A 20 m long parabolic trough collector with an aperture width of 3.5 m has a pipe receiver of 50 mm outside diameter and 40 mm inside diameter and a glass cover of 90 mm in diameter. If the space between the receiver and the glass cover is evacuated estimate: a) the overall collector heat loss coefficient (4 marks) b) temperature of the glass (2 marks) c) the useful energy gain, (2 marks) d) the exit fluid temperature. (1 marks) The following data are given: Absorbed solar radiation: 500 W/m. Receiver temperature: 260. Receiver emissivity: 0.92. Glass cover emissivity: 0.87. Circulating fluid:1350 J/kg-K. Entering fluid temperature: 220C Mass flow rate 0.32 kg/s. Heat transfer coefficient inside the pipe: 330 W/m-K. Tube thermal conductivity: 15 W/m-K. Ambient and sky temperature: 25C. Wind velocity: 5 m/s.