Question

Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).

Assertion (A): Falling film evaporators are most suitable for food that become thicker with concentration.

Reason (R): In falling film evaporator, food film moves downward under gravity instead of buoyancy force.

In light of the above statements, choose the correct answer from the options given below.

• A. Both (A) and (R) are true and (R) is the correct explanation of (A).
• B. Both (A) and (R) are true but (R) is NOT the correct explanation of (A).
• C. (A) is true but (R) is false.
• D. (A) is false but (R) is true.

Hint:

Recall which evaporator type suits liquids that get more viscous as they concentrate, and compare that with how a falling film actually moves.

Answer 1

The Correct Option is D

Start by separating the two evaporator types by how the liquid travels. In a rising film unit, vapor generated in the tube pushes liquid upward, creating strong turbulence that helps handle liquids whose viscosity increases while concentrating. In a falling film unit, liquid simply drips down the tube wall under its own weight, forming a thin, gently moving film.

Because a falling film depends only on gravity and film tension to stay attached to the tube, it needs a liquid that stays reasonably fluid throughout the run. Once concentration pushes viscosity up, the film breaks into channels, leaves dry spots on the hot wall, and the product can burn or foul the tube. That rules out falling film evaporators for foods that keep getting thicker as water leaves them, so Assertion (A) does not hold.

Reason (R) is simply describing the physical mechanism of a falling film unit, movement by gravity, not by vapor buoyancy, which is accurate on its own.

Putting these together, (A) fails while (R) stands true, matching option 4.

\[\boxed{\text{Option 4: (A) is false but (R) is true}}\]