Numerical Analysis On Condensing Process Of The Air-Steam Mixture Bubble Based On OpenFOAM

Direct contact condensation achieves high heat transfer efficiency,so it is widely used in a large number of industrial processes.Examples include waste heat recovery from natural gas boiler flue gas and boiling water reactor pressure suppression basins in nuclear power plants.In the field of waste heat recovery from the natural gas flue gas,the condensation behavior of the steam bubbles directly affects the efficiency of the recovery of waste heat from the flue gas in condensing water heaters,condensing boilers,etc.Therefore,direct contact condensation has been considered as a central issue in the development and design of these flue gas heat exchangers.The existence of both heat and mass transfer near the surface of steam bubbles containing non-condensable gases,their motion behavior and heat transfer characteristics are very complex,and the study of their condensation behavior proves to be a difficult challenge.To gain a deeper understanding of the condensation process of vapor bubbles,it is necessary to investigate the condensation process of vapor bubbles containing non-condensable gases in depth.As it is difficult to observe the flow field inside the bubble through experimental observations,it is very promising to analyze the bubble condensation process with the help of numerical simulations.This thesis builds a computational platform for simulating direct contact bubble condensation based on the multiphase flow solver ico Reacting Multiphase Inter Foam available in OpenFOAM.The resulting multiphase flow solver is used to calculate multiphase flow processes accompanied by phase changes,component diffusion processes,and automatic grid encryption.The multiphase flow model used in this solver is the volume of fluid method,the surface tension model is the continuum surface force model,the phase change model is the Lee model,and the turbulence model is the standard k-ε model with good robustness.In addition,the velocity-pressure equation and the transport equation for the phase volume fraction are solved by the pimple algorithm as well as the MULES method,respectively.The experimental process of bubble condensation in subcooled water is numerically simulated under different working conditions with reference to the experimental process of bubble condensation in related literature.The computational results obtained are in good agreement with the experimental results,and the reflected condensation law is basically consistent with the experimental conclusions,which verifies the reliability of applying the numerical model established in this thesis to study the bubble condensation process.The multiphase flow solver constructed in this paper is used to numerically simulate the condensation process of steam bubbles in supercooled water under 63 groups of different working conditions.Influence of subcooled liquid flow rate on bubble condensation process and condensation behavior of vapor bubble pairs containing non-condensable gas.The simulation results suggest that the velocity and pressure distributions of pure and noncondensable vapor bubbles are similar during the condensation process,however,the volume decay rate and the temperature gradient near the phase interface of steam bubbles containing non-condensable gases during condensation are smaller than those of pure steam bubbles,but they show a more complex shape change pattern than pure steam bubbles.Regarding the motion characteristics of the non-condensable gas-containing vapor bubbles during condensation,the subcooling degree,the initial diameter of the bubble,and the initial noncondensable gas content within the bubble have a greater influence on the deformation law of the bubble,while the subcooled liquid flow rate has a greater influence on the migration trajectory of the bubble.Also,the terminal migration velocity of bubbles increases with the increase of subcooling degree and the initial vapor mass content inside the bubble.With respect to the condensation characteristics during the condensation of bubbles containing noncondensable vapor,the condensation time of the bubbles increases nonlinearly with the initial diameter of the bubble and the subcooling degree.The terminal equivalent diameter of the bubble is linearly related to the initial diameter of the bubble and the initial non-condensable gas content inside the bubble,but decreases nonlinearly with increasing subcooling.In addition,the amount of residual steam inside the bubble as a percentage of the total initial steam at bubble volume stabilization decreases nearly linearly with increasing subcooling and initial bubble diameter,and non-linearly with increasing initial non-condensable gas content.With respect to the condensation process of multiple bubbles containing non-condensable gas vapor,when two bubbles are condensed side by side,the two bubbles will separate to the outside and the vapor in the bubbles will gather toward the outside of the outer bubble pair,and when two bubbles are arranged vertically,the two bubbles will rise vertically in the subcooled water and the vapor in the bubbles will gather toward the middle of the bubbles.