Heat transfer characteristics of parallel and counter flow Microchannel heat exchangers with varying wall resistance

Abstract

Thermal behaviors of parallel and counter flow micro-heat exchanger are investigated numerically, with emphasis on the role of wall resistance and entry effects. The influence of different parameters, such as, thermal resistance (R), Knudsen number (Kn), effectiveness (ε ) and number of transfer units (NTU) on the heat transfer characteristics are investigated. It is found that the temperature jump at the walls increase with increasing thermal resistance (R) and Knudsen number (Kn). On the other hand, the NTU increases with decreasing R and Kn. It is also found that the effect of R on ε is insignificant for parallel and counter flow. Furthermore, for counter flow microchannel heat exchangers, that the heat conduction in the separating wall and the entrance regionplays a significant role in the overall heat transfer process and thus thermally fully developed flow may not exist over a large section of the heat exchanger.