Research And Manufacture Of The Powder Sintered Multi-branch Heat Pipe And Study On Its Thermal Performance

Heat pipe is a high efficiency heat transfer element due to the passive phase change with many advantages such as high thermal conductivity,quickly starting up and high flexibility.It is widely used in heat dissipation and temperature control of high power electronic devices.However,with the development of micro-fabrication technology,the development of electronic devices are miniaturization,high-power and multi-functional modularization.The continuous improvement of integration not only increases the unit power density,but also leads to the number of internal heat sources will be more,while the relative location of heat sources and cold sources will become more complex and diverse.At present,there are some shortcomings in several ways to solve the heat dissipation of multi-heat source electronic devices.Therefore,heat dissipation of multi-heat source is still one of the key problems to be solved urgently.In order to solve above problems,a new type of multi-branch heat pipe with high thermal conductivity and good space utilization is proposed,which is suitable for the heat dissipation of multi-heat source or multi-cooling source system.It can weaken the heat source,space and other factors on the miniaturization,stability and reliability of electronic devices.The main work of this paper is as follows:(1)Two processes to manufacture multi-branch heat pipe were developed.The one is based on integral sintering and the other is based on secondary sintering.Capillary wick of the integral sintered multi-branch heat pipe is simple to manufacture and it can assure the integration of the wick,but it is difficult to manufacture the complicated structure.The branches and joints of the secondary sintered multi-branch heat pipe are separately sintered and assembled into the one.The complex multi-branch structure can be manufactured,which is beneficial to the large scale production,but it requires a second sintering and costs highly.(2)The experimental platform of temperature measurement was set up to study the heat transfer performance of multi-branch heat pipe.The influence of copper powder size on the heat transfer performance of the integral sintered multi-branch heat pipe was tested.The results show that the copper powder with the particle size of 75~100?m is the best one for the integral sintered multi-branch heat pipe.In addition,the influence of the working fluid filling ratio on the heat transfer performance of the multi-branch heat pipe with two different manufacturing methods was compared.The results show that the performance of two multi-branch heat pipe manufacturing methods is similar,and their optimal working fluid filling ratio are in the range of 75 to 100%.(3)The influence of multi-heat source condition on heat transfer performance of multi-branch heat pipes was analyzed.Firstly,the effect of different total heating power on the startup characteristics of multi-branch heat pipes was studied.Secondly,under constant total power of heating sources,the different distribution of heating power of multi-branch heat pipe on power distribution characteristics is studied.Finally,the influence of power variation of multi-branch heat pipe on the dynamic characteristics was studied.The results show that: Multi-branch heat pipe can quickly and steadily start up when the working fluid filling ratio is below 100%,and the maximum power,the maximum heat flux and the minimum thermal resistance are 160 W,318.3 W/cm2 and 0.04oC/W,respectively.When the total power of the multi-branch heat pipe is kept constant,the maximum temperature after the heat pipe reaches the steady state is always the same regardless of the power distribution among the heat sources.When multi-branch heat pipe starts up,it can be a smooth transition to another new steady-state temperature while the multi-heat source device power change.(4)The heat transfer performance of the multi-branch heat pipe in the condition of multi-cooling sources,composite heating source-cooling source-phase change material was analyzed.When the multi-branch heat pipe started up in the multi-cooling source conditions,its limit power is 190 W and the maximum temperature can be below 73 oC.When using the phase change material assisting in heat dissipation,it is necessary to select the appropriate phase transition temperature so that the working temperature of the electronic device can be kept the temperature in the solid or melted phase of phase change material,while the phase change material will lose temperature control in the liquid phase.In addition,adding appropriate amount of copper fiber in the phase change material can improve the thermal conductivity to achieve the thermal control effect of the insulation and reducing the overall temperature difference of the system effectively.