Investigation Of The Fresnel Linear Concentrating Vacuum Tube Coupling Pulsating Heat Pipe Heat Collecting Device And Its Performance

Since entering the modern society,with the rapid development of the world economy,the problems of depletion of traditional energy sources and environmental pollution have become increasingly prominent.Solar energy is a new renewable energy source.Its advantages include abundant reserves,cleanliness,and high efficiency.Reasonable development and utilization of solar energy will help alleviate the problems of energy shortage and environmental pollution.There are many ways to use solar energy,among which solar collectors are widely used.Existing solar collectors generally have the problems of complicated mechanical structure,low heat collection efficiency,and slow heat transfer speed.However,the heat transfer performance of the pulsating heat pipe is superior,and it uses the heat absorption and release process of the working fluid phase change to transfer heat.Compared with the traditional metal heat conduction,the heat transfer ability of the pulsating heat pipe is stronger,and the heat transfer speed is faster.Combined with the efficient heat transfer capability of the pulsating heat pipe,the heat collection performance of the solar collector can be significantly improved.In order to optimize the shortcomings of the existing solar collectors,based on the Fresnel lens focusing method,this thesis couples the pulsating heat pipe to the solar heat collecting system,and proposes a Fresnel linear concentrating vacuum tube coupling pulsating heat pipe heat collecting device,And carry out experimental research on its light collection and heat collection performance.The research work and conclusions made are as follows.(1)According to the existing concept,the structure of the Fresnel linear concentrating vacuum tube coupling pulsating heat pipe heat collecting device was designed.The three-dimensional model of the heat collecting device was established by the three-dimensional drawing software Solid Works.In order to determine the optimal installation inclination angle of the Fresnel lens and the vacuum collector tube,the light path simulation of the three-dimensional model was carried out using the optical simulation software Trace Pro,and 17°was determined as the optimal installation inclination angle according to the simulation results.When the solar declination angle is 23°26’,11°43’,0°,-11°43’,-23°26’,the light path simulation is performed for the heat collecting device when the focal line is tracked and when the focal line is not tracked.The annual average optical efficiency of the heat collecting device when tracking the focal line is 47.27%,and the average energy flow density is 1217.98 W/m~2;Without tracking the focal line,the annual average optical efficiency is 36.47%,and the average energy flow density is 1042.36 W/m~2.(2)In order to select the pulsating heat pipe used in the heat collecting device,the pulsating heat pipe is designed and manufactured according to the structure of the heat collecting device and the results of the light path simulation,and a test bed for testing the heat transfer performance of the pulsating heat pipe is built.The effects of liquid filling rate,heating power and length ratio of hot section to cold section on the heat transfer performance of pulsating heat pipe were experimentally studied.According to the experimental results,calculate and compare parameters such as thermal resistance,start-up time,start-up temperature and so on,measure the quality of its heat transfer performance,and analyze the reasons for the difference in heat transfer performance.Experiments show that when the filling rate of the pulsating heat pipe is 50%and the length ratio of hot section to cold section is larger,the heat transfer performance of the pulsating heat pipe is better.Therefore,the pulsating heat pipe with a filling rate of 50%is used as the heat transfer element of the heat collecting device,and the length ratio of hot section to cold section of the pulsating heat pipe is ensured as large as possible.(3)Build a Fresnel linear concentrating vacuum tube coupling pulsating heat pipe heat collection device performance research experimental platform,and perform three different heat collection performance research experiments on the heat collection device when the solar radiation intensity meets the experimental requirements.When concentrating and tracking the focal line,the maximum heat collection efficiency is 33.44%,and the average heat collection efficiency is 26.75%;When concentrating and not tracking the focal line,the maximum heat collection efficiency is 30.2%and the average heat collection efficiency is21.44%;When the vacuum heat collection tube is directly exposed,the maximum heat collection efficiency is 11.02%,and the average heat collection efficiency is 9.51%.Comparing and analyzing the simulated heat collection efficiency and the experimental heat collection efficiency when condensing and tracking the focal line,and concentrating and not tracking the focal line,it is found that the two are basically the same.The light path simulation can provide guidance for the design of solar collectors.