On Heat Transfer And Evaporation Characteristics Of Microlayer During Nucleate Pool Boiling

Boiling can achieve effective heat transfer between low temperature difference,it was widely applied in cooling system ranging from electronics components to nuclear and fusion reactor.However,due to complexity of the nucleate boiling phenomenon,the mechanism of nucleate boiling is still not well clarified until now.Understanding the mechanics of boiling is of great significance for its application.Since the 1960 s,microlayer where the thin liquid film forms between the boiling bubble and heated surface base has been experimently observed by many researchers,but the structure of the microlayer and evaporation characteristics of the microlayer is not sufficient.Although there are some research results about the microlayer thickness on the transparent heat transfer plate under low heat flux,the studies on the structure and evaporation characteristics of microlayer under the high heat flux are rarely reported,especially for the non-transparent mental heat transfer plate,the existing optics method can not provide the visual results of the microlayer.Based on VOF method,the evaporation characteristics of the microlayer for different heat transfer plates and the microlayer structure was examined in this study,the main work is as following:First,based on the experimental microlayer structure,the numerical simulation on the boiling process under four heat transfer plate was performed in order to quantificationally analyze the influence of thermal conductivity of heat transfer plates to the evaporation and heat transfer characteristics of microlayer.The results indicated that the superheat of the heat transfer surface decreases rapidly with evaporation of the microlayer and then recovers after dryout occurs.And the temperature drop at the heat transfer surface induced by microlayer evaporation was smaller for metal surfaces with relatively higher thermal conductivity compared with quartz glass heat transfer plate.The higher the thermal conductivity of the heat transfer surface,the greater the rate of microlayer evaporation.Finally,microlayer evaporation occupied approximately 40 to 70 percent of the bubble volume.Next,the simulation can not perform under non-experimental condition due to the apparent contact angle was relied on experimental data.Base on the force analysis,the contact angle model was improved.Then based on the new model,boiling numerical study under high heat flux was performed in order to examine the contribution of microlayer evaporation to the bubble growth.The dryout region occurred quickly under high heat flux than low heat flux,the existing period of the microlayer lasted shorter under high heat flux than low heat flux.