Question

A spherical naphthalene ball of 2 mm diameter is subliming very slowly in stagnant air at 25°(C) The change in the size of the ball during the sublimation can be neglecte(D) The diffusivity of naphthalene in air at 25°C is \(1.1 \times 10^{-6} \, m^2/s\). The value of mass transfer coefficient is \( B \times 10^{-3} \, m/s \), where \( B \) (up to one decimal place) is —————.

• A. 1.1
• B. 1.2
• C. 1.3
• D. 1.4

Hint:

Use Sherwood number correlations for mass transfer problems involving spheres.

Answer 1

The Correct Option is A

- The Sherwood number for a spherical geometry can be calculated as \[ Sh = 2 \implies \frac{K_L D}{D_{AB}} = 2 \] Substituting the values: \[ K_L = \frac{2 \times D_{AB}}{D} = \frac{2 \times 1.1 \times 10^{-6}}{2 \times 10^{-3}} = 1.1 \times 10^{-3} \, m/s \] 
Conclusion: 
The correct answer is option (A).