Investigation On Visualization And Heat Transfer Performance Of Micro-channel Flat Loop Heat Pipe

With the rapid development of science and technology,the degree of miniaturization and high integration of electronic components is getting higher and higher,which leads to the huge heat generation of electronic components in a narrow space,which seriously affects the work efficiency and operation stability of electronic components.As an efficient passive heat transfer device,microchannel flat loop heat pipe is widely used in the cooling of electronic equipment.In order to improve the heat transfer performance of micro-channel flat loop heat pipe,it is necessary to start from the heat transfer mechanism of micro-channel flat loop heat pipe,and study the flow boiling characteristics,bubble growth and change behavior and heat transfer performance of working fluid in microchannel flat loop heat pipe.In this thesis,a micro-channel flat loop heat pipe system with visual function is designed and built.The experimental system breaks the material limitation of the traditional heat pipe,using quartz glass with high light transmittance as the upper surface of the evaporator,and processing copper plate with micro-channels as the bottom of the evaporator,which not only realizes the purpose of visualization,but also retains the unique properties of the metal material of the evaporator itself.In the process of experimental study,by changing the working fluid mass flow rate,the input heat flux and micro-channel flat loop heat pipe evaporator,with the aid of high-speed cameras,captures the working fluid on the evaporator side in the process of the flow boiling inside of bubble growth,development,behavior and flow pattern changes of typical images;And combined the bubble growth change behavior with the heat transfer performance and critical heat transfer characteristics of the heat pipe and explore the heat transfer performance and critical heat transfer characteristics of the micro-channel flat loop heat pipe.It provides experimental and theoretical support for the analysis of bubble growth and phase change,heat transfer performance and critical heat transfer characteristics in evaporator of the micro-channel flat loop heat pipe.The research shows that the growth and change process of bubbles in the evaporator of the micro-channel flat loop heat pipe can be divided into six stages:namely single-phase flow stage,bubble isolated growth stage,bubble merging stage,elongated bubble stage,annular flow and the dry stream stage.If the mass flow rate of the working fluid is too large or too small,it is not conducive to the growth and change of the bubble.The greater the heat flow density,the more beneficial to the growth of the bubble.The tilt angle is not a direct factor in the growth and change of the bubble.In the two states of single-phase flow and two-phase flow,the larger the mass flow rate and heat flow density of the working fluid,the larger the surface heat transfer coefficient in the evaporator,and the inclination angle is not a direct factor that affects the rate of change of the heat transfer coefficient in the evaporator.In this experiment,the boiling characteristic curve of the water in the evaporator of the micro-channel flat loop heat pipe is different from the boiling characteristic curve of the water in the large space.In this experiment,after the working fluid in the evaporator reaches the local dry state,it will not immediately reach the critical heat flux density,can withstand greater heat flux density.When the mass flow rate is relatively small,in the range of 70-161.7kg/m2 s,the critical heat flow density q will increase exponentially with the mass flow rate.When the mass flow rate is relatively large,at in the range of 161.7-345.8kg/m2 s,the critical heat flow density q increases linearly with the mass flow rate.