Solar radiation is incident on the glass cover of a solar collector at a rate of 700 W/m². The glass transmits 88 percent of the incident radiation and has an emissivity of 0.90. The entire hot water needs of a family in summer can be met by two collectors 1.2 m high and 1 m wide. The two collectors are attached to each other on one side so that they appear like a single collector 1.2 m × 2 m in size. The temperature of the glass cover is measured to be 35°C on a day when the surrounding air temperature is 25°C and the wind is blowing at 30 km/h. The effective sky temperature for radiation exchange between the glass cover and the open sky is 240°C. Water enters the tubes attached to the absorber plate at a rate of 1 kg/min. Assuming the back surface of the absorber plate to be heavily insulated and the only heat loss to occur through the glass cover, determine

(a) The total rate of heat loss from the collector,

(b) The collector efficiency, which is the ratio of the amount of heat transferred to the water to the solar energy incident on the collector, 

(c) The temperature rise of water as it flows through the collector.

Transcribed Image Text:

Tsky = - 40°C Solar Solar collector 35°C Alr radlation 25°C