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 14 of 33
- A. Emissivity = 0
- B. Reflectivity = 1
- C. Absorptivity = 1
- D. Transmissivity = 1
Explanation: A black body absorbs all incident radiation, so its absorptivity is 1; correspondingly, its reflectivity and transmissivity are zero and…
Correct answer: Absorptivity = 1- A. High pressure
- B. None of these
- C. Backward feed
- D. Vacuum
Explanation: Vacuum evaporation lowers the boiling temperature, which is suitable for materials whose solubility decreases as temperature rises.
Correct answer: Vacuum- A. Condensation of the saturated vapor on a cold surface
- B. Boiling of a liquid on a hot surface
- C. Heat transfer between two highly viscous liquids
- D. Concentration of a corrosive solution by evaporation
Explanation: The Leidenfrost point is the surface temperature above which a stable vapour film forms between a hot surface and a boiling liquid.
Correct answer: Boiling of a liquid on a hot surface- A. Dowtherm
- B. Liquid metal (e.g. molten sodium)
- C. Mercury
- D. Fused salts (e.g., an eutectic mixture of 53% KNO3, 40% NaNO2and 7% NaNO3)
Explanation: Dowtherm, molten metals such as sodium, and fused salts are used as high-temperature heating media.
Correct answer: Mercury- A. 20.8
- B. 40.8
- C. 40.4
- D. 20.4
Explanation: For turbulent flow in a tube, the inside heat-transfer coefficient varies approximately as velocity^0.8.
Correct answer: 40.8- A. Through a metallic wall
- B. By direct contact of hot flue gas with air
- C. None of these
- D. hot material
- E. By heating an intermediate material (like chequor bricks) and then heating the air from this
Explanation: A regenerative air preheater first stores heat in a solid intermediate material such as chequer bricks.
Correct answer: By heating an intermediate material (like chequor bricks) and then heating the air from this- A. 6000
- B. 24000
- C. 60000
- D. 48000
Explanation: The 4000 kg of caustic soda represents 25% of the final solution, so the final solution is 4000/0.25 = 16000 kg.
Correct answer: 24000- A. 1.66
- B. 88.66
- C. 3.66
- D. Dependent on NRe only
Explanation: For fully developed laminar flow in a circular tube with constant wall temperature, the Nusselt number reaches the standard limiting value…
Correct answer: 3.66- A. Corrosiveness
- B. Fouling characteristic
- C. Viscosity
- D. None of these
Explanation: Corrosiveness, fouling tendency, and viscosity all influence whether a fluid should flow through the tubes or shell side.
Correct answer: None of these- A. 1
- B. 0
- C. 0.78
- D. 0.95
Explanation: A black body absorbs all incident radiation, so its absorptivity is unity.
Correct answer: 1- A. Exit-fluid temperature > wall temperature
- B. Exit fluid temperature = wall temperature
- C. Exit fluid temperature < wall temperature
- D. Graetz number > 100
Explanation: In the asymptotic condition, the fluid temperature approaches the constant wall temperature as the tube length becomes very large.
Correct answer: Exit fluid temperature = wall temperature- A. High vacuum in the evaporator
- B. High evaporation rate
- C. Foaming of the solution
- D. High heat transfer rate
Explanation: Foaming carries liquid droplets into the vapour outlet, producing entrainment in evaporators.
Correct answer: Foaming of the solution- A. Provide very large heat transfer co-efficient
- B. Results in making part of the heating surface inactive
- C. Results in abruptly increased velocity
- D. None of these
Explanation: When the outlet temperature approaches the heating-fluid or wall temperature, increasing the exchanger length gives negligible additional…
Correct answer: Results in making part of the heating surface inactive- A. Both A. and B.
- B. Less surface area is required for a given heat transfer rate
- C. LMTD is greater
- D. More surface area is required for a given heat transfer rate
Explanation: For the same terminal temperatures, countercurrent flow generally gives a larger LMTD than parallel flow.
Correct answer: Both A. and B.- A. 1
- B. < 1
- C. > 1
- D. None of these
Explanation: The economy of a single-effect evaporator is normally less than unity because some steam heat is consumed in heating the feed and is lost…
Correct answer: < 1- A. Heat exchanger
- B. Condenser
- C. Multiple effect evaporator
- D. Steam jacketed kettle
Explanation: A steam-jacketed kettle is suitable for small-scale evaporation because steam heats the vessel indirectly and the liquor can be evaporated…
Correct answer: Steam jacketed kettle- A. < 1
- B. > 1
- C. 1
- D. ∞
Explanation: Counter-current flow maintains a larger average temperature-driving force than parallel flow for the same terminal temperatures, so its…
Correct answer: < 1- A. Dense structure
- B. High proportion of air space
- C. High specific heat
- D. None of these
Explanation: Insulating materials contain many small air spaces, and trapped air has very low thermal conductivity.
Correct answer: High proportion of air space279. In case of a vertical tube evaporator, with increase in the liquor level, the___________________?
- A. True temperature drop increases
- B. Capacity of the evaporator is increased
- C. Capacity of the evaporator is decreased
- D. Both B. and C.
Explanation: Raising the liquor level in a vertical-tube evaporator increases the hydrostatic pressure and boiling-point elevation, reducing the…
Correct answer: Capacity of the evaporator is decreased- A. Heating volume
- B. None of these
- C. Nusselt number
- D. Heat transfer area
Explanation: The heat-transfer rate is expressed as Q = UAΔT, where U is the overall coefficient, A is the heat-transfer area, and ΔT is the…
Correct answer: Heat transfer area