Experimental Study On The Influence Of Nanostructure And Wettability On The Heat Transfer Characteristics Of Pool Boiling Regions

Boiling is one of the efficient methods of phase change heat transfer,has been wildly studied and applied to the conversion and management of thermal energy,such as high-power electronics,heat exchangers,and thermal management of nuclear systems.The rapid development of surface modification and preparation technology has promoted the realization of micro/nano-structured surface boiling enhanced heat transfer.Preparing the micro-nano structured surfaces which can enhance boiling heat transfer is the current research focus.At present,the preparation of nanostructured surfaces mainly includes the chemical deposition method and the etching method.However,surface degradation occurs during the heating process.In addition,complicated preparation methods,such as photolithography,laser etching,plasma,and ultraviolet irradiation,are very expensive.In the present research,they usually focus on the single influence of the wettability or roughness on the surface pool boiling heat transfer characteristics.In fact,the enhancement of the surface heat transfer characteristics is the result of a combination of multiple factors.Therefore,in order to study the influence of its wettability and roughness on boiling heat transfer,it is necessary to prepare a simple and non-degradable surface.There are significant differences in the heat transfer characteristics of different regions of the boiling curve.The surface has different effects in different regions.The current research mostly focuses on nucleate boiling regions or film boiling regions.There is a lack of research about all regions of the boiling curve.Based on the problems,the paper established a steady-state heating experiment facility and a transient boiling experiment facility to study the heat transfer characteristics of different surfaces during nuclear boiling,transition boiling,and film boiling.In this paper,several simple processing methods are used to prepare eight hydrophilic surfaces with different roughness,and a low surface energy treatment process is used to prepare five hydrophobic surfaces under the same substrate.The results show that the greater the roughness of the hydrophilic surface,the better the enhanced heat transfer effect in all characteristic boiling stages.The critical heat flux decrease after the hydrophobic treatment of the hydrophilic surface.However,the CHF increases with the increase of roughness of hydrophilic surfaces.In the steady-state heating experimental research,it was found that the superimposed preparation method can improve the CHF and accelerate the appearance of ONB due to the optimization of the surface structure.The relationship between the bubble detachment diameter and bubble detachment frequency are established by Buckingham's ? theory.The influence of roughness on wettability and the coupled effect of rough and wettability on bubble departure were considered through modified capillary numbers.The results show that the experimental data of the hydrophobic surface are independent of the contact angle.The correlation coefficient can be further improved when Bo=1.857Ja-0.9 and N=0.407Ja0.257.In the transient boiling experimental research,it was found that the transition boiling stage can be divided into two sub-regimes:transition film boiling and transition nuclear boiling.The transition film boiling sub-regime on the hydrophilic surface is longer than that of the hydrophobic surface,which can improve heat exchange performance.