HEAT TRANSFER AND FRICTION IN SMALL DIAMETER CHANNELS

Abstract

Applications have been developed for heat transfer in small-diameter channels of circular or rectangular shape. This article discusses the ability of existing accepted correlations to predict single-phase and two-phase heat transfer and friction in channels having small hydraulic diameters (e.g., between 0.1 and 2.0 mm). Existing equations predict the single-phase heat transfer and friction data for multiport circular and rectangular-crosssection channels having hydraulic diameters between 0.96 and 2.13 mm. However, a 1994 study by Wang and Peng on single-phase flow in multiport rectangular channels found that the same equations considerably overpredicted their data. The present investigators show that their recently developed ''equivalent Reynolds number model'' will predict the condensation coefficient of various refrigerants in tube diameters as small as 2.13 mm. However, the 1979 Shah equation begins to fail for R-134a at p p cr 0.44. The present study is important for applications where very small channel hydraulic diameters are important, such as brazed aluminum heat exchangers or in electronic equipment cooling. More data are needed on channel diameters below 1.0 mm.