Evaporation heat transfer and pressure drop of refrigerant R-134a in a plate heat exchanger

The evaporation heat transfer coefficient and pressure drop for refrigerant R-134a flowing in a plate heat exchanger were investigated experimentally in this study. Two vertical counterflow channels were formed in the exchang er by three plates of commercial geometry with a corrugated sine shape of a chevron angle of 60 deg. Upflow boiling of refrigerant R-134a in one chann el receives heat from the hot down flow of water in the other channel. The effects of the mean vapor quality mass flux, heat flux, and pressure of R-1 34a on the el,evaporation heat transfer and pressure drop were explored. Th e quality change of R-134a between the inlet and outlet of the refrigerant channel ranges from 0.09 to 0.18. Even at a very low Reynolds number, the p resent flow visualization of evaporation in a plate heat exchanger with the transparent outer plate showed that the flow in the plate heat exchanger r emains turbulent It is found that the evaporation heat transfer coefficient of R-134a in the plates is much higher than that in circular pipes and sho ws a very different variation with the vapor quality from that bl circular pipes, particularly in the convective evaporation dominated regime at high vapor quality. Relatively intense evaporation on the corrugated surface was seen from the flow visualization. Moreover, the present data showed that b oth the evaporation hear transfer coefficient and pressure drop increase wi th the vapor quality. At a higher mass flux the pressure drop is higher for the entire range of the vapor quality but the evaporation heat transfer is clearly better only at the high quality. Raising the imposed wall heat flu x was found to slightly improve the heat transfer, while at a higher refrig erant pressure, both the heat transfer and pressure drop are slightly lower . Based an the present data, empirical correlations for the evaporation hea t transfer coefficient and friction factor were proposed.