| Both gravity heat pipe and loop heat pipe are efficient phase change heat transfer devices in which the phase change flow of working fluid are used to transfer heat.They have the advantages of high thermal conductivity and high temperature uniformity.Additionally,loop heat pipe also has the characteristics of long-distance transmission and anti-gravity.According to the cooling requirements of power equipment and base station under natural convection conditions,natural cooling gravity heat pipe heat sink(NC-GHPHS)and natural cooling loop heat pipe heat sink(NC-LHPHS)are designed respectively,and the performance of the heat sink applied to heat dissipation of high-power equipment is studied.Through theoretical analysis and experimental research,the enhancement of heat dissipation capacity of the heat sink,theoretical analysis of dynamics and thermodynamic characteristics,numerical study,development of the heat sink and experimental study are focused.Meanwhile,the mechanism of natural cooling heat pipe heat sink(NC-HPHS)is studied,and the feasibility of the heat sink as heat dissipation method of high-power equipment under natural convection conditions is explored.The research mainly includes the following aspects:1.Research on the enhancement of the cooling capacity of natural cooling heat pipe heat sinkThe optimization of NC-HPHS structure can effectively enhance the natural convection cooling capacity of the heat sink.In this paper,the relationship between the natural convection heat transfer capacity and the structure size of the heat sink is described.The method of enhancing the natural convection heat dissipation capacity of the laminated fin structure is studied.The theoretical model of heat transfer and dissipation of NC-HPHS is established.The effects of fin length,height,thickness and fin spacing on the natural convection heat transfer coefficient,fin efficiency and heat transfer resistance are analyzed.The efficient optimal design method for NC-HPHS is proposed.2.Numerical investigation of natural cooling gravity heat pipe heat sinkA 3D numerical model of NC-GHPHS is developed by Fluent.The model can be used for transient calculation to analyze the phase change flow and heat transfer process inside the evaporation plate in the start-up stage.The simulation results show that the heat sink can start successfully and the flow direction of working fluid is consistent with the design direction.In addition,the model can also be used for steady-state calculation to analyze the factors which can affect the heat sink performance,including the filling ratio and heating power.The results show that the heat sink can effectively transfer the heat generated by high-power equipment and uniform the temperature of surface through the phase change and natural convection,and get the best performance when the liquid filling ratio is 40%.The numerical simulation results can provide the guidance for the optimal design of the heat sink structure size.3.Experimental investigation of natural cooling gravity heat pipe heat sinkAccording to the heat dissipation requirements of high-power electric equipment,the NC-GHPHS is developed.The micro channel inside the evaporators can enhance the heat transfer of phase change,and the stiffeners can increase the structural strength of the evaporators.The performance of GHPHS with different number of evaporators and condensers which is applied to heat dissipation of high-power equipment is experimentally studied.The working temperature of evaporators and condensers are tested,and the change rules of start-up characteristics,temperature distribution,temperature difference,thermal resistance and other performance are analyzed.The experimental results show that the heat sink has good performance under suitable working conditions and it can fully meet the cooling requirements of high-power equipment.The best filling ratio will change with the heating power.When the heating power is 3000 W,the maximum temperature difference of evaporators can also be controlled within 8 ? under appropriate filling ratio.In addition,the performance of the evaporators at different heights are different.The maximum temperature of the lower evaporator is lower than that of the upper evaporator,while the temperature uniformity of the upper evaporator is better than that of the lower evaporator.The experiments also analyze and compare the performance of the heat sinks with different number of evaporators and condensers,and reveals the matching mechanism between the evaporators,condensers and the heat dissipation requirements of power equipment.The results show that each heat sink needs a certain degree of superheat to start,and it shows good adaptability to the sudden change of the surrounding environment.4.Numerical investigation of natural cooling loop heat pipe heat sinkBased on the established theoretical model of NC-LHPHS,the heat transfer and dissipation model of NC-LHPHS is established.Meanwhile,the dynamic model of the heat sink is established,and the steady-state performance of the heat sink is calculated by combining the two models.The results show that the heating power,filling ratio and ambient temperature have an important influence on the heat transfer and heat dissipation characteristics of the heat sink.The software FLUENT is also used to build a 3D model of the LHPHS.The model is used for steady-state calculation,and the results of numerical simulation can provide the guidance for the optimal design of the heat sink structure size.In addition,the a 3D model of the capillary pump is also established.The influence of different structural parameters on the performance of the capillary pump and the flow and heat transfer process inside the capillary pump are analyzed.5.Experimental investigation of natural cooling loop heat pipe heat sinkIn view of the heat dissipation requirements of the electronic equipment with non-uniform distribution and multiple devices,the NC-LHPHS is designed and developed,which mainly includes the processing of capillary pump,evaporators and condensers.The experimental study of the heat sink is carried out.The research contents include start-up characteristics,average temperature characteristics,heat dissipation characteristics and working characteristics under different heating power,filling ratio,declining angles and so on.The experimental results show that the start-up performance of the heat sink are good,and the temperature response of the condenser is slower than that of the evaporator.The operation stability of the heat sink is also very good when it reaches the stable state,and there is no big temperature fluctuation.Meanwhile,the change rules of the heat sink performance with heating power,filling ratio and declining angle are also revealed.The temperature uniformity of the heat sink is very good when the liquid filling ratio is higher than 30%,and the maximum temperature difference of evaporator is kept within 8?.The heat sink has relatively good working performance such as uniform temperature and heat dissipation at all tilt angles except for the horizontal state,and can be applied to heat dissipation of equipment at various angles.In addition,the phase change flow behavior of the working fluid in the heat sink is recorded by high-speed camera,and the flow state of the working fluid in the heat sink under different working conditions is analyzed.The results show that the NC-HPHS can meet the requirements of low noise and small maintenance in application by using natural convection.Moreover,the NC-HPHS can also meet the uniform temperature and heat dissipation requirements of the high-power equipment due to the high thermal conductivity and high uniform temperature of phase change.The heat sink has a compact structure and can significantly reduce the volume compared with the traditional natural convection cooling device.For different application scenarios,different types of NC-HPHS can be adopted,which shows that the heat sink has broad application prospects in the field of heat dissipation of high-power equipment. |
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