Aspect Ratio Effects on the Noncracking and Cracking Heat Transfer in Microchannels

In cooling microchannels of advanced flight engines, the fuel temperature rapidly increases to facilitate endothermic cracking reactions. A cooling channel can be divided into noncracking and cracking zones. In this study, various aspect ratios were investigated via numerical simulations to determine the effects of microchannel geometry on the cooling effect. A nine-species surrogate fuel is introduced to predict the corresponding thermophysical properties. Then, one primary and three secondary cracking reactions are applied to simulate thermal cracking. The effect of the aspect ratio on the cooling performance varies in different zones. A higher aspect ratio contributes positively to a higher turbulence kinetic energy in the noncracking zone, resulting in better cooling performance. Conversely, a lower aspect ratio increases the microchannel residence time, promoting endothermic cracking reactions for an improved cooling effect. Furthermore, a cooling microchannel with a high aspect ratio in the noncracking zone and a low aspect ratio in the cracking zone is studied. The variable aspect ratios allow for leveraging of the chemical heat sink and improving the cooling performance.