Application of a Thermosiphon-Tube Drying Chamber with Waste Heat from a Charcoal Kiln
Keywords:
Thermosiphon, Drying Chamber, Waste Heat, Turmeric Drying, Energy EfficiencyAbstract
Background and Objectives: Energy efficiency and sustainability are key issues in agriculture and industry, particularly in charcoal production processes where a large amount of heat is wasted. Recovering and reusing the heat in such processes as drying, which often face a problem related to energy efficiency, leading to high energy consumption and long drying time, represents an interesting alternative to the problem. The present study focused on the development and application of a thermosyphon drying chamber that utilizes waste heat from a charcoal kiln to improve the drying efficiency. The thermosyphon drying system drew heat directly from the kiln and effectively transferred it to the drying chamber. The objectives of this research were: (1) to design and develop a thermosyphon drying chamber and (2) to evaluate the heat distribution efficiency and its effects on product quality. The study also examined the potential of thermosyphon technology to optimize drying conditions, ensuring better energy conservation while maintaining product integrity.
Methodology: The study involved the design and development of a thermosiphon drying chamber, which consists of a drying compartment and a combustion chamber. The thermosiphon system used 30 stainless steel heat pipes filled with R134a refrigerant as the working fluid to facilitate passive heat transfer. Experiments were conducted using fresh turmeric as the test material; turmeric was made into slices of different thicknesses (2, 4, and 6 mm). The drying efficiency was assessed by measuring moisture loss, water activity (aw) and color changes at 90, 120 and 150 min. Thermal efficiency measurement was also made to compare the heat retention capacity of the system with that of a conventional drying chamber.
Main Results: Drying turmeric using the thermosyphon (TS) system increased moisture loss from 64.97% (No TS) to 80.43% at 90 min of drying (2 mm thickness) and reduced water activity (aw) from 0.91 to 0.75 at the same time. Extending the drying time to 150 min further decreased aw to 0.63 (TS), while in the No TS system it remained higher at 0.87. In a hypothetical feasibility comparison, TS system enabled 2 drying cycles per day, compared to 1 cycle in the case of No TS, thereby increasing the amount of fresh turmeric that can be processed in a day from 10 kg/day to 20 kg/day; these amounts resulted in the increased yield of dried turmeric from 1.8 kg/day to 3.6 kg/day. The total income increased from 270 to 540 baht/day. Although the initial cost of the TS system was higher (9,000 Baht compared to 6,000 Baht), TS system demonstrates strong potential for increasing productivity and income.
Conclusions: Thermosyphon drying chamber utilizing waste heat from a charcoal kiln could enhance the heat transfer efficiency and reduce the drying time of turmeric more effectively than a conventional system. However, aw values that still exceeded the safety threshold highlight the limitation of the system for turmeric drying. Nevertheless, the technology may be more suitable for other herbs with different structural characteristics. Improvements in temperature and airflow control are recommended. The system shows potential for applications ranging from household to industrial scale and could help reduce the reliance on conventional energy sources in the processing of agricultural products.
Practical Application: Thermosyphon drying system can be integrated into agricultural and industrial drying operations to improve energy efficiency and reduce operating costs. The ability to utilize waste heat from a charcoal kiln makes it a sustainable option for postharvest processing, benefiting farmers and small-scale producers. Furthermore, its low-maintenance design and reduced reliance on electric heating make it an economically viable choice for remote areas with limited resources. Additionally, the low-maintenance design and reduced dependency on electrical heating elements make it an economically viable solution for remote and resource-limited areas.
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