Heat transfer and hudrodynamics in multi-phase fluidized beds

Abstract

Immersed heater-to-bed heat transfer and hydrodynamics in multiphase fluidized beds with glass bead were investigated. Individual phase holdups and heat transfer coefficients of two (gas-liquid, liquid-solid) and three phase (gas-liquid-solid) fluidized bed have been determined in a 15.2 cm ID column fitted with an axially mounted cylindrical heater. Effects of gas flow rate (0-12 cm/s), liquid flow rate (0-16 cm/s) particle size (1.7-8.0 mm) and liquid viscosity (1.0-39.0 mPas) on the heat transfer coefficient were examined. Complementary studies were also performed on gas-coal slurry, coal slurry-solid and gas-coal slurry-solid fluidized beds. Air, water and coal-mineral oil mixture were used as a gas, a liquid and a slurry phases, respectively. To examine the effects of liquid phase radial mixing on heat transfer in the bulk flow, the radial dispersion coefficients of liquid phase were determined in two (liquid-solid) and three (gas-liquid-solid) phase fluidized beds. A two resistance model was proposed to analyze the heat transfer mechanism in three phase beds. The bed height and individual phase holdups and/or bed porosity were determined from the static pressure drop methods. In gas-liquid flow beds, gas holdup decreased with increasng liquid flow rate and liquid phase viscosity, whereas it increased with gas flow rate. The gas holdup in three phase fluidized beds decreased with an increase in liquid phase viscosity. However, the liquid holdup decreased with increasing gas flow rate and particle size and increased with increasing liquid flow rate and liquid phase viscosity. The bed porosity, which is the indication of bed expansion, generally increased with increasing liquid and gas flow rates and liquid phase viscosity. However, effects of particle size on the bed porosity were dependent upon liquid phase viscosity and gas flow rate. Similar trends were observed in the beds of coal-slurry systems, since the coal-slurry could be regarded as the homogeneou...