Simulation Of Steam Condensation And Flow In Horizontal Tube

Desalination technology,acting as an open source technology to increase the fresh water resources,is developing rapidly and steadily.Low temperature multi-effect desalination technology is one of the important desalination technologies.The steam condensation in horizontal tube is an important heat transfer process inside the low temperature multiple effect desalination device.Having clear understanding of the condensation and heat transfer in tube do use to develop the low temperature multi-effect evaporation desalination technology and promote the progress of horizontal tube falling film evaporation technology.Numerical simulation is one of the means of studying the condensation process and covering the shortage of experimental research.This article set up a simulation model to obtain two phase flow characteristic and heat transfer characteristic for 100 mm tube.The VOF method was used to track the vapour-liquid interface,Lee model and CSF model were applied to calculate the condensation source term and the surface tension.The predictive accuracy of numerical model was assessed by comparing the Nusselt number with Shah et al’s empirical correlations and a reasonably good agreement was obtained.The influence of temperature difference and inlet mass flow rate on the heat flux and the average heat transfer coefficient of the pipe were analyzed.The two phases distribution of the tube were observed,and there was no complete liquid membrane around the wall.The steam can contact with the wall surface to release heat.The thickness of the wall temperature boundary layer is 20 to 30 microns.The steam axial velocity and radial velocity in the temperature boundary layer under different temperature differences were analyzed combining with the field synergy theory,and then analyzed the heat transfer temperature difference’ influence on the convective heat transfer between steam and the tube wall.The simulated tube length was then increased to 600 mm,and the two phase distribution and flow pattern change in the tube were observed.The simplified conditions of the calculation model,the solution of the control equation,the source term calculation and the solution method are all the same as the numerical simulation of the steam condensation in the 100 mm pipe.Compared with Shah and Wang yaoxuan’ empirical equations,the average absolute error is less than 8.7%,indicating that the model can simulate the heat transfer and flow process in the tube well.Annular flow and stratified flow patterns were observed in the tube,and the annular flow pattern quickly converted to stratified flow along the flow direction.The smaller the heat transfer temperature difference,the larger the steam Reynolds number was when the flow type was converted into a stratified flow.The liquid level angle increases with the increase of the heat transfer temperature,and decreases with the increase of the steam mass flow rate at the same position of the tube.The axial velocity of the liquid film decreases slightly along the direction of the tube,and the tangential velocity increases gradually with the increase of the circumference.The influence of liquid film thickness on the Nusselt number was analyzed.The friction pressure drop and the ratio of acceleration pressure drop to the total pressure drop in the pipe was analyzed with the change of temperature difference and inlet mass flow rate.