Convective Heat and Mass Transfer Modeling in Gas-Fluidized Beds

Abstract

This review examines selected mechanistic and empirical models reported in the literature to predict convective heat and mass transfer coefficients in gas-fluidized beds. The role of hydrodynamics in heat and mass transfer is briefly outlined before embarking on the modeling approaches. Both bed to wall and interphase heat transfer, are considered. In bed to wall heat transfer, the main focus of the review is the modeling of particle convective components, based on surface renewal. The concepts of transient and local heat transfer models are also discussed briefly. In the case of mass transfer, only interphase transfer is considered. Emphasis is placed on models based on combustion where mass transfer is seen to occur from a few active particles contained in a fluidized bed of inert particles.

Understanding and Predicting Bed humidity in Fluidized Bed Granulation

“…(11) can be expressed as: (14) in which V p is the particle volume and W r is the wetting surface ratio based on the particle volume. Therefore, the wetting surface in a differential element of bed height dl is: (15) in which D is the diameter at the bed height l; e is the voidage. (p/4)D 2 (1 À e) is the total particle volume in the differential element of bed height.…”

“…15 Hence, a better understanding of hydrodynamics is essential for investigating the underlying mass transfer mechanism. According to the two-phase theory of fluidization proposed by Toomey and Johnstone 16 and developed by Davidson and Harrison, 17 the bubbling fluidization is composed of the two phases as shown in Figure 3; the bubble phase which is referred to the gas bubbles and the particulate phase or emulsion phase which is referred to the fluidized solids around the bubbles.…”

Mass transfer around freely moving active particles in the dense phase of a gas fluidized bed of inert particles

“…On the other hand, only few review papers addressing (partially) this subject have appeared in the literature (La Agarwal and La Nauze, 1989;Yusuf et al, 2005), so that a more complete review of the previous work available on mass transfer in fluidized beds is considered to be useful in this context.…”

A numerical investigation of gas-particle suspensions as heat transfer media for high-temperature concentrated solar power

“…The wall-to-bed heat transfer coefficient is critical to the thermal efficiency of this new CSP concept. Various mechanistic and empirical correlations for the wall-to-bed heat transfer coefficient are available and reviewed by [21][22][23]. These models are generally restricted to a narrow range of fluidization velocities, particle sizes, and solid or gas temperatures, and their suitability for predicting the performance of this new CSP concept is uncertain.…”