Study On Condensation Heat Transfer Characteristics Of Horizontal Single Tube With Non-condensable Gas

Condensation heat transfer with non-condensable gas is very common in industrial equipment.The presence of non-condensable gas will restrict the heat exchange efficiency.Therefore,the study of condensation heat transfer with non-condensable gas can improve energy utilization.In the condensation heat transfer process with non-condensable gas,the gas and liquid films are formed after condensation of water vapor at the low temperature wall.The gas film is attached to the surface of the liquid film.Therefore,the heat tra nsfer at the gas film side consists of two parts: one is condensation heat transfer of water vapor,and the other is heat conduction of the gas film.The two parts of the heat transfer to the wall by the heat conduction of the liquid film.In this paper,a physical model of condensation heat transfer of horizontal tube with non-condensable gas was established.The correlation between gas and liquid films thickness and interface temperature were obtained considering the thermal resistance of gas and liquid interface.The C ++ language was used to calculate the condensation heat transfer parameters on the outside of the circular tube,the oval tube and the drop tube.The regularities of distribution for the gas and liquid film thicknesses,gas and liquid film thermal resistances,interface thermal resistance,condensation quantity and heat transfer coefficient along the tube wall under the difference of mixture pressure,tube wall temperature,non-condensable gas content and tube size.The results indicate that the heat transfer coefficient increases with the increase of the wall temperature and decreases with the increase of the mixing gas pressure,and decreases with the increase of the non-condensable gas content,and decreases with the increase of the equiva lent diameter with other conditions unchanged.For the equivalent diameter of elliptical tube,the other conditions remain unchanged,the larger the curvature,the easier the liquid film separation occurs,and the greater the heat transfer coefficient.Und er the comparison of circular tube,elliptical tube and drop tube which have the same equivalent diameter and heat exchange area,The average heat transfer coefficient of drop tube is 1.05 times that of oval tube and 1.2 times of that of circular tube.The drop tube has the best heat transfer effect in the three tubes,and it is the best tube type for the heat exchanger.When there is non-condensable gas outside pipe,interface thermal resistance of gas phase thermal resistance > liquid phase thermal resistance >> gas-liquid interface thermal resistance.The results obtained by establishing the model are in good agreement with the existing results,which can reflect the actual situation better and provide some theoretical guidance for heat transfer enhancement.