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 22 of 33
- A. Scaling
- B. Salty
- C. Corrosive
- D. Highly viscous
Explanation: Open-pan evaporators have simple, accessible heating surfaces and can handle highly viscous solutions that circulate poorly in compact…
Correct answer: Highly viscous- A. Convection
- B. Conduction
- C. Radiation
- D. Both A. & C.
Explanation: When warm and cold liquids are mixed, bulk fluid motion carries energy from one portion to another, so convection is the dominant mode.
Correct answer: Convection- A. 2
- B. 20.8
- C. 20.2
- D. 20.5
Explanation: Adding a second pass approximately doubles the air velocity. Since the air-side film coefficient varies roughly as velocity to the 0.8…
Correct answer: 20.8424. It is not preferable to use superheated steam in evaporators, because of its very_________________?
- A. High temperature
- B. High pressure
- C. None of these
- D. Low film co-efficient
Explanation: Superheated steam must first be desuperheated before condensation begins, and heat transfer from superheated steam has a much lower film…
Correct answer: Low film co-efficient- A. Double pipe
- B. U-tube
- C. Fixed tube
- D. Floating head
Explanation: A double-pipe heat exchanger is commonly used for chilling oil during dewaxing because it provides a simple arrangement suitable for…
Correct answer: Double pipe- A. Forced convection
- B. None of these
- C. Monochromatic radiation
- D. Steady state conduction
Explanation: A heat-transfer process whose rate changes with time is called unsteady-state or transient heat transfer.
Correct answer: None of these- A. 165.4
- B. 167.5
- C. 172.5
- D. 175
Explanation: The total thermal resistance per unit area is 0.10/0.05 + 0.20/0.10 + 1/20 = 4.05 m²·°C/W.
Correct answer: 165.4- A. At a particular temperature
- B. For circular bodies
- C. None of these
- D. Under thermal equilibrium
Explanation: Kirchhoff’s law of thermal radiation states that absorptivity equals emissivity when a body is in thermal equilibrium with its…
Correct answer: Under thermal equilibrium- A. Both A. & B.
- B. Emitter
- C. Absorber
- D. Neither A. nor B.
Explanation: A perfect black body absorbs all incident radiation and, at a given temperature, emits the maximum possible radiation.
Correct answer: Both A. & B.- A. Biot
- B. Nusselt
- C. Reynolds
- D. Prandtl
Explanation: The heat-transfer j-factor is a dimensionless correlation commonly expressed as a function of Reynolds number, often with a Prandtl-number…
Correct answer: Reynolds- A. Liquid depth over the heating surface
- B. Solution being evaporated
- C. All A., B. and C.
- D. Pressure difference between the steam chest and the vapor space above the boiling liquid
Explanation: The effective temperature drop includes the steam-to-vapour pressure difference, boiling-point elevation caused by the solution, and…
Correct answer: All A., B. and C.- A. 0.2
- B. 0.4
- C. 0.6
- D. 0.8
Explanation: For a turbulent core at a Prandtl number around 0.6, turbulent eddy transport is much greater than molecular conduction, so direct…
Correct answer: 0.6- A. There is no risk of contamination
- B. Heat transfer co-efficient are high
- C. There is no mist formation
- D. Cost of equipment is lower
Explanation: Indirect exchangers keep the two fluids separated by a wall, preventing mixing and contamination.
Correct answer: There is no risk of contamination- A. Dowtherm
- B. Air
- C. Water
- D. Molten sodium
Explanation: Air has a much lower thermal conductivity and convective heat-transfer coefficient than water, molten sodium, or Dowtherm.
Correct answer: Air- A. Long vertical evaporator
- B. Horizontal tube evaporator
- C. Agitated film evaporator
- D. Calandria vertical tube evaporator
Explanation: An agitated film evaporator uses mechanical agitation to force and renew the liquid film over the heating surface, making it suitable for…
Correct answer: Agitated film evaporator- A. Logarithmic
- B. Arithmetic
- C. Geometric
- D. Either A., B. or C.
Explanation: Radial conduction through a cylinder varies with radius, so the appropriate area is based on the logarithmic mean radius or logarithmic…
Correct answer: Logarithmic- A. Re.Gz
- B. Nu, Gz
- C. Nu, Pr, Re
- D. Nu, Pr
Explanation: For laminar flow with developing thermal conditions, the Nusselt number is commonly correlated with the Graetz number, which combines…
Correct answer: Nu, Gz- A. Heat the water from 0°C to 100°C
- B. To superheat the steam
- C. Evaporate the water
- D. Data insufficient, can't be predicted
Explanation: The latent heat required to vaporise water at 1 atm is about 2257 kJ/kg, much greater than the sensible heating from 0 to 100°C or the…
Correct answer: Evaporate the water- A. Called the view factor
- B. Expressed in terms of radians
- C. Proportional to the square of the distance between surfaces
- D. Called the angle of vision
Explanation: The solid angle subtended by a finite surface at a radiating element is commonly called its angle of vision.
Correct answer: Called the angle of vision- A. Both A. & B.
- B. Dissolved O2
- C. CO2
- D. Neither A. nor B.
Explanation: Carbon dioxide dissolves in condensate to form carbonic acid, while dissolved oxygen promotes oxidation and pitting.
Correct answer: Both A. & B.