Study On Steam Condensation Heat Transfer Mechanism Based On Field Synergy Theory

With the rapid development of the economy,the acceleration of industrialization and urbanization,the demand for condensing heat transfer is also increasing.As one of the most common physical processes,steam condensation exists widely in nature and industry.Correct understanding and rational application of condensation,an important phase change process,is of great importance to all fields of human production and life.In this paper,the ANSYS FLUENT software is adopted and the numerical simulation of the condensation and heat transfer process of pure steam and non-condensing gas(air)is conducted based on the VOF method.The main research contents and conclusions are as follows:(1)Based on VOF model,the numerical simulation model of pure steam condensation heat transfer process was established by adding phase change model,turbulence model,surface tension model and wall adhesion model.For the condensation process of non-condensable gases,the added component transport model was used to solve the problem numerically on the basis.(2)The influence factors of film condensation process of pure steam in different flow regimes on a vertical plate were simulated and analyzed.The results show that no matter it is laminar flow or turbulent film condensation process,the increase of steam velocity,wall temperature and wall contact angle will decrease the amount of steam condensation water;the increase of wall temperature will decrease the mass transfer rate of steam;and the increase of steam velocity,wall temperature and wall contact angle will increase the heat transfer coefficient of steam condensation process.However,it is obvious that the effect of steam condensation heat transfer in turbulent state is better than that in laminar state.Further,In view of laminar and turbulent vapor film condensation process,the effects of vapor mainstream velocity and wall temperature on the temperature field and vapor concentration field of vertical plate were simulated,and the mechanism of field synergy in vapor condensation process was obtained.With the increase of steam flow rate and the decrease of wall temperature,the temperature gradient in the condensation process will gradually increase.The concentration gradient decreases with the increase of steam velocity and wall temperature.However,the final heat transfer effect of steam condensation depends on the synergistic effect between temperature field and concentration field.(3)Through the numerical simulation of Ren's condensation experiment of mixed steam in a horizontal tube,the influence of the concentration of non-condensable gas(air)and the flow rate of mixed steam on the condensation heat transfer effect was studied.Increasing the concentration of non-condensable gas(air)will lead to a sharp decrease in heat transfer coefficient.With the increase of flow rate,the concentration gradient of steam decreases and the temperature gradient increases,with the synergistic effect of the two fields increased,the condensation heat transfer effect of mixed steam is enhanced.