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UBC Theses and Dissertations

Stitch weld effect on solar collector efficiency factor Lo, Andy Ka-Ming


The thermal effects of stitch welding the coolant conduits of a water-cooled flat plate solar collector to its absorber plate have been studied. A physical model of the heat transfer process from the plate to the fluid flowing inside the tube has been presented. The heat transfer coefficient based on the difference between bond temperature and fluid bulk mean temperature is an important factor in determining the collector efficiency factor F'. The upper and lower limits of the actual value of F' have been predicted by considering two extreme boundary conditions to which the fluid is subjected. For a thick and conductive tube wall, F' does not depend on spot size and spot spacing, and tends to an upper limit of 0.883. For a thin and non-conductive tube wall, the boundary condition comprises of a series of step changes in both the axial and circumferential directions of the heat flux. In this case, the heat transfer coefficient and hence F' approach their lower limits which are determined by the welding spot configuration. It was also found that F' increases with the following parameters: the spot angle; the percentage of tube length being welded; and the number of spots among which the welding is being distributed. Furthermore, the temperature distribution inside the fluid has also been computed for this case.

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