Experimental study on the flow boiling heat transfer characteristics of R32 in horizontal tubes

Abstract R32, namely the main component of R410A, is thought to be a kind of transitional alternative refrigerant in developing countries. In this paper, a set of experimental apparatus of the flow boiling heat transfer of R32 in horizontal tubes was built up. Effects of mass flux, heat flux, boiling temperature, tube sizes, vapor quality, channel geometry of heat transfer tubes on flow boiling heat transfer coefficient of R32 were investigated. The results demonstrate that flow boiling heat transfer coefficients increase with mass flux, saturated evaporating temperature and heat flux. Besides, the flow boiling heat transfer coefficients of R32 in the micro-fin tubes with tube diameters of 5 mm and 7 mm are 1.19 and 1.23 times, respectively, as large as that in the smooth tubes. Vapor quality seems to have a complicated influence on the boiling heat transfer coefficients of R32 due to the emerging dry-out point, the vapor quality of which are experimentally tested to range from 0.41 to 0.57. The change of mass flux and heat flux have influence on the vapor quality of the dry-out point. Furthermore, the experimental data in smooth and micro-fin tubes are respectively compared with the predictive values of semi-empirical correlations. It should be necessary for researchers to explore the flow boiling heat transfer characteristics of R32 in horizontal tubes, which will be of great benefit to further optimization research and applications on heat exchangers of R32.