A Study of the Flow Mechanisms Responsible for Heat Transfer Enhancement in Interrupted-Plate Heat Exchangers

Abstract

Certain compact heat exchanger cores are modeled by assemblies of parallel plates. The heat transfer in these cores may be enhanced if the plate surfaces are interrupted. The results of an experimental study of the mechanisms responsible for enhancement are reported here along with quantitative measures of the magnitude of the enhancement and the pressure drop penalty incurred. The aim of this work is to identify the important parameters and provide guidelines for designers of heat transfer surfaces and to workers attempting to correlate experimental data. Arrays of parallel plates were tested in a wind tunnel. Fluid flow phenomena were identified using the Schlieren visualization technique. Three distinctly different flow regimes are found within cores composed of in-line plates. These are classified as steady, general unsteady, and periodic unsteady flows. The periodic unsteady flow is accompanied by the emission of a strong acoustic tone. The heat transfer performance of these cores was determined using a transient heating technique. The evolution of the enhancement and the associated changes in the flow regimes are documented over a range of Reynolds number as the streamwise spacing between in-line plates is increased from zero. The results of these experiments are used to interpret the measured performance of cores consisting of staggered arrays of parallel plates and of cores formed by assembling parallel-plate arrays so that alternate plates in the streamwise direction are perpendicular to each other.