| According to the Thirteenth Five-Year Plan for Solar Energy Development of the National Energy Administration,the demand for renewable energy of our country will grow rapidly in the future for a long period of time.At the same time,the proportion of building energy consumption in the country's total energy consumption has also increased rapidly in recent years.As an important part of renewable energy,solar energy resources play an important role in reducing energy consumption in the construction field and total energy consumption in society.Solar energy utilization technology is also the current research hotspot and industry focus.Among all the solar energy utilization technologies,the photovoltaic/thermal integration(PV/T),which can achieve combined heat and power generation,has extensive research significance and application prospects.For the problem of long start-up period of natural circulation collectors with water as working medium,and gravity heat pipe collectors relying on circulation pumps,etc.,this paper studies a new type of loop heat pipe solar PV/T system through a combination of experimental research and numerical simulation,which mainly includes the following content.First of all,on the basis of related research status of PV/T technology and the application of heat pipe in the field of solar energy,this paper analyzes the existing research problems,explores the main factors that affect the performance of the system,clarifies the schematic diagram of the loop heat pipe PV/T system,and determines the specific research contents and ideas of experimental analysis and numerical simulation.According to the schematic diagram,this paper first determines the specific experiment plan,the physical quantity required to be measured,the specifications of the main equipments,the instrumentation of the measurement system and the experimental working conditions,to provide a platform basis for experimental analysis.Secondly,through experiments on system performance under different stable irradiances,it can be known that the temperature differences between inlet and outlet of PV/T unit and the average temperature rise rate increases with the increase of irradiance.The fluctuation of thermal power at 850W/m~2~1000W/m~2 can be significantly reduced,and the heat exchange effect is more stable,but the maximum thermal efficiencies has no obvious change under different working conditions.The water temperature is up to 40.64?.The energy effective utilization efficiency of photovoltaic part under high irradiance will be reduced.In addition,there is no obvious change of start-up characteristics under different irradiances.The performance at 850W/m~2 irradiance condition is the best one in the experiments.Thirdly,this paper theoretically analyzes the source term model and multiphase flow model which are suitable for this research.And the standard model verification method is used to verify the accuracy of the model and provide a basis for numerical simulation.This paper firstly establishes a three-dimensional ICEM model for the loop heat pipe flow channel and the evaporation plate.Then it uses the relevant experimental data as the boundary conditions,sets the simulation parameters reasonably,and compiles the required UDF code according to the theoretical analysis.At the same time,the thermal properties of the refrigerant are treated with variable physical properties.Fourthly,through the analysis of the simulation results under different boundary conditions,this paper finds that compared with different heat flux boundary conditions,changing the inlet mass flow rate has a greater influence on the distribution of the cross-sectional vapor volume fraction.The phase change rate in the early stage is faster than that in the late period,and the slope of dryness reduces significantly.After the heat exchange state is stable,the inlet velocities at 850W/m~2~1000W/m~2 heating boundary increase faster than other conditions,while the outlet velocity does not increase evidently.In addition,the impact of mass flow rate changes on the velocity distribution is much higher than that of heat flux changes.Increasing the cross-sectional aspect ratio will mainly affect the phase change rate in the case of high circulation flow rate,and the influence of mass flow rate on the evaporation process is further increased.Finally,the study found that increasing the inlet flow rate,heat flux boundary conditions,or cross-sectional aspect ratio will all increase the heat transfer coefficient of the flow channel.At a cross-sectional aspect ratio of 15/7.5,the maximum heat transfer coefficient differs by21.36%,and the influence of the heating boundary is lower than that of the flow rate.The maximum heat transfer coefficient after changing the aspect ratio is 1338.25W/m~2·K,and the average difference is 31.67%.The increase of heat transfer coefficient under high heating conditions is more obvious,and the influence of flow rate on heat transfer is further enhanced.In summary,this paper studies the loop heat pipe solar PV/T system through a combination of experimental research and numerical simulation.While verifying the feasibility of this type of system,the performance and operating characteristics are analyzed,and the influence of various factors under different boundary conditions is determined.This paper has a certain reference value for the system design form of the combination of loop heat pipe and solar PV/T technology. |
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