Experimental study on saturated flow boiling heat transfer of R1234yf in a horizontal 2.01 mm tube under hypergravity

Abstract Experiments on R1234yf flow boiling in a horizontal 2.01 mm copper tube under hypergravity are conducted to investigate the effect of gravity on two-phase flow boiling heat transfer coefficient (HTC). The experimental range of parameters is gravity levels of 1–3.16 g, mass fluxes of 365 and 570 kg m−2 s−1, saturation pressures of 0.62 and 0.70 MPa, heat fluxes of 47.6 and 97.5 kW m−2, and vapor qualities up to 0.985. Based on the experimental data, the effects of gravity, quality, heat flux, mass flux, and saturation pressure on the HTCs were analyzed. The results show that the HTCs increase with increasing gravity levels for the qualities up to around 0.7, and the gravity effects become indistinct and inconsistent when the quality is high (x > 0.8). The trends of the HTC variation with quality and the effects of the heat flux, mass flux and saturation pressure on the HTCs are similar under different gravity levels. When x 0.7 or higher, and they occur earlier when the gravity level is higher. The comparison of the experimental data with existing saturated flow boiling HTCs for normal gravity show that the Fang (2013b) correlation for R134a performs best with a mean absolute deviation (MAD), and that all of the top four correlations in prediction accuracy under-predict the experimental HTCs, which is consistent with the experimental results that hypergravity enhances flow boiling heat transfer.