Mixed loose clusters

Relatively large clusters of crystals (25% solids) resulted in prodncts similar to the ones made from lard. Crystals of this type of form are not snggested in cakes, icings, and cookies because they do not incorporate air during mixing. Snch loose shortenings are favorable for producing tender and flaky pie crusts. 

In contrast, the wall structure of a circulating fluidised bed consists of clusters or streamers whose properties are poorly understood. There is a distribution of voidages and thermal properties, and it would be incorrect to arbitrarily ascribe loose packed bed properties to these structures since they are expanded and likely contain many fewer particle-particle and particle-wall contact points than a loose packed b. The clusters are also convectively mixed by gas and wall shear, and have complex cloud-like radiation transfer properties. In combination, these lead to a pronounced thermal boundary layer of substantial thickness and complexity (Chen et al, 1988). This has been measured by Leckner (1991) and is illustrated in Figure 20. 

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