饱和温度及热流密度对水平管外降膜蒸发传热影响的实验研究

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

实验研究了不同热流密度、不同液膜流量下,饱和温度对R134a在水平光管外降膜蒸发传热系数的影响。结果表明:当液膜流量较小时,降膜蒸发传热系数随着液膜流量的增大迅速增大,当液膜流量较大时,降膜蒸发传热系数随着液膜流量的增大维持在一个稳定值;随着热流密度的增大,降膜蒸发传热系数表现出先增大后减小的趋势,并且随着饱和温度的升高,这一趋势增强;当热流密度较小时,饱和温度的升高有利于降膜蒸发传热,当热流密度较大时,较高的饱和温度不利于维持液膜的完整性,从而不利于降膜蒸发传热。

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.