DESIGN CONSTRUCTION AND TEST OF A HYBRID DRYING SYSTEM: A CASE STUDY OF DRIED BLACK WOOD EAR MUSHROOMS PRODUCTION BY FARMERS IN SAN SAI DISTRICT CHIANG MAI PROVINCE

Abstract

This research paper aimed to present a prototype hybrid drying system that was designed and constructed in order to reduce the time and energy consumption of the drying process. The following conditions were specified in the design of the prototype drying system: 1) the volume of the dying chamber was 2 m³, 2) the mass and moisture content of the raw material were 50 kg and 99.9% wb, respectively, 3) the moisture content of the dehydrated product was 5% wb, 4) the temperatures of hot air at the dying chamber’s inlet and outlet were 80 and 70 ํC, respectively, 5) the maximum hot air velocity was 5 m/s, 6) the ambient air temperature and relative humidity were 25 ํC and 60%, respectively, 7) the drying time was 12 hours, and 8) the design safety factor was 20%. According to the engineering design calculation, the prototype system had a thermal load of evaporating water from the raw material, with a total design safety factor of approximately 25 kW. As a result, the researchers decided to combine three different types of heat sources: a heat pump, electric heaters, and infrared heaters. The combined heating capacity of those devices is approximately 29 kW. The results of wood ear mushroom drying experiments showed that a prototype drying system provided a maximum efficiency of about 81% with the hybrid of hot air and infrared drying techniques, which was greater than using only hot air as a heat source by 6.69%. This hybrid drying technique required roughly 28% less drying time and 6% less energy than hot air drying, without compromising the appearance of dried wood ear mushrooms.