Experimental Research Of Dopwise Condensation Heat Transfer Outside The Horizontal Tube Coated PTFE Film

The experimental studies on dropwise condensation outside the horizontal circularly-groove tubes and circular tubes with different coat thickness of PTFE are carried out. Based on the model of dropwise and film condensation coexisting, some experimental data are theoretically calculated. Besides, the effect of condensation surface roughness on the condensation heat transfer is also analyzed.In the experiments, the dropwise condensation are formed well on the surface of the test tubes with PTFE coat well, and under the condition of vapor pressure a little higher than atmosphere pressure, the condensation heat transfer coefficient outside the circular tube coated with 25μm PTFE film is as 6.60～7.99 times as to that of simple circular tube; the condensation heat transfer coefficient outside the circularly-groove tube coated with 25μm PTFE film is as 3.61～4.72 times as to that of simple circularly-groove tube. The heat transfer capability of the circularly-groove tube coated with 8μm PTFE film is the best among all the other tubes, its total heat transfer coefficient is 5.4%-20.6% higher than that of simple circularly-groove tube, and 35.1%-75.4% higher than that of simple circular tube. Moreover, the heat transfer capability of the circularly-groove tube coated with 8μm PTFE film keep stability during the 100 hours endurable experiments.According to the model of dropwise and film condensation coexisting, the condensation heat transfer coefficient outside the circularly tube coated with 25μm PTFE film and the circularly-groove tube coated with 25μm PTFE film are calculated under the condition of P2 condensation pressure (74.67 kPa) and 1.29m/s cooling water rate inside the tube.Through the correlation of liquid film is modified, the results show that the error between calculations and experimental data is no more than 20%. Besides, the mechanism of dropwise condensation is slightly discussed. It is found that the roughness of condensation surface would cause the condensation heat transfer coefficient decreased.