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GATE 2025 Chemical Engineering, Q30 · Heat Transfer

The correct answers are B. Backward feed is preferred over forward feed for cold feed.; C. Backward feed is preferred over forward feed for highly viscous concentrated product..

Question

Which of the following statements regarding multiple effect evaporators is/are TRUE?

  • A. The pressure of the effect with fresh steam is the lowest for both forward feed and backward feed.
  • B. Backward feed is preferred over forward feed for cold feed.
  • C. Backward feed is preferred over forward feed for highly viscous concentrated product.
  • D. The temperature of the effect with fresh steam is the lowest for both forward feed and backward feed.

Official answer: B. Backward feed is preferred over forward feed for cold feed.; C. Backward feed is preferred over forward feed for highly viscous concentrated product.

Why

GATE 2025 official key: (B, C). The fresh-steam effect operates at the highest pressure/temperature (not lowest), ruling out (A) and (D). Backward feed is preferred for cold, viscous feeds since the feed first meets the hottest, least viscous conditions at the last effect it enters.

Explanation cross-checked for consistency. Final answer matches the official IIT answer key.

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