Numerical Study On Multiphysics Coupled Characteristics And Enhanced Heat Transfer Of Droplet Condensation In A Moist Air Environment

Dropwise condensation is currently the most efficient known heat transfer mechanism,and due to its enormous potential in industrial production,it has attracted wide attention in the industry.Previous studies have often focused on condensation occurring in ideal stationary pure vapor,considering the nonlinearity of the momentum equation and the complexity of dropwise condensation.However,in practical industrial production,non-condensable gas inevitably exists in steam,and forced gasphase flow is widely used as an efficient heat transfer enhancement method in dropwise condensation heat transfer.Recent research has shown that non-condensable gas and forced convection significantly alter the controlling factors and enhancement mechanisms of heat transfer in condensing droplets.Therefore,elucidating the heat and mass transport mechanisms of dropwise condensation under actual conditions and gaining mechanistic insights into enhanced heat transfer are of great research value.To address these issues,this study develops transient multiphysics models for different physical processes to gain a deeper understanding of the heat and mass transport mechanisms of condensing droplets in stationary or flowing moist air,aiming to provide new insights into heat transfer enhancement.The model strongly couples the flow,heat transfer,mass transfer,droplet dynamics,and complex interfacial effects between the gas-liquid phases,allowing for detailed observations of coupled condensation characteristics.The research results indicate the following:(1)For condensing droplets growing in stationary moist air in isolated mode:For small-sized droplets,thermal conduction is the dominant heat transfer mechanism.and the contribution of convective heat transfer can be neglected.The internal convection in the droplets is mainly driven by the Marangoni effect induced by temperature gradients,and the contribution of internal flow to heat transfer increases with droplet size.(2)For condensing droplets growing in forced convection moist air in isolated mode:The surface flow generated by the shear effect of the moist air on the gas-liquid interface dominates the internal convection of the droplets,greatly enhancing the heat transfer performance of dropwise condensation(1.4 to 3.3 times).When predicting the heat transfer coefficient on neutral and hydrophobic surfaces using the theoretical model,a correction factor is required to account for the enhancement of heat transfer due to internal flow.(3)For condensing droplets growing in forced convection moist air in non-isolated mode:Due to the coupling effects of external forced convection,interaction effect,and dropwise condensation,the condensation characteristics depend not only on their size and spatiotemporal distribution characteristics but also on the interaction between the droplets and the external flow.This study not only advances the understanding of the dynamic heat and mass transport mechanisms of dropwise condensation in moist air environments but also provides a reliable,flexible,and generalizable numerical model for such gas-liquid phase change problems.