Numerical simulation of heat transfer in simultaneously developing flows in parallel rectangular ducts

The F correction factor charts and the ε–NTU relations assume the overall heat transfer coefficient to be constant across the heat exchanger. In microchannel heat exchangers, the short lengths and the comparatively thick walls through which heat is conducted preclude the existence of thermally fully developed flow over a large portion of the heat exchanger. In this study, a parallel flow heat exchanger is numerically simulated to determine the impact of different parameters on the performance and the accuracy of constant heat transfer coefficient assumption. It is shown that there is significant change in the overall heat transfer coefficient in the developing region and that the three-dimensional heat transfer in the heat exchanger wall must be included in the analysis.