Free Heat Transfer Operations MCQs with Answers

• A. Increased steam economy
• B. Both A. and B.
• C. Decreased steam consumption
• D. Increased capacity

Explanation: In a multiple-effect evaporator, vapor from one effect heats the next effect, allowing the same steam to evaporate solvent repeatedly.

• A. Both A. and B.
• B. Form friction
• C. Wall or skin friction
• D. Turbulent flow

Explanation: Heat-transfer and friction analogies relate wall shear stress to heat transfer at the fluid-solid interface, so they apply to skin or wall…

• A. U1 - U2
• B. U2 - U1
• C. 1/U2 - 1/U1
• D. 1/U1 - 1/U2

Explanation: The fouling resistance is the added thermal resistance caused by deposits, so 1/U_dirty = 1/U_clean + R_f.

• A. (1/U) Vs. (1/v0.8)
• B. (1/v0.8) Vs. U
• C. v0.8 Vs . U
• D. (1/U) Vs. (1/V)

Explanation: A Wilson plot linearizes the overall-resistance relation by plotting 1/U against the inverse velocity term, commonly 1/v^0.8.

• A. 35.5
• B. 43.75
• C. 81.25
• D. 48.25

Explanation: At steady state, conduction through the wall equals convection from the oven air: (T_w − 25)k/l = (100 − T_w)(3k/l).

• A. Decreases the pressure drop
• B. Decreases the outlet temperature of cooling medium
• C. Increases the overall heat transfer coefficient
• D. None of these

Explanation: Multipassing increases the tube-side fluid velocity for the same flow rate and flow area per pass.

• A. 1
• B. 2
• C. 3.5
• D. 5.5

Explanation: Calandria evaporators use relatively short vertical heating tubes, normally below about 2 m, to limit liquid head and circulation…

• A. 1.25
• B. 1.75
• C. 2.5
• D. 3.5

Explanation: The usual minimum tube pitch is about 1.25 times the tube outside diameter, providing enough ligament between adjacent tubes for…

• A. Results in higher shell side pressure drop
• B. Can accomodate less number of tubes for a given shell diameter
• C. Facilitates easier shell side cleaning; hence is more suitable for handling high dirt factor shell
• D. side fluid
• E. Creates relatively lower turbulence on the shell side resulting in lower shell side heat transfer
• F. co-efficient

Explanation: Triangular pitch places tubes closer together and forces the shell-side fluid through more tortuous passages, giving higher turbulence and…

• A. Regenerative
• B. Finned
• C. Plate type
• D. Double pipe

Explanation: A double-pipe exchanger consists of one pipe inside another, with the flow reversing through a return leg in the common hairpin…

• A. 4
• B. 1/2
• C. 2
• D. 1/4

Explanation: A 1-4 exchanger divides the same total tube flow among four passes, so the number of tubes carrying flow in each pass is one-fourth that…

• A. 8 : 1 to 12 : 1 for both liquid-liquid and gas-gas heat exchangers
• B. Both B. & C.
• C. < 4 : 1 for gas-gas exchangers
• D. 4 : 1 to 8 : 1 for liquid-liquid exchanger

Explanation: Liquid-liquid exchangers commonly use a tube-length-to-shell-diameter ratio of about 4:1 to 8:1.

• A. nth
• B. 0.5 nth
• C. (1/n)th
• D. 1.5 nth

Explanation: For a fixed total heating surface, adding effects divides the available surface among the effects, so evaporation per unit surface is…

• A. Equal to
• B. Three fourth
• C. Half
• D. 1.5 times

Explanation: The tube sheet is normally made about equal in thickness to the tube outside diameter, subject to the stated minimum thickness of 22 mm.

• A. 1
• B. ∞
• C. 20.8
• D. 2

Explanation: Since tube-side film coefficient varies approximately as flow rate^0.8, the overall coefficient follows the same dependence only when…

• A. Flow at a very slow velocity
• B. Preferably flow outside the tube
• C. Preferably flow inside the tube for its easier internal cleaning
• D. Flow outside the tube, when the flow is counter-current and inside the tube when the flow is
• E. co-current

Explanation: A corrosive, fouling fluid is preferably passed through the tubes because the tube side can be mechanically or chemically cleaned more…

• A. Are easier to clean
• B. Are less prone to fouling
• C. Can be fitted into a smaller shell diameter hence the cost of the heat exchanger would be less
• D. None of these

Explanation: For the same heat-transfer area, smaller tubes provide more area per unit shell diameter, so the required shell can be smaller and…

• A. Tube dia of 2.5-7.5 cms, tube length of 75-200 cms and cylindrical drum dia of 1-6 metres are
• B. normally used
• C. Area of central downtake is equal to 40 to 100% of total cross-sectional area of the
• D. All A., B. & C.
• E. Liquor is inside the tube while the steam is outside the tube
• F. surrounding tube

Explanation: A short-tube calandria uses relatively short tubes with liquor inside the tubes and heating steam outside; the central downtake provides…

• A. 1.25-1.50 times
• B. Less than
• C. 2.5 times
• D. one-fourth of

Explanation: Tube pitch is commonly about 1.25 to 1.5 times the tube outside diameter, providing space for shell-side flow, fabrication, and tube…

• A. To increase the residence time of shell side fluid
• B. To increase the tube side heat transfer co-efficient by inducing turbulence
• C. To reduce the induced vibration in the tubes
• D. To provide support to the tube bundle

Explanation: Baffles increase shell-side residence time, support the tubes, and limit vibration by directing cross-flow.