Simulation And Experiment Study On The Measurement Of The Energy Flux Density On The Focal Plane Based On The Thermoelectric Effect

Dish solar concentrator reflects and converges the incident sunlight on the small size of the focal plane,which greatly improve the flux density and the energy grade of solar energy.The flux density distribution on focal plane is the key factors to evaluate the concentration effect of the condenser and play a decisive role in design,installation and efficiency analysis of the solar concentrator photovoltaic cells and the receivers of concentrating solar power.At present,two methods can measure flux density distribution of the focal plane.The direct method measuring resolution is low,and the indirect method can’t get the real energy flux density values.Therefore,to carry out the focus plane of flux density distribution features of the measuring methods and research significance of the great.On the basis of the current measurement method,a indirect measurement method based on the principle of thermoelectric effect has been proposed,which takes advantage of the armored thermocouple high temperature measurement.Armored thermocouple physical model is constructed by ANSYS software.the thermodynamic functions between flux density and output temperature of thermocouple is obtained by simulation which regards the incident energy flux density as input,the thermal conductivity and surface convection and radiation heat transfer of the armored thermocouple as boundary conditions.The energy flux density of the solar concentrator can be measured by the inverse function of this function.The experimental device is designed to verify the function which is based on the simulation of single thermocouple.The measuring surfaces of the thermocouple and the heat flux sensor are placed at the same focal point of the two Fresnel lens to ensure that the energy flux density of the two measuring surfaces is the same.Then,the relationship between the output temperature of the thermocouple and the energy flux density of the heat flux sensor can be obtained.Comparing the measured and simulated data,the results show that the relative error is less than 5% when the incident energy density is greater than 750kW/㎡.It is necessary to arrange multiple thermocouples to measure the energy flux density of the focal plane of the concentrator.Heat transfers between the thermocouples influence each other.According to the different layout position and the radiation heat transfer between each other thermocouple,The thermodynamic functions between the output temperature and energy flux density of the thermocouples at different positions are simulated,which is based On the heat transfer model of single armored thermocouple.The energy density distribution in the focal plane of the concentrator is measured by the thermocouple test device,and the measured result is compared with the outcome which is gauged by the heat flow sensor.Results show that the energy flux density distribution laws which measured by the two methods are similar.However,comparing with the thermocouple,the focal area of focal plane density profile which measured by the heat flux sensor is smaller,the color map is more slender,and the energy flow distribution curve on the X and Y axis is more steep.Based on the method of thermoelectric effect measurement,energy flux density distributions of nine focal planes which the focal length is from Z = 515 mm to Z = 595 mm every other 10 mm are analyzed.The results show that energy flux is maximum,the size is smallest,the shape is the most standardized at the focal plane of Z = 555 mm.With the increase of the distance from the focal plane,the focal spot becomes divergent,the shape is increasingly irregular.On the receiving surface,the total energy flux is increased,the optical efficiency is improved,the average energy flow is decreased,and the energy condensing ratio is reduced.The influence of the dish concentrator’s focusing effect which caused by the solar position is studied.With the change of the solar position,the focal spot of concentrator increases gradually,the focusing more and more disperse,concentrating effect becomes poor.The direction of the focal spot spread which tested by experiment is consistent with the theory.Along with the change of the solar position,The total energy flow of the receiving surface decreased by 0.3809 kW,the average energy flux density decreased by 38.08kW/㎡,the energy concentration ratio decreased by 53.15,and the optical efficiency decreased by 0.3211.This study provides a new way for the measurement of focal energy density of solar concentrator,and provides reference for concentrating power generation research and receiver structure design.