| Trough concentrating solar energy system plays a leading role in the utilization of medium and high temperature solar energy.The existing research mainly focuses on the efficiency of the solar thermal conversion of the trough collector system,and there are few researches on the wind load characteristics of the concentrator and the thermal stress of the absorber in the system.The trough concentrating solar energy heat collec-tion system is mainly built in an open outdoor place,and the wind condition is relatively complex.The arc reflector and the steel beam component of the supporting structure are all wind sensitive structures,so it is very important to study the wind load charac-teristics and structural stability of the trough concentrating device.Most of the existing trough type heat collection systems use the straight vacuum tube as the collector.The vacuum tube has the advantages of small heat loss and high efficiency,but it has high cost and is easy to be damaged in transportation and long-term use.In view of the shortcomings of vacuum tube,a metal cavity absorber based on"black cavity"principle is proposed,which has the same heat collection efficiency as vacuum tube.Based on the analysis of the heat transfer characteristics of the cavity absorber and the optimiza-tion scheme,the thermal stress of the cavity absorber is analyzed and studied,which provides the basis for the optimization of the structural performance and safe and stable use of the cavity.In this paper,the grid Boltzmann method is used to study and analyze the wind load characteristics of the trough condenser,and the mechanical analysis of the support structure of the condenser is carried out.The finite element analysis method is used to analyze the heat transfer characteristics and structure optimization of the metal cavity absorber,and to study and analyze the stress of the cavity absorber under the thermal effect.Through the experiment and calculation simulation method,the heat supply sys-tem with the research object trough condenser and cavity absorber as the main compo-nents is constructed,which is used for tobacco drying,and the reasonable matching between the solar energy collection and the heating system is realized.The research work mainly includes the following contents:(1)Based on the theory of lattice Boltzmann method,the analysis model of trough condenser is established,52 working conditions of actual environment are set up,the flow field distribution of trough condenser is calculated,and the reason is analyzed.The resistance coefficient,lift coefficient and torque coefficient of the condenser under each working condition are obtained.When the top view angle is 0°and the direction angle is 15°,the maximum resistance coefficient is 1.77032;when the top view angle is 60°and the direction angle is 15°,the maximum lift coefficient is-1.91148.When the top angle is 30°and the direction angle is 120°,there is a maximum torsion coef-ficient,which is-0.4545.The wind pressure distribution,eddy current shape and change rule are calculated and analyzed in detail when the top view angle is 60°and the direction angle is 0°.(2)Using ANSYS software to analyze the structural mechanics of the concentrator support structure,and obtain the inherent modal frequency of the structure.By applying different working conditions,the stress and strain changes of the concentrator bracket are obtained.According to the analysis results,the concentrator bracket is optimized and improved.After the optimized design,the first-order natural frequency of the con-centrating device is increased to 6.46 Hz by 5.388 Hz,which avoids the resonance phenomenon of low-order frequencies.After the wind load is applied,the maximum displacement of the optimized support structure is reduced from 12.9 mm to 8.2 mm,which improves system stability and concentrating efficiency.(3)Using the optical principle,the distribution law of photothermal conversion on the endothermic surface of the cavity collector is analyzed.Three kinds of cavity col-lectors with different structures were established.The temperature field and velocity field distribution of the cavity were obtained by simulation calculation,and the cavity structure with better heat transfer performance was obtained.Through the simulation calculation and experimental research,the variation law of the working fluid tempera-ture in the cavity collector with the direct solar radiation intensity,the variation law of the pressure loss inside the pipe and the working temperature,and the temperature var-iation law of the constant temperature inlet working fluid at different flow rates are obtained.(4)By using ANSYS software to study the thermal-stress coupling problem of the cavity collector,the distribution law of thermal stress and strain of the cavity collector is obtained.The research results show that the temperature gradient of the cavity col-lector is divided into the inlet section,the rib part of the cavity and the middle part of the middle outer wall under cooling conditions.During the cooling process,the high temperature area is concentrated in the rib part and the inlet section of the cavity,and the low temperature area is concentrated.The outer wall area of the middle area.Near the exit and the inlet,as well as the maximum thermal strain and maximum stress,the thermal strain and stress in the internal rib area of the cavity are significantly higher than other areas.As the convective heat transfer coefficient of the cavity increases,the maximum equivalent stress increases.In the range1000W/(m~2×k)where the convec-tion coefficient does not exceed,the maximum equivalent stress does not exceed the yield strength of the material.At the same time,the maximum shape variable is in the range of 5.8834mm~5.6061mm,and the first-order natural mode frequency of the cav-ity collector under thermal stress is calculated.It is 90.882 Hz.(5)Based on the condenser,bracket structure and cavity absorber studied in this paper,the experimental platform of tobacco drying is built.The platform provides the heat source with the trough solar energy concentrating and collecting system,and uses the drying pipe to realize the rapid dehydration of tobacco.The movement equation and heat balance equation of tobacco in the process of high temperature air drying are derived.The factors affecting the drying effect,such as speed and temperature,are analyzed by using simulation method,which are consistent with the experimental test data.The best drying condition of tobacco based on the trough solar concentrating sys-tem is determined.The experimental results show that the solar concentrating and col-lecting system can meet the heat demand of 200℃ for tobacco drying. |
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