Evaporation heat transfer enhancement and pressure gradient of R-513A in a horizontal smooth tube.

Experimental studies to determine the average heat transfer coefficient (hav) and frictional pressure gradient (ΔPF/L) of R-513A flowing through a horizontal smooth tube during evaporation are investigated. The experimental setup comprises a double-tube heat exchanger with supplied water circulating inside the annulus in the opposite direction. The average heat transfer coefficient ratio (hav,513A/hav,134a) and frictional pressure gradient ratio ((ΔPF/L)513A/((ΔPF/L)134a) of R-513A and R-134a were compared in this study. The experimental results show hav and ΔPF/L obtained from R-513A are about 0.96 and 0.95 times lower than R-134a, respectively. For R-513A, the hav is lower due to a decreased convective effect, whereas the lower ΔPF/L is due to decreased flow resistance. The Nusselt number (Nu) is higher than R-134a, whereas the two-phase friction factor (fTP) is slightly higher. [ABSTRACT FROM AUTHOR]