Comparative calculations of the heat transfer coefficient during refrigerant boiling in tubes

DOI: 10.17586/1606-4313-2020-19-2-65-72
UDC 621.565

Comparative calculations of the heat transfer coefficient during refrigerant boiling in tubes

Koshelev S. V., Slastikhin Yu. N., Eydeus A. I.

For citation: Koshelev S.V., Slastikhin Yu.N., Eideyus A.I. Comparative calculations of the heat transfer coefficient during refrigerant boiling in tubes. Vestnik Mezhdunarodnoi akademii kholoda. 2020. No 2. p.65-72

Abstract
The article is aimed at identifying the most suitable heat transfer coefficient (HTC) correlations for refrigerant flow boiling in conventional horizontal tubes with an inner diameter dT > 3 mm. A review of the HTC correlations is made. The conditions under which the HTC correlations in macro-channels can be extended to mini-channels are discussed. The analysis of a number of published works is carried out the accuracy of the methods for predicting HTC during boiling liquids in tubes, five best correlations were selected. In various combinations, 21 correlations are among the best. Five of them were used in our computer program. After its expansion, the average HTC αci was also determined by 15 other correlations for 11 variants of the boiling conditions of the refrigerants R134a, R22, R290, R32, R404A, R407C, R410A, and R507. The range of variation of the boiling temperature t0 = –15…+5 oC, diameter dT = 6…13,84 mm, mass velocity wρ = 100…500 kg/(m2·s), heat flux density q = 3750…15000 W/m2,  vapor quality at the beginning of the boiling zone хн= 0,01…0,1   and at the outlet хв= 0,9…0,95. Comparison of the calculation results was carried out according to three indicators, and the most suitable methods are: a) which, with the same initial data, give the closest values of the average HTC; b) for which the ratio of the largest HTC to the lowest one in all cases does not exceed 1.4 for all refrigerants; c) local HTC for which have the greatest values at vapor qualities  corresponding to the annular flow regime. These conditions are met by a computer program with certificate No. 2015610039, as well as the methods by Wattelet et al. (1994), Kattan et al. (1998), and Fang et al. (2017), although the latter does not take into account changes in local HTC.

Keywords: refrigerants, boiling, horizontal tubes, heat transfer coefficient, calculation methods, choice.


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