Flow Pulsation Amplitude Research Articles

Influence of high pressure pulsating excitation on pipe joint sealing based on multiscale contact analyses

Most of the leakage faults in hydraulic pipeline systems occur in the pipe joint. The research on the high-pressure sealing and reliability of the pipe joint is very important in the application of civil aircraft parts. On the basis of studying the characteristics of pressure pulsating fluid, this paper explores the influence of a high pressure pulsating fluid on the sealing performance of flameless extruded pipe joints and analyzes the influence of the internal fluid pulsating amplitude and fluid under different pressures on the contact stress distribution of the sealing surface of the pipe joint. The results show that with the increase in flow pulsation amplitude from 0.5% to 5%, the amplitude of contact stress on the sealing surface decreases with creep time, which makes the sealing performance better. However, the effective working time of the joint as a whole decreases from 2000 to 194 h. The high-stress area of the contact surface expands as the fluid pressure increases, and the high internal fluid pressure obviously improves the sealing effectiveness and reliability of the pipe joint. In addition, the influence of fluid pulsation amplitude on the leakage rate of the joint is much greater than that of the fluid pressure.

Experimental study to establish an evaluating method for the responsiveness of liquid flowmeters to transient flow rates

An aim of this research work is to establish an evaluation method concerning a responsiveness of flowmeters for a transient flow rate. To this end, reference flow metering systems for the transient flow are proposed in this paper. Because a behavior of the responsiveness depends on the type of flowmeter, evaluations using different parameters, such as response time to sudden rise and sudden fall in flow rate, response to the frequency and amplitude of flow pulsation, mean characteristic and so on are needed. To achieve a precise evaluation, two reference flow metering methods for transient flow rates are proposed in this paper. One is a high-response weighing method and the other is a velocity profile measurement method using the ultrasonic pulsed Doppler method (UPDM). Since the behaviors of the transient flow rate measured by both methods show good agreement, we conclude them to be useable as a reference flow metering system.

Identification of pulsating flow effects with CNT nanoparticles on the performance enhancements of thermoelectric generator (TEG) module in renewable energy applications

In this study, performance assessment of a thermoelectric generator module located in between two channels where carbon-nanotube/water nanofluid streams flow is studied with combined effects of nanoparticle inclusion and flow pulsations. The finite element method is used to solve the 3D unsteady coupled fluid flow, heat transfer and electric field equations. Different pertinent parameters effects such as Reynolds number (between 250 and 1000), nanoparticle volume fraction (between 0 and 0.04), pulsating flow frequency (Strouhal number between 0.01 and 0.1) and amplitude (between 0.25 and 0.95) on the power generation are examined. It is observed that flow pulsation changes the dynamic features of thermoelectric power generated in the device. Higher power values are obtained when Reynolds number, flow pulsation amplitude and nanoparticle solid volume fraction rise. However, the effect is reverse for higher pulsation frequencies. Including nano sized particles further enhances the performance of the device with flow pulsation. It is also observed that 24.4 % enhancement in the power are achieved for nanofluid with flow pulsation when lowest and highest pulsation amplitudes are compared. At lowest pulsation frequency and highest amplitude 14.2 % enhancement in power is obtained for water as compared to steady flow case while this amount rises to 31 % for carbon nanotube nanofluid at the highest solid volume fraction. System identification method is used to obtain dynamic lower order model of the system for different pulsation amplitudes to predict the time dependent power generated in the thermoelectric generator device. • TEG module performance with flow pulsation and nanofluid is examined. • Higher amplitudes, ϕ, Re number and lower frequency resulted in higher powers. • When amplitudes are varied, 24.4% power enhancement is obtained with pulsation. • As compared to steady case, 31% enhancement is seen with nanofluid and pulsation. • System identification is used to construct dynamic model of the TEG module.

Numerical analysis on the flow instability of parallel channels in water wall of an ultra-supercritical CFB boiler

Abstract A general calculation model based on the time-domain method is established for analyzing flow instability in parallel channels. In this model, the governing equations of mass, momentum, and energy are discretized and solved using the first-order upwind scheme. A numerical computational program called Dynsys is developed in Fortran language to analyze the flow instability occurring in the water wall of an ultra-supercritical CFB boiler with annular furnace. Comparing the calculation results of Dynsys with the experimental results shows that the model is reasonable and accurate for practical engineering application. On the basis of the validated model, the typical parallel channels in water wall of ultra-supercritical CFB boiler are simulated. Results show that, under the condition of invariable inlet pressure, temperature, and total mass flow rate, as well as 1.2 times heat flux disturbance applied on the parallel channels of ultra-supercritical CFB boiler, the fluctuation of inlet flow rate versus time in two channels is out of phase. In addition, the amplitude of flow pulsation decreases with time first and then returns to the steady state. Therefore, the flow in the parallel channels of ultra-supercritical CFB boiler with annular furnace is stable. Compared with the flow instability in single channel, the calculating results show that the flow in parallel channels was more stable within the range of parameters in the present paper.

Forced convection and thermal predictions of pulsating nanofluid flow over a backward facing step with a corrugated bottom wall

In this study, laminar forced convection of pulsating nanofluid flow over a backward-facing step with a corrugated bottom wall was numerically examined by using finite volume method. Part of the bottom wall downstream of the step was corrugated and kept at constant temperature. Effects of Reynolds number, length and height of the surface corrugation wave, nanoparticle volume fraction, amplitude and frequency of flow pulsation on the fluid flow and heat transfer were numerically investigated. It was observed that average Nusselt number enhances as the Reynolds number, length and height of the corrugation wave increase. Average Nusselt number versus Strouhal number shows a resonant type behavior and flow pulsation amplitude increment results in heat transfer enhancement. Average heat transfer rate increases with the inclusion of the nanoparticles but the rate of enhancement depends on the nanoparticle solid volume fraction interval. An efficient computational strategy for the thermal performance prediction of the system was developed by using proper orthogonal decomposition and artificial neural networks.

Effect on the flow and heat transfer characteristics for sinusoidal pulsating laminar flow in a heated square cylinder

Two-dimensional numerical simulation is performed to understand the effect of flow pulsation on the flow and heat transfer from a heated square cylinder at Re = 100. Numerical calculations are carried out by using a finite volume method based on the pressure-implicit with splitting of operators algorithm in a collocated grid. The effects of flow pulsation amplitude (0.2 ≤ A ≤ 0.8) and frequency (0 ≤ f p ≤ 20 Hz) on the detailed kinematics of flow (streamlines, vorticity patterns), the macroscopic parameters (drag coefficient, vortex shedding frequency) and heat transfer enhancement are presented in detail. The Strouhal number of vortices shedding, drag coefficient for non-pulsating flow are compared with the previously published data, and good agreement is found. The lock-on phenomenon is observed for a square cylinder in the present flow pulsation. When the pulsating frequency is within the lock-on regime, time averaged drag coefficient and heat transfer from the square cylinder is substantially augmented, and when the pulsating frequency in about the natural vortex shedding frequency, the heat transfer is also substantially enhanced. In addition, the influence of the pulsating amplitude on the time averaged drag coefficient, heat transfer enhancement and lock-on occurrence is discussed in detail.

Numerical investigation of pulsating flow around a discrete heater in a channel

In this study, the forced convection heat transfer around a discrete heater located in a channel subjected to laminar pulsating air flow is numerically investigated. Simulations are conducted for six different frequencies and three different amplitudes, while the Reynolds number ( Re = 125) and Prandtl number ( Pr = 0.71) remain constant for all cases. The impact of the important governing parameters such as the Womersley number ( Wo) and the amplitude of flow pulsation ( A o) on heat transfer rate from discrete heaters is examined in detail. The instant velocity and temperature profiles are obtained to determine of the role of dimensionless parameters for pulsating flow. The numerical results show that thermal transport from the heater is greatly affected by the frequency and amplitude of the flow pulsation. The results given are dimensionless parameters.

Heat transfer from pulsating flow in a channel filled with porous media

A numerical study is made of heat transfer characteristics from forced pulsating flow in a channel filled with fluid-saturated porous media. The channel walls are assumed to be at uniform temperature. The Brinkman-Forchheimer-extended Darcy model is employed. The time-dependent, two-dimensional governing equations are solved by using finite-volume techniques. Numerical solutions are obtained for quasi-steady periodic states. Flow and temperature fields are examined over ranges of the principal parameters, i.e. the amplitude of flow pulsation A, the pulsation frequency parameter M [≡H( ω 2ν ) 1 2 ] , the Darcy number Da (≡ K H 2 ) , the thermal conductivity ratio R κ (≡ κ eff κ ) , and the heat capacity ratio R c {≡ (ϱC p ) eff [ε(ϱC p )] } . The impact of pulsation is discernible in the cycle-averaged temperature distribution. In comparison with the case of non-pulsating flow, the presence of flow pulsation brings forth a reduction in heat transfer in the entrance region and an enhancement of heat transfer at moderate downstream regions. Farther downstream, the influence of pulsation is meager. The magnitudes of changes in heat transfer depend upon A, M, Da, R κ , and R c. The effect of pulsation on heat transfer between the channel wall and the fluid is more pronounced for small M and large A. Explicit influences of Da, R κ , and R c on the flow and heat transport characteristics are also scrutinized.

Flow pulsation and network structure in mesenteric microvasculature of rats.

Red cell velocity was measured by a fiber-optic laser-Doppler anemometer microscope in microvessels of the mesentery of spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto control rats (WKY) with high temporal resolution. Based on the velocity data, the propagation velocity of flow pulse along single microvessels as well as the arteriovenous distributions of the mean volumetric flow, the amplitude of flow pulsation, and the phase lag of the flow relative to the systemic pressure were analyzed in relationship to the vessel wall rheology and the network topology. The propagation velocity was 3.5-134 cm/s in arterioles of 12-43 microns in diameter, and it increased with increasing diameter. The mean volumetric flow exhibited a power law relationship to the vessel diameter, in which the exponents were 3.16 and 3.30 for arterioles and 3.03 and 2.85 for venules in SHR and WKY, respectively. The exponents for arterioles were > 3 (P < 0.1) and different between SHR and WKY (P < 0.12). The amplitude of the flow pulsation also varied in a power law with the vessel diameter, whose exponents for arterioles were 3.41 and 3.52 for SHR and WKY, respectively. The flow phase lag increased gradually with decreasing vessel diameter in arterioles and increased comparatively rapidly with increasing vessel diameter in venules, which suggests more compliant vessel walls for venules than arterioles. The slope of the increase in the flow phase lag with the vessel diameter in arterioles of SHR was larger than that for WKY (P < 0.05). This difference in the flow phase lag distribution and the difference in the exponent of the mean flow rate vs. diameter relationship may reflect that the number of small arterioles relative to large ones is reduced in SHR microvasculature compared with that in WKY.

Pulsatile flow in a 90.DEG. branched tube. (1st report Experimental study on the flow ratio and branching losses for turbulent flow)

The flow ratio and loss coefficient for a 90° branched tube are experimentally investigated for steady and pulsatile flow conditions. The Reynolds number defined at the upstream point is varied within the range of Re=3×1049×104, and the frequency of the pulsating flow is f=0.171.5Hz. The main results obtained here can be summarized as follows: (1) The flow ratio of the branch tube does not show clear dependence on the Reynolds number Re, frequency f or pulsating compliance of flow. (2) The loss coefficient of a branch tube for pulsatile flow is almost the same as the steady flow in the branch side but decreases slightly in the main branch with increasing amplitude of flow pulsation β.