Investigation of Flow Boiling in Circulating Three-Phase Fluidised Bed: Part II: Theoretical Correlation

The following part of this paper reviews existing theoretical correlations to predict the behaviour of two-phase (liquid–solid) and three-phase (liquid–solid–vapour) fluidised beds as well as models describing heat transfer coefficients. Moreover, a theoretical correlation is developed to describe heat transfer during boiling in a three-phase circulating fluidised bed. The approach uses earlier work on two-phase (liquid–vapour) flow boiling, two-phase (liquid–solid) fluidised beds and three-phase (liquid–vapour–solid) circulating fluidised beds. The correlation developed is validated against experimental data obtained in Part I of the presented paper. The model's ability to predict the experimental data has been successfully demonstrated. The developed expression for heat transfer coefficients is written as follows:

αT.F.B.-[(αnb)tR+(αcb)tR]1/tR
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i.e.,
αT.F.B.=[{(αnpb,p·FNB)bE}tR+{αLS·FCB·f(U)}tR]1/tR.

When applied to experimentally obtained data for stainless steel particles (dp=1.5,2.0 and 2.5 mm, εp=16%), the correlation is able to predict the experimental data within a 20% maximum deviation. In the above correlation, f(U) and bE are original to this work deduced from experimental observations.