Increase In Pulsation Amplitude Research Articles

Effects of intermittent pulsating flow on the performance of multi-channel cold plate in electric vehicle lithium-ion battery pack

In order to address the thermal management of electric vehicle lithium-ion battery pack, the intermittent pulsating flow is proposed to apply in the multi-channel cold plate of electric vehicle lithium-ion battery pack. Extensive numerical investigations on the maximum temperature (Tb,max) and maximum temperature difference (ΔTb,max) and of the lithium-ion battery pack, transfer coefficient (h), pressure loss (Δp), efficiency index (EI), pump power (Ppump), and energy consumption (W) of the multi-channel cold plate under intermittent pulsating flow and pulsating flow are conducted. Results show that Tb,max and ΔTb,max under intermittent pulsating flow is lower than those under pulsating flow at the first half of the whole discharging process, which suggests that the intermittent pulsating flow can make the lithium-ion battery pack achieve better temperature characteristics. However, W of cold plate under intermittent pulsating flow is much higher than that under pulsating flow at the same pulsation amplitude and frequency. It is always increased at the fixed pulsation frequency with the increase of pulsation amplitude and reaches the minimum value at the pulsation frequency of 3 Hz when the pulsation amplitude is fixed.

A Numerical Study on the Cement Slurry Penetration Performance of the Cyclic Grouting Method with High-Frequency Pulsating Pressure

The performance of traditional steady grouting is sometimes limited; therefore, a new high-frequency pulsed grouting method is proposed. Through the CFD method, this paper studies the cement slurry penetration performance of cyclic grouting under the influence of pulsating pressure and steady pressure. Firstly, the penetration shape and flow fields of the two grouting methods are investigated. Secondly, the effects of pulsation parameters on penetration performance are studied. Finally, the influence of various working conditions, such as soil properties, grout parameters, grouting pipe length, and back pressure, on penetration distance is also investigated. The results show that pulsating grouting achieves better penetration performance compared with steady pressure grouting. With the increase in frequency, pulsating grouting exhibits superior performance, while with the increase in pulsation amplitude, the penetration distance initially increases and then decreases. This is because part of the pulsating pressure is lower than the back pressure, which weakens the pulsating effect. As viscosity and back pressure increase and as porosity and particle size decrease, the proportion of lateral diffusion in pulsating grouting relative to steady pressure grouting increases. This indicates that lateral penetration performance achieves optimal results under high-flow-resistance conditions. However, when the flow resistance becomes excessively high, the vertical penetration distance may be affected. This study is expected to improve the grouting efficiency and provide a better understanding of pulsating grouting design and operation.

Thermal performance analysis of artificially roughened solar air heater under turbulent pulsating flow with various wave shapes

This paper presents a numerical investigation of the operation of a solar air heater (SAH) with cylindrical shape ribs under turbulent pulsating flow based on thermal and frictional considerations. Turbulence and thermal natures of flow physics are modeled by taking the relevant governing equations into the account using RNG k−ε turbulence model and transient state Reynolds-Averaged Navier-Stokes (RANS) equations. The pulsating flow is modeled with four different wave shapes including rectangular, sinusoidal, triangular, and sawtooth functions. The influence of various factors such as wave shape, Reynolds number (Re), frequency, and amplitude of pulsating flow on the thermal and hydraulic performance of SAH has been evaluated. Results indicated that the SAH with ribbed absorber section under pulsed flow has a larger Nu number compared to the air heater with smooth duct under steady flow. Moreover, the pulsating flow with a sawtooth velocity profile leads to the greatest value of the thermo-hydraulic performance parameter (THPP). The growth of pulsation frequency up to 200 enhances the heat transfer coefficient of the air heater while for frequencies larger than 200, the thermal performance declines. In addition, the increase in pulsation amplitude has a negative effect on the THPP. It was proved that the increment of the Re number enhances the THPP. Up to 53.3% improvement of THPP can be achieved by applying pulsed flow with sawtooth wave shape and ribbed absorber section compared to air heat with smooth duct under steady flow.

Numerical Investigation on Spray Characteristics With Upstream Flow Pulsation of a Pintle Injector

The volume of fluid (VOF) model and the adaptive mesh refinement (AMR) method are used to study the spray characteristics of a gas–liquid pintle injector and the effects of mass flow pulsation of liquid on it. A pintle injector is a thrust adjusting device that changes the injection area using movable parts. Pressure pulsation in the supply pipeline is simulated by periodically changing the mass flow rate of the inlet. Spray characteristics with constant and pulsating upstream flows are compared with each other. The effect of frequency and amplitude of upstream liquid flow pulsation on the spray performance was studied. The results reveal that holding the mass flow rate of the upstream liquid flow constant, under the impact of gas flow, the liquid block, the liquid filament, and a large number of small droplets are peeled off from the liquid film. The film breakup position stays relatively fixed, and the spray has a conical shape. However, when the upstream liquid flow is pulsating, the film breakup position changes periodically, and the spray has a “Christmas tree”-shape. The pulsation frequency has little effect on the spray angle. But it strongly determines the droplet size and the spatial distribution of the spray. In addition, the pulsation amplitude can enhance the phenomenon of “Christmas tree.” With the increase in pulsation amplitude, the liquid film at the outlet of the pintle injector appears with a periodic phenomenon of “contraction–expansion.”

Study on flow characteristics of bidirectional sinusoidal liquid pulsed gas-liquid-solid multiphase fluidized bed

Gas-liquid-solid three-phase fluidized bed has been widely used in chemical, biotechnology and environmental industries for its advantages of large inter-phase contact area, high heat/mass transfer efficiency and intense reaction process. In this work, the bidirectional sinusoidal liquid pulsed GLS fluidized bed was proposed to improve the interphase relative velocity and reaction efficiency. The effects of particle properties and pulsed liquid amplitude/frequency on the flow characteristics were studied by numerical simulations and experiments. In a complete circulation period, the average axial solids holdup is larger near the middle region of the fluidized bed and gradually decreases along the upper and lower inlets. With the increase of pulsation amplitude or period, the axial average gas holdup distribution uniformity and the liquid-solid relative velocity increase significantly. Compared with the conventional upward gas-liquid-solid fluidized bed, the bidirectional fluidized bed can further improve the liquid-solid relative velocity and reaction efficiency. The obtained studies have important implications for better design, scale-up and operation of gas-liquid-solid multiphase fluidization systems.

Cerebrovascular Pulsation and Width of Subarachnoid Space During Electroconvulsive Therapy

The mechanism of electroconvulsive therapy (ECT) has not been comprehensively explained. A new noninvasive method of monitoring intracranial homeostasis during and after ECT provides additional insight into the mechanism of ECT. The investigations on changes in the width of the subarachnoid space (SAS) and intracranial pulsation amplitude by near infrared-transillumination/backscattering sounding method can throw new light on changes in type and volume induced by ECT. In this study, a new method of noninvasive investigation of width of SAS and intracranial pulsation parameters was used. This method has been called near infrared-transillumination/backscattering sounding. The method consists of light beam analysis in near infrared whereby the light beam is emitted by an emitting diode. The light beam passes through head's anatomic layers, is reflected multiple times in SAS, and returns outward-to be recorded by the receiving diode. The novelty of this method is the patented invention that allows skin flow under the probe to be eliminated and thereby "to look" under the skull bone. After ECT, a highly significant increase in pulsation amplitude was observed. The pulsation amplitude rose by a factor of 2.5 times after a mean of 90 seconds after the ECT stimulus. A pause in SAS pulsation-not longer than 26 seconds-directly after administration of electroshocks was observed. After approximately 90 seconds, the amplitude decreased slowly, and this was consistent in all analyzed cases. A decrease in SAS width was also observed.

Ensemble Characteristics of the ZZ Ceti Stars

We present the observed pulsation spectra of all known non-interacting ZZ Ceti stars (hydrogen atmosphere white dwarf variables; DAVs) and examine changes in their pulsation properties across the instability strip. We confirm the well established trend of increasing pulsation period with decreasing effective temperature across the ZZ Ceti instability strip. We do not find a dramatic order of magnitude increase in the number of observed independent modes in ZZ Ceti stars, traversing from the hot to the cool edge of the instability strip; we find that the cool DAVs have one more mode on average compared to the hot DAVs. We confirm the initial increase in pulsation amplitude at the blue edge, and find strong evidence of a decline in amplitude prior to the red edge. We present the first observational evidence that ZZ Ceti stars lose pulsation energy just before pulsations shut down at the empirical red edge of the instability strip.

Enhanced Heat-Source Cooling by Flow Pulsation and Porous Block

A numerical study has been carried out for forced pulsating flow in a parallel-plate channel with a porous-block-attached strip heat source at the bottom wall. Both the transient non-Darcy flow model taking the effects of the impermeable boundary, inertia, as well as variable porosity into consideration for the momentum equation and local thermal equilibrium model with thermal dispersion for energy transport were employed inside the porous region. Through the use of a stream function-vorticity transformation, the solution of the coupled governing equations for the porous/fluid composite system is obtained using the control-volume method. Comprehensive time-dependent flow and temperature data are calculated and averaged over a pulsation cycle in a periodic steady state. The effects of the important governing parameters, such as the particle diameter, the blockage ratio, pulsation frequency, and pulsation amplitude on the flow behavior in the vicinity of the porous block and the heat transfer rate from the heater are documented in detail. The results show that the cycle-space averaged Nusselt number for pulsating flow is higher than that for steady flow. The heat transfer enhancement factor increases with the increase of particle diameter, pulsation frequent, and blockage ratio, but decreases with the increase of pulsation amplitude. The method combining flow pulsation with a particle-porous heat sink can be considered as an augment heat transfer tool for cooling high-speed electronic devices.

The effects of ouabain on the electrical and mechanical activities of embryonic chick heart cells in culture

The effects of ouabain were studied on cultured embryonic chick heart cells. Micro-electrode recordings of the transmembrane electrical activity and photometric measurements of cell pulsation were used to evaluate glycoside effects in spontaneously beating and electrically-driven cells. Ouabain concentrations higher than 10 −8 m increased the beating frequency. At 10 −5 m frequency began to rise within 1 min and irregular beats (bi- and trigeminy) and bursts of discharges were often seen. The positive chronotropic effect started to decline after about 2 min as the first signs of membrane depolarization became detectable and cells came to a final standstill within 3 to 10 min. The duration of the action potentials was not shortened throughout these chronotropic effects of ouabain. The inotropic influences of ouabain were sudied on electrically-driven cells to exclude indirect effects of the chronotropic action. Increase of pulsation amplitude was found using 10 −8 m. Superfusion with 10 −5 m ouabain resulted in a distinct increase in the pulsation amplitude within 1 min. Then relaxation became slower, pulsation duration increased and the baseline of the cell pulsation began to rise. The development of incomplete relaxation finally led to systolic standstill of the cell. The results indicate that the single or grouped cardiac cells in culture insensitive to β-receptor agonists not only exhibit inhibitory effects but also stimulatory and toxic effects of ouabain on excitation and contraction, except action potential shortening.

Undamped Free Pulsations of an Ideal Bubble

For large bubbles (for example of diameter much greater than 3×10-4 cm for air bubbles in water at atmospheric pressure) the effects of surface tension on the motion may be ignored. It is then possible to put the equation of motion on a dimensionless basis. Solutions of this generalized equation have been obtained. Quantitative results are presented graphically and show, for example, the increase in period which occurs with increase in pulsation amplitude. The effects of variation of the compression exponent are also brought out. These dimensionless results are quite general in regard to external pressure, liquid density and bubble size. For comparison, a sample solution is given for a small bubble with allowance for surface tension. Discussion covers both the correlation of the results with available experimental evidence, and also various implications of the results, for example, in regard to forced pulsation.