| Boiling is one of the most efficient heat transfer methods.It is possible to achieve efficient energy transfer in a relatively small temperature range with a small weight/power ratio due to its ultra-high heat transfer rate.Basic research on boiling heat transfer will reveal the mechanism of boiling behavior.It will directly beneficial to the development of high-power equipment and high-tech electronic systems by providing new dimensions of modeling and simulation for engineering design and development.With the rapid development of micro-nano manufacturing technology,it is possible to design structured surfaces in the micro-nano scale space to further enhance boiling heat transfer,and it is difficult to control a large number of characteristic parameters of nanostructured surfaces by experimental research.At present,most molecular simulation researches are studying bubble nucleation and rapid boiling based on the change of single wettability and surface structure.There is a lack of a unified understanding of the mechanism about the bubble growth,detachment and the heat transfer performance on the micro/nanostructure surface of mixed wettability.The temperature increases linearly under the boundary condition of constant energy addition heating,which does not meet the temperature response in the actual working environment due to lack of heat sink.Hence,the paper proposed that the temperature response of a semi-infinite object surface heated by constant high heat flux can reasonably describe the temperature rise of a surface under high heat flux transient heating conditions in molecular dynamics simulation studies.Then the effects of hydrophilic and hydrophobic patterned surface on the nucleation behavior and boiling heat transfer under high heat flux transient heating conditions based on the flat plate and nanostructured substrate were studied by molecular dynamics simulation methods.The results show that,the temperature response boundary condition of the metal surface under high heat flux transient heating conditions is more in line with the temperature response in the actual working environment,and it can be well applied to this kind of molecular dynamics simulation research.For the flat-based mixed wettability surface,the surface with the hydrophilic area accounts for 60%to 70%of the total wall surface has the maximum heat flux,and the bubble nucleation time is close to the nucleation time on the all hydrophilic surface,which is conducive to bubble nucleation and enhance boiling heat transfer.For hydrophilic/hydrophobic patterned nano groove,heterogeneous nucleation occurs on the all hydrophobic surface and homogeneous nucleation occurs on the all hydrophilic surface.The bubble formed from the hydrophobic region of the patterned nano groove,rather than at the corner of all hydrophobic groove.As the wettability of hydrophobic regions increases,the type of bubble nucleation changes from heterogeneous nucleation to homogeneous nucleation.The boiling heat transfer performance is affected by micro-convection and the evaporation of the microlayers beneath the bubble.The heat flux above the patterned nano grooves decreases with the increase of the wettability of the hydrophobic part of the nano-grooves,and super-hydrophilic substrate with the modification of the super-hydrophobic structure has the highest heat transfer performance. |
