The Thermal Performance And Model Analysis Of Evacuated Tube Collector On Tilted Surface

Under the general policy of national"13th Five-Year Plan"and industrial restructuring,evacuated tube collectors are facing enormous market investment opportunities.The industry is expected to usher in new development opportunities.At the same time,vigorously promoting the application of solar energy thermal utilization in civil buildings is the necessary way to achieve energy conservation and emission reduction and promote sustainable development.This paper is the evacuated tube collector system of Hebei University of Technology in Tianjin as the research object.On the basis of establishing a more accurate calculation model of solar radiation amount on tilted surfaces,the thermal performance of evacuated tube collectors were investigated experimentally.Then,using Trnsys software as the carrier,the experimental formulas are used to modify the corresponding modules in the software in order to achieve better simulation results.First of all,this paper tested the solar radiation data on the horizontal and tilted surfaces with various tilt angles.A correction method for the horizontal incident angle of the direct radiation was proposed.A coupled calculation model based on the diffuse radiation model is established by calculating and analyzing the diffuse radiation data on tilted surfaces.The results show that the deviation between calculated and measured values can be controlled within 5.3%.Secondly,the main factors influencing the thermal performance of evacuated tube collectors are determined by theoretical analysis,set up a test platform for evacuated tube collector with different layout（horizontal and vertical）.The influence of meteorological conditions,tilt angles,working medium flow rate,reflector plate and other parameters on the thermal performance of evacuated tube collectors are analyzed through experiments.It is found that if the tilt angles of the collector are small,the vertical collector with evacuated tube can be selected.If the tilt angles of the collectors are large,the horizontal collector with evacuated tube is recommended.For the collector with a total area of 2.9m²,the average efficiency of the horizontal collector is 1.4 percentage points higher than that of the vertical collector when the flow rate is 100kg/h.The efficiency of the two collectors is the same when the flow rate is 208kg/h.When the flow rate continues to increase,the efficiency of the 500kg/h vertical collector is 5.3 percentage points higher than that of the horizontal collector.The total heat loss coefficient of the collector is 4.7367 from the test data,and the instantaneous efficiency formula isη=0.852-10.23T_i^*-0.053GT_i^*2.Compared with the formula provided by the manufacturer,it is found that the intercept increases by11.9%.The main reason is that the metal reflector on the back of the collector has reflective effect on sunny days,which makes the collector efficiency significantly improved.Finally,in this paper,FORTRAN language is used to modify the solar radiation calculation model in meteorological module,At the same time,the simulation system of TRNSYS vacuum tube collector is established by recompiling the existing modules of collector and modifying the coefficient of incident angle of the software.Through the verification and improvement of the system,the relative deviation between simulation results and test data is finally reduced from 12.6%to 6.4%.by using this simulation model,the optimum angle of solar radiation in Tianjin area is about 30°from the south region and the optimum angle in other different latitudes.