Ma, Fangfang, Gao, Wenfeng, Liu, Tao, Lin, Wenxian, and Li, Ming (2013) An experimental study on the impacts of key parameters of all-glass evacuated tubes on the thermal performances of all-glass evacuated tube solar water heaters. Journal of Renewable and Sustainable Energy, 5. 023140. pp. 1-14.

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Abstract

In this paper, the effects of the stagnation parameter Y, the solar irradiance under stagnation H, and the average heat loss coefficient ULT of individual all-glass evacuated solar collector tubes, which were identified as the major parameters to characterize the thermal performance of the tubes, on the thermal performance of all-glass evacuated tube solar water heaters consisted of such evacuated tubes were investigated by experiments. The experiments were conducted to obtain the heat gain Qs produced by six all-glass evacuated tube solar water heaters with the similar specifications but manufactured by different producers. Each heater consisted of 20 all-glass evacuated solar collector tubes and one tube from each heater was selected randomly to measure its Y, H, and ULT . The experimental results show that both H and ULT have effects on Qs , with Qs decreasing when H or ULT increases, but H has more significant effects on Qs than ULT does. However, Y does not have significant effects on Qs . It is apparent that one effective way to increase the heat gain of an evacuated tube solar water heater is to reduce H and ULT of individual all-glass evacuated solar collector tubes. An error analysis was conducted which clearly shows that the errors caused by the uncertainties associated with the measured Qs , Y, H, and ULT have negligible effects on these results.

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