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

Step 1: Look at what a falling film evaporator does. The liquid enters at the top of a heated tube and flows down as a thin film purely because of gravity. There is no vapor push involved in moving the liquid, unlike a rising or climbing film evaporator where vapor bubbles carry the liquid upward.

Step 2: Check Reason (R). It says the film moves downward under gravity instead of buoyancy force. This is exactly how a falling film evaporator works, so (R) is true.

Step 3: Check Assertion (A). It claims falling film evaporators suit foods that get thicker as they concentrate. In practice the opposite is true. As a liquid concentrates and its viscosity rises, a thin gravity driven film cannot stay continuous on the tube wall. Dry patches form, the product scorches, and fouling increases. Foods that thicken on concentration are handled better in rising film or forced circulation evaporators, where turbulence keeps the liquid mixed and wetted on the surface. So (A) is false.

Step 4: Since (A) is false and (R) is true, the matching option is the one that states exactly this.

Why the other options fail: Options 1 and 2 need (A) to be true, which it is not. Option 3 needs (R) to be false, but (R) correctly describes gravity driven flow, so option 3 is wrong too.