Harvesting the low-temperature geothermal energy for agricultural drying with two-phase closed thermosyphon: An experimental study

Due to the decline in the availability of fossil fuel and its destructive impact on the environment, there is a need to accelerate the use of more sustainable and safer environmental energy. The geothermal energy is one of renewable energy with abundant sources, especially in Indonesia where the source of low-temperature geothermal energy (LTGE) spreads around the country. However, several challenges exist in regard to its use, such as expensive investment to drill the source of energy and issues of silica scaling. To solve these challenges and boost the utilization of LTGE, a technology that can easily harvest is needed. A potential technology that is capable of handling this issue is the two-phase closed thermosyphon (TPCT). Therefore, this study aims to investigate the thermal performance of TPCT as a heat pipe heat exchanger (HPHE) to harvest LTGE for agricultural drying. The TPCT was made from a copper tube with a 1-inch diameter and 700 mm in length. Demineralized water with a 55% filling ratio was used as the working fluid. The vacuum pressure inner TPCT was -50 cmHg and -70 cmHg. A total of 18 pcs of TPCTs were used, with 30 fins made from a copper plate. Furthermore, the LTGE source was simulated using hot water that can be adjusted and flowed by a pump. The experimental results showed that the vacuum pressure on the TPCT greatly affected the heat transfer performance of the system. Also, the highest TPCT-HPHE effectiveness was 0.31, obtained with a vacuum pressure at TPCT, hot water temperature, and air velocity of -70 cmHg, 80 °C, and 0.2 m/s, respectively. From the results, it was concluded that TPCT can be proposed as a good candidate technology to harvest and accelerate the utilization of the LTGE resource.