Abstract
Abstract An experimental investigation was made into the internal, laminar-flow, heat-transfer characteristics of a tube similar to the type used in tube-in-strip solar collector plates. For such a tube it was shown that there could be a significant variation in the circumferential wall temperature. Some evidence was obtained that this could lead to higher heat-transfer rates than would be obtained in a tube with uniform wall temperature. It was found that 100 Btu per hr ft2 deg F could be justified for the film heat-transfer coefficient in the calculation of fin-efficiency factors for solar collectors whereas it has been the practice in recent publications to use values of 40 to 60 Btu per hr ft2 deg F. A study of the flow characteristics in the conventionally laminar region showed that unsteady effects, indicated by temperature fluctuations, existed at Reynolds numbers well below the usual lower limit of transition at a Reynolds number of 2000. It was concluded that early transitional effects were being induced by natural convective cross circulation.
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