Thin-Layer Drying Characteristics of Fresh and Sun-Dried Buckwheat Hay

Highlights Thin-layer drying of fresh and sun-dried buckwheat hay was studied at 30°C to 180°C and 12.5% to 60% relative humidities. Buckwheat hay drying occurred in the falling-rate period. Partial sun-drying of the hay could reduce drying time by 50%. The D eff values of fresh flowers, leaves, and stems ranged from 1.4×10 -10 to 60×10 -10 m 2 /s. Abstract. Thin-layer drying characteristics of fresh and sun-dried buckwheat hay were studied at 30°C to 180°C, 12.5 to 60% relative humidities, and 0.2 m/s constant air velocity. The hay was harvested on three different times with a 10 to 12 d interval between the harvesting times. Half of the harvested hay was sun-dried on the field for 4 d (referred to as sun-dried hay). The drying behavior of flowers, leaves, and stems of the fresh and sun-dried hay was characterized. Moisture content of the fresh buckwheat flower was 0.777 to 1.633 (decimal dry basis), and fresh stems had a maximum moisture content of 5.64. Moisture content of the fresh hay decreased with the increase of growth time. Sun-drying on field could decrease more than half of the moisture content of the harvested fresh hay. Flowers, leaves, and stems needed varying drying times to reach their equilibrium moisture contents. The order of the drying time from the fastest to the slowest was flowers, leaves, then stems. Sun-dried and later harvested hay needed less drying time. The logarithmic model was the best fit for all drying processes of the flowers, leaves, and stems at different harvesting times and drying conditions. The effective moisture diffusivity of both fresh and sun-dried hay ranged from 1.4×10-10 to 60× 10-10 m2/s depending on different experimental conditions. The activation energy of the hay was from 21.08 to 33.85 kJ/mol. A power equation was the best equation to describe the drying constant of hay with their drying temperature. Keywords: Activation energy, Combination drying, Hay drying, Thin-layer drying, Water diffusivity.