Question 1 A cross-section of a collector tube assembly in a domestic solar water heater is shown in Figure Q1. Water fl

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Question 1 A Cross Section Of A Collector Tube Assembly In A Domestic Solar Water Heater Is Shown In Figure Q1 Water Fl 1 (134.7 KiB) Viewed 56 times

Question 1 A cross-section of a collector tube assembly in a domestic solar water heater is shown in Figure Q1. Water flows at 0.014 kg s-through the thin-walled copper inner tube of diameter 22 mm and length 12 m, which is surrounded by a glass (soda lime) outer tube of outer diameter 50 mm and wall thickness 3 mm. The annular space between the tubes is filled with air. The convection heat transfer coefficient, between the internal air and both of tubes, is 8 W m ²K-!. The glass outer tube is exposed to ambient air at 18°C, with a convection heat transfer coefficient of 65 W m-2K-!, and the effective sky temperature is -12°C. Mirrors (not shown) are arranged so that solar irradiation is incident on the whole surface of the inner tube at a rate of 380 W m2, and the whole surface of the tube is effectively exposed to the sky. The emissivity of the tube is 0.85 for all wavelengths and the glass is fully transparent for all wavelengths. Throughout this question, consider a location where the water temperature is 37°C. copper inner tube glass outer tube 380 W/m2 irradiation on copper inner tube air water air, 18°C, 65 W m2 K-1 022 mm Ø50 mm Figure Q1 Cross-section of a solar collector tube assembly. (a) Calculate the convection heat transfer coefficient between the tube wall and the water. [5] (b) Draw and label a thermal resistance network to model all of the heat transfer processes in the solar collector. [6] (c) Use the thermal resistance network to estimate the temperature of the inner tube. If your method is iterative, take an initial guess of 40°C, calculate just one iteration, and explain how you would proceed. [14]