Question

Assertion A: The physical properties and fluid velocity of the system influences the mass transfer coefficient.
Reason R: Flow condition impact the boundary layer thickness which controls the convective mass transfer.
In the light of the above statements, choose the most appropriate answer:

• A. Both A and R are correct and R is the correct explanation of A
• B. Both A and R are correct but R is NOT the correct explanation of A
• C. A is correct but R is not correct
• D. A is not correct but R is correct

Hint:

Higher fluid velocity creates more turbulence, which "squeezes" the boundary layer. A thinner boundary layer means a shorter distance for molecules to travel, leading to a much higher mass transfer coefficient!

Answer 1

The Correct Option is A

Concept: The convective mass transfer coefficient ($k_m$) is analogous to the heat transfer coefficient. It characterizes the rate of mass transfer between a moving fluid and a surface or another phase.

Step 1: Evaluate Assertion A.
The mass transfer coefficient is a function of system geometry, fluid velocity, and physical properties such as density, viscosity, and molecular diffusivity. This is typically represented by dimensionless correlations like $Sh = f(Re, Sc)$. Thus, Assertion A is correct.

Step 2: Evaluate Reason R.
Mass transfer occurs through a concentration boundary layer. The thickness of this boundary layer ($\delta_c$) is determined by the flow conditions (velocity and turbulence). A thinner boundary layer results in less resistance and a higher mass transfer coefficient. Thus, Reason R is correct.

Step 3: Establish the connection.
The mass transfer coefficient is influenced by velocity and properties precisely because those factors determine the boundary layer's characteristics. Therefore, R is the correct explanation for A.