Free Heat Transfer Operations MCQs with Answers
645 Heat Transfer Operations MCQs from Chemical Engineering, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.
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645 questions · page 7 of 33
- A. T1 - T2
- B. T1 - Ta
- C. None of these
- D. T2 - Ta
Explanation: Radiative heat exchange depends on the fourth powers of absolute temperatures, such as T₁⁴ − T₂⁴, rather than on any simple temperature…
Correct answer: None of these- A. And the surface conductance increase
- B. Cumulatively decreases
- C. Remain constant
- D. Cumulatively increases
Explanation: Condensate formed at the top flows downward and joins the condensate already present, so the laminar film becomes cumulatively thicker…
Correct answer: Cumulatively increases- A. White lead
- B. Black
- C. Grey
- D. Light cream
Explanation: White lead reflects most incident radiation, giving it a very low absorption coefficient compared with black, grey, or light-coloured…
Correct answer: White lead- A. Radiation
- B. Natural convection
- C. Forced convection
- D. Conduction
Explanation: Forced convection occurs when fluid motion is produced by an external device or pressure change, such as a pump, fan, or compressor.
Correct answer: Forced convection- A. Total
- B. Monochromatic
- C. Neither A. nor B.
- D. Both A. & B.
Explanation: Kirchhoff’s radiation law relates emissive power and absorptivity for both total radiation and radiation at a specified wavelength, called…
Correct answer: Both A. & B.- A. Zero
- B. Maximum
- C. Minimum
- D. Infinity
Explanation: For parallel flow, equal hot- and cold-stream outlet temperatures make the terminal temperature difference zero.
Correct answer: Zero- A. Mainly confined to a thin film of fluid near the surface
- B. Uniformly distributed throughout the fluid
- C. In the central core of the fluid
- D. None of these
Explanation: Near a solid-fluid interface, the fluid velocity falls to zero and a strong temperature gradient develops across a thin boundary film.
Correct answer: Mainly confined to a thin film of fluid near the surface- A. Concentration boundary layer lies inside the thermal boundary layer
- B. Thermal boundary layer lies inside the concentration boundary layer
- C. Thermal & concentration boundary layers are of equal thickness
- D. Hydrodynamic (i.e., momentum) boundary layer is thicker than the other two
Explanation: Prandtl number compares momentum diffusivity with thermal diffusivity, while Schmidt number compares momentum diffusivity with mass…
Correct answer: Thermal boundary layer lies inside the concentration boundary layer- A. Condensation
- B. Radiation
- C. Conduction
- D. Natural convection
Explanation: Thermal diffusivity, α = k/(ρCp), governs the penetration of temperature changes into a material and is central to heat conduction…
Correct answer: Conduction- A. 0
- B. 1
- C. > 1
- D. < 1
Explanation: A cross-flow exchanger does not achieve the ideal countercurrent temperature distribution, so its LMTD correction factor is below unity.
Correct answer: < 1- A. Stefan-Boltzmann's
- B. Wien's displacement
- C. Planck's
- D. None of these
Explanation: Wien's displacement law states that the wavelength of maximum emission varies inversely with absolute temperature: λmaxT = constant.
Correct answer: Wien's displacement- A. Low density
- B. High viscosity
- C. Partial ionisation
- D. Dense structure
Explanation: Water conducts heat relatively well among liquids because its polar molecules form a strongly connected, hydrogen-bonded structure…
Correct answer: Partial ionisation- A. Transient heat conduction
- B. Natural convection
- C. Forced convection
- D. Radiation
Explanation: The Biot number, Bi = hLc/k, compares internal conduction resistance with surface convection resistance and is especially important in…
Correct answer: Transient heat conduction- A. Absorbs
- B. Transmits
- C. Reflects
- D. None of these
Explanation: A diathermanous material allows thermal radiation to pass through it, so it transmits radiation.
Correct answer: Transmits- A. Increases rapidly with temperature rise
- B. Is almost independent of temperature
- C. Both B. and C
- D. Is almost independent of pressure
Explanation: For a fixed concentration, boiling-point elevation is approximately ΔTb = Kb m, and its dependence on temperature and pressure is weak…
Correct answer: Both B. and C- A. Maximum resistance in the series
- B. Minimum resistance presents in the series
- C. Average of all resistances
- D. Sum of all resistances
Explanation: For conductive resistances arranged in series, the same heat rate passes through each resistance and the temperature drops add.
Correct answer: Sum of all resistances- A. 0.5
- B. 1
- C. > 2
- D. 1.5
Explanation: Prandtl and Reynolds analogies coincide when Pr = 1, because the momentum and thermal diffusivities are then equal.
Correct answer: 1- A. Having the value of Ao/Ai > 2
- B. Thick walled
- C. Thin walled having the value of Ao Ai/< 2
- D. Both B. and C.
Explanation: For a thin-walled cylinder, the inner and outer areas are close enough that their arithmetic mean can represent the heat-transfer area.
Correct answer: Thin walled having the value of Ao Ai/< 2- A. Only counter-flow of fluids
- B. Only parallel-flow of fluids
- C. Smaller pressure drop compared to 1-2 exchanger
- D. Both counter and parallel-flow of the fluids
Explanation: In a 2-4 exchanger, the multiple tube passes and shell-side flow arrangement produce both parallel-flow and counter-flow sections.
Correct answer: Both counter and parallel-flow of the fluids- A. 0.75 D
- B. 0.50 D
- C. 0.25 D
- D. None of these
Explanation: A 25% baffle cut means that 25% of the shell diameter is removed from the baffle, leaving a baffle height of 75% of the shell inside…
Correct answer: 0.75 D