Numerical and experimental analysis of oscillating flow and heat transfer in a channel with heated blocks inside

In this study, the flow and heat transfer through a channel having heat dissipating blocks have been considered. Air enters the channel with an oscillating velocity. By performing the experimental and numerical studies, the effects of oscillation on the flow and heat transfer were investigated. The problem was considered as two-dimensional and time-dependent. Numerical studies carried out for laminar and turbulent flows cases. It is assumed that the volumetric heat generation takes place in the blocks. To model the turbulence k-? model was used. A computer program was developed based on the control volume approach and SIMPLE algorithm. The hybrid scheme was used for the discritization of the convective terms. The time-dependent terms were discretized using the fully implicit scheme. The Gauss-Seidel iteration technique was used for solving the algebraic equations. The velocity, pressure, and temperature distributions were obtained for all grid points at different instants of the injection period. Over the block surface, the instantaneous local Nusselt number, instantaneous area-averaged Nusselt number and area and time averaged Nusselt number along the period of injection were calculated using the temperature distribution.For experimental studies, a test setup was established. Experimental data was obtained for steady and oscillary flow cases. Geometrical dimensions of the channel and the blocks were kept constant. The calculations were carried out for different Reynolds numbers (Re=250, 500, 750, 1000, 10000, 20000, 30000 and 40000), oscillation amplitudes (0.0Uo, 0.2Uo, 0.4Uo, 0.6Uo and 0.8Uo), oscillation frequencies (1, 2, 3, 4, 5 and 6 Hz) and heat generation (0.025, 0.050, 0.075, 0.25, 0.50, 1.0 and 1.5 W/cm3). By performing the experimental and numerical studies, the effects of Reynolds number, heat generation in the blocks, and amplitude and frequency of oscillating inlet velocity on the flow and heat transfer were investigated. In this study, the following results were obtained.The surface temperature of the first block is the lowest. The block temperature increases in the flow direction (with block number). Similarly, the Nusselt number of the first block has the highest value. The block Nusselt number decreases with the block number. As the Reynolds number of the flow increases, temperature decreases and Nusselt number increases for all the blocks. With the increase of the heat generation in blocks, the surface temperature of block increases. For laminar conditions, as the oscillation frequency and amplitude of the flow increases, block temperatures decrease and Nusselt number increases for all blocks. For turbulent conditions, oscillation frequency of 3 Hz is a critical value for Re=20000 and Re=30000. Under this critical value of frequency, the bock temperature decreases and Nusselt number increases with decreasing oscillation frequency. Above the critical value of frequency, the block temperature increases and Nusselt number decreases with increasing oscillation frequency. For Re=40000, the critical frequency is 5 Hz. For all Reynolds number, if the oscillation frequency is less than critical value, the Nusselt number increases with increasing oscillation amplitude. However, if the oscillation frequency is greater than critical value, the Nusselt number decreases with increasing oscillation amplitude.