minichannels, heat transfer coefficient, condensation
The use of micro- and mini-channels in heat exchanger has increased in recent decades. They contribute to increasing efficiency and reducing refrigerant charge and compactness of heat exchangers. The aim of this study is to experimentally determine the heat transfer coefficient in mini-channels of two-phase flow processes with the low GWP refrigerant R32 and compare it with the values provided by some of the correlations developed by other researchers. In the existing literature there are a few publications studying the refrigerant R32. R32 has medium flammability, classified as A2 by ASHRAE. European air conditioning manufactures point to use R32 instead of R410A. R32 has lower global warming potential (GWP = 675) than R410a (GWP = 2088). Environmental improvements must also be considered. R32 is a single component refrigerant so recycling is easier than R410A process; also R32 is safer than R410A according to NFPA classification, although R410A flammability is lower than R32 because of the addition of R125. An installation for the study of condensation processes has been constructed at the “Technical University of Cartagena”. The more relevant results of heat transfer coefficient will be presented in this paper. The analysed data have been measured for R32 flowing through aluminium square multiport tubes with a hydraulic diameter of 1.17 mm and compared with R410A. The influence of saturation temperature (or pressure), flow velocity, and vapour quality in heat transfer coefficient have been studied. The values considered for these variables are: saturation pressure corresponding to 30, 35, 40, 45, and 50ºC; flow velocities from 100 to 700 kg/(s•m2); vapour quality from 0.05 to 0.9.