Free Heat Transfer Operations MCQs with Answers

• A. Increases
• B. None of these
• C. Remains same
• D. Decreases

Explanation: A decrease in BWG number means a thicker tube wall, so the inside diameter becomes smaller for the same outside diameter.

• A. 6.5 mm
• B. 6.5 cms
• C. Equal to tube I.D
• D. Equal to tube O.D

Explanation: The minimum ligament, or clear distance between adjacent tubes, in a square pitch layout is about 6.5 mm.

• A. The corrosive and fouling fluid should be preferably routed through the tubes
• B. Higher pressure fluid stream should be routed through the shell side
• C. Lower flow rate fluid should be routed through the shell side
• D. The viscous fluid should be routed through the shell side

Explanation: The higher-pressure fluid should preferably pass through the tubes because tubes can be designed and tested more economically for high…

• A. Is economical in operation
• B. Employs high velocity, high heat transfer rate and less heating surface requirement
• C. Employs a centrifugal pump placed between external downtake from vapor drum and inlet to
• D. Both B. & C.
• E. tube bundle

Explanation: Forced circulation evaporators use a centrifugal pump to drive liquor through the tube bundle at high velocity, increasing heat-transfer…

• A. Heat transfer between corrosive fluids
• B. Counter-current heat transfer systems
• C. Co-current heat transfer systems
• D. Cases where temperature difference between the shell and the tubes is more (>50°C)

Explanation: A floating head allows the shell and tubes to expand independently, so it is suitable when the shell-to-tube temperature difference is…

• A. Decreases very rapidly
• B. Increases very rapidly
• C. Remains constant
• D. Increases linearly

Explanation: As the temperature drop or approach becomes more severe, the exchanger temperature profile departs further from the ideal counter-current…

• A. Containing suspended solids flows at high velocity
• B. Containing suspended solids flows at low velocity
• C. Is highly viscous
• D. Is of high specific gravity

Explanation: Suspended solids deposit more readily when liquid velocity is low, adding thermal resistance and requiring a fouling factor in design.

• A. Hydrostatic head is required for refluxing the condensate
• B. Only the function of condensation is to be carried out
• C. Both the functions of condensation & sub cooling are carried out in a single unit
• D. Sub-cooling of condensate is desired

Explanation: A vertical condenser permits condensate to flow downward by gravity, allowing condensation and subsequent sub-cooling in the same unit.

• A. Salting
• B. Scaling
• C. Viscous
• D. Foamy

Explanation: Long-tube vertical evaporators are particularly suitable for foaming liquors because the liquor travels rapidly through the tubes and…

• A. Horizontal tube evaporator
• B. Short tube vertical evaporator
• C. Long tube vertical evaporator
• D. None of these

Explanation: In a horizontal-tube evaporator, heating steam condenses inside the horizontal tubes while the liquor flows over the outside surfaces.

• A. Low corrosiveness
• B. High specific heat
• C. Low dirt factor
• D. Low viscosity

Explanation: Water removes substantial heat because its specific heat is high, so a relatively large amount of energy is absorbed for each degree of…

• A. 0.5 to 0.8
• B. 0.25 to 0.50
• C. 0.05 to 0.15
• D. 0.8 to 0.9

Explanation: Rotary dryers normally operate with a small fraction of their internal volume occupied by solids, commonly about 0.05 to 0.15.

• A. Both A. & B.
• B. difference
• C. Economic limit reached, when the plant cost exceeds the saving of steam
• D. Practical limit reached, due to low heat transfer rate because of inadequate temperature
• E. Neither A. nor B.

Explanation: Adding effects eventually gives too little temperature difference per effect, reducing heat-transfer rates, while the extra equipment also…

• A. G0.8
• B. G0.5
• C. G0.2
• D. G1.5

Explanation: For turbulent flow in tubes, standard correlations such as Dittus-Boelter contain the mass-velocity term approximately to the 0.8 power.

• A. 0.99
• B. 0.95
• C. 0.80
• D. 0.55

Explanation: A correction factor below about 0.80 indicates an inefficient exchanger arrangement and a rapidly declining temperature-driving force.

• A. 2
• B. ½
• C. 8
• D. 4

Explanation: In a 1–2 exchanger, splitting the tubes into two passes approximately doubles the tube velocity, making friction loss about four times…

• A. Baffle spacing
• B. Clearance
• C. Pitch
• D. None of these

Explanation: Shell-side cross-flow area is determined from the shell diameter, baffle spacing, tube pitch and tube-to-tube clearance.

• A. Height is 25% of the I.D. of the shell
• B. Height is 75% of the I.D. of the shell
• C. Spacing is 75% of its height
• D. Width is 25% of its height

Explanation: A 25 percent segmental baffle cut means that 25 percent of the shell diameter is removed from the baffle.

• A. O.D. of the tube for square pitch
• B. Shortest distance between two adjacent tube holes
• C. Shortest centre to centre distance between adjacent tubes
• D. None of these

Explanation: Tube pitch is measured from the centre of one tube to the centre of the adjacent tube, using the shortest centre-to-centre distance.

• A. More
• B. Same
• C. Twice
• D. Less

Explanation: Triangular pitch gives greater shell-side turbulence and a larger heat-transfer coefficient than square pitch under comparable conditions.