Abstract
Aerodynamics, temperature variations in the annulus, and the moisture reduction of paddy in a paraboloid-based spouted bed (PBSB) dryer without draft tube and with solid and porous draft tubes were investigated. Draft tube caused a rapid decrease in the peak pressure drop and minimum spouting velocity when compared with PBSB without a draft tube. Pressure drops with draft tubes were 17 to 30% of the values for the PBSB without a draft tube. Temperature distribution along the bed height in the annular region during drying of paddy was also investigated. Heat-up in the spouted bed without draft tube was more rapid. The experiments were conducted for 70, 90, and 110 °C inlet air temperatures. The required length of drying time to dry the paddy with an initial moisture content of 0.35 db to a moisture content below 0.15 db could be reduced by 50–60% using a temperature of 110 °C instead of 70 °C. No constant rate period was observed. Drying took place in the falling rate period. Drying time decreased in the case of porous draft tube rather than the solid one. The highest drying rates were achieved by spouted bed without draft tube. Drying rates were in the range of 0.62–0.1, 0.51–0.06, and 0.37–0.06 (db.min−1) for the spouted bed without draft tube, with porous, and solid draft tubes, respectively.
Highlights
Rice is an important crop because of the fact that it is a fundamental food for more than half of the world’s population
The effects of the solid and porous draft tubes introduced into the paraboloid-based spouted bed (PBSB) on (a) thermal behavior of the annular region, (b) aerodynamics of the PBSB, and (c) moisture reduction of paddy, were investigated
Peak pressure drop and minimum spouting velocity for PBSB with a draft tube decreased rapidly compared to PBSB without a draft tube
Summary
Rice is an important crop because of the fact that it is a fundamental food for more than half of the world’s population. In an operation like solids drying, use of porous draft tubes in a spouted bed helps in the lateral transport of hot air from spout to annulus region, thereby providing better contact between solid and fluid phases in the annular region as well [7]. Spouted-bed bases with the same volume in different shapes—spherical, cone, and paraboloid—were used for the drying experiments to investigate the effect of the spouted-bed base shape on drying. The highest drying rate was achieved for drying in a paraboloid-based spouted bed [13]. In this study, drying of paddy was conducted in a paraboloid based spouted bed dryer (PBSB). The effects of the solid and porous draft tubes introduced into the PBSB on (a) thermal behavior of the annular region, (b) aerodynamics of the PBSB, and (c) moisture reduction of paddy, were investigated. The effect of the air inlet temperature in point of drying kinetics of paddy was studied
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