| Different from the traditional heat pipe,the loop heat pipe is a two-phase heat exchange device where the evaporator and the condenser are separated.The capillary force provided by the capillary core inside the evaporator drives the flow of the working medium,and avoids the shortcomings of the two-phase working medium of the traditional heat pipe in the same pipeline.After decades of development,loop heat pipes have been developed into a variety of types according to factors such as use,shape and so on.Among them,the small flat loop heat pipe is a good solution for the heat dissipation of small and medium-sized electronic equipment.With the gradual in-depth exploration of loop heat pipes,many unique phenomena and shortcomings of loop heat pipes were discovered.Researchers are also constantly proposing various solutions to solve the problems that arise when loop heat pipes work.However,in the application process of small flat-type loop heat pipes,due to the relatively thin evaporator,problems such as serious heat leakage,short capillary core life,temperature fluctuations,and unstable start-up still seriously restrict the small flat loop heat pipes development of.In this paper,the internal structure of the loop heat pipe is redesigned based on the research of the same research group and other researchers,and the carbon fiber felt that has been studied in detail by this research group is used as the capillary core.The working performance of the loop heat pipe was studied using ethanol,acetone,and ethanol:acetone=1:1(volume ratio)as working fluid.In addition,combined with the operation of the working fluid inside the loop heat pipe,the cause of the above problems was thoroughly explored,and the loop heat pipe system was visually transformed.Quartz glass is used as the top cover,and a specially designed sealing structure and material are used to achieve stable visual operation.The internal flow and phase change process of the working fluid are clearly recorded,and the specific causes of temperature fluctuations and operational failures are analyzed.Under the conditions of stable start-up and operation of the loop heat pipe,this paper has conducted detailed tests on the start-up performance and temperature fluctuation of the loop heat pipe from the five aspects of liquid filling rate,power,placement angle,working fluid type and cooling temperature.Research and summarize the corresponding laws.The working conditions that are most conducive to the start up and stable operation of the loop heat pipe are determined.In addition,this article explores all three types of temperature fluctuations.Compared with other published research results,several second-type temperature fluctuations and transitional temperature fluctuations are found in this paper.Through the visualization equipment,the reason for its occurrence was analyzed,and it was found that the reason for the temperaturefluctuation was only related to the pressure change inside the loop heat pipe,flow resistance,pipeline volume,working fluid properties,etc.No working fluid bubbles were found in the condenser and liquid pipeline The type of temperature fluctuations generated.This paper compares the heat transfer performance under different working conditions,and finds the influence trends of four influencing factors,such as power,placement angle,liquid filling rate,working fluid type and cooling temperature,on the loop heat pipe,and is determined by experimental data The limit working performance of the loop heat pipe used in the test was obtained.Combined with the analysis in Chapters 3 and 4,the working conditions of the loop heat pipe in practical application are given.That is,the conditions of rapid start,smooth operation,and strong heat transfer capability.After the experimental research of this subject,it is found that the loop heat pipe used in this experiment still has some room for improvement.This article gives the design improvement suggestions and verification results of the flat loop heat pipe. |
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