Study On Heat Transfer Law Of Thermosyphon In Thermoelectric Energy Conversion

Forest resources are of great significance to the economic and social development and the improvement of ecological environment.It is necessary to use sensors to monitor forest environment in real time.The problem of sensor power supply in forest is an important restricting factor for the further development of monitoring technology.Using the temperature difference between forest soil and air environment for thermoelectric energy conversion,the sensor can be powered in situ.Based on the theory of heat transfer and experiments,the heat transfer law of two-phase closed thermosyphon is studied,and the heat transfer model of thermoelectric power generation system is established.(1)The thermal resistance model of thermosyphon is established based on the thermal resistance theory of heat transfer.The characteristics of phase change heat transfer in working medium are analyzed,the theory of area thermal resistance is put forward,and the model of the influence of working inclination angle on the heat transfer performance of thermosyphon is established.The actual heating area is defined,and the calculation formula of the actual heating area is given according to the three parameters of working medium filling rates,heating length ratio and working inclination angle.According to the principle of equal total thermal resistance,the equivalent thermal conductivity is defined,and the heat transfer performance evaluation model of thermosyphon is established.(2)The experimental test system of thermosyphon is designed,and the device which can meet the heat transfer performance test of thermosyphon is built.The experiments of copper two-phase closed thermosyphon with ethanol as working medium were carried out.The heat transfer performance of 30 kinds of working conditions was tested,with working inclination angles of 15 °,30 °,45 °,60 °,75 ° and 90 ° and heat transfer rates of 20 W,30W,40 W,50W and 60 W.The relevant parameters in the theory of area thermal resistance of thermosyphon are measured.The experimental results show that the main reason for the influence of the working inclination angle on the heat transfer resistance of the thermosyphon is that the inclined process of the thermosyphon changes the actual heating area of the evaporation section.Three kinds of copper thermosyphon with length of 220 mm,320mm and 500 mm were studied.The heating power was 20 W,30W,40 W,50W and 60 W.The equivalent heat conduction coefficient was measured.The experimental results show that the heat transfer performance evaluation model can effectively evaluate the heat transfer performance of two-phase closed thermosyphon,and can also be used as a comparison of heat transfer performance between two-phase closed thermosyphon of different sizes.(3)The heat transfer process of forest soil thermoelectric power generation system includes soil heat transfer,solid fin heat transfer,thermosyphon and heat transfer with air environment.The heat transfer process of each part of the thermoelectric power generation system is studied.It is found that the temperature distribution in the heat transfer process between the soil and the heat absorbing fins has a special symmetry,and the number of distribution periods is equal to the number of fins.The heat transfer process between copper sleeve and fins is solved by shape factor method,and the thermal resistance between two isothermal surfaces is obtained.The heat transfer model of thermoelectric power generation system is established,and the influence mechanism of relevant parameters in the model and the experimental measurement method are given.In this thesis,the theoretical model of heat transfer of thermosyphon is established,and the equation of the influence of working angle,heat transfer rate and other factors on the heat transfer performance is obtained,which can provide theoretical basis for the application of related fields.The heat transfer test system of thermosyphon with complete components is designed,which can meet the test requirements by changing the size and achieve the experimental purpose.Optimizing the heat transfer performance of forest soil thermoelectric power generation system can improve the efficiency of thermoelectric conversion,and also provide theoretical basis for the study of related forms of heat transfer law.