Subtopic: Simultaneous heat and mass transfer in agricultural processing operations
Question Statement:
Which of the following statements regarding simultaneous heat and mass transfer in food processing operations are CORRECT?
Options:
(A) When Lewis number $Le = 1$, the thermal boundary layer thickness equals the concentration boundary layer thickness
(B) In convective air drying, the wet-bulb depression is the driving force for sensible heat transfer
(C) Freeze drying involves simultaneous sublimation mass transfer and sublimation heat transfer under high vacuum
(D) Mass transfer Biot number ($Bi_m = k_c L / D_{AB}$) compares internal mass transfer resistance to convective boundary layer resistance
Answer Key:
A, B, C, D
Step-by-Step Solution & Explanation
All statements are fundamental principles of coupled transport phenomena:
- $Le = \alpha / D_{AB} = 1 \implies \delta_t = \delta_c$.
- Sensible heat flux drives evaporation based on $(T_a - T_{wb})$.
- Freeze drying operates below the triple point where ice sublimates directly into vapor driven by heat conduction through the dry layer.
- Mass transfer Biot number compares internal diffusion resistance to external convective transfer.