This work compares the condensation heat transfer and pressure drop for zeotropic refrigerant R-454C and its individual components, R-32 and R-1234yf, in horizontal microfin tubes. One microfin tube has a 4 mm outer diameter, 0.18 mm wall thickness, and a surface area ratio of 1.56. The second tube has a 8 mm outer diameter, 0.25 mm wall thickness and a surface area ratio of 1.62. HFOs and HFC/HFO blends like R-454C have low global warming potential and can be alternatives to HFC refrigerants when retrofitting a system or producing new equipment. However, there is an additional mass transfer resistance present during phase change for a zeotropic mixture, which results in reduced heat transfer performance. Microfin tubes enhance heat transfer through multiple mechanisms: they increase the internal surface area of the tube, the fins drain condensate from the fin tip to the trough region, and they produce secondary flow structures. These enhancement mechanisms are shown to counteract the degradation in heat transfer performance for R-454C in the 4 mm microfin tube.
Presently, there is limited data of HFO/HFC mixtures in microfin tubes. Thus, experiments are conducted for complete condensation of R-454C, R-1234yf and R-32. Experimental heat transfer and pressure drop measurements are compared to well-established correlations from the literature. Heat transfer enhancement factors and pressure drop penalty factors are used to determine the optimum operating conditions for the microfin tubes.