Optimization Study of Collector’s Absorber Coating Parameters for Solar Thermal Heat Collection Applications

Abstract

The ability of a solar collector to transform (absorb) as much of the solar energy it receives into useful heat, minimizing loses of the converted energy to the environment, determines the effectiveness of the collector. These capabilities are functions of the absorber plate parameters, design and ambient conditions. This study experimentally examined the effect of absorber coating vis-a-vis coating thickness on the overall performance of flat-plate solar collectors.  The samples consist of three mild steel absorber plates of 50mm by 10 mm and 1mm of thickness each, named Samples A, B and C. Sample A was uncoated, a thin film (less than 1mm thickness) of acrylic resin is deposited on Sample B, while Sample C was thickly coated with the same resin at a thickness of approximately 1mm. It was discovered that acrylic resin actually increases the solar absorbance of the thin (lightly) coated absorber plate sample by 21%, over the uncoated sample. It was noted that when the layers of coatings were increased (thick coating), the absorbance dropped sharply by about 50% lower than that of thin coating (lightly coated). Thick coating reduced the absorbance of solar energy of uncoated sample by about 32%. It is therefore evident that lightly coated metal sample have a far better absorbance value than that with thick coating. In order to validate the result, the samples were subjected to an on-site solar thermal investigation under the same atmospheric conditions. The Samples A, B and C recorded average plate temperatures of 68oC, 92oC and 85oC respectively. Therefore, the thinner the coating of a substrate, the higher the absorptivity.