Portal de Periódicos da CAPES

An evaluation of a transverse slatted flat plate collector

1982; Elsevier BV; Volume: 28; Issue: 2 Linguagem: Inglês

10.1016/0038-092x(82)90287-0

1471-1257

K.I. Guthrie, W.W.S. Charters,

Solar Energy Systems and Technologies

Abstract It is generally accepted that the insertion of a type of honeycomb structure into the air gap between the absorber plate and the transparent cover of a flat plate solar collector will suppress convection if the honeycomb dimensions are matched to the particular dimensions and operating temperatures of the collector. However relatively little research has been carried out to characterise the effectiveness of a convection suppression device under actual operating conditions. This paper surveys the experimental work carried out at the University of Melbourne, Mechanical Engineering Department, and its relationship to other experimental and theoretical research, reported in the literature. The experimental program involved the comparative testing of two collectors, identical except that one was fitted with a convection suppression device made of parallel glass slats placed laterally across the collector between the absorber plate and the cover glass. Testing was carried out in a laboratory situation with five convection suppression devices of differing aspect ratio ( 0.625 1 – 4.8 1 ), and the most effective of these devices (aspect ratio 4.8 1 ), was tested in the Melbourne University Solar Testing Area under a range of actual operating conditions. In the laboratory tests, the ability of the honeycomb to suppress convection was tested, whilst in the outdoor tests, the influence of the honeycomb on the transmission of solar radiation to the absorber plate was also evaluated. It was found that at high operating temperatures the convection suppression device gave rise to considerable improvement in performance. A forty percent improvement in instantaneous thermal efficiency was produced for fluid temperatures of approx. 100°C. However, if the collector is not oriented correctly the overall improvement in thermal performance will not be as large, due to the decrease in solar transmittance caused by the honeycomb. This indicates the probable need for some form of collector tilt adjustment during the year if the long-term thermal performance is to be optimised.