| In order to break through the bottleneck of the current chip performance and power consumption limitation,more ultra-thin heat dissipation schemes have been proposed,such as ultra-thin heat pipe,VC cavity,etc.While the structure optimization of capillary wick is the wick problem to improve the two-phase dissipative heat efficiency,and the demand for high-performance capillary wick is also more and more urgent.The capillary wick with high aspect ratio microchannel structure proposed in this study has the characteristics of large capillary force of traditional capillary wick,but also has the advantages of stable reflux of large flow of working medium which is difficult to achieve by traditional capillary wick and is suitable for ultra-thin structure.At present the theory and numerical simulation study most confined to limited number of microchannel,difficult to apply to high aspect ratio microchannel array capillary wick study.Therefore,this research is based on theoretical research.The concept of porous media is used to establish the flow heat transfer model,and the numerical simulation process of micro-channel array capillary wick is simplified.The experimental verification is carried out,and the optimized design is applied to the silicon based ultra-thin loop heat pipe.In this paper,the numerical simulation of rectangular microchannel parallel array is simplified.Part of the microchannel full-size geometric model is established.A basic model of flow in microchannel is established based on the concept of porous media.The flow resistance of working medium in microchannel is characterized by loss of flow pressure-drop with the introduction of the effects of depth to width ratio(AR),hydraulic diameter,inlet velocity and other parameters on fluid flow in microchannel.The numerical simulation of micro-channel and porous media suction without initial velocity is carried out and a formula to characterize the capillary force including dimensional parameters such as depthwidth ratio is established.Then,add capillary force by writing UDF.The porous media model of single-phase flow and gas-liquid two-phase flow is realized,and the numerical simulation effect of using porous media model instead of microchannel array is finally achieved.The theoretical model is verified by the visualization experiments of silicon-based microchannel array capillary wick heat exchangers with different depth-width ratios,and the results show that the theoretical model is feasible.The results can simplify the numerical study of microchannel array and also play a guiding role for the subsequent experimental research.At the same time,with the method of numerical simulation,combining the theory of flow model simulating calculate microchannel array with the different depths and different widths of the phase change heat transfer.Then,calculating of heat transfer coefficient by the result of the heat transfer temperature-difference.The relationship between the change of heat transfer coefficient and the crosssection size of the micro-channel is established.The depth and width of the microchannel are introduced as parameters through data fitting,and the prediction formula of comprehensive heat transfer coefficient is established.Visualized heat transfer experiments of microchannel array capillary wick evaporators with different depth-width ratios are carried out to verify the applicability of the prediction formula.After the theoretical and numerical simulation of the flow and heat transfer in the rectangular parallel array microchannel,this paper applied the microchannel in the u-LHP(micro loop heat pipe)as the evaporator capillary wick.After theoretical research and comparative analysis,the size of microchannel with high comprehensive performance is selected which the depth is 180 μm,the width are 12 μm and 16 μm.And the silicon based plate micro-loop heat pipe is designed and fabricated to meet the requirements of visualization experiment.The feasibility of using microchannel array as evaporator is verified by visual heat transfer experiments.The operation process of microchannel array as evaporator is analyzed,and the influence of microchannel on the performance of loop heat pipe is discussed.In this study,a theoretical model of flow heat transfer in rectangular parallel array microchannel is obtained.and through experiment verify its applicability and feasibility of application to the design of micro capillary loop heat pipe evaporator wick guide,and prepared a silicon based ultra-thin miniature loop heat pipe that can run stably.The experimental results show that the capillary force generated by the microchannel capillary wick ensures the supplement of working medium and the circulating operation of the loop heat pipe.At the same time,it improves the efficiency of evaporation and achieves the standard of stable operation and efficient heat dissipation.The theoretical model obtained in this study can greatly simplify the design process of microchannel capillary wick,and has guiding significance for the design of rectangular parallel array microchannel in the practical application process. |
