynamics an and introduction to spontaneous pattern formation. Topics covered include elastic surfaces, flow through elastic tubes, pulsatile flows, effects of entrances, branches, and bends, shearing flows, effects of increased Reynolds number, inviscid flows, rheology in complex fluids, statistical mechanics, diffusion, and self-assembly.

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Succi, Sauro. Flows at Moderate Reynolds Numbers. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780199592357.003.0018.

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This chapter presents the application of LBE to flows at moderate Reynolds numbers, typically hundreds to thousands. This is an important area of theoretical and applied fluid mechanics, one that relates, for instance, to the onset of nonlinear instabilities and their effects on the transport properties of the unsteady flow configuration. The regime of Reynolds numbers at which these instabilities take place is usually not very high, of the order of thousands, hence basically within reach of present day computer capabilities. Nonetheless, following the full evolution of these transitional flows requires very long-time integrations with short time-steps, which command substantial computational power. Therefore, efficient numerical methods are in great demand. Also of major interest are steady-state or pulsatile flows at moderate Reynolds numbers in complex geometries, such as they occur, for instance, in hemodynamic applications. The application of LBE to such flows will also briefly be mentioned

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Whittle, Ian. Raised intracranial pressure, cerebral oedema, and hydrocephalus. Oxford University Press, 2011. http://dx.doi.org/10.1093/med/9780198569381.003.0604.

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The brain is protected by the cranial skeleton. Within the intracranial compartment are also cerebrospinal fluid, CSF, and the blood contained within the brain vessels. These intracranial components are in dynamic equilibrium due to the pulsations of the heart and the respiratory regulated return of venous blood from the brain. Normally the mean arterial blood pressure, systemic venous pressure, and brain volume are regulated to maintain physiological values for intracranial pressure, ICP. There are a range of very common disorders such as stroke, and much less common, such as idiopathic intracranial hypertension, that are associated with major disturbances of intracranial pressure dynamics. In some of these the contribution to pathophysiology is relatively minor whereas in others it may be substantial and be a major contributory factor to morbidity or even death.Intracranial pressure can be disordered because of brain oedema, disturbances in CSF flow, mass lesions, and vascular engorgement of the brain. Each of these may have variable causes and there may be interactions between mechanisms. In this chapter the normal regulation of intracranial pressure is outlined and some common disease states in clinical neurological practice that are characterized by either primary or secondary problems in intracranial pressure dynamics described.

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Capitoli di libri sul tema "Pulsating fluid-flow"

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Shuvo, Abdul Aziz, e A. K. M. Monjur Morshed. "Numerical Investigation of Pulsating Flow Characteristics of Fluid in a Rough Circular Microchannel". In Lecture Notes in Mechanical Engineering, 477–86. Singapore: Springer Singapore, 2021. http://dx.doi.org/10.1007/978-981-15-5183-3_51.

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Iervolino, Michele, Marcello Manna e Andrea Vacca. "Pulsating Flow through Porous Media". In Notes on Numerical Fluid Mechanics and Multidisciplinary Design, 167–73. Berlin, Heidelberg: Springer Berlin Heidelberg, 2010. http://dx.doi.org/10.1007/978-3-642-14139-3_20.

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Zamir, M. "Equations of Fluid Flow". In The Physics of Pulsatile Flow, 23–37. New York, NY: Springer New York, 2000. http://dx.doi.org/10.1007/978-1-4612-1282-9_2.

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Chavan, Vedant U., e C. M. Sewatkar. "Effect of Reynolds Number, Strouhal Number and Amplitude of Oscillation on Pulsating Flow Characteristics Through a Circular Pipe". In Fluid Mechanics and Fluid Power – Contemporary Research, 353–62. New Delhi: Springer India, 2016. http://dx.doi.org/10.1007/978-81-322-2743-4_34.

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Hamilton, Robert, Justin Dye, Andrew Frew, Kevin Baldwin, Xiao Hu e Marvin Bergsneider. "Quantification of Pulsatile Cerebrospinal Fluid Flow within the Prepontine Cistern". In Acta Neurochirurgica Supplementum, 191–95. Vienna: Springer Vienna, 2012. http://dx.doi.org/10.1007/978-3-7091-0956-4_37.

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Hecklau, M., V. Zander, W. Nitsche, A. Huppertz e M. Swoboda. "Active Secondary Flow Control on a Highly Loaded Compressor Cascade by Periodically Pulsating Jets". In Notes on Numerical Fluid Mechanics and Multidisciplinary Design, 199–207. Berlin, Heidelberg: Springer Berlin Heidelberg, 2010. http://dx.doi.org/10.1007/978-3-642-14243-7_25.

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van Buren, Simon, e Wolfgang Polifke. "Heat Transfer in Pulsating Flow and Its Impact on Temperature Distribution and Damping Performance of Acoustic Resonators". In Notes on Numerical Fluid Mechanics and Multidisciplinary Design, 97–111. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-53847-7_6.

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Abstract A numerical framework for the prediction of acoustic damping characteristics is developed and applied to a quarter-wave resonator with non-uniform temperature. The results demonstrate a significant impact of the temperature profile on the damping characteristics and hence the necessity of accurate modeling of heat transfer in oscillating flow. Large Eddy Simulations are applied to demonstrate and quantify enhancement in heat transfer induced by pulsations. The study covers wall-normal heat transfer in pulsating flow as well as longitudinal convective effects in oscillating flow. A discussion of hydrodynamic and thermal boundary layers provides insight into the flow physics of oscillatory convective heat transfer.

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Ali, Mohammad, Kazi Shafi Sami e Amanullah Kabir Tonmoy. "Numerical Study on Pulsatile Flow of Non-Newtonian Fluid Through Arterial Stenosis". In Lecture Notes in Mechanical Engineering, 119–28. Singapore: Springer Singapore, 2021. http://dx.doi.org/10.1007/978-981-15-5183-3_13.

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Sebastian, B. T., e P. Nagarani. "Effect of Boundary Absorption on Dispersion of a Solute in Pulsatile Casson Fluid Flow". In Springer Proceedings in Mathematics & Statistics, 389–95. Cham: Springer International Publishing, 2015. http://dx.doi.org/10.1007/978-3-319-12307-3_56.

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Bergsneider, Marvin, A. A. Alwan, L. Falkson e E. H. Rubinstein. "The Relationship of Pulsatile Cerebrospinal Fluid Flow to Cerebral Blood Flow and Intracranial Pressure: A New Theoretical Model". In Intracranial Pressure and Neuromonitoring in Brain Injury, 266–68. Vienna: Springer Vienna, 1998. http://dx.doi.org/10.1007/978-3-7091-6475-4_77.

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Atti di convegni sul tema "Pulsating fluid-flow"

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Shuvo, Abdul Aziz, AKM M. Morshed, Md Shariful Alam Emon, Amitav Tikadar e Titan C. Paul. "Heat Transfer Characteristics of a Phase Change Material Fluid in Microchannels Under Pulsating Flow Condition". In ASME 2019 Heat Transfer Summer Conference collocated with the ASME 2019 13th International Conference on Energy Sustainability. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/ht2019-3608.

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Abstract In this study numerical investigation has been conducted employing pulsating flow in a MicroChannel Heat Sink (MCHS) with phase change material (N-eicosane) as the coolant. The numerical investigation was conducted with H1 boundary condition and laminar pulsating flow condition using commercial software FLUENT. Heat transfer and pressure drop characteristics of the MCHS was calculated for the PCM with different amplitude and frequency of the pulsation and compared with that of the water and PCM under constant velocity flow. Heat transfer performance of the MCHS for both the PCM fluid and water increases for the pulsating flow and it increases with the amplitude of the pulsation; however, pressure drop in case of pulsating flow of PCM fluid remains same compared to the steady flow of PCM. Simulation also has been repeated in this study for two different aspect ratio of the channel.

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Simonetti, Marco, Christian Caillol, Pascal Higelin, Clément Dumand e Emmanuel Revol. "Heat Transfer Investigation in Engine Exhaust-Type Pulsating Flow". In International Conference of Fluid Flow, Heat and Mass Transfer. Avestia Publishing, 2017. http://dx.doi.org/10.11159/ffhmt17.138.

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Sidenko, Natalia, e Egils Dzelzitis. "Flow features in channels with pulsating fluid movement regime". In 19th International Scientific Conference Engineering for Rural Development. Latvia University of Life Sciences and Technologies, Faculty of Engineering, 2020. http://dx.doi.org/10.22616/erdev.2020.19.tf229.

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Sidenko, Sandra, Egils Dzelzitis e Natalia Sidenko. "Thermohydraulic efficiency assessment for pulsating fluid flow in channels". In 20th International Scientific Conference Engineering for Rural Development. Latvia University of Life Sciences and Technologies, Faculty of Engineering, 2021. http://dx.doi.org/10.22616/erdev.2021.20.tf211.

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Tubaldi, E., M. Amabili e F. Alijani. "Nonlinear Vibrations of Plates in Axial Pulsating Flow". In ASME 2014 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/imece2014-37283.

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A theoretical approach is presented to study nonlinear vibrations of thin infinitely long rectangular plates subjected to pulsatile axial inviscid flow. The case of plates in axial uniform flow under the action of constant transmural pressure is also addressed for different flow velocities. The equations of motion are obtained based on the von Karman nonlinear plate theory retaining in-plane inertia via Lagrangian approach. The fluid model is based on potential flow theory and the Galerkin method is applied to determine the expression of the flow perturbation potential. The effect of different system parameters such as flow velocity, pulsation amplitude, pulsation frequency, and channel pressurization on the stability of the plate and its geometrically nonlinear response to pulsating flow are fully discussed. In case of zero uniform transmural pressure numerical results show hardening type behavior for the entire flow velocity range when the pulsation frequency is spanned in the neighbourhood of the plate’s fundamental frequency. Conversely, a softening type behavior is presented when a uniform transmural pressure is introduced.

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Bakhtiar, Sadia, e Farid Ullah Khan. "Energy harvesting from pulsating fluid flow for pipeline monitoring systems". In 2019 International Symposium on Recent Advances in Electrical Engineering (RAEE). IEEE, 2019. http://dx.doi.org/10.1109/raee.2019.8887005.

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Liu, Huan-ling, Ping LIU e David Nobes. "Heat Transfer and Flow Characteristics in a Tube with Small Tube Inserts in a Pulsating Flow". In International Conference of Fluid Flow, Heat and Mass Transfer. Avestia Publishing, 2018. http://dx.doi.org/10.11159/ffhmt18.127.

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Tian, Jing-da, Pu-zhen Gao e Bao Zhou. "Study on Resistance Characteristics of Single-Phase Pulsating Flow in the Horizontal Rectangular Channel". In 2012 20th International Conference on Nuclear Engineering and the ASME 2012 Power Conference. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/icone20-power2012-54257.

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The resistance characteristic of single-phase pulsating flow was experimentally investigated. Using de-ionized water, experiments were conducted in the horizontal rectangular channel with 5.647mm inner diameter, considering three factors that were average flow, pulsation amplitude and pulsation period. Experiments focused on the turbulent region, and the atmospheric pressure and temperature conditions were maintained throughout the experiments. It was found that compared with steady flow in the same channel, the friction coefficient λ under the pulsating conditions was not only affected by the Reynolds number Re, but was also related to pulsation period and pulsation amplitude. And under the pulsating conditions, the Re-λ curve became pulsation circle, it resulted from the acceleration acting on the fluid and the phase difference between Re and λ.

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Karami, Mohammad, Mojtaba Jarrahi, Ebrahim Shirani e Hassan Peerhossaini. "Mixing Enhancement in a Chaotic Micromixer Using Pulsating Flow". In ASME 2014 4th Joint US-European Fluids Engineering Division Summer Meeting collocated with the ASME 2014 12th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/fedsm2014-21360.

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This study determines the simultaneous effects of spatial disturbance and flow pulsation on micromixing by using three different metrics: concentration distribution, Lyapunov exponent and axial vorticity. Numerical simulations are performed for both steady and pulsating flows through a microchannel made up of C-curved repeating units. Moreover, a straight microchannel is analyzed to compare the effects of chaotic advection and molecular diffusion, the main mechanisms of transverse mixing in the chaotic and straight mixer respectively. Simulations are carried out in the steady flow for the Reynolds number range 1≤Re≤50 and in the pulsating flow for velocity amplitude ratios 1≤β≤2.5, and the ratio of the peak oscillatory velocity component to the mean flow velocity, Strouhal numbers 0.1≤St≤0.5. It was found that chaotic advection improves mixing without significant increase in pressure drop. The analysis of concentration distribution implied that full mixing occurs after Reynolds number 50 in the steady flow. When the flow is pulsatile, small and moderate values of the Strouhal number (0.1≤St≤0.3) and high values of velocity amplitude ratio (β ≥ 2) are favorable conditions for mixing enhancement. Moreover, mixing has an oscillating trend along the microchannel due to the coexistence of regular and chaotic zones in the fluid. These results correlate closely with those obtained using two other metrics, analysis of the Lyapunov exponent and axial vorticity.

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Mehta, Balkrishna, e Sameer Khandekar. "Local Experimental Heat Transfer of Single-Phase Pulsating Flow in a Square Mini-Channel". In ASME 2013 4th International Conference on Micro/Nanoscale Heat and Mass Transfer. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/mnhmt2013-22105.

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Disturbing the flow with a particular pulsating frequency alters the thermal and hydrodynamic boundary layer thus affecting the inter-particle momentum and energy exchange. Due to this enhanced mixing, augmentation in the heat transfer is expected. Obviously, the parameters like pulsating frequency vis-à-vis viscous time scales and the imposed pulsating amplitude will play an important role in the enhancement of the heat transfer. Several numerical heat transfer and fluid flow studies on pulsating flows have been reported in the literature but the conclusions are not coherent. Lack of experimental study in hydrodynamics as well as in heat transfer of laminar pulsating flows attracts to revisit this problem especially, in mini-channels. Technological developments in measurement and instrumentation have enabled to experimentally investigate the thermo-hydrodynamic study of laminar pulsating flows in mini-channels as an augmentation technique for heat transfer. In this work, we have undertaken the experimental measurements of heat transfer of single-phase laminar pulsating flow in square mini-channel of cross-section 3 mm × 3 mm. The study is done at two different pulsating frequency 0.05Hz and 1Hz (Womersley number, Wo = 0.8 and 3.4 respectively). These two values are chosen because velocity profile exhibits different characteristic for Wo > 1 (annular effect, i.e., peak velocity near the wall) and Wo < 1 (conventional parabolic profile). The heat transfer study has been done in a square channel of made on polycarbonate sheet with one side heating. Heater (made of SS, 70 microns thin strip, negligible thermal inertia) itself is one of the walls of the square channel making constant heat flux thermal condition and its instantaneous temperature is measured by using pre-calibrated InfraRed camera. Fluid bulk mean temperature has been determined by energy balance and one K-type thermocouple is also placed in the fluid at the outlet cross-section. By using these temporal data, space averaged instantaneous Nusselt number has been obtained. It is observed that for measured frequency range, the overall enhancement in the heat transfer is not attractive for laminar pulsating flow in comparison to steady flow of same time-averaged flow Reynolds number. It is found that the change in species transport is either marginal or highly limited and is primarily occurring in the developing length of the channel/ plate. Enhancement of species transport due to such periodic pulsatile internal flows, over and above the non-pulsatile regular flow conditions, is questionable, and at best, rather limited.

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