Heat transfer and pressure drop during refrigerants condensation in compact heat exchangers

This paper consists of the analysis of research on refrigerant condensation in minichannels and compact heat exchangers cooled with either water or air. An analysis of the state of knowledge of the research on refrigerant condensation in minichannels and mini-heat exchangers, so-called multiports, was performed. Directions for further research in this field were indicated. The authors present results for the condensation of refrigerants R134a, R404A, R407C and R410A in a pipe containing minichannels with internal diameters of d(i) = 0.5,0.64,0.7,1.2,1.6,2.0, and 2.5 mm; and mini-condensers constructed in the form of two bundles of tubular stainless steel minichannels with an internal diameter d = 0.64 mm and length L = 100 mm. Exchanger M4 contained four minichannels and M8 contained 8 minichannels. In each case the average values of the heat transfer coefficient and frictional pressure drop throughout the condensation process (x = 1-0) were designated. The impact of the vapour quality of the refrigerant and the mass flux density on the intensity of heat transfer and flow resistance were illustrated. A correlation was proposed to determine the local value of the heat transfer coefficient over a wide range of changes in the heat-flow parameters of the refrigerant. A comparative analysis of test results for various refrigerants in both minichannels and mini-heat exchangers was made. Experimental studies have shown that the value of the heat transfer coefficient alpha(x) depends on the value of the heat flux density q on the cooled surface. This relationship is particularly noticeable in the case of large changes in the value of the heat flux density (q = 500-35,000 W . m(-2)). It was also confirmed that the per-channel intensity of heat exchange in multiports is lower than in the case of a single minichannel with the same internal diameter. (C) 2020 Elsevier Ltd. All rights reserved.