Experimental study on effect of saturation temperature and heat flux on falling film evaporation heat transfer outside horizontal tubes

Experimentally studies the effect of saturation temperature on the falling film evaporation heat transfer coefficient of R134a outside the horizontal plain tube under various heat fluxes and liquid film flow rates. The results show that when the liquid film flow rate is low, the heat transfer coefficient increases rapidly with the increase of liquid film flow rate, and when the liquid film flow rate is high, the heat transfer coefficient maintains almost constant with the increase of liquid film flow rate. With the increase of heat flux, the heat transfer coefficient shows a trend of increasing at first and then decreasing, and this trend becomes more pronounced with the increase of saturation temperature. When the heat flux is low, the increase of saturation temperature is beneficial to the falling film evaporation heat transfer. When the heat flux is high, the higher saturation temperature does harm to the integrity of the liquid film, and deteriorates the falling film evaporation heat transfer.