EVALUATION OF SOLAR COLLECTOR

Abstract

An investigation for the evaluation of the per-formance of flat plate solar collectors without any tracking facility has been carried out both experimen-tally and analytically. An experimental facility, consisting of two flat plate solar collectors having aluminium tubes of I.D. 19 mm with collector area 1.35m x im and in x in and one flat plate solar collector having copper tubes of I.D. 19 mm with collector area in x lm, was raised for this investigation. All the three collectors had an ordinary single glass cover plate. The distance between the collector plate and glass cover plate was maintained constant and equal to 100 mm for all the three collectors. The experiments were conducted for the Indian conditions specially prevailing at Roorkee in the months of May and June 1982 from 1000, hours to 1700 hours. The flow rate of the heat transfer medium i.e. water was varied from , 2.5 x 10-3 to 10 x 10-3 kg/s with the help of a constant head water tank. The experimental facility had suitable provisions for the measurement of flow rate and tempera-tures. The incident solar energy radiations were measured with the help of a pyranometer. The study has revealed that in all the collectors it is possible to obtain maximum rise in temperature of i1. the water between 1100 hours and 1400 hours and specifi-cally at 1200 hours when the sun is just at the top. Further, the study has revealed that the useful energy gain is always more for the collector having larger collector area. Thus the aluminium collector having collector area 1.35m x lm always collects more energy in comparison to other two collectors employed, even though the material of construction of one of these two collector tubes is copper. However, for the same collec-tor area i.e. in x lm; the collector having copper tubes is more efficient than the collector having aluminium tubes. Collector having copper tubes is 10 to 20 per cent more efficient than its counter part, depending upon the flow rate of water in the tubes. A distinct phenomena observed in this investigation is that the rise in temperature of the water flowing in collector tubes is being influenced by the residence time of the fluid at lower values of Reynolds number i.e. upto a value of 700. Upto this value the temperature rise decreases as Reynolds number increases. However, beyond this value of 700 there is no change in temperature rise with increase in the value of Reynolds number. This suggests that in the former case residence time of the fluid in tubes is the controlling factor while in the latter case inside heat transfer coefficient also plays an equal role and both the factors influence the rise in temperature....