Heat transfer and flow patterns in a minichannel with various acoustic standing wave configurations and thermal boundary conditions

Abstract

In this work, we investigate the effects of acoustic standing wave configurations and thermal boundary conditions on heat transfer and flow patterns in the minichannel cavity subjected to acoustic standing wave fields. Upon differential heating, the fluid properties such as density, speed of sound, and acoustic impedance become inhomogeneous. When this heated inhomogeneous fluid is subjected to acoustic fields, the resulting acoustic body force which is proportional to impedance gradient induces fluid convection and determines the heat transfer. We observed that the heat transfer and fluid motion vary significantly with respect to thermal boundary conditions, wavenumber (quarter, half, and full-wave), and direction of the standing wave; this can be attributed to the fact that the acoustic body force is strongly dependent on the position of inhomogeneity. We have studied 18 different combinations of wave configurations and thermal boundary conditions to understand their effects on heat transfer and flow patterns. It is observed that certain combinations favor heat transfer, whereas few others don't. The results of all the cases are explained clearly and compared with natural convection to understand the effectiveness of the heat transfer process due to the acoustic field. For both ethanol and water, maximum heat transfer is achieved when the acoustic standing full wave is applied perpendicular to the hot bottom plate and cold top plate, we obtained the maximum heat transfer increase of 3.18 times in ethanol and 2.49 times in water when compared to the natural convection. For ethanol, heat transfer is reduced to 0.21 times of natural convection, when the quarter-wave is applied parallel to the hot bottom plate and top cold plate such that node is at top plate and antinode is at the bottom plate. For water, heat transfer is reduced to 0.51 times of natural convection, when half-wave is applied parallel to the hot bottom plate and cold top plate.