The Multi-Directional Solar Thermal Integrated Absorber with Evacuated Tube (MSiA-ET) in Solar Air Dryer Applications

Abstract

An efficient solar collector design that effectively absorbs solar energy and converts it into heat is required during intermittent solar radiation. Existing Flat Plate Collector (FPC) and Heat-Pipe Evacuated Tube Collector (HP ETC) are designed for water heating required storage tanks, while an additional heat exchanger is required for air heating application which leads to extra spacing and cost. The installation also needs to be tilted at the correct angle and positioned to south/north facing to optimize the system performance. These could lead to design limitations. Therefore, this study aims to design, develop and investigate the thermal performance of an Evacuated Glass-Thermal Absorber Tube Collector (EGATC) for air heating applications. EGATC was designed from a conventional HP ETC, and the performance was compared through parameter and performance experimental setup. The three days performance experiments showed EGATC performed better with daily outlet temperature increased by 9.0%, 7.2%, and 4.9%, respectively, with an average of 7.0% compared with HP ETC. EGATC also had greater efficiency compared to HP ETC, with the average efficiency for EGATC being 51.3% compared with HP ETC's 41.8%. EGATC's inner absorber was designed to create a double pass flow with the ventilated chamber. The parameter experiment shows the design could increase the outlet temperature by a difference of 6.3% (for stainless-steel inner absorber compared with insulation material inner absorber). Regarding energy storage, the stainless-steel inner absorber also had an advantage compared to the insulation material inner absorber, with a 1.3% difference. On the effect of other parameters such as inner absorber surface area air contact (perforated fin), outer absorber selective coating surface, outer absorber wall thickness, double layer non-vacuum glass tube, single layer transparent outer glass tube, and single-layer thin film inner glass tube was investigated by parameter experimental setup on energy storage. It was proven that the outlet temperature, energy store, and energy buffer could be enhanced with the combination of wind speed 0.9 m/s, zero (0) perforated fin, non-coating outer absorber, and 1 mm outer absorber wall thickness. It was also reported that double-layer vacuum glass tubes promise better thermal performance enhancement compared with double-layer non-vacuum glass tubes, single-layer transparent outer glass tubes, and single-layer thin film inner glass tubes. The mathematical equation of each EGATC component was formulated based on the first law of thermodynamics. The total acceptable error of 5% shows that the model at each node was valid. The performance curves for those 0 fins (equation), 0 fin (experimental), and 3 fins (experimental) were obtained. The results showed that the efficiency (collector + storage) was affected by the number of fins. The efficiency (collector + storage) was 68.7%, 71.2%, and 71.0%, respectively. In conclusion, the application of EGATC in air heating applications proved beneficial to the application of solar drying processes, especially in equatorial climate countries such as Malaysia.