Comparative analysis of flow boiling characteristics of an R290/R1270 mixture and R290 in a plate heat exchanger with offset strip fins

In this study, saturated flow boiling characteristics of R290/R1270 (65 %/35 % w) mixture and pure R290 were investigated experimentally in a plate heat exchanger embedded with offset strip fins. The experiment was carried out at three mass fluxes (G = 20 - 60 kg m-2 s-1), four heat fluxes (q = 7.5 - 15 kW m-2), three saturation temperatures (Tsat = 5 - 15 degrees C), and eight mean vapor qualities (xm) at increasing inlet vapor quality (xin = 0.1 - 0.8). The results showed that convection dominated the boiling process at higher xm (0.49 - 0.9), irrespective of the fact that nucleate boiling dominated at lower xm (0.15-0.49) values regardless of the working conditions. The heat-transfer coefficient (HTC) and frictional pressure drop (FPD) of R290/R1270 were strongly influenced by the range of G. R290/R1270 exhibited a higher HTC value than R290 for xm (<0.5), whereas the HTC of R290 dominated at higher xm (>0.5) values. Consequently, R290/R1270 generally performed better in the nucleate-boiling region, whereas R290 performed better in the convective-boiling region. The average HTC of the R290/R1270 mixture was 3.34 % higher than that of R290, whereas the average FPD of the R290/R1270 was 18.11 % lower than that of R290. Finally, correlations for R290/R1270 in the form of Nusselt number and the two-phase friction factor have been established, and they demonstrated high reliability with mean absolute errors of 11 % and 12 %, respectively.