engleski

INFLUENCE OF THE GOODNESS OF APSORBER AND TUBE CONTACT ON FLAT PLATE SOLAR COLLECTOR EFFICIENCY

This work analyses the influence of the contact between absorber and tube, as well as the influence of the emission and absorbsion coefficient of a selective coat and the transmission coefficient of glass, on the flat plate type solar collector efficiency. The analysis is performed experimentally and computationally by varying the overall heat transfer coefficient kkontakt defined for the heat flux from an absorber to water flowing in a tube when analysing influence of contact on efficiency, and by varying &#949 ; ; (emission coefficient), a (absorption coefficient) and &#964 ; ; (transmission coeficient) when analysing corresponding influences. First part of the paper provides the test data for two collectors of the same construction but having different number of the brazed joints between absorber and tube. Better contact yields in average 15-20% increase in the efficiency. Based on the measurements the overall heat transfer coefficient kkontakt is computed for both tested collectors in order to investigate a possible further increase in the collector efficiency with higher values of kkontakt i.e. having additionally improved contact between absorber and tube. The results indicate noticeable increase in the collector efficiency with kkontakt - up to 40% when compared to the test results for the collector with the worse cThis work analyses the influence of the contact between absorber and tube, as well as the influence of the emission and absorbsion coefficient of a selective coat and the transmission coefficient of glass, on the flat plate type solar collector efficiency. The analysis is performed experimentally and computationally by varying the overall heat transfer coefficient kkontakt defined for the heat flux from an absorber to water flowing in a tube when analysing influence of contact on efficiency, and by varying &#949 ; ; (emission coefficient), a (absorption coefficient) and &#964 ; ; (transmission coeficient) when analysing corresponding influences. First part of the paper provides the test data for two collectors of the same construction but having different number of the brazed joints between absorber and tube. Better contact yields in average 15-20% increase in the efficiency. Based on the measurements the overall heat transfer coefficient kkontakt is computed for both tested collectors in order to investigate a possible further increase in the collector efficiency with higher values of kkontakt i.e. having additionally improved contact between absorber and tube. The results indicate noticeable increase in the collector efficiency with kkontakt - up to 40% when compared to the test results for the collector with the worse contact. Further analysis have shown a significant increase of up to 10% in collector efficiency when both increasing the values of &#964 ; ; from &#964 ; ; =0.9 to &#964 ; ; =0.96 and decreasing the values of &#949 ; ; from &#949 ; ; =0.106 to &#949 ; ; =0.05.ontact. Further analysis have shown a significant increase of up to 10% in collector efficiency when both increasing the values of &#964 ; ; from &#964 ; ; =0.9 to &#964 ; ; =0.96 and decreasing the values of &#949 ; ; from &#949 ; ; =0.106 to &#949 ; ; =0.05.

solar collectors; measurements; contact; absorber emissivity; glazing transmittance; efficiency

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