Condensation heat transfer of superheated vapour of R1234ze(E) and R134a inside a brazed plate heat exchanger

Abstract

The recent restrictions on the use of refrigerants with high Global Warming Potential (GWP) have pushed the research to consider alternative solutions, such as the HydroFluoroOlefins, as possible replacements. Even though they are generally mildly flammable, their GWP is significantly lower compared to those of the HydroFluoroCarbons. This paper presents experimental measurements of R1234ze(E) and R134a heat transfer coefficients during condensation inside a brazed plate heat exchanger. Experimental tests during condensation heat transfer have been conducted considering different degrees of superheating, subcooling and outlet vapour quality. The condensation temperature varies between 34.6 °C and 42.3 °C and the refrigerant mass flux is between 9 kg m-2 s-1 and 49 kg m-2 s-1. The results showed that the heat transfer coefficients measured with R134a are between 4% and 8% higher than those of R1234ze(E). Complete condensation experiments showed that an increase in the liquid subcooling degree significantly reduces the thermal performance at low refrigerant mass velocities. In some cases, the plate area occupied by liquid refrigerant reached almost 30% of the overall heat transfer area, thus decreasing by 2.7 times the average heat transfer coefficient when passing from 3 K to 8 K subcooling degree. A comparison with the predictions of some empirical models is also presented to assess which one can better predict the experimental data.