Influence of Ni-P Coating Microstructure on Condensation Heat Transfer

The higher heat transfer performance due to dropwise condensation as compared with filmwise condensation has been of considerable interest to many researchers around the world. In this study, the effect of microstructure of Ni-P coating on condensation heat transfer performance was reported. The Ni-P deposits with various microstructures, such as nano-crystalline, amorphous and co-existence of both, could be obtained on the low carbon steel tube by adjusting the electroless plating processing parameters. The experimental results show that the steel tube with electroless Ni-P coating can greatly improve the performance of condensation heat transfer compared to un-coated steel tubes. The condensation state on tubes with Ni-P coating depends on the cooling water flow rate and steam temperature, it shows the co-existence state of both dropwise and filmwise on most working conditions. At the same time, the heat transfer efficiency of condensation is improved with the decreasing of the amounts of nanocrystalline phase in Ni-P deposit, because it can increase the free surface energy of surface. Therefore, increasing the degree of amorphous state of Ni-P coating will provide a better dropwise condensation effect.