Experimental Investigation Of Convection Condensation Heat Transfer In Heat Pipe Heat Exchanger For Flue Gas Heat Recovery Use

The heat efficiency of condensing boiler is improved intensively by reduced the exit flue gas temperature in for recovering the latent heat. In order to investigate the convection condensation heat transfer characteristics of flue gas and the heat transfer enhancement of self-assembled monolayer at heat pipe surface, the experiments have been conducted with a steam-air mixture used to simulate the flue gas. The main influential factors of the condensate mass, total heat transfer capacity and convection condensation heat transfer coefficient are found as follows: the vapor volume fraction, the mixture inlet temperature and Re number, and the condensation behavior on the heat transfer surface.The experimental system is designed, processed, assembled and debugged firstly, and then the experiments are taken under the adiabatic situation. The experiments are taken under the atmospheric pressure with Re number range of mixture of 1010-2525, the temperature range of 70-120℃, and the vapor volume fraction of 0-20%. The experimental results show that the condensate mass and convection-condensation heat transfer coefficient increase with the increase of the vapor volume fraction and the mixture Re number, and the decrease of the mixture inlet temperature; the total heat transfer quantity increase with the increase of the vapor volume fraction and the mixture Re number and inlet temperature. The maximum Nu number is 158 in results, and the corresponding convection condensation heat transfer coefficient is 515W/m~2·K.The surface of heat pipe which is modified with self-assembled monolayer from octadecanethiol can promotes dropwise condensation which has a great improvement in convection condensation heat transfer in experimental results and mechanism analysis. The enhancement ratio increase with the increase of the vapor volume fraction, and the decrease of the mixture Re number and inlet temperature. The maximum ratio of 1.58 is obtained.According to the experimental results and the analysis of the heat transfer process when the steam in mixture condenses into water on the surface of heat pipe, a new dimensionless number Fr has been proposed. And two correlation equations of convention condensation heat transfer coefficient, in the situation of hot air with high moisture flows across the tube bundles with filmwise condensation and dropwise condensation, have been obtained as well.