Drying kinetic of peppercorns in a rectangular fluidized-bed with wavy surfaces

摘要

The paper presents the comparative study of drying peppercorns in a rectangular fluidized-bed and a rectangular fluidized-bed with wavy surfaces. This experimental work has been carried out in two different drying bed configurations: rectangular bed and rectangular bed with wavy surface (called “wavy surface bed”). The wavy surface bed is used to produce a stronger turbulence flow inside. For each run of both beds, inlet hot air at 80°C is used for drying peppercorns with initial moisture content at about 82.5% w.b. The inlet air velocity is adjusted to be 1.0Umf, 1.1Umf and 1.3Umf (Umf= minimum fluidization velocity of peppercorns) as desired. Drying time and weight of peppercorns are measured in 5 minute intervals for 120 minutes for each run. The experimental results show that in the rectangular bed, the peppercorns show low oscillating and it becomes dense bed. This causes low heat transfer rate between peppercorns and hot air leading to slower mass transfer of moisture in the peppercorns. In the wavy surface bed, the peppercorns has high fluctuations due to unsymmetrical flow in the bed creating a sustainable oscillating flow with stronger turbulence of hot air and it causes dilute bed, resulting in higher heat and mass transfer in peppercorns. Closer examination reveals that for a similar operating condition, the rectangular wavy surface bed performs better than the rectangular bed.