Question

Given below are two statements, one is labelled as Assertion A and the other is labelled as Reason R
Assertion A: Velocity of air inside a suction hose conveying granular material will be higher than the terminal velocity of the material.
Reason R: Terminal velocity of a particle is equal to the air velocity at which a particle remains suspended in a column of air.
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:

To transport particles vertically, the air velocity must be about 2 to 3 times their terminal velocity to ensure stable pneumatic transport and prevent blockages.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Pneumatic conveying systems use a flowing stream of air to transport bulk granular materials (such as grains or seeds) through pipes or hoses.
The aerodynamic behavior of the particles in the air stream determines whether they are suspended, transported, or deposited.

Step 2: Detailed Explanation:
Let us evaluate both statements:
- Assertion A: "Velocity of air inside a suction hose conveying granular material will be higher than the terminal velocity of the material."
This is correct.
For a vertical conveying system to transport particles upward against gravity, the aerodynamic drag force exerted by the moving air must be greater than the gravitational force acting on the particles.
This means the air velocity inside the hose must exceed the terminal velocity of the particles to prevent them from falling back down.
- Reason R: "Terminal velocity of a particle is equal to the air velocity at which a particle remains suspended in a column of air."
This is correct.
By definition, terminal velocity (\(v_t\)) occurs when the downward gravitational force (\(F_g\)) is balanced by the upward drag force (\(F_d\)).
At this velocity, the net force is zero, and a particle remains suspended in a steady vertical column of air.
- Relationship between A and R:
Since the terminal velocity is the minimum air velocity required to keep a particle suspended, the conveying air velocity must be higher than this terminal velocity to lift and transport the particles.
Therefore, both statements are true, and R is the correct explanation of A.

Step 3: Final Answer:
The correct option is (A).