An experimental investigation on R245fa and R1233zd(E) flow boiling at high saturation temperatures in a horizontal small diameter channel

The current study presents an investigation on flow patterns, pressure-drop and heat transfer coefficient for the refrigerants R1233zd(E) and R245fa flowing at saturation temperatures (Tsat) between 75 degrees C and 95 degrees C inside a horizontal 2 mm diameter tube. Experimental results are reported for mass velocities of 176-570 kg/m2s and heat fluxes of 18.1-54.5 kW/m2. As expected, the pressure gradient increases as the mass velocity increases and the saturation temperature decreases. Flow image analysis indicated that the pressure gradient peak is associated with disturbance interfacial waves damping. Heat transfer coefficient data indicated strong contribution of nucleate boiling effects for most of the experimental conditions. The higher the saturation temperature and the heat flux, the higher the heat transfer coefficient, regardless of the vapor quality range. In general, the effect of mass velocity on the heat transfer coefficient was only marginal, with exception of low Tsat and heat flux con-ditions. Two of 20 pressure-drop prediction methods predicted more than 90% of the database within error bands of +/- 30%. Overestimation of heat transfer coefficient data was verified for most of the 16 evaluated prediction methods, especially at high Tsat. Only two methods predicted more than 80% of data within an error band of +/- 30%.