Condensation of a low-pressure refrigerant inside a multiport minichannel

In the present paper experimental heat transfer coefficients taken during condensation of the low pressure fluid R236ea inside a multiport minichannel tube are presented. The test tube consists of eleven paralel rectangular minichannels with hydraulic diameter equal to 1,4mm. The present authors have already measured condensation heat transfer coefficients of medium and high-pressure fluids R134a and R410A. The fluid used here presents a significantly lower reduced pressure in comparison with the above fluids. This means that the range of the reduced pressures in the experimental database will be significantly widened in order to develop accurate predictive correlations for the condensation HTC in presence of significant properties variation. The experimental runs are carried out at mass velocities ranging from 200 to 600 kgm-2s-1 over the entire vapor quality range. Experimental results of two-phase heat transfer coefficient are compared against some semi empirical models available in the open literature. The paper shows that most of the models fairly well predict heat transfer coefficients at low mass velocity but they all seem to under-predict experimental values at higher gas velocities. This disagreement could be explained with the presence of the liquid entrainment in the minichannels.