Extended Correlations for Staggered Round Tube Plain Fin Heat Exchangers

This paper develops a semi-empirical expression for heat transfer in round tube plain fin heat exchangers that have relatively large fin pitch. Empirical heat transfer correlations currently available in the public domain are necessarily limited in their range of applicability, and their functional forms are generally not designed to converge to well-known physical results, for example when parameters such as fin or tube pitch become large as in the case of frost-tolerant evaporators designed for refrigeration applications. The approach taken here begins with a simple superposition of a fin array and tube bank, and then adds empirically-based terms to account explicitly for the streamwise vortices that form at fin-tube junctions and the spanwise von Karman vortex streets shed from the tubes. Comparisons with available data show good agreement for heat exchangers having large fin pitch, where these effects are dominant. Developing flow effects are also treated explicitly. The resulting expression provides a framework for modifying the purely empirical correlations developed for air conditioning applications, and bridging the gap to sparser data available for refrigeration coils.