Free Heat Transfer Operations MCQs with Answers

• A. 1.49
• B. 1
• C. 4.88
• D. None of these

Explanation: Converting the units gives 1 Btu/(hr·ft·°F) = 0.252 × 9/(0.3048 × 5) kcal/(hr·m·°C) ≈ 1.49. Therefore, option a is correct.

• A. Black & smooth
• B. Black & rough
• C. White & smooth
• D. White & rough

Explanation: A black surface absorbs and emits radiation strongly, while a rough surface generally has higher emissivity than a polished smooth…

• A. Brick
• B. Air
• C. Water
• D. Silver

Explanation: Silver has a very high thermal conductivity because its free electrons transport energy efficiently.

• A. Steam pressure
• B. Feed temperature
• C. Number of effect
• D. Both B. & C.

Explanation: Evaporator economy is strongly improved by using multiple effects and by feeding the solution hot, because less live steam is required per…

• A. Buffer zone
• B. Viscous sub-layer
• C. Both A. and B.
• D. Turbulent core

Explanation: For Prandtl number greater than one, thermal diffusivity is lower than momentum diffusivity, so the thermal boundary layer lies inside the…

• A. 1
• B. > 1
• C. < 1
• D. > 5

Explanation: When Prandtl number is less than 1, momentum diffuses more slowly than heat, so the thermal boundary layer becomes thicker than the…

• A. Remain unaffected
• B. Increases
• C. Increases exponentially
• D. Decreases

Explanation: Radiation intensity decreases as the source-receiver distance increases, following an inverse-square relationship for a point source.

• A. Decreases
• B. Increases
• C. Remains unchanged
• D. Increases exponentially

Explanation: For many liquid solutions, increasing solute concentration disrupts molecular energy transport and generally lowers thermal conductivity.

• A. d2T/dZ2 > 0
• B. d2T/dZ2 = 0
• C. d2T/dZ2 < 0
• D. dT/dZ = 0

Explanation: The endpoint temperature differences are 80 - 60 = 20°C and 50 - 30 = 20°C, so the temperature difference remains constant along the…

• A. Resistances in parallel
• B. Capacitors in series
• C. Resistances in series
• D. None of these

Explanation: In steady heat conduction, the same heat flux passes through each resistance in series, just as the same electric current passes through…

• A. High viscosity
• B. Low temperature gradients
• C. High co-efficient of thermal expansion
• D. Low density change with temperature

Explanation: Natural convection is strengthened by a large coefficient of thermal expansion because a given temperature difference produces a larger…

• A. St = f1/2
• B. St = f/4
• C. St = 4f
• D. St = f/2

Explanation: Reynolds analogy equates heat and momentum transfer as St = f/2 when f denotes the Fanning friction factor.

• A. The heat transfer rate is low in view of the large temperature drop
• B. It is difficult to maintain
• C. It is not economic
• D. None of these

Explanation: Film boiling creates a vapour film that acts as an insulating layer between the heating surface and liquid.

• A. Heat sensitive material can be handled
• B. Most concentrated liquid is at highest temperature
• C. There is no additional cost of pumping
• D. Equal heat transfer co-efficients exist in various effects

Explanation: In backward feed, the most concentrated and viscous liquid is heated in the last effect, where the temperature is highest.

• A. Does not affect
• B. Decreases
• C. Increases
• D. May increase or decrease, depends on the type of baffle

Explanation: Shell-side baffles force the fluid across the tubes instead of allowing it to flow mainly parallel to them.

• A. 3 x 10^5
• B. 3 x 10^12
• C. 3 x 10^10
• D. 3 x 10^8

Explanation: Electromagnetic radiation travels through vacuum at the speed of light, approximately 3 × 10^8 m/s.

• A. Facilitate cleaning of the exchanger
• B. Relieve stresses caused by thermal expansion
• C. Increase the heat transfer area
• D. Increase log mean temperature gradient

Explanation: A floating head allows one tube-sheet assembly to move relative to the shell.

• A. Bleed point
• B. Vent
• C. Catchall
• D. Baffle

Explanation: A catchall or entrainment separator is installed in the vapour line to intercept liquid droplets carried over with the vapour.

• A. Not related with
• B. Greater than
• C. Equal to
• D. Smaller than

Explanation: The pressure-drop equivalent diameter uses the full wetted perimeter, whereas the heat-transfer equivalent diameter uses only the heated…

• A. Accounts for additional resistances to heat flow
• B. Does not provide a safety factor for design
• C. Is a dimensionless quantity
• D. None of these

Explanation: A fouling factor represents the added thermal resistance caused by deposits such as scale, corrosion products, or biological films.