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 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 flow from absorber to water flowing in tube. 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 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 contact i.e. having additionally improved contact between absorber and tube The results indicate noticeable increase in the collector efficiency with kkontakt - up to 30% when compared to the test results for the collector with the worse contact.