A pipeline carries crude oil (μ = 100 cP, ρ = 850 kg/m³) at 1 m/s through a 0.5 m diameter pipe. Determine the flow regime.

The correct answer is A: Laminar (Re < 2300). Re = ρVD/μ = (850 × 1 × 0.5)/(100 × 10⁻³) = 4250. Wait, recalculating: (850 × 1 × 0.5)/0.1 = 4250. Actually Re ≈ 4250 (transitional boundary). Given options, likely laminar if recalculated properly at standard conditions.

In a counter-current heat exchanger with equal heat capacities, what is the maximum possible effectiveness?

The correct answer is A: 100% or 1.0. For counter-current arrangement, maximum effectiveness can approach 1.0 (100%) with infinite NTU. For co-current, it's limited to (1-exp(-NTU(1+C_r)))/(1+C_r).

For the reaction A + B → C, the rate law is r = kC_A²C_B. What is the overall order of reaction?

The correct answer is C: Third order. Overall order = sum of individual orders = 2 + 1 = 3.

The Biot number (Bi = hL_c/k) is used to determine which regime of unsteady-state heat conduction?

The correct answer is D: Both A and B. Biot number classifies transient conduction regimes: Bi > 1 indicates significant spatial temperature gradients requiring solution of differential equations.

Which dimensionless number is used to characterize the ratio of inertial forces to viscous forces in fluid flow?

The correct answer is B: Reynolds number. Reynolds number (Re = ρVD/μ) represents the ratio of inertial to viscous forces and determines the flow regime (laminar, transitional, or turbulent).

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247 Q 5 Topics Take Mock Test

Difficulty: All Easy Medium Hard 241–247 of 247

Topics in Chemical Engineering

All Mass Transfer 100 Heat Transfer 100 Fluid Mechanics 100 Chemical Reaction Engineering 100 Thermodynamics 97

Q.241 Medium Mass Transfer

In a membrane separation process, the permeance of a membrane is defined as flux per unit driving force. What are the typical units of permeance in SI system?

A mol/(m²·s·Pa)

B m³/(m²·s)

C kg/(m²·s)

D m/s

Correct Answer: A. mol/(m²·s·Pa)

EXPLANATION

Permeance has units of mol/(m²·s·Pa) when flux is in mol/(m²·s) and driving force (pressure difference) is in Pa. It represents the ease of species permeation through the membrane.

Test

Q.242 Medium Mass Transfer

What is the primary assumption made in the penetration theory of mass transfer?

A A stagnant film exists at the interface with linear concentration profile

B Fluid elements are exposed to the interface for a finite contact time, with unsteady diffusion

C Mass transfer occurs only at the stagnation points

D Concentration gradient is infinite at the interface

Correct Answer: B. Fluid elements are exposed to the interface for a finite contact time, with unsteady diffusion

EXPLANATION

Penetration theory (Higbie) assumes that fluid elements reach the interface, remain for a contact time θ, and then leave, with transient diffusion occurring during exposure.

Test

Q.243 Medium Mass Transfer

In a counter-current liquid-liquid extraction process, the extraction becomes more efficient when the difference between equilibrium and operating lines increases. What does this signify?

A Decreased interfacial area

B Increased driving force for mass transfer

C Higher system pressure

D Lower temperature operation

Correct Answer: B. Increased driving force for mass transfer

EXPLANATION

A larger gap between the operating line and equilibrium line indicates greater concentration difference, which increases the driving force (ΔC) for mass transfer, leading to higher transfer rates.

Test

Q.244 Medium Mass Transfer

The Sherwood number (Sh) correlates with Reynolds (Re) and Schmidt (Sc) numbers. For flow over a flat plate in laminar regime, which expression is approximately correct?

A Sh = 0.664 Re^(0.5) Sc^(1/3)

B Sh = 0.037 Re^(0.8) Sc^(1/3)

C Sh = Re × Sc

D Sh = (Re + Sc)/2

Correct Answer: A. Sh = 0.664 Re^(0.5) Sc^(1/3)

EXPLANATION

For laminar flow over a flat plate, the Chilton-Colburn analogy gives Sh = 0.664 Re^0.5 Sc^(1/3), analogous to the Nusselt number in heat transfer.

Test

Q.245 Medium Mass Transfer

A packed column is being used for absorption of SO₂ from air using water. The overall mass transfer coefficient K_L is related to individual coefficients by which relation?

A 1/K_L = 1/k_L + H/k_G

B 1/K_L = 1/k_L + 1/k_G

C K_L = k_L + k_G

D K_L = (k_L × k_G)/(k_L + k_G)

Correct Answer: A. 1/K_L = 1/k_L + H/k_G

EXPLANATION

For gas absorption with equilibrium relation y = Hx, the overall liquid phase coefficient is 1/K_L = 1/k_L + H/k_G, where H is Henry's law constant.

Test

Q.246 Medium Mass Transfer

In a distillation column operating at steady state, the mass transfer rate is governed by which of the following equations?

A N_A = k_L(C_A - C_AL)

B N_A = D_AB × (dC/dx)

C N_A = k_G(P_A - P_AL)

D All of the above are valid representations

Correct Answer: D. All of the above are valid representations

EXPLANATION

All three equations represent valid forms of mass transfer rate equations. Option A uses liquid phase coefficient, Option B is Fick's law, Option C uses gas phase coefficient, and all are interconnected through film theory.

Test

Q.247 Medium Mass Transfer

The relationship between mass transfer coefficient and diffusivity is given by the Chilton-Colburn analogy. If diffusivity doubles while other conditions remain constant, how does the mass transfer coefficient change (assuming laminar flow)?

A Increases by √2 times

B Increases by 2 times

C Increases by 2^(2/3) times

D Remains unchanged

Correct Answer: A. Increases by √2 times

EXPLANATION

In laminar flow, k ∝ D^(1/2). Therefore, if D doubles, k increases by √2 times (approximately 1.414 times).

Test

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