Research On Laser Etching Process And Heat Transfer Performance Of Micro Heat Pipe With Composite Grooves Capillary Structure

With the rapid development of microelectronics technology,the micro heat pipe with high thermal conductivity,good isotherm and fast thermal response has become the ideal element for the heat dissipation of microelectronic products.The heat transfer performance of micro heat pipe mainly depends on the structure of the suction core,the optimization and improvement of the suction core structure has been the focus and hotspot of domestic and foreign scholars.In this paper,the plate micro heat pipe with composite groove suction core structure is manufactured by laser,and its heat transfer performance is studied.The specific work is as follows:(1)Based on the calculation model of the basic parameters such as the effective capillary radius and the maximum capillary pressure,the theoretical model of heat transfer limits of the composite grooved micro heat pipe is established.Through taking the structural parameters of composite groove and physical parameters of working liquid into the theoretical models,the theoretical values of heat transfer limits is calculated,founding that under 30 ?,50 ?,70 ? working temperature,the heat transfer performance of micro heat pipe were bound by capillary limit,so the maximum capillary pressure is used as the evaluation index for the quality of composite grooves.(2)Exploring the laser forming mechanism of the composite grooves,the influence of different laser parameters on the morphology and size of composite groove was analyzed by single factor experiment,the optimal laser etching process parameters were also obtained.The results show that the forming mechanism of composite groove is mainly photothermal effect,molten material of vaporizing pressure is deposited on the surface of main groove and then form a secondary groove under the action of secondary adhesion.The optimal laser etching process parameters are: laser average power 20 W,laser pulse width 100 ns,laser repetition frequency 40 kHz,laser scanning speed 150 mm/s,laser scanning times 25.The composite groove is well formed under these parameters,and providing larger capillary pressure for liquid reflux.(3)The shell material,liquid types and liquid filling rates of micro heat pipe were selected,and measuring the capillary pressure of three different liquids by measuring fluid velocity with SLR cameras and measuring capillary rise height with infrared thermograph,its reasons are also analyzed.After the processing of central frame and vacuum injectionpipe,the laser preparation of composite grooves,the assembling and welding of micro heat pipes,the test of air tightness,the vacuuming and liquid injection,the sealing,the preparation of plate micro heat pipe with composite grooves was completed.(4)The experimental platform for heat transfer performance of micro heat pipe was set up,then the start-up performance and steady-state performance of composite grooved micro heat pipe with different liquids and different filling rate were tested.The results showed that in the start-up performance test,the start-up time of water-micro heat pipe was the shortest at80% filling rate,the start-up time is 52s;acetone-micro heat pipe and ethanol-micro heat pipe were the fastest to start at 100% filling rate,the start-up time are 44 s and 48 s respectively.In the steady-state performance test,the optimal liquid filling rate of micro heat pipe used water,acetone,ethanol as working substance are 100%,120% and 100%respectively,the ultimate thermal conductivity under the optimal liquid filling rate is 22 W,14W and 11 W respectively.Finally,comparing the experimental results and theoretical results,found that the theoretical value and experimental value of capillary limit for the composite grooved flat micro heat pipe under the condition of using water as working substance,100% liquid filling rate,50 ? working temperature were 24.58 W and 22 W respectively,the two are pretty close.