Condensation and evaporation of R32/R1234ze(E) and R744/R32/R1234ze(E) flow in horizontal microfin tubes

The heat transfer characteristics of the low global warming potential refrigerant mixture R744/R32/R1234ze(E) in a horizontal microfin tube were investigated in this study. The condensation heat transfer coefficient of R744 /R32/R1234ze(E) (9/29/62 mass %) is somewhat lower than that of other mixtures, e.g., R744/R32/R1234ze(E) (4/43/53 mass %) and R32/R1234ze(E) (40/60 mass %) and (30/70 mass %), at an average saturation temperature of 40◦C, mass flux of 200 kg m⁻²s⁻¹, and heat flux of 10 kWm⁻². The temperature glides of R744/R32/R1234ze(E) (9/29/62 mass%) and (4/43/53 mass %) and R32/R1234ze(E) (30/70 mass %) and (40/60 mass %) are 18, 11, 10, and 8 K, respectively, at 40^◦C. Likewise, the magnitude of the heat transfer coefficient decrease is strongly affected by the temperature glide. The data for the evaporation heat transfer coefficient indicated similar effects of the temperature glide. At an average saturation temperature of 10^◦C, the evaporation heat transfer coefficient of R744/R32/R1234ze(E) (9/29/62 mass %) is slightly lower than that of other mixtures. The temperature glides of R744/R32/R1234ze(E) (9/29/62 mass %) and (4/43/53 mass%) and R32/R1234ze(E) (30/70 mass %) and (40/60 mass %) are 22, 13, 11, and 9 K, respectively. The pressure gradients of these refrigerants are almost equal, and the difference is within the measurement uncertainty. The experimental pressure gradient agrees well with the predictions proposed for single components.