The Effect of Diameter on Boiling Heat Transfer from the Outside of Small Horizontal Tubes

Recent studies have suggested that tube diameter is a relevant parameter which should be included when correlating heat transfer data for pool boiling on horizontal tubes. However, there are few data for tubes of diameter less than 8 mm, and the diameter effect for small tubes has not been determined. This paper reports the results of an experimental investigation using tubes of 1–6 mm diameter. Tests have been carried out with water and refrigerant R141b at heat fluxes ranging from 1 to 90% of the critical heat flux. The results indicate that correlations which show an inverse relationship between heat transfer coefficient and diameter should not be applied for tubes of less than 6 mm diameter. Conventional pool boiling correlations derived from data acquired from boiling on wires and flat plates yielded acceptable results when applied to the test data from this study.