Estimation and experimental validation of the circulation time in a 2D gas-solid fluidized beds

The circulation time is defined as the time required for a group of particles to reach the freeboard from the bottom of a fluidized bed and return to their original height. This work presents an estimation and validation of the circulation time in a 2D gas solid bubbling fluidized bed under different operating conditions. The circulation time is based on the concept of the turnover time, which was previously defined by Geldart [1] as the time required to turn the bed over once. The equation t(c,est)=2Ah '/Q(b) is used to calculate the circulation time, where A is the cross-section of the fluidized bed, h' is the effective fluidized bed height and Q, is the visible bubble flow. The estimation of the circulation time is based on the operating parameters and the bubble phase properties, including the bubble diameter, bubble velocity and bed expansion. The experiments for the validation were carried out in a 2D bubbling fluidized bed. The dense phase velocity was measured with a high-speed camera and non intrusive techniques such as particle image velocimetry (PIV) and digital image analysis (DIA), and the experimental circulation time was calculated for all cases. The agreement between the theoretical and experimental circulation times was satisfactory, and hence, the proposed estimation can be used to reliably predict the circulation time. (C) 2012 Elsevier B.V. All rights reserved.