Font Size: a A A

Experimental Study On Heat Transfer And Preparation Of Nickel-Ammonia Low-temperature Loop Heat Pipe Based On Optimized Pore Parameters

Posted on:2021-03-13Degree:MasterType:Thesis
Country:ChinaCandidate:C JiangFull Text:PDF
GTID:2532306020458494Subject:Mechanical Manufacturing and Automation
Abstract/Summary:PDF Full Text Request
With the rapid development of aerospace technology and the high integration of electronic devices,heat dissipation has become a major factor limiting its development.Common single-phase heat dissipation,pump-driven two-phase heat dissipation,and traditional gravity heat pipes have significant application limitations.As a new type of phase change thermal element,the loop heat pipe has the advantages of accurate temperature control,no external power source,anti-gravity operation,etc.,which has attracted the attention of many scholars.The loop heat pipe is mainly composed of five parts:evaporator,vapor line,condenser,liquid line,and reservoir.The porous wick inside the evaporator is the most important and core part of the loop heat pipe.The performance of the capillary wick is directly related to the performance of the loop heat pipe.Therefore,in this paper,a capillary wick is used as the research object,and a nickel-based double-diameters capillary wick is prepared by using a salt-dissolving pore-forming technology.(30kN,40kN,50kN,60kN)Change the internal pore size and pore size distribution of the capillary wick,and use the self-built capillary suction test bench and gas resistance test bench for the key parameters of the capillary wick(suction speed,total suction mass,Permeability)to analyze the effect of the two on the performance of the capillary wick.It was found that as the proportion of pore-forming agent increased,the suction performance of the capillary wick gradually increased,but the impact of the cold pressing pressure on the performance of the capillary wick was small.After completing the research on the effect of pore former ratio and cold pressing pressure on capillary wick performance under normal conditions,this paper selects a group of capillary wicks with the best performance(high suction speed and high permeability)to make loop heat pipes.The self-designed high-precision vacuum perfusion experimental bench and heat transfer experimental bench were used to complete the loop heat pipe perfusion and heat transfer experiments.In the heat transfer experiment,the start-up and heat transfer performance of the loop heat pipe were first tested,and then the loop heat pipe heat transfer limit,thermal resistance,and continuous variable load were experimentally tested and compared with related literature.In the end,it was found that:1.The loop heat pipe appeared "reverse flow" when the low-power heat load started,and the duration of the "reverse flow" gradually decreased with the increase of the heat load until it disappeared.2.As the thermal load power increases,the overall operating temperature of the loop heat pipe rises,the startup time becomes shorter,and the thermal resistance shows a downward trend.3.In the continuous variable load experiment,the gas-liquid distribution inside the loop heat pipe changes rapidly to reach equilibrium.Finally,this paper studies the heat transfer performance of loop heat pipes under different operating conditions(different heat sink temperature,different liquid level distribution inside the evaporator,and variable load experiments)and compares it with related literature.It was finally found that 1.As the heat sink temperature increased,the overall operating temperature of the loop heat pipe increased.2.Under the condition of gravity,most of the working fluid is accumulated inside the evaporator of the loop heat pipe,which requires a certain degree of superheat in its operation.Therefore,the temperature of the loop heat pipe is the highest in this case.When the angle is too large,due to the effect of gravity,most of the working fluid accumulates in the evaporator when heated,and the gas working fluid floats up into the liquid pipeline,which causes the"reverse start" phenomenon.At this time,the loop heat pipe fails to start.3.The temperature in the case of anti-gravity is second only to the case of paragravity,but there is a case where the temperature of the evaporator first rises and then decreases when the heat load changes.The reason is that the liquid working fluid accumulates in the reservoir and is at the evaporation end.When heated,the liquid working medium inside the reservoir needs to be pumped to the evaporator through the capillary action of the porous medium.The return of the cold liquid working medium will cause the trend of first rise and then decrease when the hot load step changes.4.When the loop heat pipe starts in a horizontal condition,the temperature will produce a corresponding step change when the heat load changes,and the situation of rising first and then falling will not be in a more balanced state,and the reaction to the change of heat load will be faster.
Keywords/Search Tags:nickle-based capillary wick, low temperature loop heat pipe, capillary suction experiment, heat transfer experiment, pore-forming agent
PDF Full Text Request
Related items