Compound Parabolic Concentrator Solar Collector Research Articles

Charcoal-methanol adsorption refrigerator powered by a compound parabolic concentrating solar collector

A compound parabolic concentrating solar collector (CPC) of concentration ratio 3.9 and aperture area 2.0 m 2 was used to power an intermittent solid adsorption refrigerator and ice maker using activated charcoal (carbon) as the adsorbing medium and methanol as the working fluid. The copper tube receiver of the CPC was packed with 2.5 kg of imported adsorbent 207E3, which was only utilised when the performance of activated charcoal (ACJ1, produced from local coconut shells) was found to be inferior to the imported adsorbent. Up to 1 kg of ice at an evaporator temperature of −6°C was produced, with the net solar coefficient of performance (COP) being of the order of 0.02. Maximum receiver/adsorbent temperature recorded was 154°C on a day when the insolation was 26.8 MJ/m −2. Temperatures in excess of 150°C are undesirable since they favour the conversion of methanol to dimethyl ether, a noncondensable gas which inhibits both condensation and adsorption. The major advantage of this system is its ability to produce ice even on overcast days (insolation ∼ 10 MJ/M −2).

Analysis of the incidence angle of the beam radiation on CPC

Analytic expressions have been derived for the projected incidence angles ϑ l and ϑ t from a two-dimensional compound parabolic concentrator solar collector. For a CPC the fraction of the incident rays on the aperture at angle ϑ, which reaches the absorber, depends only on the ϑ l angle. In this paper, a mathematical expression for ϑ l and ϑ t has been calculated to determine the times at which acceptance of the sun's beam radiation begins and ceases for a CPC consisting of arbitrary orientation.

A Numerical Study of the Natural Convection in CPC Solar Collector Cavities with Tubular Absorbers

The laminar free convection in a compound parabolic concentrator (CPC) solar collector cavity is numerically simulated using the finite element method. Results are presented for representative CPC collectors with tubular absorbers of concentration ratio 2. The effect of Grashof number, truncation and tilt angle were investigated. Generally, higher rates of heat transfer between the tubular absorber and the flat cover plate of the cavity are associated with larger Grashof numbers and shallower cavities. The maximum heat transfer rates occur when the tilt angle is about 60 deg. Contour plots are obtained for the field variables and these provide an insight into the spatial characteristics of the convective mechanisms within the cavity.

Truncation of CPC solar collectors and its effect on energy collection

Analytic expressions are derived for the angular acceptance function of two-dimensional compound parabolic concentrator solar collectors (CPC's) of arbitrary degree of truncation. Taking into account the effect of truncation on both optical and thermal losses in real collectors, we also evaluate the increase in monthly and yearly collectible energy. Prior analyses that have ignored the correct behavior of the angular acceptance function at large angles for truncated collectors are shown to be in error by 0–2% in calculations of yearly collectible energy for stationary collectors.