Heat transfer and hydrodynamics in a gas-solid fluidized bed with vertical immersed internals

An investigation of the influence of a bundle of intense vertical immersed tubes on the local heat transfer coefficients and related gas hydrodynamics of bubble frequency and gas holdup was conducted in a gas-solid fluidized bed of 0.14 m inside diameter. The heat transfer coefficient and bubble frequency and gas holdup were measured using an advanced non-invasive fast response heat transfer probe and sophisticated optical fiber probe techniques, respectively. A circular configuration of 30 vertical immersed tubes of 0.0127 m diameter occupying 25% of the cross-sectional area was employed. Glass bead solid particles with an average particle size of 210 μm and 2500 kg/m3 solid density which representing Geldart B type was used. The experiments were performed at different superficial gas velocities, axial heights, and radial positions. It was found that the local heat transfer coefficient and local gas hydrodynamics are directly related, such that the immersed heat exchanger tubes enhanced the heat transfer by increasing the bubble frequency and local gas holdup. The current common correlations available in the literature do not predict well our results. Hence, a new correlation that account for the effect of bubble frequency and gas holdup in addition to other parameters have been developed. The effective dimensionless groups have been correlated with a good mean relative deviation value of 4.84% between the experimental and predicted values.