For a sharp-edged orifice, the coefficient of contraction (Cc) typically ranges between:

The correct answer is B: 0.60-0.65. The coefficient of contraction for sharp-edged orifices is typically 0.60-0.65 due to the vena contracta effect where the jet contracts after leaving the orifice.

In radiation heat transfer, the Stefan-Boltzmann constant σ has a value of 5.67 × 10⁻⁸ W/(m²·K⁴). A black body at 500 K radiates heat. If the temperature is doubled to 1000 K, by what factor does the radiated heat increase?

The correct answer is D: 16 times. According to Stefan-Boltzmann law, Q = σAT⁴. When T increases from 500 K to 1000 K, the factor becomes (1000/500)⁴ = 2⁴ = 16 times. Radiation is highly temperature-dependent due to the fourth-power relationship.

For a reversible reaction at equilibrium, which statement is true?

The correct answer is B: Forward reaction rate = Reverse reaction rate. At equilibrium, the net rate is zero because forward and reverse reaction rates are equal.

In a shell-and-tube heat exchanger (1 shell pass, 2 tube passes), the effectiveness is lower than counter-current primarily because:

The correct answer is A: Part of the flow behaves co-currently. In 1-2 arrangement, portion of shell-side flows co-currently with tube-side, reducing overall effectiveness compared to true counter-current.

A stripping operation is being designed to remove dissolved CO₂ from water using air. The mass transfer is primarily limited by:

The correct answer is B: The liquid phase resistance. For CO₂-air-water system, CO₂ has low solubility in water, making the liquid phase the controlling resistance in mass transfer.

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Chemical Engineering
Heat Transfer

Process design, thermodynamics, reactions

49 Q 5 Topics Take Mock Test

Difficulty: All Easy Medium Hard 11–20 of 49

Topics in Chemical Engineering

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

Q.11 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.12 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.13 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.14 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.15 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.16 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.17 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.18 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.

Test

Q.19 Medium Heat Transfer

A condenser operates with steam at 100°C condensing on a tube bank at 20°C. The saturation temperature drop is negligible. Which phase of condensation provides maximum heat transfer rate?

A Initial droplet formation phase

B Dropwise condensation phase

C Filmwise condensation phase

D All phases provide equal heat transfer

Correct Answer: B. Dropwise condensation phase

EXPLANATION

Dropwise condensation provides heat transfer coefficients 5-10 times higher than filmwise condensation because liquid droplets continuously shed, exposing fresh surface to direct contact with steam. However, filmwise condensation is more common industrially due to stability issues with dropwise condensation.

Test

Q.20 Medium Heat Transfer

A heat pipe is used to transfer heat from an electronic component at 80°C to ambient air at 25°C through evaporation and condensation. What is the primary advantage of a heat pipe over conventional conduction cooling?

A Higher thermal conductivity

B Effective thermal conductivity can be 1000 times higher than pure conduction

C Lower cost of fabrication

D Ability to function in vacuum conditions

Correct Answer: B. Effective thermal conductivity can be 1000 times higher than pure conduction

EXPLANATION

Heat pipes achieve very high effective thermal conductivity (often >1000 times that of copper) through the latent heat of evaporation and condensation of working fluid, making them ideal for high-power electronics cooling despite the small cross-sectional area.

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