A concentrating solar collector consists of a parabolic reflector and a collector tube of diameter D, through which flows a working fluid that is heated with concentrated solar irradiation. Throughout the day, the reflector is slowly repositioned to track the sun. For wind conditions characterized by a steady, horizontal flow normal to the tube axis, the local heat transfer coefficient on the tube surface varies, as shown in the schematic for various reflector positions.
(a) Estimate the value of the average heat transfer coefficient over the entire collector tube surface for each of the three cases.
(b) Assuming the tube receives the same amount of solar irradiation in each case, which case would have the highest collector efficiency?