Comparison work about different empirical formulas for the boiling heat transfer coefficient in separated heat pipe system

Two-phase closed thermosiphon is a kind of heat transfer equipment with high thermal conductivity. It can transfer heat for long distance by boiling and condensing. Thus, it is important to study the heat transfer character of the boiling process in the evaporator. In this paper, we have compared mainly 7 different heat transfer formulas by other researches and our experiment results. Such formulas include Rohsenow formula (1951), Cooper formula (1984), Labuntsov formula (1973), Kutateladeze formula (1990), Kruzhilin formula (1947), Imura formula (1979) and Hasna formula (2017). Rohsenow formula is derived in theoretical for nucleate boiling process in pool boiling. Cooper formula is mainly for refrigerating coolants. Imura formula is an empirical formula based on the experiment result of the two phased closed thermosiphon. Hasna formula has the same pattern as the Cooper formula but it is used for separated heat pipe system. Labuntsov formula, Kutateladeze formula and Kruzhilin formula are all for the nucleate boiling. Five coolants are used for comparison including R744, R134a, R22 and R410A. The results show that, Imura formula’s calculating results are all less than the experiment results. Cooper formula accords very well with the experiment results for Freon coolant, but for R744, the relative error is as large as 62%. Rosenow formula’s average error is about 29%, and the variation trend is close to the experiment results.