Experimental Study On Steam Condensation And Heat Transfer In Vacuum Horizontal Tube With Mesh Core Inserted

The study of steam condensation in vacuum horizontal pipe is of great significance to the design of low-temperature multi-effect seawater desalination heat transfer equipment.An experimental platform for steam condensation resistance and heat transfer in a vacuum horizontal tube was established in order to study the flow resistance of saturated steam when condensing in aluminum brass tube with inner diameter of 27mm.The experiment was carried out when the mass flow rate changes between 3 and 7 kg/(m~2·s)with steam saturation temperature varies from 50°C to 70°C.The heat transfer temperature differences in this experiment are 3°C,5°C and 7°C,respectively.The results show that the flow resistance per unit length increases with the increase of vapor mass flow rate and vapor quality.It also increases with the increase of vapor saturation temperature.However,the influence of heat transfer temperature difference on flow resistance is very small.The decrease of saturation temperature affected by flow resistance increases with the increase of vapor quality,and the increase rate decreases gradually.At last,the experimental data was comparied with a correlation which was porposed to calculate the flow resistance of steam condensation flow in a vacuum horizontal tube.The result shows that the error of the correlation in calculating the condensation flow resistance in tubes with different diameters is±20%.The average condensation heat transfer coefficient is at the peak when the vapor quality is 0.7-0.6,and then it decreases with the decrease of vapor quality.The higher the saturation temperature is,the higher the average heat transfer coefficient is.The heat transfer zone of the stratified flow includes the film condensation zone on the top of the pipe and the convection condensation zone at the bottom of the pipe.The boundary Angle and wetting Angle are roughly the same.The local heat transfer coefficient in the film condensation zone is significantly higher than that in the convection condensation zone.By comparing the experimental data with the correlation formula of local heat transfer coefficient proposed by our research group,it is found that the calculation error range of the film condensation zone on the top of the pipe is+40%--15%,and the calculation error of the convection transfer zone on the bottom of the tube is within 40%.The existing heat transfer enhancement technology shows that the capillary action of mesh core will change the liquid level of condensate in the pipe and improve the heat transfer characteristics of condensation.In view of this phenomenon,an external diameter of 12mm,2000mm long mesh core is inserted into the experimental tube.Through measurement,it is found that due to the surface tension of the wire mesh,when the vapor quality is less than 0.5,the wetting angle after inserting the mesh core is higher than that of the smooth tube.After inserting the mesh core,the total pressure drop increases but the average heat transfer coefficient decreases.The range of enhanced heat transfer influencing factor PEC under experimental conditions is always lower than 1.The capillary effect of the stainless steel wire mesh selected in this experiment is weak and do not enhance heat transfer...