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 9 of 33
- A. Increasing the tube length
- B. Enhancing the fluid pumping rate
- C. Keeping the heat transfer surface clean
- D. None of these
Explanation: Deposits and dirt add thermal resistance between the fluid and the wall, lowering the overall heat-transfer coefficient.
Correct answer: Keeping the heat transfer surface clean- A. Ellipse
- B. Circular arc
- C. Parabola
- D. Straight line
Explanation: For a body cooling in a large surroundings at nearly constant temperature, Newton's law gives dT/dt proportional to the temperature…
Correct answer: Straight line- A. White & rough
- B. Black & rough
- C. White & polished
- D. Black & polished
Explanation: Radiation is greatest from a surface with high emissivity, and black, rough surfaces have much higher emissivity than white or polished…
Correct answer: Black & rough- A. Mass diffusivity to thermal diffusivity
- B. Thermal diffusivity to mass diffusivity
- C. Momentum diffusivity to thermal diffusivity
- D. Thermal diffusivity to momentum diffusivity
Explanation: Prandtl number is defined as the ratio of momentum diffusivity, represented by kinematic viscosity, to thermal diffusivity.
Correct answer: Momentum diffusivity to thermal diffusivity165. Rate of heat transfer by vaporisation from pools of water is affected by the ____________________?
- A. Nature of heating surface and distribution of bubbles
- B. Surface tension of water
- C. Viscosity of water
- D. All A., B. and C.
Explanation: Pool-boiling heat transfer depends on bubble formation and departure, which are influenced by surface condition, surface tension and…
Correct answer: All A., B. and C.- A. Facilitate removal of non-condensable gases
- B. Remove the product
- C. Admit the feed
- D. Create vacuum
Explanation: Bleed points allow trapped air and other non-condensable gases to escape from the evaporator.
Correct answer: Facilitate removal of non-condensable gases- A. Increases
- B. Decreases
- C. Remains unchanged
- D. Increases exponentially
Explanation: For steel, increasing temperature generally increases lattice scattering of conducting electrons, so thermal conductivity decreases over…
Correct answer: Decreases- A. Same as average heat transfer co-efficient for tube side
- B. Zero
- C. Infinity
- D. None of these
Explanation: At the tube entrance, the thermal boundary layer starts with essentially zero thickness, so the local temperature gradient and hence the…
Correct answer: Infinity- A. Interfacial tension
- B. Liquid viscosity
- C. Hot surface temperature
- D. Liquid density
Explanation: Interfacial tension strongly controls the force holding a vapour bubble to the heated surface and therefore affects the size and rate of…
Correct answer: Interfacial tension- A. Type of absorbing surface
- B. None of these
- C. Surface area and temperature of the heat source
- D. Distance between the heat source and the object receiving the heat
Explanation: Radiation exchange depends on the absorbing surface, separation distance, emitting area and temperature, so each listed factor can affect…
Correct answer: None of these- A. 1
- B. 1/2
- C. 2
- D. 4
Explanation: With the same total flow and tube dimensions, a double-pass exchanger sends the flow through roughly half as many parallel tubes during…
Correct answer: 2- A. Brinkman number
- B. Stanton number
- C. Peclet number
- D. Schmidt number
Explanation: The Schmidt number, Sc = ν/D, compares momentum diffusivity with mass diffusivity and belongs primarily to mass transfer.
Correct answer: Schmidt number- A. Kopp's
- B. Antoine
- C. Lee's
- D. Kistyakowsky
Explanation: Kopp's equation correlates the thermal conductivity of a solid with temperature.
Correct answer: Kopp's- A. Temperature distribution is independent of time
- B. Temperature distribution is dependent on time
- C. Heat flows in one direction only
- D. Three dimensional heat flow is concerned
Explanation: Unsteady or transient conduction is identified by a temperature field that changes with time, even if heat flows in only one direction.
Correct answer: Temperature distribution is dependent on time- A. t = 283 s
- B. t = 800 s
- C. t = 400 s
- D. t = 356 s
Explanation: For a semi-infinite rod with a suddenly fixed end temperature, temperature depends on x divided by the square root of time.
Correct answer: t = 800 s- A. 1 to 2
- B. 1000 to 2000
- C. 100 to 500
- D. 5 to 10
Explanation: For water near ordinary engineering temperatures, the Prandtl number is commonly of the order of 5 to 10, decreasing as temperature rises.
Correct answer: 5 to 10- A. Contaminated cooling
- B. Smooth clean
- C. Clean and dirt free
- D. Polished
Explanation: Dropwise condensation is promoted by a contaminated or coated surface that does not allow the condensate to spread as a continuous film.
Correct answer: Contaminated cooling- A. Decrease
- B. First increase and then decrease
- C. First decrease and then increase
- D. Increase
Explanation: For a cylindrical pipe, adding insulation first increases the outer area and can increase heat loss until the critical insulation radius…
Correct answer: First increase and then decrease- A. 0.5
- B. 1
- C. 0
- D. 2
Explanation: An opaque body transmits no radiation, so its absorptivity and reflectivity account for all incident radiation. Therefore, α + ρ = 1.
Correct answer: 1- A. Basket type
- B. Long tube vertical
- C. Short tube vertical
- D. Horizontal tube
Explanation: In a horizontal-tube evaporator, steam is passed inside the horizontal tubes while the liquor flows over their outer surfaces.
Correct answer: Horizontal tube