Free Heat Transfer Operations MCQs with Answers

• A. Grey
• B. White
• C. Black
• D. Any colour

Explanation: The basic Stefan-Boltzmann law, E = σT⁴, describes total emission from an ideal black body.

• A. 1 kcal/hr. m2°C
• B. 4.88 kcal/hr. m.2°C
• C. 1 kcal/hr. m2.°K
• D. None of these

Explanation: Converting Btu to kcal, square feet to square metres, and degrees Fahrenheit to degrees Celsius gives approximately 4.88 kcal/(h·m²·°C).

• A. Basket type
• B. Horizontal
• C. Long tube vertical
• D. None of these

Explanation: A basket-type evaporator uses an annular downtake, allowing liquid circulation around the heating-surface basket.

• A. Increases
• B. Decreases
• C. Remains unchanged
• D. May increase or decrease; depends on its composition

Explanation: For liquids such as fresh lubricating oil, thermal conductivity generally decreases as temperature rises because increased molecular…

• A. 1-2 heat exchanger
• B. 3-2 heat exchanger
• C. 1-1 heat exchanger
• D. 2-4 heat exchanger

Explanation: A 1-1 exchanger has only one tube-side pass, so the same flow is distributed through a longer flow area with lower velocity and pressure…

• A. Nucleate
• B. Saturated
• C. Pool
• D. Local

Explanation: Local boiling occurs when the bulk liquid is below its saturation temperature but the liquid immediately next to the heated surface…

• A. High
• B. Low
• C. Extremely low
• D. No

Explanation: At high Prandtl numbers, momentum diffusivity is much greater than thermal diffusivity, so heat conduction is relatively negligible in the…

• A. Log mean temperature difference
• B. Approach
• C. Arithmetic mean temperature difference
• D. Geometric mean temperature difference

Explanation: The temperature difference between the two fluids at an exchanger end is called an approach temperature difference, or approach.

• A. CPA > CPB
• B. CPA < CPB
• C. kA < 0.5 kB
• D. kA >2 kB

Explanation: At steady state the same heat flux passes through both plates, so the temperature drop is proportional to thickness divided by…

• A. Re and Pr
• B. Re and Gr
• C. Pr and Gr
• D. Re and Sc

Explanation: For forced convection, the Nusselt number is commonly correlated using Reynolds number for the flow regime and Prandtl number for the…

• A. In low range of temperature differences
• B. In high range of temperature differences
• C. Because of its low cost
• D. To prevent corrosion of the tube bundles

Explanation: A floating tube bundle allows the tubes to expand and contract independently of the shell, so it is preferred when the temperature…

• A. Medium
• B. Temperature
• C. None of these
• D. Surface

Explanation: The Stefan-Boltzmann constant is a universal physical constant, with a fixed value of approximately 5.67 × 10⁻⁸ W/m²·K⁴.

• A. Occupies smaller space
• B. Is more economical
• C. Is easy to operate and maintain
• D. All A., B. and C.

Explanation: Shell-and-tube exchangers are suitable for large areas because they provide a relatively compact arrangement, reasonable cost, and…

• A. > 10
• B. 10
• C. < 10
• D. Either B. or C., depends on the mass of the body

Explanation: Under Newton’s law of cooling, the cooling rate decreases as the body approaches its surroundings’ temperature.

• A. 0.5 to 50
• B. 1 to 100
• C. 10 to 100
• D. 100 to 1000

Explanation: Most engineering heat-transfer radiation lies roughly within the infrared region, commonly taken as about 0.5 to 50 micrometres for this…

• A. Condense the steam flowing in the pipeline
• B. Remove water resulting from partial condensation of steam
• C. Stop the supply of steam
• D. None of these

Explanation: A steam trap automatically discharges condensate formed when steam loses heat while retaining live steam in the pipeline.

• A. None of these
• B. Outlet temperature of both the hot and cold fluid are same
• C. Outlet temperature of hot fluid is less than the outlet temperature of the cold fluid
• D. Cold fluid is heated to a certain temperature by condensing steam (isothermal fluid)

Explanation: When one fluid condenses, its temperature remains essentially constant, so the terminal temperature differences are the same…

• A. Remove non-condensable gases
• B. Purge the condenser
• C. Facilitate easy cleaning of tubes
• D. None of these

Explanation: Vent pipes release air and other non-condensable gases from the condenser, since these gases reduce the effective condensing area and…

• A. Lower tube side pressure drop
• B. Higher tube side heat transfer co-efficient
• C. Lower shell side pressure drop
• D. Higher shell side heat transfer co-efficient

Explanation: In a 1-2 exchanger, the fluid makes two tube passes, approximately doubling its velocity compared with a 1-1 exchanger.

• A. Von-Karman
• B. Reynolds
• C. Prandtl
• D. Colburn

Explanation: The correction factor involving 5(Npr − 1)√(f/2) accounts for the difference between momentum and heat diffusivity in the Prandtl analogy.