Experimental investigation and modelling of flow boiling heat transfer of c3f8/c2f6 blends

Abstract

We have obtained an extensive data set of heat transfer coefficient (HTC) measurements in (R-218, C3F8)/(R-116, C2F6) zeotropic refrigerant blends. A horizontal thin-wall tube with a circular cross-section and diameter of 4 mm was used as an evaporator. The data covers heat fluxes from 3.5 to 10 kW.m-2, mass fluxes from 91 to 264 kg.m-2s-1 and C2F6 fractions from 0 to 25% molar. Various flow regimes were clearly identified via the HTC measurements on both the top and bottom of the tube. Boiling liquid was observed to pool at the bottom of the tube at low mass fluxes, while an annular flow regime was achieved at higher mass fluxes. The C3F8/C2F6 saturated fluorocarbon blends are zeotropic, exhibiting the usual behaviour where the HTC of the blend is lower than those of its pure components. A comparison between the data and several models of flow boiling heat transfer is presented. The comparison includes a flow map that predicts various flow boiling regimes inside a horizontal pipe.