Subtopic: Thin layer drying models and falling rate period
Question Statement:
Which of the following statements regarding the physics of grain drying is/are TRUE?
Options:
(A) Agricultural food grains dry almost entirely in the falling rate drying period, with internal liquid/vapor diffusion controlling the rate
(B) Page's thin-layer equation modifies Newton's cooling law analogy as $MR = \exp(-k t^n)$
(C) The critical moisture content marks the boundary between constant rate and falling rate drying periods
(D) In the constant rate drying period, the grain surface temperature stays at the dry bulb temperature of the drying air
Answer Key:
A, B, C
Step-by-Step Solution & Explanation
1. Grain internal structure restricts water mobility, rendering constant rate period negligible or non-existent in biological seeds (A is true).
2. Page's empirical model introduces exponent $n$ to overcome Henderson & Pabis overprediction at long times (B is true).
3. Critical moisture content $M_c$ is where free surface moisture is exhausted (C is true).
4. During constant rate drying, surface moisture evaporates freely, cooling the surface down to the wet bulb temperature, not dry bulb (D is false).