Heat transfer characteristics in a liquid-solids fluidisation bed: Effect of particle diameter and fluids

Present work deals with experimental study of heat transfer from column wall to fluidised bed for different fluids (Newtonian and non-Newtonian) and particle sizes. Fluids considered are water, sodium silicate (SS) and carboxymethyl cellulose (CMC) with different concentrations. The influence of bed-voidage (ε) and superficial liquid velocity (v_s) for different particle size, on heat transfer coefficient (h) is studied. For an increase in superficial liquid velocity, bed-voidage is increased and hence the heat transfer coefficient. The particle size is increased from 3.7744 mm to 6.09854 mm. For both Newtonian and non-Newtonian fluids, it is observed the value of heat transfer coefficient increased, attained a maximum value at a bed-voidage of ≈0.7 and then decreased. For 22 % SS, 2.5 % CMC and 3.5 % CMC, the fluidisation system is in aggregate regime, whereas for 14 % S.S. and water, regime changed from particulate to aggregate. Furthermore, heat transfer mechanism from wall-to-bulk of bed has been established and it is found that temperature profiles in radial direction is not flat and there is significant contribution to overall heat transfer resistance from the bulk of the bed.