Research On Heat Transfer Characteristics Of Air-water Droplet Impacting Wall

In recent years,the heat fluxes which are generated by electronic equipments increases with the rapid miniaturization and integration of electronic components.Therefore,there are much more needs for the heat dissipation of the electronic equipments and it is an efficient method for high heat flux removal to use the phase-change heat transfer.Nowadays,microchannel heat sinks,jet impingement and spray cooling are there kinds of efficient method for high heat flux removal.However,there might be a thin refrigerant film on the surface of heat radiating plate,which might cause the failure of electronic components for humidity.To address this problem,the mechanism of the film formation on heat exchange surface was researched during droplet swarm impacted on a heated wall combined with heat transfer,and a new physical model was present,which was that airflow and droplet swarm impacted on heated wall without film formation on the heated wall.The following aspects were researched in this thesis:1.The Infinite Thermal Conductivity model was used to research a single droplet evaporation and motion characteristics in the natural conditions.The results showed that the diameter,velocity,and move distance of the single droplet varied with its initial diameter,which served as a theoretical underpinning for researching heat transfer between droplets and heated wall.The VOF model was applied to simulate dynamic variation and heat transfer characteristic after the droplet impacting on heated wall,and the flow fields and temperature fields internal droplet were studied in detail.2.A two-dimensional steady-state DPM model was used to study the droplet swarm evaporation and motion characteristics in the natural conditions and the results showed that the diameter,temperature,and velocity of the droplet swarm varied with its different initial velocity and diameter.A three-dimensional unsteady DPM model was used to study the effect of the initial velocity,diameter and flux of droplet swarm on the heat transfer efficiency and film characteristics on heated wall,and concluded that the nonhomogenous temperature distribution was the result of different velocity of film on heated wall.3.The mechanism of the film formation on heat exchange surface was studied during micro-droplet swarm impacted on a heated wall.On the basis of above mechanism,The change law of the mass flow rate of droplet swarm varying with time was derived in consideration of the emission,evaporation,impact of droplet swarm and the heat conduction of heated plate,which served as a theoretical underpinning for experiment design.The effect of the initial velocity and diameter of droplet swarm on the heat transfer efficiency on heated wall was also studied.