Influence Of Microstructure And Wettability On Bubble Dynamics

With the continuous development of science and technology,microelectronic components are widely used in medicine,power,chemical industry,nuclear energy,environment,petroleum,metallurgy and other fields.The high integration of microelelctic untis makes the heat flux keep increasing continuously,and heat dissipation becomes one of the main obstacles to their large-scale applications.Traditional fan cooling and liquid convective cooling technologies can not meet the thermal mangament requirement of the high heat flux microelectric components.In order to enhance the heat dissipation capability of microelectric components,more and more researchers have focused on the cooling technology by using phase change heat transfer.High performance cooling technology based on phase change cooling has wide application prospects in the field of high heat flux electronic components.Phase change cooling technology has the advantages of high heat transfer efficiency,but at the same time there are still some problems such as high boiling incipience temperature and flow instability.The heat transfer efficiency needs to be further improved to meet the increasing heat flux and heat dissipation requirements.At present,heat transfer enhancement by using Micro-Nanostructure and surface wettability modification has become one of the main research hotspots and frontier areas in the field of engineering thermophysics.The effects of surface microstructures and wettability on boiling heat transfer are mainly attributed to changing the surface energy,the size and distribution of nucleation cavity and the capillary pumping capacity of the heated surface.The study of bubble dynamics and two-phase heat transfer mechanism under different matching conditions between microstructure and wettability has important theoretical and engineering value for the development of new and efficient heat transfer surfaces.In order to further reveal the combined effect of micro-structure and wettability,the bubble dynamics on two-dimensional planar structures with uniform and non-uniform wettability were numerically studied based on VOF model of FLUENT software.As for the planar microstructures and the cavity microstructures,the bubble interface expansion characteristics and the variation of the three-phase contact line during the period from bubble formation to its detachment were studied,and the effects of microstructures and wettability on the detachment time and radius of the detaching bubble were obtained.Based on the concept of fluid splitting,this paper presents a new heat transfer enhancement technology for two-phase flow in microchannels.The periodic splitting of liquid and bubbles along the microchannel was realized by innovative splitting micro-structure design.The periodic splitting of liquid makes the thermal boundary layer redeveloping at each splitting zone,thus reducing the average heat transfer resistance.When one big bubble is divided into two small bubbles,the surface area increases remarkably,and the vapor-liquid heat transfer area and the micro-convection effect around the bubbles increase,thus enhancing the multiphase heat transfer in microchannels.Based on the VOF model,the heat transfer characteristics of two-phase flow in the microchannels with and without splitting structures were studied numerically under constant wall temperature boundary condition.The flow velocity and temperature fields in parallel microchannels and split microchannels were obtained,and the effect of bubble splitting structure on the flow and temperature fields was revealed.The mechanism of heat transfer enhancement of two-phase flow in microchannels by fluid splitting is disclosed.The work of this paper is mainly based on numerical simulation.Due to the complexity of the phase change model,the effects of different combination of micro?structure and wettability on bubble dynamics was only conducted at room temperatureand multiphase heat transfer were investigated without considering phase change.Eventhough,the results of this paper can be used as a guidance for the further study of vapor bubble dynamics and boiling heat transfer performance.The splitting microstructure proposed in this paper provides a new idea for the innovative design of microchannel heat exchangers.