A solar flux of 700 W/m*m is incident on a flat-plate solar collector used to heat water. The area of the collector is 3 m*m , and 90% of the solar radiation passes through the cover glass and is absorbed by absorber plate. The remaining 10% is reflected away from the collector. Water flows through the tube passages on the back side of the absorber plate and is heated from an inlet temperature Ti to an outlet temperature To. The cover glass, operating in at temperature of 30 C, has emissivity of 0,94 and experiences radiation exchange with the sky at -10 C. The convection coefisient between the cover glass and the ambient air at 25 C is 10 W/m*m K.
a) Perform an overall energy balance on the collector to obtain an expression for thr rate at which useful heat is collected per unit ares of the collecter , Q. Determine the value Q ?
b) Calculate the temperature rise of the water , To-Ti if the flow rate is 0,01 kg/s. Assume the spesific heat of the water to be 4179 J/kg.K ?
c) The collector efficiency N is defined as ratio of the useful heat collected to the rate at which solar energy is incident on the collector. What is the value N ?