Experimental investigation on flow boiling heat transfer and pressure drop of refrigerants R32 and R290 in a stainless steel horizontal tube

The purpose of this paper is to present new flow boiling heat transfer and pressure drop data in a single, horizontal smooth stainless steel tube of 6.0 mm internal diameter, in which R32 and R290 (propane) are employed as working fluids. The cross sectional average heat transfer coefficients are obtained by measuring the temperatures at the top, bottom, left and right sides of the channel. The experimental trends are analyzed for different operating conditions in terms of mass velocity (from 150 to 300 kg/(m2 s)) and heat flux (from 10 to 40 kW/m2). The saturation temperature is fixed to 25 °C for the heat transfer data and to 25 and 35 °C for the pressure drop experiments. The effects of the operative parameters and of the working fluids on local heat transfer coefficients and frictional pressure drop are discussed and the experimental data are finally compared with some of the available correlations taken from scientific literature