Structure Optimization And Thermal Performance Of Double Tube And Multi Curved Trough Air Collector For Solar Greenhouse

As an important part of facility agriculture in China,solar greenhouse brings great economic benefits to the agricultural planting industry in China.It effectively solves the problem of winter anti season vegetable planting in northern China.However,most of the traditional solar greenhouses adopt passive heat collection and storage.Once the complex weather occurs,the control ability of the solar greenhouses to the thermal environment will be limited.Therefore,the dynamic solar heat collection and heating technology will be introduced into the solar greenhouses to meet the needs of the winter greenhouse crops for the thermal environment.However,the research on active heat collection and storage technology of solar greenhouse is not deep enough,especially the high-performance solar collector developed for solar greenhouse in Northwest China is lack of systematicness.For this reason,this paper uses the method of numerical simulation analysis and field experiment to carry out a series of research on the structure optimization and thermal performance of double tube multi curved groove air collector used in solar greenhouse.The main research contents and results are as follows.Firstly,based on the structural characteristics of the double tube multi curved groove air collector,the concentrating characteristics are analyzed,and with the light convergence rate as the evaluation index,the influence of different solar incidence angle and structural parameters on the concentrating efficiency of the collector is simulated and analyzed by using the optical software TracePro.The results show that the concentrating efficiency of the collector decreases with the increase of the solar incidence angle.When the solar incidence angle is greater than7°,the light convergence rate is less than 50%.The structural parameters of the collector will also affect the concentrating efficiency.When the solar incidence angle is less than 7°,when the width of the light inlet is 570mm～670mm,the total height is 545mm～745mm,the width of the light outlet is 210mm～230mm,the height of the secondary reflection plane mirror is40mm～80mm,the light convergence rate of the collector can reach more than 85%.Secondly,the orthogonal experiment is used to analyze the influence of four structural factors on the concentrating efficiency,and the optimal structural parameters are obtained according to the maximum signal-to-noise ratio of each factor.The results show that when the width of the light inlet is 670mm,the width of the light outlet is 210mm,the total height is545mm,the height of the secondary mirror is 40mm,and the coordinates of the center of the two tubes are(-30,70)and(40,158)the solar incidence angle is 0°～7°,the light convergence rate can reach 100%.Thirdly,combined with the research of the optical performance of the double tube multi curved groove air collector,the heat transfer performance of the optimized collector structure is simulated and analyzed.Based on the theory of heat transfer and fluid mechanics,a three-dimensional physical model of double tube and multi curved groove air collector is established by FLUENT software.By analyzing the heat transfer characteristics of the collector under different factors and the influence on the safety of the collector tube,the optimal operation scheme of the collector is finally obtained.When the air velocity in the tube of the 2 m double tube multi curved groove air collector is 2.2m/s,the instantaneous heat collection and the instantaneous heat collection efficiency are 1050W and 71%,respectively,when the solar radiation intensity is 1100W/m~2 and the air inlet temperature is 285K.Finally,according to the climate conditions and the heat storage capacity of the wall in Lanzhou area,it is found that the 10m heat collection system can basically meet the needs of the solar greenhouse in Lanzhou area,so the solar energy collection system composed of five groups of unit double tube multi curved surface trough air collectors is selected to be applied to the solar greenhouse in series.The inlet and outlet temperature of the solar energy collection system is collected,the instantaneous heat collection and the instantaneous heat collection efficiency of the solar energy collection system are calculated,and the actual engineering application effect of the solar energy collection system is analyzed as the evaluation index of thermal performance.The influence of solar radiation intensity and wind speed in the tube on the instantaneous heat collection and efficiency of the solar collector system is measured and analyzed.The accuracy of the optical model and heat transfer model of the collector is further verified.During the experiment,the accumulated heat of solar energy collection system in sunny days was 14～34MJ,and the total solar energy of 633 MJ was provided by the solar energy collection system in 28d.In this paper,the structure of double tube and multi curved groove air collector is optimized,and the influence of various factors on the collector performance is analyzed.The collector is applied to the actual project to test its heat collection effect.The research results can provide reference for the structure optimization and application of double tube and multi curved groove air collector in the solar greenhouse in Lanzhou area.