The GATE Grind

GATE 2025 AG – Question 41

Dairy and Food Engineering · Preservation of Food · 2 marks · Multiple select

Which are NOT correct assumptions for deriving Plank’s food-freezing-time equation? Select all that apply.

  1. The ice front moves from the freezing medium into the food block at a uniform rate.
  2. Food physical-property data are accurate.
  3. Initially the entire food is at a distinct freezing point.
  4. Sensible heat changes during freezing are sufficiently high.

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Show answer and explanation

Correct answer: (B) Food physical-property data are accurate.; (D) Sensible heat changes during freezing are sufficiently high.

Explanation

Plank’s approximation treats phase change at a specified freezing temperature and neglects sensible-heat cooling; D therefore contradicts its latent-heat approximation. Accurate property data are desirable input quality, not a model assumption about the freezing physics, so the official key selects **B, D**. The source’s A also deserves qualification: the classical growing-layer conduction resistance makes actual front speed vary; a uniform freezing-front speed is not generally implied by the integrated Plank equation. The official grading is retained with this limitation stated.

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