| The micro heat pipe 1s a efficient heat conducting element by cycle phase transition of working fluid.Capillary pressure,as a key index parameter for evaluating the quality of wick structure,has been a hot topic for scholars at home and abroad.In recent years,how to increase the capillary pressure of micro heat pipes has become a key issue in the research of micro heat pipes,which the most effective method is to optimize the wick structure and its size of micro heat pipes.In this paper,the influence of the size of wick structure on the capillary pressure and heat transfer performance of the micro heat pipes with composite grooves is studied by theory and experiment,and then the size of wick structure is optimized to enhance the heat transfer performance of MHP with composite grooves.The specific work is as follows:(1)The mathematical model of liquid reflux driven by capillary pressure of wick structure was established.The relationship between the capillary pressure of the wick and the structural parameters of the composite grooves was obtained,and the model highlights the role of the capillary pressure of the wick in driving the working fluid flow.At the same time,the theoretical simulation of the heat and mass transfer characteristics of the micro heat pipe with composite grooves was established.The heat transfer characteristics of the micro heat pIpe were analyzed by the model,and the maximum heat flux of the micro heat pipe 1s used as the evaluation index of heat transfer performance,the influence of the structure size of the wick on the heat transfer performance of the micro heat pipe was solved.(2)According to the characteristics of laser processing,the wick structure of composite grooves with different grooved width and grooved depth and single groove with the same structural size were prepared by the method of scale-out multiple scanning and controlling laser processing process parameter,and it 1s provided the samples for the experimental study of the capillary pressure of the wick of the composite groove and the heat transfer performance of the micro heat pipe.(3)According to the theory of capillary phenomenon,the capillary rising test method for composite grooves was designed.The capillary pressure test of composite grooves with different structural parameters was carried out to verify the influence of the structural parameters of wick on capillary pressure.In addition,the composite grooves and the single groove under the same structural parameters were tested for capillary pressure.The results show that with the main grooved width in the range of 40?m?60?m and the main grooved depth in the range of 80?m?120?m,capillary pressure of the micro heat pipe with composite grooves increases with the decrease of the grooved width,and increases with the increase of the grooved depth.On the other hand,the composite grooves provides a capillary pressure of about 11.7%higher than a single groove,the results not only shows the superiority of the composite grooves,but also highlights that the secondary groove can effectively enhance the capillary pressure.(4)Before the heat transfer performance test of the micro heat pIpe,prepared the test sample of the micro heat pipe with composite grooves according to the micro-heat pIpe processing technology,and the micro heat pipe heat transfer performance test platform was improved on the basis of the previous research of the research group,and the start up performance and steady-state performance of MHP are used as the technical indexes,the influence of different wick structures and parameters on the heat transfer performance of MHP was analyzed by the experiments.The experimental results show that the main grooved width in the range of 40?m?60?m,and the main grooved depth in the range of 80?m?120?m,with the decrease of grooved width,the start up performance and steady state performance of micro heat pipe are both improved.And with the increase of grooved depth,the start up performance and steady state performance of micro heat pipe are also improved.On the other hand,the starting time of micro heat pipe with composite grooves is 30 s,the minimum temperature difference is 3.01 C,and the minimum heat conduction resistance is 0.135 C/W.The starting time of micro heat pipe with single groove is 39s,the minimum temperature difference is 3.77 C,the minimum thermal resistance is 0.17 C/W.The heat transfer performance of micro heat pipe with composite grooves 1s obviously better than the single groove,which verifys the advantages of the composite groove wicks used in micro heat pipe.(5)In summary,the structural parameters of the composite grooves in this paper:the main grooved width is 40.8?m,the main grooved depth is 115.4?m,the secondary grooved width is 35.2?m,the secondary grooved depth is 34.4?m,and the grooved spacing is 90?m,the starting time of the composite grooves is 29s,the minimum temperature difference is 3.02?,and the minimum thermal resistance is 0.135?/W.The results indicate that the micro heat pipe has large capillary pressure and superior heat transfer performance.The th.eoretical and experimental conclusions are consistertt,which indicates that the wick steucture of composite groove of this study should be designed as a small-width,large-depth to ensure heat transfer performance. |
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