Characteristic Research Of Parabolic Trough Collector Under Nonuniform Energy Flux Density In Cold Region

Cold regions have high latitude,low ambient temperature,small amount of rainfall,and much wind and sand,so dust deposition of the mirror and the end loss of parabolic trough collector have significant influence on thermal characteristic of concentrator.Based on the climate characteristics of cold region,this paper is that dust accumulation of the mirror and end loss of the parabolic trough collector are to calculate and simulate the characteristic research of the parabolic trough collector.Furthermore,a energy flux density distribution measurement system of parabolic trough collector is developed and studied by experiments.Main research work includes following aspects:(1)Based on the characteristic of parabolic trough geometry and application of dimensionality reduction method,the influences of many factors,including a solar incident angle??the deviation distance of distance of the absorber axis along the X-axis and Y-axis and the system tracking error,are simulated and analyzed for energy flux density distribution of absorber in this paper.Different?corresponds to different the absorber energy flux density distribution and its peak value,and the peak energy flux density increases with the increase of absorber axis along the X-axis.The absorber energy flux density distribution is different with the increasing of positive and negative deviation of absorber axis along the Y-axis.As the system tracking deviation increases,the intercept factor gradually decreases.And when the tracking deviation of the system is more than 10 mrad,the absorber energy flux density distribution has basically lost its original distribution.(2)Theoretical research on the effect of dust deposition on the concentrating and heat collecting characteristic of parabolic trough collector are carried out.According to the overlap model,the incident model of dust deposition affecting reflectance of parabolic trough collector can be obtained,and basing on the model and the geometric structure of the mirror,the incident model considering the tilt angle?of parabolic trough collector can be derived.The relative reflectance decreasing value of the mirror is inversely proportional to?,and fitting the indicator function.By setting on the experimental measuring points at different positions of the concentrator,the variation of the decreasing in specular reflectance caused by dust accumulation with different wavelengths of light is studied.The result show that the decrease of relative reflectance of mirror surface at three different positions increase first and then decrease with the inceraesing of the wavelength.Based on the angle of incident model considering the tilt angle of?,a simulation model of dust deposition on the mirror is established to simulate the thermal efficiency of the collector with different dust deposition conditions such as mirror cleaning,mirror half dust deposition,mirror all dust deposition and dust thickness.When the mirror is cleaning,the thermal efficiency of the collector is 75.91%.When the mirror is all dust deposition,the thermal efficiency of the collector is 27.59%.(3)The analysisl research on the end loss of parabolic trough collector with east-west orientation is carried out.The rate of end loss decreases with the length L of the collector.During the period of from morning to evening,the rate of end loss decreases first and then increases with the time,and At 12:30,the minimum value is reached.At the same time,the peak energy flux density in the circumferential direction of the absorber is 48.67kW/m~2.By using infrared thermal image,the temperature gaps of the absober length and the absorber circumferential before and after the end loss are 11.3?and 9.4?respectively.The methods to compensate or reduce the end loss effect by extending the absorber tube,and setting an end plane mirror at one end of parabolic trough collector and inclining an angle of parabolic trough collector are presented,the application condition of different methods is discussed,and feasibility of the methods is analyzed.(4)The energy flux density distribution influence of clean mirror and the natural dust accumulation of 25 days for the mirror are studied experimentally,considering on various deviation factors on the energy flux density distribution of the absorber.By using an CCD camera and Lambert target,experimental investigates on the energy flux density distribution of focus spot of the absorber tube.Clean mirror and its direct normal irradiance is about 50W/m~2 lower than that of the natural dust accumulation of 25 days,while the measured peak value of the clean mirror condition is about 15 kW/m~2higher than that of the natural dust accumulation of 25 days.Meanwhile,obtaining the relative standard uncertainty of the measurement is about 5.39%.