Study Of Vapor-liquid Pulsating Flow And Heat Transfer Characteristics In Self-driven Thermal Spreader

The self-driven vapor-liquid pulsating phase change thermal spreader is an effective heat transfer component based on the principle of evaporation-condensation phase change heat transfer.Due to the good heat transfer performance,simple structure,good temperature uniformity,strong environment adaptability and low gravity sensitivity of the thermal spreader,it has been a good choice to meet the heat dissipation requirements of electronic components with high heat flux density and high power consumption.Therefore,it has important academic value and application prospect to carried out the research on the heat transfer performance of self-driven vapor-liquid pulsating phase change thermal spreader and reveal its internal flow and heat transfer characteristics.Until now,lots of theoretical and experimental researches has been carried out by the scholars from various countries to study the heat transfer characteristics of self-driven vapor-liquid pulsating phase change thermal spreader.However,more attention is paid to the heat transfer characteristics of the self-driven vapor-liquid pulsating phase change thermal spreader with single heat source.The research on the heat transfer performance of the self-driven vapor-liquid pulsating phase change thermal spreader under multiple heat sources is still lacking,especially the insufficient understanding of the flow and heat transfer characteristics of the thermal spreader under different working conditions(different working inclination angles and different heating modes).Therefore,a self-driven vapor-liquid pulsating phase change thermal spreader with serpentine channel has been developed in this paper,and the effects of working inclination angles and thermal loads on the flow and heat transfer characteristics of the thermal spreader under different heating modes have been studied.In summary,the main research contents and conculsions of this paper are as follows:(1)The self-driven vapor-liquid pulsating phase change thermal spreader with uniform and non-uniform single circuit serpentine channels is designed and developed respectively,and a test platform of heat transfer performance of thermal spreader with multiple heating sources has been built.The effects of the working inclination angle and thermal load on the fluid flow,temperature uniformity and heat transfer performance of the two types of serpentine channel thermal spreader under three multi-heat source heating modes are studied,and the difference of heat transfer performance between the thermal spreader with uniform and non-uniform single circuit serpentine channels is analyzed.The results indicate that,the single circuit serpentine channel thermal spreader has four operation modes at 0° working inclination angle,including static state,small pulsation,pulsation accompanied by circulation and continuous cycle operation,and the heat transfer performance of the thermal spreader is the best when the thermal spreader is in the continuous cycle operation mode.The heat transfer performance of non-uniform single circuit serpentine channel thermal spreader is better than that of uniform single circuit serpentine channel thermal spreader.The studies also find that the angle has little effect on the heat transfer performance of two types of single circuit serpentine channel thermal spreader.In the upper heating mode of double heat sources,the change range of the heat transfer performance of uniform and non-uniform single circuit serpentine channel thermal spreader in the range of 0° to 90° working inclination angle is<10%.In the lower heating mode of double heat sources,the heat transfer performance of non-uniform single circuit serpentine channel thermal spreader is better than that of uniform single circuit serpentine channel thermal spreader.In the full heating mode of four heat sources,the flow of working fluid in the uniform single circuit serpentine channel thermal spreader is difficult,resulting in lower heat transfer performance.However,the thermal resistance of the non-uniform single circuit serpentine channel thermal spreader is lower than that of the aluminum plate and is less sensitive to the working inclination angle.(2)Based on the research results of single circuit serpentine channel thermal spreader,a composite serpentine channel thermal spreader is designed and developed.The effects of thermal load and working inclination angle on the fluid flow,temperature uniformity and heat transfer performance of the composite serpentine channel thermal spreader are studied experimentally,and the effects of channel structure(uniform and non-uniform serpentine channel)on the heat transfer performance of composite thermal spreader are analyzed and compared.The results show that in the upper heating mode of double heat sources,with the increase of thermal load,the working fluid in the composite serpentine channel thermal spreader experiences static state,intermittent pulsation,pulsation accompanied by circulation and continuous cycle operation.With the increase of the working inclination angle,the change of heat transfer performance of the composite uniform and non-uniform serpentine channel thermal spreader is not obvious,indicating that both of them have good anti-gravity capability.In the lower heating mode of double heat sources,the difference of heat transfer performance between the two types of composite serpentine channel thermal spreader decreases with the increase of working inclination angle.The heat transfer performance of the non-uniform composite serpentine channel thermal spreader in the range of 0° to 90° working inclination angle can be 3 times of the aluminum plate.The relative change in the range of 0° to 90°working inclination angle is<10%,and the heat transfer performance of the non-uniform composite serpentine channel thermal spreader is 2.4 times of the non-uniform single circuit serpentine channel thermal spreader.In the full heating mode of four heat sources,the heat transfer performance of the two types of composite serpentine channel thermal spreader changes shows the similar trend in different working inclination angles with that under the two heating modes.The heat transfer performance of the non-uniform composite serpentine channel thermal spreader in the range of 0° to 90° working inclination angle can be 1.8 times of the aluminum plate,which is about 40%higher than that of the non-uniform single circuit serpentine channel thermal spreader.(3)In order to further understand the vapor-liquid two-phase flow and heat transfer performance of self-driven thermal spreader in multi-heat source mode,a series channel self-driven thermal spreader is designed and developed,and the influence of working inclination angle and thermal load on the temperature pulsation characteristics and heat transfer performance of self-driven thermal spreader under non-uniform heating mode is studied.The results indicate that the flow state of the working fluid in the channels of left and right sides of the series channel self-driven thermal spreader is coupled and mutually influence with each other.In the uniform and non-uniform multi-heat source heating mode,the self-driven thermal spreader experiences static state(S),intermittent pulsation(S&P),pulsation accompanied by circulation(P&C)and continuous cycle operation(C)with the increase of thermal load.In the uniform heating mode,the difference of heat transfer performance between the left and right sides of the thermal spreader is small,and the thermal spreader shows the best heat transfer performance when the working inclination angle is 0°while becomes the worst at 90°.The difference of heat transfer performance between different working inclination angles is reduced with the increase of thermal load.In the non-uniform heating mode,when the thermal spreader at 0° working inclination angle,better operation performance can be obverserved on the heating side with high thermal load.If the heating unevenness is the same,when the high thermal load side is at a lower position,the working fluid in the thermal spreader is easier to start and the operation state is better with the increase of working inclination angle.In addition,better temperature uniformity of the thermal spreader can be obtained with higher position of the heating side with high thermal load.However,when the thermal load has increased to a certain extent,the influence of the height of high thermal load side on the thermal resistance becomes weak,and the heat transfer performance of the left and right sides of the thermal spreader is almost the same.