Convective heat transfer enhancement in a confined passageway

Abstract

First, a study is made of the heat transfer characteristics of a fully-developed pulsating flow in a channel. The fluid at the channel inlet is of temperature $T_o$, and the channel walls are at uniform temperature $T_w$. Concern is directed to the thermally developing region. The unsteady Navier-Stokes equations are solved numerically to simulate a relatively slow throughflow at Re=50, Pr=0.7. Comprehensive time-dependent flow data are obtained for wide ranges of two key parameters, i.e., the pulsation amplitude 0 ≤ A ≤ 0.75, and the nondimensional pulsation frequency M up to 10.0. When M is low, the velocity profiles resemble much of the quasi-steady solutions. When M is large, the effects of oscillation are confined to a narrow zone adjacent to the walls. The changes in the Nusselt number Nu due to pulsation are pronounced in the entrance region, say X/(ReㆍPr) < 1.0, and the impact of pulsation on Nu is minor at far downstream locations. The effects of M on Nu are noticeable when M is small and moderate. At high pulsation frequencies, heat transfer is little affected by the addition of pulsation. Detailed analyses on local behavior of heat transfer are made by using Fourier-series representations of the numerical results. These exercises indicate that, due to pulsation, both heat transfer enhancement and reduction can be expected in various axial locations of the channel. Based on these numerical results, physically plausible explanations are offered to interpret the axial behavior of heat transfer. Second, 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 for the flow in the channel. The time-dependent, two-dimensional governing equations are solved by using finite-volume techniques. Numerical solutions are obtained for quasi-steady periodic states. F...