Numerical Simulation Study Of Flow Characteristics Between Transverse Tube Drops Under Disturbance

The horizontal tube falling film evaporator has the characteristics of low heat transfer temperature difference,high heat transfer coefficient and low operating temperature.It more applications in the fields of seawater desalination,refrigeration and energy power.When gas flows across the horizontal tube bundle of falling film,the analysis and study of the twophase flow and liquid film spreading morphology and process have important reference value for the optimization of evaporator performance.At present,there is little literature on the influence of contact angle on the flow performance of horizontal tube and the two-phase dynamic characteristics of gas flowing through horizontal tube.In this paper,the wetting characteristics of horizontal tube falling film evaporator and the two-phase flow process under the action of liquid film spreading and spoiler are studied theoretically and numerically.Firstly,the flow process of falling film with different wettability on horizontal tube surface is studied and analyzed.With the decrease of surface wetting property,the axial spreading length of the liquid film at the top of the tube is gradually shortened.With the increase of the contact angle,the position of the "separation point" gradually moved to the top of the tube.When the contact angle increased to 50°,the "channel flow" was formed,the width of the liquid film decreased continuously,and finally the liquid film rupture tended to be stable.With the enhancement of surface wetting properties,the axial spreading length of the liquid film at the top of the tube decreases gradually.When the contact angle is more than 30°,the liquid film begins to rupture and the surface of the horizontal tube begins to show hydrophobicity.Secondly,the influence of contact angle on liquid film distribution under different variable conditions is analyzed.The maximum film thickness is proportional to the contact angle,while the maximum film width is inversely proportional to the contact angle.The thickness of liquid film has little change with the spray height,and the liquid film width increases obviously with the increase of the spray height.The increase of flow rate leads to the increase of film width,but the variation trend is similar,but the influence on film thickness is small.The maximum film width increases with the increase of pipe diameter,and the increase of pipe diameter will lead to the fracture of the film.Finally,the influence of the transverse gas turbulence on the migration characteristics of the fluid between tubes is analyzed.The theoretical quantification formula of fluid migration distance between tubes is established.The displacement of the liquid column increases with the increase of the transverse airflow speed,and the liquid column decreases near the spray hole in a nearly vertical state,while the displacement range of the lower liquid column is larger.The smaller the water flow,the greater the spray height,the greater the liquid column offset.At low transverse wind speed,the influence of tube diameter and working fluid on the migration distance of liquid column is relatively small.At high transverse wind speed,the migration distance of the liquid column with small tube diameter is larger,and the migration degree of the liquid column is obviously greater than that of water when the working medium is ethanol.The ultimate wind speed of transverse airflow increases with the increase of water flow.