For an ideal gas undergoing isothermal expansion from V₁ to V₂, the entropy change is:

The correct answer is A: ΔS = nR ln(V₂/V₁). For isothermal process: dS = dq_rev/T = nR dV/V, integrating gives ΔS = nR ln(V₂/V₁). Temperature is constant, so entropy change depends only on volume change.

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?

The correct answer is A: Maximum adsorption capacity. In Langmuir isotherm, q_m represents the maximum (monolayer) adsorption capacity when the adsorbent surface is completely saturated.

Which statement is correct about the residence time distribution (RTD) in an ideal plug flow reactor?

The correct answer is B: All molecules spend the same residence time τ. In ideal PFR, E(t) = δ(t-τ), meaning all molecules have identical residence time equal to τ

In an isothermal CSTR, if feed concentration C_A0 = 10 mol/m³ and outlet concentration C_A = 2 mol/m³, conversion is:

The correct answer is B: 0.8 or 80%. Conversion X = (C_A0 - C_A)/C_A0 = (10-2)/10 = 0.8 = 80%

A fluid with dynamic viscosity of 0.8 Pa·s and density of 900 kg/m³ flows through a circular pipe. What is the kinematic viscosity of this fluid?

The correct answer is A: 8.89 × 10⁻⁴ m²/s. Kinematic viscosity ν = μ/ρ = 0.8/900 = 8.89 × 10⁻⁴ m²/s

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Chemical Engineering

Process design, thermodynamics, reactions

247 Q 5 Topics Take Mock Test

Difficulty: All Easy Medium Hard 161–170 of 247

Topics in Chemical Engineering

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

Q.161 Medium Heat Transfer

For turbulent flow in a rough pipe, the friction factor is determined by both Reynolds number and relative roughness (ε/D). According to the Moody chart, in the complete turbulence zone, the friction factor becomes independent of:

A Reynolds number

B Relative roughness

C Pipe diameter

D Fluid viscosity

Correct Answer: A. Reynolds number

EXPLANATION

In the complete turbulence zone (very high Reynolds numbers), the friction factor depends only on the relative roughness (ε/D) and becomes independent of Reynolds number. This is because inertial forces completely dominate over viscous forces.

Test

Q.162 Medium Heat Transfer

The effectiveness-NTU (Number of Transfer Units) method is preferred over LMTD method when designing heat exchangers because:

A It requires less computational effort

B LMTD method cannot handle cases where outlet temperatures are unknown (design problems)

C NTU method is always more accurate than LMTD

D NTU method eliminates the need for correction factors

Correct Answer: B. LMTD method cannot handle cases where outlet temperatures are unknown (design problems)

EXPLANATION

In heat exchanger design, outlet temperatures are unknown, making the LMTD method iterative and cumbersome. The NTU method (ε-NTU) directly uses inlet temperatures and known parameters to find the outlet temperatures without iteration, making it ideal for design problems.

Test

Q.163 Medium Heat Transfer

In the design of a heat recovery steam generator (HRSG) for a combined cycle power plant, the approach temperature is 5°C. If the exhaust gas inlet temperature is 450°C and the approach temperature represents the difference between exhaust gas exit and steam outlet temperatures, what is the steam outlet temperature?

A 440°C

B 445°C

C 455°C

D 460°C

Correct Answer: B. 445°C

EXPLANATION

The approach temperature is defined as: Approach = T_gas,out - T_steam,out. Given that typical exhaust exit from HRSG is around 450°C and approach is 5°C, T_steam,out = 450 - 5 = 445°C.

Test

Q.164 Medium Heat Transfer

The Colburn factor (j) for heat transfer is related to the Nusselt number. For turbulent flow over a flat plate, the typical correlation is j ≈ 0.037·Re^(-0.2). What does the Colburn factor represent?

A The ratio of heat transfer coefficient to mass transfer coefficient

B A dimensionless factor relating Nusselt, Reynolds, and Prandtl numbers with St = j/Pr^(2/3)

C The effectiveness of the heat exchanger

D The friction factor for momentum transfer

Correct Answer: B. A dimensionless factor relating Nusselt, Reynolds, and Prandtl numbers with St = j/Pr^(2/3)

EXPLANATION

The Colburn factor (j) is a dimensionless group that relates heat transfer characteristics to flow properties. It connects the Stanton number to the Prandtl number: St = j/Pr^(2/3), allowing transfer of empirical heat transfer data to different systems.

Test

Q.165 Medium Heat Transfer

In a parallel-flow heat exchanger with hot inlet temperature Th,in = 100°C, cold inlet temperature Tc,in = 30°C, and hot outlet temperature Th,out = 60°C, what is the hot fluid capacity rate ratio if the cold outlet temperature is 50°C?

A 0.5

B 1.0

C 1.5

D 2.0

Correct Answer: A. 0.5

EXPLANATION

For energy balance: Ch(Th,in - Th,out) = Cc(Tc,out - Tc,in). So Ch(100-60) = Cc(50-30), which gives Ch/Cc = 20/40 = 0.5. This is the capacity rate ratio.

Test

Q.166 Medium Heat Transfer

The thermal entrance length for laminar flow in a pipe is given by x_th/D ≈ 0.05·Re·Pr. For water flowing in a 25 mm diameter pipe with Reynolds number of 1000 and Prandtl number of 7, what is the thermal entrance length?

A 0.875 m

B 1.75 m

C 8.75 m

D 17.5 m

Correct Answer: A. 0.875 m

EXPLANATION

x_th = 0.05 × Re × Pr × D = 0.05 × 1000 × 7 × 0.025 = 8.75 m. This is the distance from the entrance where thermal development is completed (approximately 99% developed).

Test

Q.167 Medium Heat Transfer

In heat exchanger design for petrochemical plants, fouling resistance (Rf) is critical. For a crude oil preheater, the typical internal fouling resistance is 0.0005 m²·K/W. If the design duty is 5 MW, what is the maximum temperature difference loss due to fouling on a surface area of 100 m²?

A 2.5 K

B 5 K

C 10 K

D 25 K

Correct Answer: A. 2.5 K

EXPLANATION

Using Q = UAΔT and considering fouling resistance: ΔT_fouling = Q × Rf / A = 5×10⁶ × 0.0005 / 100 = 25 K. However, for the temperature loss specifically attributed to fouling layer: ΔT = Rf × (Q/A) = 0.0005 × (5×10⁶/100) = 2.5 K.

Test

Q.168 Medium Heat Transfer

The Grashof number (Gr) is used to characterize natural convection. For natural convection heat transfer, which of the following correctly describes the Grashof number?

A Gr = (ρ²gβΔT L³)/(μ²) - ratio of buoyancy forces to viscous forces

B Gr = (hL)/k - ratio of convective to conductive heat transfer

C Gr = (ρVL)/μ - ratio of inertial to viscous forces

D Gr = (cp·μ)/k - ratio of viscous diffusion to thermal diffusion

Correct Answer: A. Gr = (ρ²gβΔT L³)/(μ²) - ratio of buoyancy forces to viscous forces

EXPLANATION

The Grashof number Gr = (ρ²gβΔT L³)/(μ²) represents the ratio of buoyancy forces to viscous forces in natural convection. It determines the onset of natural convection and its intensity.

Test

Q.169 Medium Heat Transfer

In a cross-flow heat exchanger where both fluids are unmixed, the effectiveness (ε) is lower than in a counter-flow arrangement. What is the main reason for this?

A Cross-flow has higher friction factors leading to energy losses

B The logarithmic mean temperature difference (LMTD) is smaller in cross-flow due to mixing limitations

C The mean temperature difference in cross-flow is less favorable than counter-flow due to the inability of fluids to follow the temperature gradient optimally

D Cross-flow requires more surface area for the same duty

Correct Answer: C. The mean temperature difference in cross-flow is less favorable than counter-flow due to the inability of fluids to follow the temperature gradient optimally

EXPLANATION

In cross-flow (especially unmixed-unmixed), the temperature gradients are not as favorable as counter-flow because one or both fluids cannot maintain continuous temperature gradient alignment, resulting in lower effectiveness and hence lower LMTD correction factor.

Test

Q.170 Medium Heat Transfer

Which of the following methods is most suitable for measuring the convective heat transfer coefficient in real-time industrial applications?

A Analytical solution of Fourier's law with boundary layer equations

B Thermographic imaging with infrared cameras to monitor surface temperature variations

C Direct measurement using a heat flux sensor mounted on the surface

D Numerical simulation using Computational Fluid Dynamics (CFD)

Correct Answer: B. Thermographic imaging with infrared cameras to monitor surface temperature variations

EXPLANATION

Thermographic imaging using infrared cameras is a non-intrusive, real-time method that can measure surface temperature variations across the heat transfer surface without disturbing the flow, making it practical for industrial monitoring.

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