Free Heat Transfer Operations MCQs with Answers

• A. 0.2 D
• B. 0.5 D
• C. 0.66 D
• D. 0.80 D

Explanation: Baffles should not be placed too close because this restricts shell-side flow and increases pressure drop; a usual minimum spacing is…

• A. Multipass fixed tube sheet
• B. None of these
• C. Single pass fixed tube sheet
• D. U-tube

Explanation: U-tube exchangers allow the tubes to expand and contract freely because each tube bends at the U-bend.

• A. Both B. & C.
• B. Refract
• C. Reflect
• D. Absorb or emit

Explanation: An ideal black body absorbs all incident radiation and therefore neither reflects nor transmits it; textbook treatments often express the…

• A. 970
• B. 180
• C. 3.97
• D. Data insufficient, can't be predicted

Explanation: For water, the specific heat is approximately 1 BTU/(lb·°F). Thus, sensible heat absorbed is 1 × (212 − 32) = 180 BTU.

• A. Kirchoff's
• B. Fourier's
• C. Planck's
• D. None of these

Explanation: Integrating Planck's spectral blackbody radiation law over all wavelengths gives the Stefan-Boltzmann law.

• A. 2 √(A1 . A2)
• B. √(A1 + A2)
• C. ½ √(A1 . A2)
• D. √(A1 . A2)

Explanation: The geometric mean of two positive quantities is the square root of their product.

• A. 2
• B. 1/2
• C. 4
• D. 1/4

Explanation: In a multipass shell-and-tube exchanger, the tube-side return loss is commonly taken as four velocity heads.

• A. Liquid metal
• B. Aqueous solution
• C. Water
• D. Lube oil

Explanation: Prandtl number is the ratio of momentum diffusivity to thermal diffusivity, and liquid metals have exceptionally high thermal diffusivity.

• A. Linear
• B. Hyperbolic
• C. Parabolic
• D. None of these

Explanation: With uniform internal heat generation in a cylinder, the radial conduction equation gives temperature varying with the square of radius.

• A. Convection becomes important
• B. Conduction becomes important
• C. Sub-cooled boiling occurs
• D. Radiation becomes important

Explanation: Beyond the Leidenfrost point, a stable vapour film separates the liquid from the hot surface, reducing direct conduction and convection.

• A. Evaporation
• B. Extractive distillation
• C. Leaching
• D. Absorption

Explanation: A Duhring plot compares the boiling point of a solution with that of the pure solvent at the same pressure.

• A. Steady state conduction
• B. Radiation
• C. Forced convection
• D. Natural convection

Explanation: View factor, also called configuration factor, specifies how much radiation leaving one surface reaches another.

• A. Scaling characteristics
• B. High viscosity
• C. Both A. & B.
• D. Neither A. nor B.

Explanation: Forced circulation keeps liquid moving rapidly through the heating tubes, reducing deposition and handling viscous liquids better.

• A. Colburn
• B. None of these
• C. Prandtl
• D. Reynolds

Explanation: The Reynolds analogy equates the heat-transfer and momentum-transfer relationships, giving the approximate relation Stanton number, Nst…

• A. Grashoff number
• B. Sherwood number
• C. Euler number
• D. Strouhal number

Explanation: The Grashof number measures the relative importance of buoyancy to viscous forces and is central to natural-convection heat transfer.

• A. Is thicker than hydrodynamic boundary layer
• B. And the hydrodynamic boundary layers are identical
• C. Is thinner than hydrodynamic boundary layer
• D. Disappears

Explanation: When Prandtl number exceeds one, momentum diffuses more rapidly than heat, so the velocity or hydrodynamic boundary layer is thicker.

• A. On polished surfaces
• B. None of these
• C. In the absence of agitation
• D. On rough surfaces

Explanation: Rough surfaces contain cavities that trap vapour and act as sites for bubble formation, so they promote nucleate boiling.

• A. > 0.6
• B. < 0.5
• C. 0.5
• D. < 0.1

Explanation: For turbulent heat transfer, molecular conduction in the turbulent core is usually negligible when the Prandtl number is greater than…

• A. 1200 W/m2.K
• B. 333 W/m2.K
• C. 894 W/m2.K
• D. 287 W/m2.K

Explanation: Add the fouling resistance to the clean exchanger resistance: 1/U = 1/400 + 1/2000 = 0.003 m²·K/W.

• A. Grashoff
• B. Nusselt
• C. Prandtl
• D. Stanton

Explanation: The dimensionless group Cpμ/k compares momentum diffusivity with thermal diffusivity and is the Prandtl number.