Free Heat Transfer Operations MCQs with Answers

• A. 2.5 metres
• B. 6 metres
• C. 10 metres
• D. 0.5 metre

Explanation: Heat-exchanger tubes are commonly manufactured in practical lengths such as 2.5 and 6 m, while 10 m tubes are generally too long for usual…

• A. Characteristic of process fluid
• B. All A., B. and C.
• C. Suspended solids in the fluid
• D. Velocity of process fluid containing suspended solids

Explanation: Fouling depends on the fluid characteristics, the concentration of suspended solids, and their velocity because these factors control…

• A. 1000
• B. 3000
• C. 5000
• D. 10000

Explanation: Entrance and developing-flow effects influence the inside film coefficient at lower Reynolds numbers, but their effect becomes negligible…

• A. 1250
• B. 2500
• C. 7500
• D. 15000

Explanation: Condensing steam provides a high heat-transfer coefficient, and for ordinary design conditions a value near 7500 kcal/(h·m²·°C) is…

• A. Layout
• B. Both A. & B.
• C. Pitch
• D. Neither A. nor B.

Explanation: Shell-side velocity is affected by the free flow area between tubes. Changing tube layout or tube pitch changes this area, so either…

• A. 3-5
• B. 8-15
• C. 5-11
• D. 12-18

Explanation: The minimum carbon-steel shell thickness of a shell-and-tube exchanger increases with shell diameter and commonly falls in the approximate…

• A. Permits the use of less tubes in a given shell diameter
• B. Facilitates comparatively easier external cleaning because of large clearance
• C. Permits the use of more tubes in a given shell diameter
• D. Both B. and C.

Explanation: Triangular pitch places tubes more closely than square pitch, so more tubes fit within the same shell diameter.

• A. √(2d)
• B. √d
• C. √(2πd)
• D. d

Explanation: The equivalent diameter is 4A/P, where A is flow area and P is wetted perimeter. For a square duct, 4(d²)/(4d) equals d.

• A. Orifice
• B. Segmental
• C. Disk and ring
• D. Independent of the type of

Explanation: Orifice baffles force the shell-side stream through restricted openings, producing strong jetting and the greatest pressure loss among the…

• A. 1/2 and 8
• B. 1/64 and 1/8
• C. 1/8 and 1/64
• D. 1/2 and 5

Explanation: The usual tube-sheet hole groove dimensions are about 1/8 inch in width and 1/64 inch in depth.

• A. It makes condenser compact
• B. More thinner tubes can be used
• C. Pressure drop is reduced
• D. It reduces heat transfer area

Explanation: Using multiple tube-side passes increases the cooling-water velocity and therefore the tube-side heat-transfer coefficient, reducing the…

• A. Hold baffle in space
• B. Fix the tubes in position
• C. Account for thermal strain
• D. None of these

Explanation: Tie rods run through the tube bundle and maintain the spacing of the segmental baffles, usually together with spacer tubes.

• A. 0.01 to 1
• B. 1.5 to 2.5
• C. 5 to 10
• D. 10 to 20

Explanation: Rotary dryers are generally designed economically for a modest number of heat-transfer units, about 1.5 to 2.5.

• A. Tube dia is 3-6 cms, while tube length in 3-6 metres
• B. Steam is fed to the shell, whereas the liquor is filled inside the tube
• C. None of these
• D. Liquor level is maintained at 1/3rd to 1/2 of the height of the tube

Explanation: All three statements describe normal features of a long-tube vertical evaporator: steam is outside the tubes, liquor flows inside them…

• A. 4(0.86P2 - πd2/4)/πd
• B. (P2 - πd2/4)/πd
• C. 4(0.86P2 - πd2)/πd
• D. (4P2 + πd2/4)/πd

Explanation: Equivalent diameter is four times the flow area divided by the wetted perimeter.

• A. Reducing scale deposition
• B. Creating turbulence
• C. Fixing the tubes
• D. Increasing pressure drop

Explanation: Shell-side baffles force the fluid to flow across the tubes rather than straight along the shell, increasing mixing and turbulence and…

• A. Equal to
• B. Four times
• C. Twice
• D. Half

Explanation: Segmental baffles must be stiff enough to support the tube bundle and resist vibration, so their thickness is commonly about twice the…

• A. Triangular pitch
• B. Square pitch
• C. Diagonal square pitch
• D. Heat transfer rate is independent of tube arrangement

Explanation: Triangular pitch packs more tubes into a given shell area and produces stronger shell-side turbulence, giving a higher heat-transfer rate…

• A. (kcal/hr.m2.°C)-1
• B. (BTU/hr.ft2. °F)-1
• C. (W/m2.°K)-1
• D. (kcal/hr. m. °C)-1

Explanation: A cooling-water fouling resistance is commonly about 0.001 to 0.003 hr·ft²·°F/Btu, representing the added resistance caused by deposits on…

• A. Half
• B. Twice
• C. Thrice
• D. Five times

Explanation: For comparable conditions, condensate drains more effectively from a horizontal tube surface and the condensation coefficient is commonly…