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 (T_sat = 5 – 15 °C), and eight mean vapor qualities (x_m) at increasing inlet vapor quality (x_in = 0.1 – 0.8). The results showed that convection dominated the boiling process at higher x_m (0.49 – 0.9), irrespective of the fact that nucleate boiling dominated at lower x_m (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 x_m (<0.5), whereas the HTC of R290 dominated at higher x_m (>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.