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Proceedings of Symposium on Energy Engineering in the 21<sup>st</sup> Century (SEE2000) Volume I-IV

ISSN:
1-56700-132-7 (Print)

AIR-SIDE HEAT TRANSFER ENHANCEMENT MECHANISMS OF COMPACT HEAT EXCHANGERS WITH INTERRUPTED SURFACES

L. Winston Zhang
Research and Development Modine Manufacturing Company

Abstract

Air-side heat transfer enhancement mechanisms in three types of interrupted surfaces: parallel-plate, louvered and convex-louvered fins in compact heat exchangers are analyzed. It is found that boundary layer restarting is the major enhancement mechanism in all these interrupted surfaces. Vortex shedding can be generated at sufficiently high Reynolds numbers. However, vortex shedding may or may not provide additional enhancement in heat transfer, depending on the type of interrupted surface employed. Effects of varying geometric parameters have been studied in these interrupted surfaces. In the parallel-plate fins, vortex shedding occurs at much lower Reynolds numbers in the inline and one offset geometry than that in another offset geometry. Different flow characteristics in the louvered fins have been analyzed and the important geometric parameters such as fin pitch to louver pitch ratio have been identified. This study also shows that other mechanisms such as flow impingement seen in convex-louvered fins can provide additional heat transfer enhancement. However, the enhanced heat transfer is usually associated with increased pressure drop penalty, especially, with the more aggressive enhancement mechanisms.