Investigation on the thermal performance of evacuated glass-thermal absorber tube collector (EGATC) for air heating application

Existing design of Heat-Pipe Evacuated Tube Collector (HP ETC) for solar water heating require storage tank and additional heat exchanger required for air heating application which leads to the extra spacing and costing requirement. HP ETC have better thermal performance to produce high outlet temperature than flat plate collector (FPC), especially during diffuse solar radiation. But HP ETC normally focusing on water heating system. Furthermore, HP ETC and FPC installation need to be positioned either to south or north facing to ensure the solar thermal collector absorbs more solar radiation. Meanwhile, HP ETC need to be tilt at the correct angle to maximize the performance of the system. These could lead to design limitation. The aim of this research is to develop the new design of Evacuated Glass-Thermal Absorber Tube Collector namely EGATC for drying application. It was developed from conventional HP ETC evacuated glass tube. In this study comparison result of EGATC and HP ETC performance were evaluated. The three days outdoor experiment proves that the performance of EGATC was better than HP ETC in air heating application which is provide higher outlet temperature. Based on the result, EGATC (Day 1: 50.9 oC, Day 2: 53.9 oC, Day 3: 49.2 oC) performed better with slightly higher temperature at outlet temperature compare with HP ETC (Day 1: 46.7 oC, Day 2: 50.3 oC, Day 3: 46.9 oC). It is concluded that EGATC have better performance in term of temperature different and outlet temperature as compared to HP ETC. EGATC (Day 1: 53.6%, Day 2: 50.6%, Day 3: 49.8%) also have greater efficiency in term of heat storage capability as compared to HP ETC (Day 1: 42.7%, Day 2: 41.6%, Day 3: 41.1%). Regarding energy buffer storage, EGATC have better energy storage compared to HP ETC at sudden weather change such as diffuse solar radiation during clouds. The outlet temperature of EGATC (42.3 oC) was remained slightly higher compared to HP ETC (39.9 oC) at the beginning. The outlet temperature gradually drops slower during discharging period until the end of the experiment for 15 minutes towards outlet temperature 41.1oC and 37.2oC for both EGATC and HP ETC with temperature difference 1.2oC and 2.7oC respectively.