Thermal performance of solar air collector with transparent honeycomb made of glass tube

Abstract

Transparent honeycomb structure with thin-walled glass tube as the honeycomb unit is designed and applied to a flat-plate solar air collector. Experiments are performed for solar collectors with six different honeycomb sizes. The emphasis is to study the effects of diameter and aspect ratio of the honeycomb unit on the transmittance and efficiency of the solar collector. It is shown that for the same diameter but different aspect ratios, there are large temperature differences between the collector’s exits; the smaller the aspect ratio, the larger the exit temperature, with a maximum difference of 10°C; for the same aspect ratio but different diameters, the temperature differences are small; the maximum temperature difference between the collectors with and without honeycombs is 12°C. A theoretical expression for the honeycomb transmittance is derived with a simplified method. The result shows that the honeycomb transmittance is only related with the aspect ratio and the materials’ optical properties but not the actual size of the honeycomb.