| In order to study the operation and control characteristics of trough collector,this paper simulates and experimentally studies the operation law of trough collector and the control mode of outlet temperature.The main contents and conclusions are as follows:(1)The thermal performance of evacuated collector tube is analyzed.A one-dimensional heat transfer model and a one-dimensional steady-state heat loss model of vacuum collector tubes are established.The accuracy of the heat loss model is verified by comparing with the experimental data of Schott 2008 PTR70 evacuated tubes.The GUI is used to create a calculation interface for heat loss,which can quickly obtain the heat loss data of the vacuum collector and analyze the factors affecting the heat loss.The results show that the heat loss of the collector and the temperature of the glass tube increase with the increase of the temperature of the absorption tube,the temperature of the outer wall of the glass tube increases with the increase of the temperature of the environment,and decreases with the increase of the wind speed.The influence of ambient temperature and wind speed on heat loss of collector tube is negligible.(2)The simulation model of trough collector system is established by TRNSYS software.The steady-state performance of the system is analyzed.The dynamic performance of the collector system is analyzed by using the radiation conditions of sunny and cloudy weather in June in Nanjing.The results show that the outlet temperature of the working substance of the collector is positively correlated with DNI and inlet temperature,and negatively correlated with the flow rate of the working substance.The sudden change of DNI and working fluid flow is delayed greatly,and there is a hidden danger of over-temperature for the sudden decrease of flow and outlet temperature;the flow trend of heat conducting oil is basically consistent with that of DNI;furthermore,the collection efficiency of the collector system is larger at sunrise and sunset,and decreases slightly at noon when DNI is higher.(3)An experimental platform of trough collector system with a length of 48 m and an opening width of 5.77 m was built.The change of collector inlet and outlet temperatures with DNI,collector efficiency and heat loss per unit length were tested and studied,and compared with the simulation results.The results show that the trend of temperature difference between inlet and outlet of working fluid and DNI of trough collector is basically the same,and the instantaneous heat collection efficiency ranges from 0.51 to 0.64,the error between experiment and simulation is less than 3.7%;with the increase of flow rate,the heat loss per unit tube length decreases gradually,and the heat loss per unit tube length decreases.The thermal efficiency increases gradually.(4)The outlet temperature of trough collector is controlled by means of fuzzy PID control.With the help of Simulink,a fuzzy-PID control model for outlet temperature of trough collector is built,and the difference between the fuzzy-PID control mode and the traditional PID control mode is compared.The results show that compared with the traditional PID control,the fuzzy PID control has no overshoot,the adjustment time is shortened by 320 seconds,and it can reach a stable state 100 seconds ahead of the time of DNI disturbance.The deviation of the exit temperature control of the fuzzy PID control mode is(±0.8℃)in sunny days and(±1.5℃)in cloudy days. |
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