Research On The Characteristics Of Film Evaporation And Drying Outside Horizontal Tubes

Falling film evaporation is an efficient way of heat transfer,which is widely used in refrigeration and air conditioning industry.Falling film evaporation is a complicated phase transition process.Due to its complicated heat transfer mechanism,there is still no theory to explain the process completely.Therefore,relevant research has very important theoretical and practical significance.In this paper,the geometrical volumetric method（VOF）phase interface capture method and the Open Foam multiphase flow solver of Tanasawa phase transformation model were used to simulate the falling film evaporation process outside a horizontal tube.The effects of wall heat flux,tube diameter and inlet liquid film flow on local heat transfer coefficients along the tube circumference were analyzed.At the same time,considering the influence of solid heat conduction,the fluid-structure coupling simulation of solid tube wall and liquid film heat transfer was carried out.Finally,the evaporative and evaporative characteristics of falling film outside the horizontal tube are analyzed numerically.The influence of different liquid film flow rate,heat flux density and pipe diameter on local heat transfer coefficient of pipe wall was simulated numerically.The results show that the local heat transfer coefficient of the upper part of the tube increases uniformly with the increase of liquid film flow.Below the critical heat flux,the local heat transfer coefficient increases uniformly with the increase of wall heat flux.The critical heat flux and critical liquid film flux at a certain liquid film flux were studied numerically,and the drying map was drawn according to the critical heat flux and critical liquid film flux data.Three-dimensional simulation can reflect some heat transfer characteristics along the axial direction and capture the evaporation phenomenon more clearly.Not only was the temperature in the dry spot too high,but also the temperature in the area near the dry spot covered by liquid film also increased sharply.The study found that water in the working medium,diameter of 25.4 mm of falling film evaporation in the simulation,when the liquid film flow rate was 0.073,0.103,0.168,0.226,and 0.284 kg·m^-1·s^-1,critical heat flux density were 78.8,78.8,94.6,126 and 160 k W·m^-2.And when the diameter is 50.8 mm,the critical heat flux density of the liquid film flow 70,78.8,78.8,respectively,100 and 126 k W·m^-2.