Question Bank • QB_APE_EXP_020 MCQ • 1 Mark

Section 6: Agricultural Process Engineering

Evaporation and Drying

Subtopic: Osmotic dehydration and freeze drying

Question Statement:

Freeze drying (lyophilization) operates on the principle of:

Options:

  • (A) Sublimation of ice directly into vapor below the triple point pressure of water ($611.73\text{ Pa}$)
  • (B) Atmospheric evaporation at the wet bulb temperature
  • (C) Superheated steam drying under positive pressure
  • (D) Osmotic mass transfer driven by hypertonic sugar solutions

Answer Key:

A

Step-by-Step Solution & Explanation

Freeze drying removes water by sublimation from frozen state directly to vapor phase without passing through the liquid state. This requires operating below the triple point of water ($T_t = 0.01^\circ\text{C}, P_t = 0.6117\text{ kPa}$).
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