Chemical Engineering questions for GATE and PSU exams are built on a handful of core subjects applied in many ways. Practice spans fluid mechanics, heat transfer, mass transfer, chemical reaction engineering, thermodynamics, process control and instrumentation, and plant design economics. Numerical solutions carry the assumptions written out, because the assumption is usually what separates a correct answer from a plausible one.
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.22Medium
Which of the following equations is used to calculate the mass transfer coefficient in laminar flow over a flat plate?
Answer: A
The Ranz-Marshall correlation for laminar flow over a flat plate is Sh = 0.664 Re^(21) Sc^(31), derived from boundary layer theory.
Q.23Easy
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.24Hard
For a binary diffusion process, the flux equation according to Fick's law in terms of mole fractions is given by:
Answer: B
The molar flux equation in terms of mole fractions is N_A = cD_AB(dy_A/dz) + y_A(N_A + N_B), accounting for bulk flow effects.
Q.25Easy
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.26Medium
Which correlation is commonly used for mass transfer in turbulent pipe flow?
Answer: D
Both Gnielinski correlation (modified form) and Chilton-Colburn analogy (j_D = j_H = j_f/2) are applicable for turbulent pipe flow mass transfer.
Q.27Medium
In a distillation column, the interface equilibrium at the liquid-vapor boundary can be described by:
Answer: C
Raoult's Law applies to ideal solutions (high concentration), while Henry's Law applies to dilute solutions. The choice depends on the system behavior.
Q.28Hard
For a countercurrent liquid-liquid extraction process, the Kremser equation is used. What is the minimum number of stages required if the separation factor is 2.0 and the extraction factor is 1.5?
Answer: D
The Kremser equation requires initial and final solute concentrations or minimum separation requirements, which are not provided in the question.
Q.29Easy
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.30Medium
In a membrane separation process, the Sherwood number (Sh) for mass transfer at the membrane surface is defined as:
Answer: D
Sherwood number is defined differently for liquid (Sh = k_L * L / D_AB) and gas phases (Sh = k_G * R_g * T / (P * D_AB)), depending on the system.
Q.31Medium
A stripping operation is being designed to remove dissolved CO₂ from water using air. The mass transfer is primarily limited by:
Answer: B
For CO₂-air-water system, CO₂ has low solubility in water, making the liquid phase the controlling resistance in mass transfer.
Q.32Medium
The mass transfer rate from a solid sphere dissolving in a flowing liquid can be described using the Ranz-Marshall correlation. Which parameter is NOT included in this correlation?
Answer: C
The Ranz-Marshall correlation for a sphere is Sh = 2 + 0.6 Re^(21) Sc^(31). Froude number (related to gravity effects) is not part of this correlation.
Q.33Medium
In a wetted wall column for gas absorption, the liquid film thickness (δ) affects the mass transfer rate. Increasing δ will:
Answer: B
The liquid phase mass transfer coefficient k_L is inversely related to film thickness: k_L = D_AB/δ. Increasing δ decreases k_L and hence the mass transfer rate.
Q.34Hard
For a dilute binary gas mixture diffusing through a stagnant layer, the diffusion coefficient D_AB can be estimated using the Chapman-Enskog theory. Which statement is correct?
Answer: B
According to Chapman-Enskog theory, D_AB ∝ T^(23)/P for gases. Thus, D_AB is inversely proportional to pressure at constant temperature.
Q.35Easy
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.36Hard
For simultaneous momentum and mass transfer in a boundary layer, the Chilton-Colburn analogy relates j_D to friction factor f_D by:
Answer: A
The Chilton-Colburn analogy states that j_D = j_H = f_D/2, assuming equivalent Pr and Sc values, relating mass transfer to friction factor.
Q.37Easy
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.38Medium
A spray tower is used for absorption where droplets fall through a rising gas stream. The interfacial area in such a system primarily depends on:
Answer: A
Interfacial area 'a' in spray towers is directly proportional to the total surface area of droplets, which depends on droplet size (smaller droplets = larger area) and droplet density.
Q.39Hard
For a hollow fiber membrane contactor used in gas-liquid mass transfer, the overall mass transfer coefficient K_OL is related to individual coefficients by:
Answer: B
For gas-liquid systems, 1/K_OL = 1/k_L + 1/(m*k_G), where m is the distribution coefficient. This accounts for both liquid and gas side resistances.
Q.40Medium
In the design of a sieve tray distillation column, the mass transfer efficiency (Murphree efficiency) accounts for:
Answer: A
Murphree efficiency (E_M) reflects that equilibrium is not achieved on real trays due to limited contact time and finite mass transfer rates in the actual column.
