| Flat-plate solar collector(FPSC)is the device that converts solar radiation energy into thermal power.And FPSC has the advantages of simple structure,strong pressure bearing ability and high thermal efficiency,it is one of the most important ways of solar energy thermal utilization.However,at present,the FPSC has some problems of durability and reliability.Such as the thermal performance reducing because of the exposure aging,the water samples contain heavy metal elements because of stagnation and so on.Based on the durability and reliability of the FPSCs with three different coatings(the blue-film coating,the black chromium coating and the anode oxidizing coating),the research of thermal performance reduction of FPSCs before and after exposure aging were carried out.Meanwhile,the kinds and contents of heavy metal elements in water samples of stagnation were also investigated experimentally.The main research work of this paper are as follows:(1)According to the basic structure of the FPSC,the energy balance equation in the process of photothermal conversion were analyzed,and the heat loss of each part of FPSC were also shown.Meanwhile,based on the variation of the optical performance of the heat-absorbing coating and thermal efficiency,the calculation formula for measuring the FPSCs thermal performance attenuation because of exposure aging was given.(2)Based on the FPSC thermal performance testing platform and the steady-state experimental method in national standard,the thermal performance of FPSCs with three coatings(the blue-film coating,the anode oxidizing coating and the black chromium coating)before and after exposure aging were tested.And the absorptivity and emissivity of the three coating samples before and after exposure aging were also tested,so the aging degree of the coating surface was also observed by means of electron scanning microscope.It was shown that the thermal performance of the blue-film coating FPSC,the black chromium coating FPSC and the anode oxidizing coating FPSC were 0.76,0.73 and 0.69,respectively.After exposure aging,the thermal performance decreased by 9.21%,8.22% and 5.8%,respectively.The absorptivity of three different coating samples after exposure aging was above 0.9,and the highest emissivity was 0.1,0.14 and 0.27,respectively.So the results showed that the exposure aging had smaller influence on the absorptivity of the heat-absorbing coatings,and had a greater influence on the emissivity.Although the thermal performance of blue-film coating FPSC is higher,its durability and reliability is poor.(3)The kinds and contents of heavy metal elements in water samples of the FPSC after stagnation were detected by ICP-OES(inductively coupled plasma optical emission spectrometry).So the changeable rule of the heavy metal elements content with the stagnation time were also obtained.It was shown that 9 kinds of heavy metal elements(Pb,Ni,Cu and so on)were detected in water samples of FPSCs stagnation.And the changeable rule of heavy metal content in water samples showed that the heavy metal content increases with the FPSCs stagnation time,the heavy metal content increases to the peak value and then decreases with the FPSCs stagnation time,and then it decreases to the lower content gradually.By comparing and analyzing the detection results with the water quality standards for urban water supply,the contents of heavy metal elements As,Pb and Sb in water samples of FPSCs stagnation were exceeded the limit of the standard in varying degrees.The research work were carried out in this paper showed that FPSCs should avoid long-time exposure and stagnation as far as possible,and the conclusions provide a certain reference for the efficient and stable operation of the FPSCs. |
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