Transport Processes and Separation Process Principles (Includes Unit Operations) Fourth Edition

9.9. DRYING IN FALLING-RATE PERIOD BY DIFFUSION AND CAPILLARY FLOW

9.9A. Introduction

In the falling-rate period, the surface of the solid being dried is no longer completely wetted, and the rate of drying steadily falls with time. In Section 9.7 empirical methods were used to predict the time of drying. In one method the actual rate-of-drying curve was numerically or graphically integrated to determine the time of drying.

In another method an approximately straight line from the critical free moisture content to the origin at zero free moisture was assumed. Here the rate of drying was assumed to be a linear function of the free moisture content. The rate of drying R is defined by Eq. (9.5-3):

Equation 9.5-3

When R is a linear function of ...