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A south-facing flat plate solar water heater with a tilt angle of 45 degrees is located on top of the RLC building at Manhattan College, with a latitude of 41°N. The water heater provides hot water for the RLC building and has the following specifications: Single glazing cover with at=0.0370, where "pis the glazing thickness and "a" is the glazing absorptivity. The absorbing plate to cover the glazing distance is 20 mm. The absorber plate absorptance a=0.9 (independent of direction) The glass emittance, e=0.85 The wind heat transfer coefficient, 8 W/m² °C, and ambient air temperature is 8°C. The backside of the solar heater is well insulated. 1. Estimate the glass cover transmittance along, 30° solar incident angles. The glass refractive index is 1.6 (10 points). 2. An initial estimate of the glass cover temperature is 30°C and the absorbing plate average temperature is 110°C. Calculate the radiative heat transfer coefficient between the plate and glass cover (15 points). 3. Calculate the convective heat transfer coefficient between the absorbing plate and glass cover. Use v =1.96x10m/s?, k-0.0293 W/m°C and Pr=0.7 for air properties (15 points) 4. Estimate the loss coefficient from the absorbing plate (15 points). 5. Calculate the collector efficiency factor when the loss coefficient is 3 W/m²K, the absorbing plate thickness is 0.7 mm, and are consist of tubes with diameters of 12mm. The spacing between tubes is 180mm. The absorbing plate is made of a copper alloy with thermal conductivity of 380 W/m °C. The heat transfer coefficient between the tube wall and water is 250 W/m2°C. The thermal resistance of the bond between tubes and plate is zero (15 points)
6. A2mx2m solar absorber plate is at 400 K while it is exposed to solar irradiation. The surface is diffuse and its spectral absorptivity is a 0, for 0> 2. >0.5 m a=0.8, for 0.5 g mà >lum a-0, for mi >2um a -0.9 for å >2um Determine absorptivity, reflectivity and emissivity of the absorber plate (15 points) 7. A counter-flow heat exchanger is located between a solar water heater and a water storage tank. The hot fluid coming out of the collector is an antifreeze fluid with a specific heat of 3850 J/kg K, a flow rate of 1.25 kg's and a temperature of 62°C. The fluid on the storage tank side is water at a flow rate of 0864 kg's and enters the heat exchanger at 350C. The UA of the heat exchanger is 6500 W/K. Calculate the heat transfer between the two fluids and outlet temperatures. (15 points)