Study On Influence Of Gravity And Lubricating Oil On Flow Condensation Heat Transfer In Mini-channel

With the development of space industry,the application of vapor compression heat pump/refrigeration system in space has been paid more and more attention.The condensation heat transfer in microgravity environment is an important part.Due to the demand of spacecraft for heat dissipation,mini-channel heat exchangers are mostly used,and the lubricating oil that is difficult to be recovered under micro-gravity will have a great impact on heat transfer.It is of great significance to study the influence of gravity and lubricating oil in mini-channel on condensing heat transfer for the design and development of aerospace application condenser.In this paper,R134 a refrigerant was taken as the research object,and a three-dimensional numerical model of flow condensation heat transfer in a tiny channel was established,and the effects of gravity and lubricating oil on condensation heat transfer were simulated.The main results are as follows:(1)The heat transfer and pressure drop characteristics of flow condensation in mini-channel under different gravity conditions were studied.It was found that under the influence of gravity,the condensed liquid film converges to the bottom of the channel.By changing the shape of the channel,increasing the mass flow rate and decreasing the hydraulic diameter,the specific gravity of surface tension or inertial force can be increased and the influence of gravity can be weakened.Under the condition of no gravity,the condensation heat transfer coefficient in the channel is lower than that under the condition of normal gravity,while the condensation pressure drop gradient is slightly higher.The less the gravity action is under the condition of normal gravity,the smaller the difference is under the condition of no gravity.In addition,the gravity independence criterion of flow condensation in the existing research was analyzed,and a new gravity independence criterion was fitted based on the research data.(2)The heat transfer and pressure drop characteristics of flow condensation of oil-bearing working medium in mini-channel were studied.It was found that the effect of lubricating oil on the heat transfer coefficient of flow condensation in the channel was opposite to that on the pressure drop gradient.The higher the oil concentration was,the lower the heat transfer coefficient of condensation under the same vapor quality,and the greater the pressure drop gradient was.At the same oil concentration,the influence factor of oil increases with the decrease of vapor quality,mass flow rate and the increase of channel hydraulic diameter.(3)The flow process of the annular liquid film in the narrow fin channel was studied and the mechanism of the fin’s influence on the flow condensation heat transfer was analyzed.The results showed that the fin structure has a significant effect on the heat transfer performance due to the destruction of the liquid film,and the shorter and more densely distributed fin is more conducive to the improvement of the overall condensation heat transfer performance in the channel.In addition,the fin structure also enhances the gravity independence of condensation heat transfer.