Subtopic: Simultaneous heat and mass transfer in agricultural processing operations
Question Statement:
In simultaneous heat and mass transfer during the constant-rate drying period of wet biological materials, the wet-bulb surface temperature remains steady because:
Options:
(A) Convective heat transferred to the food surface from the surrounding air is exactly balanced by the latent heat of vaporization
(B) The thermal conductivity of the food material rises to infinity
(C) Moisture diffusion within the internal solid matrix encounters zero resistance
(D) The ambient air relative humidity approaches 100%
Answer Key:
A
Step-by-Step Solution & Explanation
During the constant-rate drying period, water evaporates from a continuous liquid film on the surface. The rate of convective sensible heat transfer $q = h A (T_a - T_s)$ precisely balances the latent heat required for vaporization $\dot{m} \lambda$, maintaining the surface at the constant wet-bulb temperature $T_s = T_{wb}$.