Which of the following is the correct definition of mass transfer coefficient in a binary diffusion system?
Answer: A
Mass transfer coefficient (k) is defined as the rate of mass transfer per unit interfacial area per unit concentration difference, with units of length/time.
Q.2Easy
What is the Schmidt number (Sc) in mass transfer? Select the most accurate definition.
Answer: A
Schmidt number is Sc = kinematic viscosity/diffusivity = μ/(ρ × D_AB). It is a dimensionless number analogous to Prandtl number in heat transfer.
Q.3Easy
In the film theory of mass transfer, what is assumed about the concentration profile across the stagnant film?
Answer: A
Film theory assumes a linear concentration gradient across the stagnant boundary layer, making the analysis mathematically simple and suitable for engineering calculations.
Q.4Easy
A textile industry needs to determine the diffusivity of dye in water at 25°C. The Stokes-Einstein equation is: D_AB = kT/(6πμr). What does 'r' represent?
Answer: A
In the Stokes-Einstein equation, r is the molecular radius (or hydrodynamic radius) of the solute particle diffusing through the solvent.
Q.5Easy
A cooling tower is designed for evaporative cooling where water evaporates into dry air. The mass transfer occurs due to:
Answer: A
In evaporative cooling towers, mass transfer is driven by the difference in water vapor concentration between the saturated air at the water surface and the bulk air stream (concentration gradient).
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Q.6Easy
The eddy diffusivity (ε_D) in turbulent flow represents contribution of _____ to overall mass transfer.
Answer: B
Eddy diffusivity (ε_D) accounts for the enhanced mass transfer due to turbulent mixing and eddy formation. Total diffusivity = D_AB + ε_D in turbulent regions.
Q.7Easy
In the context of mass transfer, what does the Schmidt number (Sc) represent?
Answer: A
Schmidt number (Sc = ν/D_AB) represents the relative importance of momentum diffusion and mass diffusion in a fluid.
Q.8Easy
In a gas absorption process using a packed tower, if the interfacial area 'a' increases, how does it affect the mass transfer rate?
Answer: B
Since mass transfer rate = k_G * a * ΔP, an increase in interfacial area directly increases the mass transfer rate (linear relationship).
Q.9Easy
A gas absorption column operates at steady state. The overall mass transfer coefficient K_G is determined to be 2.5 kmol/(m²·s·atm). If the driving force is 0.8 atm, what is the mass flux?
Answer: B
Using N_A = K_G * ΔP = 2.5 × 0.8 = 2.0 kmol/(m²·s). This is a direct application of the mass transfer rate equation.
Q.10Easy
The mass transfer coefficient k_L in liquid phase absorption typically has units of:
Answer: A
The liquid phase mass transfer coefficient k_L has units of m/s or cm/s, representing the rate of mass transfer per unit concentration difference.
Q.11Easy
In an adsorption process on activated carbon, the Langmuir isotherm is given by q = (q_m * K * C)/(1 + K*C). What does 'q_m' represent?
Answer: A
In Langmuir isotherm, q_m represents the maximum (monolayer) adsorption capacity when the adsorbent surface is completely saturated.
Q.12Easy
In gas-liquid mass transfer, the Henry's Law constant (H) represents the:
Answer: A
Henry's Law constant (P = H*x) represents the equilibrium partial pressure of a gas over a solution, indicating gas solubility in the liquid.
Q.13Easy
What is the primary difference between diffusion and convection in mass transfer operations?
Answer: A
Diffusion is the movement of species due to concentration gradient (molecular level), while convection is the bulk movement of fluid carrying dissolved or suspended species.
Q.14Easy
In Fick's second law of diffusion, which parameter represents the rate of change of concentration with time?
Answer: A
Fick's second law: ∂C/∂t = D(∂²C/∂x²), where ∂C/∂t represents the temporal change in concentration.
Q.15Easy
The mass transfer coefficient is typically expressed in units of:
Answer: A
Mass transfer coefficient (k) has dimensions of velocity: m/s. It represents the driving force (concentration difference) per unit area per unit time.
Q.16Easy
In a binary diffusion process, the mass transfer coefficient 'k_c' has dimensions of:
Answer: A
The mass transfer coefficient k_c is defined as molar flux per unit concentration difference, having dimensions of velocity (Length/Time), commonly expressed in cm/s or m/s.
Q.17Easy
Which of the following best describes the Schmidt number (Sc) in mass transfer?
Answer: B
Schmidt number Sc = ν/D_AB where ν is kinematic viscosity and D_AB is mass diffusivity. It represents the relative importance of momentum and mass transport.
Q.18Easy
For a spherical particle undergoing mass transfer, the Sherwood number correlation for creeping flow (Re << 1) is approximately:
Answer: B
For a spherical particle in creeping flow with negligible convection, the Sherwood number approaches the purely diffusive limit of Sh = 2, independent of Reynolds and Schmidt numbers.
Q.19Easy
In liquid-liquid extraction, the distribution coefficient K_D is defined as the ratio of solute concentration in:
Answer: A
The distribution coefficient K_D = C_solvent/C_aqueous at equilibrium, determining the driving force for extraction and the selectivity of the separation process.
Q.20Easy
In equimolar counter-diffusion between two gases A and B, what is the relationship between their molar fluxes?
Answer: A
In equimolar counter-diffusion, the molar fluxes of the two components are equal in magnitude but opposite in direction, hence N_A = -N_B.
