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Articoli di riviste sul tema "Pulsating fluid-flow"

Autore: Grafiati

Pubblicato: 4 giugno 2021

Ultima modifica: 4 febbraio 2022

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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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3

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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5

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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6

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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7

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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8

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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9

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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10

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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11

Zhang, Nan. "Pulsating Flow Induced Vibration in a Rotor-Seal System". Advanced Materials Research 542-543 (giugno 2012): 66–69. http://dx.doi.org/10.4028/www.scientific.net/amr.542-543.66.

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The pulsating flow is an important factor affecting the performance of the rotor-seal system. From the point of view of pulsating flow induced vibration, the nonlinear models of the rotor-seal system with the pulsating fluid flow are established. Based on the numerical simulations by Matlab/Simulink, the characteristics of pulsating flow induced vibration with the flow velocity in a form of sine wave or/and a constant have been quantitatively analyzed. The investigation also demonstrates that the proposed models, from the point of view of pulsating flow induced vibration, can be effectively applied to the analysis of the rotor-seal system.

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12

Yu, Jiu Yang, Wen Hao Yang, Wei Lin, Li Jun Liu, Qian Liu, Si Hao Nie, Yi Wen Chen e Jing Zhu. "Numerical Analysis on Convection Heat Transfer of Pulsating Flow in a Spiral Fluted Tube". Advanced Materials Research 516-517 (maggio 2012): 941–44. http://dx.doi.org/10.4028/www.scientific.net/amr.516-517.941.

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The mechanism of heat transfer enhancement of pulsating flow in a spiral fluted tube was researched by CFD (computational fluid dynamics) software FLUENT. Numerical results showed that pulsating flow leads to cyclical fluctuation of outlet pressure and the extent of fluctuation increases with increasing the pulsating flow frequency. Moreover, the pulsating flowing causes whirlpools near the spiral flute and the vortices generate, drift, and fall off periodically. The optimum pulsating frequency in the spiral fluted tube is 6HZ and the optimum amplitude A is equal to 0.7 approximately when the Reynolds number is 1683.

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13

Lv, Kun, Jin Wen Su e Xi Ping Chen. "Self-Localization for Robot Based on the White Line". Advanced Materials Research 308-310 (agosto 2011): 1375–78. http://dx.doi.org/10.4028/www.scientific.net/amr.308-310.1375.

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By numerical simulation computation, after passing the pulsating flow, enhanced heat transfer mechanism in spirally fluted tubes was researched. Numerical result shows that pulsating flow can cause the outlet pressure to fluctuate cyclical and the extent of fluctuation increases with the pulsating flow frequency. The pulse flowing can make the fluid generate the whirlpool nearby the spirally fluted tubes and the phenomenon of periodic production, drift, and fall-off appears. Because of the vortex, the fluid motion and relative motion are enhanced. The pulse flowing can improve the coordination level between velocity and temperature, thus has strengthened the heat transfer effect.

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14

Yu, Jiu Yang, Wen Hao Yang, Yan Yang Wu, Wei Lin, Li Jun Liu e Qian Liu. "Numerical Analysis on Convection Heat Transfer in a Spirally Fluted and Field Synergy Principle Analysis". Advanced Materials Research 308-310 (agosto 2011): 1410–15. http://dx.doi.org/10.4028/www.scientific.net/amr.308-310.1410.

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Abstract (sommario):

By numerical simulation computation, after passing the pulsating flow, enhanced heat transfer mechanism in spirally fluted tubes was researched. Numerical result shows that pulsating flow can cause the outlet pressure to fluctuate cyclical and the extent of fluctuation increases with the pulsating flow frequency. The pulse flowing can make the fluid generate the whirlpool nearby the spirally fluted tubes and the phenomenon of periodic production, drift, and fall-off appears. Because of the vortex, the fluid motion and relative motion are enhanced. The pulse flowing can improve the coordination level between velocity and temperature, thus has strengthened the heat transfer effect.

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15

Yin, Zhi Ren, Li Jun Yang e Run Ze Duan. "CFD Simulation of Heat Transfer of Pulsating Gas in a Pipe". Applied Mechanics and Materials 687-691 (novembre 2014): 623–26. http://dx.doi.org/10.4028/www.scientific.net/amm.687-691.623.

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Numerical Simulation of pulsating flow in a pulse combustor tailpipe was performed using computational fluid dynamics (CFD) method. The flow in the pipe was characterized by periodic pulsating. The influence of this pulsating includes incomplete flow development and high level of convective heat transfer rate, and both were considered and investigated by the CFD model. Compared with the steady flow condition, results showed that the heat transfer coefficient and Nusselt number were 2.35 times higher.

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16

Yuan, Hong, Zhao Wang, Quan Gao e Ting Fu. "Numerical study on the flow and heat transfer of water-based Al2O3 forced pulsating nanofluids based on self-excited oscillation chamber structure". Thermal Science, n. 00 (2021): 167. http://dx.doi.org/10.2298/tsci200906167y.

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In this study, the flow and heat transfer characteristics of the forced pulsating Al2O3/water nanofluid were numerically studied. The pulsating excitation of the nanofluid is provided by the Helmhertz self-excited oscillating cavity. The large eddy simulation method is used to solve the equation, and the local Nusselt number and heat transfer performance index are used to analyze the heat transfer characteristics of the nanofluid in the self-excited oscillation heat exchange tube. In addition, the effect of different downstream tube diameters on heat transfer enhancement is discussed. The research results show that the existence of the countercurrent vortex can increase the disturbance of the near-wall fluid, thereby improving the mixing degree of the near-wall fluid and the central mainstream. As the countercurrent vortex migrates downstream, pulse enhanced heat transfer is realized. Furthermore, it was also found that when the downstream tube diameter d2=1.8d1, the periodic effect of the local Nusselt number of the wall is the best and the heat transfer performance index has the most stable pulsation effect within a pulsation cycle. But when d2=2.0d1, the change curve of heat transfer performance index in a pulsating period is the highest, the maximum value is 3.95.

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17

Malathy, T., e S. Srinivas. "Pulsating flow of a hydromagnetic fluid between permeable beds". International Communications in Heat and Mass Transfer 35, n. 5 (maggio 2008): 681–88. http://dx.doi.org/10.1016/j.icheatmasstransfer.2007.12.006.

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18

Khudayarov, B. A., KH M. Komilova e F. ZH Turaev. "Numerical Simulation of Vibration of Composite Pipelines Conveying Pulsating Fluid". International Journal of Applied Mechanics 11, n. 09 (novembre 2019): 1950090. http://dx.doi.org/10.1142/s175882511950090x.

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Vibration problems of pipelines made of composite materials conveying pulsating flow of gas and fluid are investigated in the paper. A dynamic model of motion of pipelines conveying pulsating fluid flow supported by a Hetenyi’s base is developed taking into account the viscosity properties of the structure material, axial forces, internal pressure and Winkler’s viscoelastic base. To describe the processes of viscoelastic material strain, the Boltzmann–Volterra integral model with weakly singular hereditary kernels is used. Using the Bubnov–Galerkin method, the problem is reduced to the study of a system of ordinary integro-differential equations (IDE). A computational algorithm is developed based on the elimination of the features of IDE with weakly singular kernels, followed by the use of quadrature formulas. The effect of rheological parameters of the pipeline material, flow rate and base parameters on the vibration of a viscoelastic pipeline conveying pulsating fluid is analyzed. The convergence analysis of the approximate solution of the Bubnov–Galerkin method is carried out. It was revealed that the viscosity parameters of the material and the pipeline base lead to a significant change in the critical flow rate. It was stated that an increase in excitation coefficient of pulsating flow and the parameter of internal pressure leads to a decrease in the critical flow rate. It is shown that an increase in the singularity parameter, the Winkler base parameter, the rigidity parameter of the continuous base layer and the Reynolds number increases the critical flow rate.

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Huang, Shan Bo, Liang Gong e Zhao Min Li. "Numerical Study on Pulsating Laminar Flow in Annular Space for Power-Law Fluid". Applied Mechanics and Materials 394 (settembre 2013): 86–91. http://dx.doi.org/10.4028/www.scientific.net/amm.394.86.

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A mathematical model of pulsating laminar flow inside an annular space for power-law fluid was established basing on the background of petroleum engineering. The characteristic of pulsating flow was obtained by employed SIMPLE algorithm. The investigation result shows that the velocity profile and axial pressure gradient are affected by the frequency, amplitude, liquidity index and annular distance of reciprocating motion and the affection is violent near the inner wall.

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Bhargava, R., H. S. Takhar, S. Rawat, Tasveer A. Bég e O. Anwar Bég. "Finite Element Solutions for Non-Newtonian Pulsatile Flow in a Non-Darcian Porous Medium Conduit". Nonlinear Analysis: Modelling and Control 12, n. 3 (25 luglio 2007): 317–27. http://dx.doi.org/10.15388/na.2007.12.3.14690.

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The present analysis is motivated by the need to elucidate with more accuracy and sophistication the hydrodynamics of non-Newtonian flow via a channel containing a porous material under pulsating pressure gradient. A one-dimensional transient rheological model for pulsating flow through a Darcy-Forcheimmer porous channel is used. A modified Casson non-Newtonian constitutive model is employed for the transport fluid with a drag force formulation for the porous body force effects. The model is transformed and solved using a finite element numerical technique. Rheological effects are examined using a β parameter which vanishes in the limit (Newtonian flow). Velocity profiles are plotted for studying the influence of Reynolds number, Darcy number, Forchheimer number and the β (non-Newtonian) parameter. The channel considered is rigid with a pulsatile pressure applied via an appropriate pressure gradient term. The model finds applications in industrial filtration systems, pumping of polymeric fluids etc.

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Zhang, Y. F., T. Liu e W. Zhang. "Nonlinear Resonant Responses, Mode Interactions, and Multitime Periodic and Chaotic Oscillations of a Cantilevered Pipe Conveying Pulsating Fluid under External Harmonic Force". Complexity 2020 (28 agosto 2020): 1–26. http://dx.doi.org/10.1155/2020/9840860.

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The nonlinear resonant responses, mode interactions, and multitime periodic and chaotic oscillations of the cantilevered pipe conveying pulsating fluid are studied under the harmonic external force in this research. According to the nonlinear dynamic model of the cantilevered beam derived using Hamilton’s principle under the uniformly distributed external harmonic excitation, we combine Galerkin technique and the method of multiple scales together to obtain the average equation of the cantilevered pipe conveying pulsating fluid under 1 : 3 internal resonance and principal parametric resonance. Based on the average equation in the polar form, several amplitude-frequency response curves are obtained corresponding to the certain parameters. It is found that there exist the hardening-spring type behaviors and jumping phenomena in the cantilevered pipe conveying pulsating fluid. The nonlinear oscillations of the cantilevered pipe conveying pulsating fluid can be excited more easily with the increase of the flow velocity, external excitation, and coupling degree of two order modes. Numerical simulations are performed to study the chaos of the cantilevered pipe conveying pulsating fluid with the external harmonic excitation. The simulation results exhibit the existence of the period, multiperiod, and chaotic responses with the variations of the fluid velocity or excitation. It is found that, in the cantilevered pipe conveying pulsating fluid, there are the multitime nonlinear vibrations around the left-mode and the right-mode positions, respectively. We also observe that there exist alternately the periodic and chaotic vibrations of the cantilevered pipe conveying pulsating fluid in the certain range.

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Bitla, Punnamchandar, e Telikicherla Kandala Venkatacharyulu Iyengar. "Pulsating flow of an incompressible micropolar fluid between permeable beds". Nonlinear Analysis: Modelling and Control 18, n. 4 (25 ottobre 2013): 399–411. http://dx.doi.org/10.15388/na.18.4.13969.

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The paper deals with the pulsating flow of an incompressible micropolar fluid through a channel bounded by permeable beds. The fluid is injected into the channel from the lower permeable bed with a certain velocity and is sucked into the upper permeable bed with the same velocity. The flow between the permeable beds is assumed to be governed by micropolar fluid flow equations and that in the permeable regions by Darcy law. The Beavers–Joseph (BJ) slip boundary conditions are used at the interfaces of the permeable beds. The governing equations are solved analytically and the expressions for velocity, microrotation, mass flux and shear stress are obtained. The effects of diverse parameters on the velocity and microrotation are studied numerically and the results are presented through graphs.

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Wang, Xun, Cheng Si Yang, Xin Xin Mao e Tong Han. "Visualization Experiment on the Start-up Performance of the Close Loop Pulsating Heat Pipe". Advanced Materials Research 550-553 (luglio 2012): 3150–54. http://dx.doi.org/10.4028/www.scientific.net/amr.550-553.3150.

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Through the visualization experiment, the behavior evolution of the vapor and liquid slugs in the pulsating heat pipe (PHP) was investigated in the start-up process. Optical visualization results indicate that the flow pattern mainly is slug flow in the start-up process. In the early stage of the start-up process, the distribution of vapor and liquid slugs was random at the beginning, and then gradually develops to the other form which can easily pulsate in the PHP. In the later stage, pulsation stagnation in short time and reversing of the flow direction of the working fluid could be found at low heat load, when there exists the circulation flow in the PHP. Circulation was formed along a certain direction at high heat load. In addition, the PHP can be started up with less time and lower minimum start load by using working fluid which has lower latent heat.

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Fu, S. C., R. M. C. So e W. W. F. Leung. "A Lattice Boltzmann and Immersed Boundary Scheme for Model Blood Flow in Constricted Pipes: Part 2 - Pulsatile Flow". Communications in Computational Physics 14, n. 1 (luglio 2013): 153–73. http://dx.doi.org/10.4208/cicp.171011.190712a.

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AbstractOne viable approach to the study of haemodynamics is to numerically model this flow behavior in normal and stenosed arteries. The blood is either treated as Newtonian or non-Newtonian fluid and the flow is assumed to be pulsating, while the arteries can be modeled by constricted tubes with rigid or elastic wall. Such a task involves formulation and development of a numerical method that could at least handle pulsating flow of Newtonian and non-Newtonian fluid through tubes with and without constrictions where the boundary is assumed to be inelastic or elastic. As a first attempt, the present paper explores and develops a time-accurate finite difference lattice Boltzmann method (FDLBM) equipped with an immersed boundary (IB) scheme to simulate pulsating flow in constricted tube with rigid walls at different Reynolds numbers. The unsteady flow simulations using a time-accurate FDLBM/IB numerical scheme is validated against theoretical solutions and other known numerical data. In the process, the performance of the time-accurate FDLBM/IB for a model blood flow problem and the ease with which the no-slip boundary condition can be correctly implemented is successfully demonstrated.

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Khaibullina, A. I., e A. R. Khairullin. "A numerical study of heat transfer in the in-line tube bundle under pulsating fluid flow conditions". Vestnik IGEU, n. 4 (2019): 12–21. http://dx.doi.org/10.17588/2072-2672.2019.4.012-021.

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Shell-and-tube heat exchangers are widely used in different industries. Even a small increase in the efficien-cy of shell-and-tube heat exchangers can lead to significant energy savings. One of the ways to improve the efficiency of shell-and-tube heat exchangers is the use of pulsating flows for the enhancement of heat ex-change. Despite the fact that heat transfer in the tube bundle cross flow in steady-state conditions has been studied quite well, there is limited data on heat transfer in pulsating flow, which means that the problem of finding regularities of heat transfer with pulsating flows in tube bundles is still important. The work employs the incompressible Reynolds averaged Naviere-Stokes (URANS) equations and the continuity equation. Heat transfer is described by the convective heat transfer (Fourier-Kirchhoff) equation. The calculations are performed using Ansys Fluent. A numerical study has been conducted of the effects of forced asymmet-rical pulsating flow on heat exchange in in-line tube bundle cross-flow conditions. In the numerical experi-ment the Reynolds number Re ranged from 1000 to 2000, the relative pulsating amplitude A/D – from 1 to 2, the Strouhal number Sh – from 0,77 to 1,51, the Prandtl number and the duty cycle had fixed values: Pr = 7,2,  = 0,25. The relative transverse and longitudinal pitch was s1,2/D = 1,3. It has been found that pulsating flows lead to the enhancement of heat transfer in the whole range of the studied operating parameters. An increase in A/D and Sh leads to bigger Nusselt number Nu. An increase in the Re number leads to a de-crease in the Nu ratio in pulsating and steady flow conditions. The general correlation obtained based on the numerical study results can be used to predict heat transfer in a pulsating flow in the range of the studied geometric and operating parameters. More research is needed to predict heat transfer in a wider range of operating parameters and with other tube bundle configurations.

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26

Li, Jiasheng, Paul Croaker, Jin Tian, Mahmoud Karimi e Hongxing Hua. "Fluid-Structure Interaction Analysis of Hydrofoils in a Pulsating Flow". MATEC Web of Conferences 45 (2016): 04007. http://dx.doi.org/10.1051/matecconf/20164504007.

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27

GORMAN, D. G., J. M. REESE e Y. L. ZHANG. "VIBRATION OF A FLEXIBLE PIPE CONVEYING VISCOUS PULSATING FLUID FLOW". Journal of Sound and Vibration 230, n. 2 (febbraio 2000): 379–92. http://dx.doi.org/10.1006/jsvi.1999.2607.

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28

Zhang, Nan. "Pulsating Flow Induced Vibration in the Seal System". Applied Mechanics and Materials 602-605 (agosto 2014): 642–45. http://dx.doi.org/10.4028/www.scientific.net/amm.602-605.642.

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The oscillating flow is an important factor affecting the performance of the rotor–seal system. From the point of view of flow induced vibration, the nonlinear models of the rotor-seal system are presented for the analysis of the self-excited vibration, which is induced by interaction between the unstable seal fluid flow and the vibrating rotor. The nonlinear characteristics of flow induced vibration in the rotor-seal system are analyzed, and the nonlinear phenomena in the unbalanced rotor-seal system are investigated using the nonlinear model with the flow induced vibration.

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29

Wang, Yiwen, Peng Shen, Minli Zheng, Pengqiang Fu, Lijia Liu, Jingyue Wang e Lishan Yuan. "Influence of Impeller Speed Patterns on Hemodynamic Characteristics and Hemolysis of the Blood Pump". Applied Sciences 9, n. 21 (4 novembre 2019): 4689. http://dx.doi.org/10.3390/app9214689.

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A continuous-flow output mode of a rotary blood pump reduces the fluctuation range of arterial blood pressure and easily causes complications. For a centrifugal rotary blood pump, sinusoidal and pulsatile speed patterns are designed using the impeller speed modulation. This study aimed to analyze the hemodynamic characteristics and hemolysis of different speed patterns of a blood pump in patients with heart failure using computational fluid dynamics (CFD) and the lumped parameter model (LPM). The results showed that the impeller with three speed patterns (including the constant speed pattern) met the normal blood demand of the human body. The pulsating flow generated by the impeller speed modulation effectively increased the maximum pulse pressure (PP) to 12.7 mm Hg, but the hemolysis index (HI) in the sinusoidal and pulsatile speed patterns was higher than that in the constant speed pattern, which was about 2.1 × 10−5. The flow path of the pulsating flow field in the spiral groove of the hydrodynamic suspension bearing was uniform, but the alternating high shear stress (0~157 Pa) was caused by the impeller speed modulation, causing blood damage. Therefore, the rational modulation of the impeller speed and the structural optimization of a blood pump are important for improving hydrodynamic characteristics and hemolysis.

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30

Tan, S. D., A. M. Kuijpers-Jagtman, C. M. Semeins, A. L. J. J. Bronckers, J. C. Maltha, J. W. Von den Hoff, V. Everts e J. Klein-Nulend. "Fluid Shear Stress Inhibits TNFα-induced Osteocyte Apoptosis". Journal of Dental Research 85, n. 10 (ottobre 2006): 905–9. http://dx.doi.org/10.1177/154405910608501006.

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Bone tissue can adapt to orthodontic load. Mechanosensing in bone is primarily a task for the osteocytes, which translate the canalicular flow resulting from bone loading into osteoclast and osteoblast recruiting signals. Apoptotic osteocytes attract osteoclasts, and inhibition of osteocyte apoptosis can therefore affect bone remodeling. Since TNF-α is a pro-inflammatory cytokine with apoptotic potency, and elevated levels are found in the gingival sulcus during orthodontic tooth movement, we investigated if mechanical loading by pulsating fluid flow affects TNF-α-induced apoptosis in chicken osteocytes, osteoblasts, and periosteal fibroblasts. During fluid stasis, TNF-α increased apoptosis by more than two-fold in both osteocytes and osteoblasts, but not in periosteal fibroblasts. One-hour pulsating fluid flow (0.70 ± 0.30 Pa, 5 Hz) inhibited (−25%) TNF-α-induced apoptosis in osteocytes, but not in osteoblasts or periosteal fibroblasts, suggesting a key regulatory role for osteocyte apoptosis in bone remodeling after the application of an orthodontic load.

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31

González, Rodrigo, Aldo Tamburrino, Andrea Vacca e Michele Iervolino. "Pulsating Flow of an Ostwald—De Waele Fluid between Parallel Plates". Water 12, n. 4 (25 marzo 2020): 932. http://dx.doi.org/10.3390/w12040932.

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Abstract (sommario):

The flow between two parallel plates driven by a pulsatile pressure gradient was studied analytically with a second-order velocity expansion. The resulting velocity distribution was compared with a numerical solution of the momentum equation to validate the analytical solution, with excellent agreement between the two approaches. From the velocity distribution, the analytical computation of the discharge, wall shear stress, discharge, and dispersion enhancements were also computed. The influence on the solution of the dimensionless governing parameters and of the value of the rheological index was discussed.

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32

Khudayarov, B. A., e F. Zh Turaev. "Mathematical modeling parametric vibrations of the pipeline with pulsating fluid flow". IOP Conference Series: Earth and Environmental Science 614 (18 dicembre 2020): 012103. http://dx.doi.org/10.1088/1755-1315/614/1/012103.

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33

YOSHIZAWA, Masatsugu, Eiji HASEGAWA, Hiroyoshi NAO e Yasushi TSUJIOKA. "Lateral vibration of a flexible pipe conveying fluid with pulsating flow." Transactions of the Japan Society of Mechanical Engineers Series C 51, n. 471 (1985): 2828–36. http://dx.doi.org/10.1299/kikaic.51.2828.

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34

Sharma, Megha, e Basant Singh Sikarwar. "Flow and heat transfer of fluid in a pulsating heat pipe". Journal of Physics: Conference Series 1369 (novembre 2019): 012019. http://dx.doi.org/10.1088/1742-6596/1369/1/012019.

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35

Dhahri, H., K. Slimi e Sassi Ben Nasrallah. "Entropy Generation for Pulsating Flow in a Composite Fluid/Porous System". Journal of Porous Media 11, n. 6 (2008): 557–74. http://dx.doi.org/10.1615/jpormedia.v11.i6.40.

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36

YOSHIZAWA, Masatsugu, Hiroyoshi NAO, Eiji HASEGAWA e Yasushi TSUJIOKA. "Lateral Vibration of a Flexible Pipe Conveying Fluid with Pulsating Flow". Bulletin of JSME 29, n. 253 (1986): 2243–50. http://dx.doi.org/10.1299/jsme1958.29.2243.

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37

Vezeridis, Peter S., Cornelis M. Semeins, Qian Chen e Jenneke Klein-Nulend. "Osteocytes subjected to pulsating fluid flow regulate osteoblast proliferation and differentiation". Biochemical and Biophysical Research Communications 348, n. 3 (settembre 2006): 1082–88. http://dx.doi.org/10.1016/j.bbrc.2006.07.146.

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38

Herrera-Valencia, Edtson Emilio, Fausto Calderas, Luis Medina-Torres, Mariano Pérez-Camacho, Leonardo Moreno e Octavio Manero. "On the pulsating flow behavior of a biological fluid: human blood". Rheologica Acta 56, n. 4 (28 febbraio 2017): 387–407. http://dx.doi.org/10.1007/s00397-017-0994-3.

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39

Yamaguchi, R. "Distribution of Mass Transfer Rate and Wall Shear Stress Behind Simple Rectangular Stenosis in Pulsating Flow". Journal of Biomechanical Engineering 111, n. 1 (1 febbraio 1989): 47–54. http://dx.doi.org/10.1115/1.3168339.

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Abstract (sommario):

The distributions of mass transfer rate and wall shear stress in sinusoidal laminar pulsating flow through a two-dimensional asymmetric stenosed channel have been studied experimentally and numerically. The distributions are measured by the electrochemical method. The measurement is conducted at a Reynolds number of about 150, a Schmidt number of about 1000, a nondimensional pulsating frequency of 3.40, and a nondimensional flow amplitude of 0.3. It is suggested that the deterioration of an arterial wall distal to stenosis may be greatly enhanced by fluid dynamic effects.

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40

Chen, Yang, Yongqing He e Xiaoqin Zhu. "Non-Contact Monitoring on the Flow Status inside a Pulsating Heat Pipe". Sensors 20, n. 20 (21 ottobre 2020): 5955. http://dx.doi.org/10.3390/s20205955.

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The paper presents a concept of thermal-to-electrical energy conversion by using the oscillatory motion of magnetic fluid slugs which has potential to be applied in the field of sensors. A pulsating heat pipe (PHP) is introduced to produce vapor-magnetic fluid plug–slug flow in a snake-shaped capillary tube. As the magnetic fluid is magnetized by the permanent magnet, the slugs of magnetic fluid passing through the copper coils make the magnetic flux vary and produce the electromotive force. The peak values of induced voltage observed in our tests are from 0.1 mV to 4.4 mV. The effects of the slug velocity, heat input and magnetic particle volume concentration on the electromotive force are discussed. Furthermore, a theoretical model considering the fluid velocity of the working fluid, the inner radius of the PHP and the contact angle between the working fluid and the pipe wall is established. At the same time, the theoretical and experimental results are compared, and the influences of tube inner radius, working fluid velocity and contact angle on the induced electromotive force are analyzed.

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41

Et al., Navruzov Kuralbay. "Pulsing Flows of a Viscous Incompressible Liquid in a Pipe with Elastic Walls". Psychology and Education Journal 58, n. 2 (1 febbraio 2021): 1436–44. http://dx.doi.org/10.17762/pae.v58i2.2293.

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Abstract (sommario):

As you know, the recent intensive introduction into practice of flexible pipelines made of polymer synthetic materials, pulsating fluid flow in elastic pipes is of great importance. As you know, the recent intensive introduction into practice of flexible pipelines made of polymer synthetic materials, pulsating fluid flow in elastic pipes is of great importance. By solving the problem, the necessary hydrodynamic parameters will be determined, such as pressure distributions, velocities, flow rates, the speed of propagation of the pulse wave pressure and their decay. For the first time in this article, a decrease in hydraulic resistance in a pulsating flow through pipes due to the elasticity of the wall will be determined. The dependence of the dimensionless value of the pressure pulse wave on the vibrational number was investigated .The speed of the pulse wave was compared with the speed of Moens-Korteweg , and significant differences were revealed between them occurring at lower values of the Womersley oscillatory parameter, at large values of which significant differences are not observed. The dependence of the reciprocal damping per wavelength on the vibrational number , was also investigated; it was shown that the damping is free at smaller values of the Womersley vibrational parameter, practically equal to zero, and at large values of which it asymptotically approaches unity.

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42

Ishino, Yojiro, Manabu Suzuki, Tomoaki Abe, Norio Ohiwa e Shigeki Yamaguchi. "Flow and heat transfer characteristics in pulsating pipe flows (effects of pulsation on internal heat transfer in a circular pipe flow)". Heat Transfer - Japanese Research 25, n. 5 (1996): 323–41. http://dx.doi.org/10.1002/(sici)1520-6556(1996)25:5<323::aid-htj5>3.0.co;2-z.

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43

Shang, Fumin, Shilong Fan, Qingjing Yang, Chaoyue Liu e Jianhong Liu. "Study on heat transfer characteristics of single-layer double-row pulsating heat pipe". Thermal Science, n. 00 (2021): 253. http://dx.doi.org/10.2298/tsci210226253s.

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Abstract (sommario):

The structure and inclination angle of a pulsating heat pipe are critical factors influencing the heat transfer performance and operation mode. In this work, a single-layer double-row pulsating heat pipe is designed, and the start-up and heat transfer characteristics of pulsating heat pipe at limit angles (0?,90?, and 180?) are experimentally investigated. Also, the operation mode and heat transfer characteristics are studied through IR imager and temperature profiles. The study highlighted that the pulsating heat pipe has excellent operation characteristics in the limit angle. When the inclination angle is 0?, the double-row structure improves the start-up performance; at 90? inclination, the pulsating heat pipe starts the fastest, and the heat transfer resistance keeps the smallest in the whole test. When the inclination angle is 180?, the pulsating heat pipe has the best thermal sensitivity but weak working fluid flow capacity during operation.

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44

El Masry, O. A., e K. El Shobaky. "Pulsating slurry flow in pipelines". Experiments in Fluids 7, n. 7 (luglio 1989): 481–86. http://dx.doi.org/10.1007/bf00187066.

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45

SHINTANI, Tomofumi, Arata MOTOKI, Kiyotaka YAMASHITA e Masatsugu YOSHIZAWA. "Planar Vibration of a Curved Fluid-Conveying Pipe due to Pulsating Flow". Proceedings of the JSME annual meeting 2002.7 (2002): 145–46. http://dx.doi.org/10.1299/jsmemecjo.2002.7.0_145.

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46

NOGAMI, Naoto, e Masaki ENDO. "Relation between Wave Phenomenon and Fluid Temperature in Pulsating Flow in Pipe". Proceedings of the Fluids engineering conference 2019 (2019): OS10–06. http://dx.doi.org/10.1299/jsmefed.2019.os10-06.

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47

Shimada, Kunio, e Shinichi Kamiyama. "Pulsating Flow of Magnetic Fluid in a Pipe under Fluctuating Magnetic Field." JSME International Journal Series B 37, n. 1 (1994): 71–76. http://dx.doi.org/10.1299/jsmeb.37.71.

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48

Nejat, Amir, Farshad Kowsary, Amin Hasanzadeh-Barforoushi e Saman Ebrahimi. "Unsteady pulsating characteristics of the fluid flow through a sudden expansion microvalve". Microfluidics and Nanofluidics 17, n. 4 (8 febbraio 2014): 623–37. http://dx.doi.org/10.1007/s10404-014-1343-9.

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49

Dacanal, G. C., G. Feltre, M. G. Thomazi e F. C. Menegalli. "Effects of pulsating air flow in fluid bed agglomeration of starch particles". Journal of Food Engineering 181 (luglio 2016): 67–83. http://dx.doi.org/10.1016/j.jfoodeng.2016.03.004.

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50

Ghosh, A. K., e Pintu Sana. "On hydromagnetic flow of an Oldroyd-B fluid near a pulsating plate". Acta Astronautica 64, n. 2-3 (gennaio 2009): 272–80. http://dx.doi.org/10.1016/j.actaastro.2008.07.016.

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