In a jacketed CSTR for an endothermic reaction, increasing the heat transfer area per unit volume of reactor primarily affects which parameter?

The correct answer is C: Reaction rate and operating temperature stability. Increased heat transfer area improves heat supply rate for endothermic reactions, allowing higher operating temperatures with better temperature control and stability.

In the design of a CSTR for a reaction with Arrhenius parameters: Ea = 50 kJ/mol, A = 10⁵ s⁻¹, what is the approximate k at 50°C?

The correct answer is C: 4.2 × 10⁴ s⁻¹. k = A·exp(-Ea/RT) = 10⁵·exp(-50000/(8.314×323)) = 10⁵·exp(-1.86) ≈ 10⁵ × 0.156 ≈ 1.56 × 10⁴ s⁻¹. Closest is option C.

In industrial scale-up of absorption columns, the L/G ratio (liquid to gas ratio) is adjusted to:

The correct answer is B: Maintain operating line slope and absorption efficiency while avoiding flooding. L/G ratio determines the operating line slope in McCabe-Thiele diagram. Proper L/G balances absorption efficiency and prevents flooding/weeping, critical for scale-up design.

In a packed column used for gas absorption, the NTU (Number of Transfer Units) approach is preferred over HTU when:

The correct answer is C: The gas and liquid flow rates are both variable. NTU accounts for changing concentrations along the column height and is more versatile for varying flow rates, while HTU is better for constant flow conditions with linear equilibrium.

For a binary ideal solution at constant T and P, the Gibbs energy of mixing is:

The correct answer is D: Both A and C. For ideal solutions: ΔH_mix = 0 and ΔS_mix = -R(x₁ ln x₁ + x₂ ln x₂), so ΔG_mix = -TΔS_mix = RT(x₁ ln x₁ + x₂ ln x₂) < 0, making mixing spontaneous.

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247 Q 5 Topics Take Mock Test

Difficulty: All Easy Medium Hard 181–190 of 247

Topics in Chemical Engineering

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

Q.181 Medium Heat Transfer

Which heat exchanger type provides the maximum temperature effectiveness under the same flow conditions?

A Counter-flow

B Parallel flow

C Cross-flow with both fluids unmixed

D Cross-flow with one fluid mixed

Correct Answer: A. Counter-flow

EXPLANATION

Counter-flow heat exchangers are most effective because they maintain the maximum temperature gradient throughout the exchanger length, resulting in higher heat transfer rates and effectiveness compared to parallel or cross-flow configurations.

Test

Q.182 Medium Heat Transfer

A steel rod (k = 50 W/m·K) of diameter 10 mm and length 100 mm is exposed to air at 25°C with h = 20 W/m²·K. The rod is maintained at 100°C at one end. Calculate the fin efficiency if m = √(hP/kA) = 8.37 m⁻¹.

A 0.85

B 0.72

C 0.65

D 0.58

Correct Answer: B. 0.72

EXPLANATION

mL = 8.37 × 0.1 = 0.837. Fin efficiency η = tanh(mL)/(mL) = tanh(0.837)/0.837 = 0.688/0.837 ≈ 0.72

Test

Q.183 Medium Heat Transfer

In radiation view factor calculations, the reciprocity relation F₁₂·A₁ = F₂₁·A₂ ensures:

A Energy conservation in radiation exchange

B Symmetry of radiating surfaces

C Both (a) and (b)

D Gray body approximation validity

Correct Answer: A. Energy conservation in radiation exchange

EXPLANATION

Reciprocity relation ensures energy conservation: heat leaving surface 1 striking surface 2 equals heat leaving 2 striking 1 on reciprocal basis.

Test

Q.184 Medium Heat Transfer

The convective heat transfer coefficient 'h' for natural convection from a vertical surface at constant temperature increases with height due to:

A Increase in boundary layer thickness

B Increase in buoyancy-driven velocity

C Both (a) and (b) effects competing

D Decrease in local Grashof number

Correct Answer: C. Both (a) and (b) effects competing

EXPLANATION

While boundary layer grows (reducing h), buoyancy increases velocity and local Gr increases (increasing h). Combined effect shows h varies as x^(-1/4).

Test

Q.185 Medium Heat Transfer

The mean free path (λ) in gas kinetic theory at standard conditions is approximately 60 nm. This implies that at atmospheric pressure, heat conduction in gases is primarily through:

A Molecular diffusion

B Radiation

C Convection

D Bulk fluid motion

Correct Answer: A. Molecular diffusion

EXPLANATION

Small mean free path (60 nm << device dimension) ensures continuous medium behavior and heat transfer via molecular diffusion.

Test

Q.186 Medium Heat Transfer

The Peclet number (Pe = Re·Pr) in convective heat transfer indicates that:

A Pe >> 1 means convection dominates over conduction

B Pe

C Both (a) and (b) are correct

D Pe is independent of flow velocity

Correct Answer: C. Both (a) and (b) are correct

EXPLANATION

Pe represents relative importance of convection to diffusion: Pe >> 1 indicates convection dominance, Pe << 1 indicates diffusion dominance.

Test

Q.187 Medium Heat Transfer

In a recuperative heat exchanger, the effectiveness (ε) is defined as the ratio of actual heat transfer to:

A Maximum possible heat transfer (C_min·ΔT_max)

B Mean heat transfer of inlet conditions

C Logarithmic mean temperature difference

D Outlet temperature difference

Correct Answer: A. Maximum possible heat transfer (C_min·ΔT_max)

EXPLANATION

Effectiveness ε = Q_actual/Q_max = Q/(C_min(T_h,in - T_c,in)) for counterflow and parallel flow exchangers.

Test

Q.188 Medium Heat Transfer

In laminar flow through a circular tube with constant wall temperature, the Nusselt number is constant at Nu ≈ 3.66. This means:

A Heat transfer coefficient varies linearly with tube length

B Heat transfer coefficient is constant along the tube

C The entrance effects are negligible

D Both (b) and (c) are correct

Correct Answer: C. The entrance effects are negligible

EXPLANATION

Constant Nu in fully developed laminar flow indicates entrance effects are negligible and thermal profile is established.

Test

Q.189 Medium Heat Transfer

In forced convection heat transfer, the Colburn factor (j_H) is related to which dimensionless numbers?

A j_H = St·Pr^(2/3) = (Nu)/(Re·Pr^(1/3))

B j_H = Nu/Re

C j_H = Bi·Fo

D j_H = Gr/Ra

Correct Answer: A. j_H = St·Pr^(2/3) = (Nu)/(Re·Pr^(1/3))

EXPLANATION

The Colburn analogy relates Stanton number to Nusselt, Reynolds, and Prandtl numbers: j_H = St·Pr^(2/3) = Nu/(Re·Pr^(1/3)).

Test

Q.190 Medium Heat Transfer

For a circular fin of diameter d and length L attached to a surface at temperature T₀, the fin effectiveness approaches zero when:

A mL → 0 (where m = √(hP/kA_c))

B mL → ∞

C h/k ratio is very high

D L/d ratio is minimized

Correct Answer: B. mL → ∞

EXPLANATION

When mL → ∞, the temperature along the fin drops rapidly and efficiency decreases, approaching zero as the fin becomes ineffective.

Test

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