Shrinkage during the Constant Rate Period

The flow of liquid in ceramic green bodies of liquid volvune fraction, i[=l - 4 ], has been shown to follow permeability models for the flow of liquid relative to ceramic particles [8,9] given in spherical coordi- 

TABLE 14.1 Spherical Green Body Drying Kinetics by Mass 

Boundary layei—mass transfer Boundary layer—heat transfer 

11) and for this reason is included inside the differential. However, this flow transport coefficient is assumed to be constant [18], albeit unrealistically, in order to attempt a solution of the preceding equation for a sphere with a constant flux at the surface that is, 

To maintain a flow of liquid to the surface at a constant rate, the green body must shrink. A solution to this equation gives the shrinkage at various radii in the spherical green body as a fiinction of time during the constant rate period. The boundary conditions for this equation are 

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