Research On Simulation Model Of Steam Condensation Outside A Horizontal Tube

Condenser is one of the key equipments in the thermodynamic cycle of the secondary loop in nuclear power plant.The exhaust steam from the turbine is discharged into the shell side of condenser,steam condenses at the outer surface of the cooling pipes which are arranged at the shell side of condenser and the latent heat of vaporization is released,the heat is transferred to the circulating cooling water in the tube side through conduction.The flow and heat transfer of steam in the outer surface of the cooling pipe is the key to realize the heat transfer function of the condenser.This process has an important influence on the performance of the condenser,therefore,it is necessary to study the condensation process of steam with a certain flow rate outside the horizontal tube,which is of great significance to improve the heat transfer efficiency of the condenser.The complexity of the two phase condensation problem is to solve governing equations of the boundary layer,to simplify calculation,most researchers ignore one or more factors in the governing equations,such as the inertial term,the convection term,the pressure gradient term,the volume force term and the steam film.All the above factors in the governing equations are considered in this paper,on account that the presence of non-condensable gas in the condenser will affect the condensation process,the non-condensable gas factor is also taken into account in this paper.Basing on the boundary layer theory,the simulation model of the progress that steam with non-condensable gas flows vertically downwards the horizontal tube at certain speed and condenses outside the tube is established in this paper.After solving the governing equations in numerical methods,the velocity distribution,temperature distribution and the concentration distribution of non condensing gas in the condensate film and the mixed gas boundary layer are obtained finally,on the basis of the above,the related parameters such as the thickness of condensation film,the heat transfer coefficient and the interfacial shear stress are also obtained.In this paper,the distribution of the parameters in the films obtained by numerical solution is analyzed in detail.The stratified flow characteristics is obviously shown in the tangential velocity distribution;There is no continuity in normal velocity distribution between the gas and liquid interface,and the higher the normal velocity is,the better the heat transfer effect is;The temperature distribution in the liquid film is basically linear;Even a smallamount of non-condensable gas contained in the mainstream will cause a high concentration at the gas-liquid interface;Along the circumferential direction,the heat transfer coefficient decreases and the liquid film gets thinner with the increase of the angle.In this paper,the influence factors of steam condensation outside of the tube are also studied by changing the flow parameters.The results show that the heat transfer coefficient increases with the increase of the steam flow rate;The heat transfer coefficient decreases with the increase of the vapor-wall temperature difference,the diameter of the tube and the concentration of the non-condensable gas.In this paper,the effects of different flow conditions on the distribution of the parameters in the films are also analyzed in detail.