Subtopic: Preservation of food by cooling and freezing
Question Statement:
Identify the assumption(s) which is/are NOT correct for deriving Plank's equation for food freezing time.
Options:
(A) Ice front moves from the freezing medium into the food block at a uniform rate.
(B) Physical property data of food material are accurate.
(C) Initially the whole food material is at a distinct freezing point.
(D) Sensible heat changes during the freezing process are sufficiently high.
Official Answer Key:
B, D
Step-by-Step Solution & Explanation
Plank's model assumes properties are constant (not necessarily that available property data are “accurate” — this framing is not a genuine model assumption) and, critically, it neglects sensible-heat effects, treating the freezing process as driven almost entirely by latent heat removal at a single freezing point with a uniformly advancing ice front. So the assumption that sensible-heat changes are “sufficiently high” contradicts the model (D), and (B) is not a valid physical assumption of the derivation. (A) and (C) are genuine simplifying assumptions of Plank's model.
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