pulsating flow

In this paper, the pulsating flow and forced convection heat transfer in a pipe filled with porous medium is investigated. The pipe is under a constant heat flux. The governing equations of the problem includes continuity, Brinkman momentum equation and energy equation. Using complex analysis technique, an analytical solution for velocity profile and temperature distribution are obtained. Also, the effect of various design parameters on velocity profile and temperature distribution is studied. Results show that the pulsating effect on velocity and temperature profile increases with the increase of Darcy number and dimensionless amplitude of pressure gradient but decreases with the increase of viscosity ratio parameter, Prandtl number and dimensionless frequency. For high dimensionless frequency (Ω>30), the maximum velocity and temperature tend to be constant due to the decrease in wave amplitude.

Heat transfer enhancement has been the goal of many researches carried out over the past three decades. Employing the modified fluids, changing the flow geometry, and active methods are among the commonly used techniques. The effects of three referred techniques, employing pulsation flow as active method, nanofluids instead of conventional fluid as modified fluids and helical-coil tube as changing the flow geometry on the fluid flow and heat transfer have been investigated numerically. The results of interests with pulsation flow and non-pulsation flow have been presented. In this research, the results indicated that, the coil pitch tube and coil diameter have a minor effect on the Nusselt number (5 and 7%, respectively). But the Reynolds number has a major effect on the Nusselt number, so that by increasing the Reynolds number from 5000 to 100000, the Nusselt number will be enhanced by more than 200%. The nanofluid pressure drop and heat transfer coefficient increased with nanoparticles volume fraction. In addition, by introducing a concept as the performance evaluation criteria, the mutual effects of the pressure drop and Nusselt number were investigated with referred concept. Performance evaluation criteria revealed that employing the nanofluid in lower Reynolds numbers yields higher effects on the fluid flow and heat transfer.

Fluid flow around and heat transfer from a rectangular flat plane with constant uniform heat flux in laminar pulsating flows is studied, and compared with our experimental data. Quantitatively accurate, second-order schemes for time, space, momentum and energy are employed, and fine meshes are adopted. The numerical results agree well with experimental data. Results found that the heat transfer enhancement is caused by the relative low temperature gradient in the thermal boundary layer, and by the lower surface temperature in pulsating flows. In addition, the heat transfer resistance is much lower during reverse flow period than that during forward flow period. The flow reversal period is about 180 degree behind the pulsating pressure waves. Besides, spectrum results of the simulated averaged surface temperature showed that the temperature fluctuates in multiple-peaked modes when the amplitude of the imposed pulsations is larger, whereas the temperature fluctuates in a single-peaked mode when the amplitude of the imposed pulsation is small.