Designing and Evaluating an Innovative Solar Air Collector with Transpired Absorber and Cover

Abstract

Applying solar collectors is a popular tool for harnessing solar energy. In this work, a flat plate solar air collector was investigated under direct solar radiation in an endeavor to enhance the thermal efficiency of solar air collector with a slatted glass cover, perforated absorber aluminum sheets (porosity 0.0177, 0.0314 and absorber thickness of 1.25, 2.5 mm) which is the most suitable for a solar dryer. The effects of porosity and thickness on absorber performance of collector were evaluated. Six levels of air mass flow rates (0.0056 to 0.0385 kg m −2 s −1 ) were adopted. The tests were conducted in three replications on very clear sky days in September and October. The experimental results showed that thermal efficiency of collector was increased by an increase in the porosity of the absorber. The absorber with lower porosity showed a better thermal efficiency at lower air mass flux. In the minimum air flow rate, absorber efficiency with porosity 0.0177 and 0.0314 was 0.31 and 0.29, respectively, whereas at the maximum flow, efficiency showed an enormous change of 0.83 and 0.88, respectively. This solar air heater can be used for drying agricultural products, heating the space of greenhouse, and so forth.

Recent investigations in solar flat plate collectors

“…Zomorodian and Zamanian [20] studied two porous aluminum absorbers painted matt black. with effective surface area 106 × 75 cm, porosity 1=0.0177 (hole diameter 3 mm and pitch of 2 cm) and 2=0.0314 (hole diameter 2 mm and pitch of 1 cm) and thicknesses of 1=1.25 and 2=2.5 mm to investigate the porosity and thickness effect on air heater thermal efficiency at flow rates 0.0056 to 0.0385 kg m 2 s. A maximum thermal efficiency of 0.88 was achieved for the most porous and thicker absorber plate at the highest air mass flow rate, but at very low air flow rates the absorber porosity showed a reversed effect on the efficiency.…”

“…20 Influence of the rings attached on the inside of tubes [13] Water outlet temperature was increased 21 glass cover incorporating lenses [15] Increases the efficiency and outlet temperature 22 Double glazing with an argon gas filled between two glass panes [16] Increases the efficiency 23 Various inserts in tube [19] Mesh insert performs best in laminar regime, in turbulent range, concentric coils is better 24 Porous aluminum absorbers [20] Maximum efficiency for the more porous and thicker absorber at the highest air mass flow rate, but at very low air flow rates the absorber porosity shows a reversed effect 25 collector with heat storage materials such as sand, sand with iron scraps, gravel and gravel with iron scraps [25] Gravel with iron scraps gives better efficiency than other storage materials VII. CONCLUSION Change in geometric features of collectors discussed.…”

Thermal Performance Study of Solar Air Dryers for Cashew Kernel: A Comparative Analysis and Modelling Using Response Surface Methodology (RSM) and Artificial Neural Network (ANN)

“…Considerable efforts have been made to introduce solar dryers of various types for the drying process, especially for cashew kernel drying, to replace conventional systems. Design and testing of several types of single, double, and multipass solar air dryers are accomplished for evaluating their performance characteristics [5,6]. Seshachalam et al [7] constructed an indirect three-pass solar dryer for drying carrot pieces and examined its effectiveness.…”

Sustainable Energy for Drying of Cashew Kernels – Experimental Research

“…Small and cottage industries rely on the local supply and the processing is mostly during the summer between February to May. Solar air heating systems have been used for drying several agricultural and food products [9]. These can be utilized to replace present conventional systems in cashew processing industries.…”