Conference Year

2014

Keywords

Condensation, Evaporation, Azeotropic mixture, R32, R1234ze(E)

Abstract

R1234ze(E) has been anticipated to become an alternative of conventional refrigerant R410A for air conditioning systems. Latest studies revealed that the COP of R1234ze(E) alone is unexpectedly lower than that of R410A, mainly caused by irreversible loss in consequent of the small volumetric capacity. To increase volumetric capacity as maintaining the global warming potential (GWP) less than 300, adding R744 and R32 into R1234ze(E) has been attempted recently. For understanding the transport phenomenon of this ternary mixture, the heat transfer coefficient and pressure gradient of in a horizontal microfin tube is experimentally investigated in this study. Experimental data of R744/R32/R1234ze(E) (4/43/53 mass%) are compared to R32/R1234ze(E) (40/60 mass%) as the combination of GWP 300; data on R744/R32/R1234ze(E) (9/29/62 mass%) are compared to R32/R1234ze(E) (30/70 mass %) as the combination of GWP 200. At average saturation temperature of 40 oC, mass flux of 200 kg m-2s-1, and heat flux of 10 kWm-2, condensation heat transfer coefficient of R744/R32/R1234ze(E) (9/29/62 mass%) is somewhat lower than that of other mixtures R744/R32/R1234ze(E) (4/43/53 mass%), R32/R1234ze(E) (40/60 mass%) and (30/70 mass%). The temperature glide of R744/R32/R1234ze(E) (9/29/62 mass%), (4/43/53 mass%), R32/R1234ze(E) (30/70 mass%), and (40/60 mass%) is approximately 18, 11, 10, and 8 K, respectively, at 40 oC. Likewise, the magnitude of decrease in heat transfer coefficient is much related to the temperature glide during condensation. Similar effects of temperature glide is seen in data of evaporation heat transfer coefficient. At average saturation temperature of 10 oC, the evaporation heat transfer coefficient of R744/R32/R1234ze(E) (9/29/62 mass%) is slightly lower than that of other mixtures. The temperature glide of R744/R32/R1234ze(E) (9/29/62 mass%), (4/43/53 mass%), R32/R1234ze(E) (30/70 mass%), and (40/60 mass%) is approximately 22, 13, 11, and 9 K, respectively. The pressure gradient of those refrigerants are almost equal, and the difference is within measurement uncertainty. The experimental pressure gradient agrees well with prediction of Kubota et al. (2001), Filho et al. (2004), Newell and Shah (2001).

2337_presentation.pdf (214 kB)
Condensation and Evaporation of R744/R32/R1234ze(E) flow in Horizontal microfin Tubes

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