Compact and microchannel heat exchangers: A comprehensive review of air-side friction factor and heat transfer correlations

This review focuses on the thermal-hydraulic performance correlations for the air-side of compact and microchannel heat exchangers. These correlations are presented in tables, mainly in terms of Colburn j-factor and fanning friction factor (f), based on each type of fin arrangements with appropriate constraints including Reynolds number ranges, geometrical parameter limits, and fitting uncertainties. The correlations used for air-side arrangements of mini/micro channels, which are constructed in slabs, are the same as those used for the compact heat exchangers. In particular, these correlations are used for louver-fin, wavy-fin, offset strip-fin, and extended surfaces (plain fins and pin fins) arrangements. However, the correlations proposed for fin-and-tube (round) are only valid for the compact heat exchangers. We have also compared some correlations with the experimental data of Kays and London standard reference. Some performance correlations are generalized (as one correlation for each j- and f-factor) to represent all louver-fin types. However, other fin arrangements have distinct correlations based on their specific geometry. The most reported correlations are valid for dry fin conditions, whereas there are limited correlations devoted to wet or frost surfaces. A guideline based on this study is provided to facilitate the use of correlations for various configurations.