The influences of sidewall proximity on flow and thermal performance of a microchannel with large-row pin-fins

Sidewall proximity, characterized by the gap distance (G) between border pin-fin column and sidewall in a pin-finned microchannel with in-line arrangement, plays a significant role on pressure drop and heat transfer characteristics. To better understand the thermal performance and explore the underlying mechanisms, a comprehensive comparison is numerically developed among three representative microchannels with gap-to-diameter ratios (G/D) of 0.6, 1.0 and 1.4, respectively. The Reynolds number investigated in this paper varies from 13 to 202. It is found that the gap distance severely influences flow distribution, streamline structure, velocity field and temperature distributions in a pin-finned microchannel. At a fixed Reynolds number, pressure drop of microchannel is continuously decreased while heat transfer is first enhanced and then reduced with the increase of gap distance. Among the three models, the microchannel with G/D = 1.0 possesses a comparatively superior heat transfer performance. In addition, extremely low local Nusselt numbers on both the base surface and the pin-fin surface near sidewall seriously deteriorate the overall heat transfer performance of the microchannel with G/D = 0.6. Furthermore, unremarkable heat transfer performance is also observed from the microchannel with G/D = 1.4 for its obvious decline of local Nusselt number on inner regions in spite of a rise on border region. Taking heat transfer and pressure drop into account simultaneously, the results show that a very small gap distance (i.e., G/D = 0.6) should be avoided for design of a pin-finned microchannel. Microchannels with middle gap distances (i.e., G/D = 0.9, 1.0, 1.1) have a relatively better overall thermal performance, which separately provide a superiority of 10.6–13.6% (G/D = 0.9), 10.0–13.5% (G/D = 1.0), 8.2–14.4% (G/D = 1.1) compared to the microchannel with G/D = 0.6. Finally, new correlations of friction factor and Nusselt number are developed by considering the effects of sidewall proximity.