Free Heat Transfer Operations MCQs with Answers

• A. Give larger area per tube
• B. Use metal fins of low thermal conductivity
• C. Facilitate very large temperature drop through tube wall
• D. Are used for smaller heat load

Explanation: Fins extend the heat-transfer surface, giving a much larger area for a given tube size, especially when one fluid has a low heat-transfer…

• A. Long tube
• B. Falling film
• C. High pressure
• D. None of these

Explanation: A falling-film evaporator provides a short residence time and thin liquid film, limiting thermal damage to heat-sensitive juice.

• A. D-1.8
• B. D0.2
• C. D-0.2
• D. D1.8

Explanation: Since Nu = hD/k and Nu is proportional to Re^0.8, while Re is proportional to D at fixed velocity and fluid properties, h is proportional…

• A. Arithmetic
• B. Either A. or C.
• C. Geometric
• D. Logarithmic

Explanation: For radial conduction through a cylinder, area changes with radius, so the exact resistance contains ln(r2/r1).

• A. Tube diameter
• B. Tube layout
• C. Tube pitch
• D. Number of baffles

Explanation: Shell-side velocity is controlled mainly by the available shell-side flow area, which is changed by tube layout, tube pitch, and baffle…

• A. Parallel
• B. Same in either A , B. or C.
• C. Counter flow
• D. Mixed

Explanation: When one fluid is condensing or evaporating, its temperature remains nearly constant, so the terminal temperature differences and LMTD do…

• A. Supersaturated
• B. Wet
• C. Saturated
• D. None of these

Explanation: Saturated steam condenses directly at nearly constant temperature and releases its latent heat efficiently, giving a high film…

• A. Tar
• B. Coal
• C. Nitrogen
• D. Iron

Explanation: Iron has a much higher thermal conductivity than coal, nitrogen, or tar, allowing heat to pass through it more readily.

• A. Has the unit m2 /sec
• B. All A., B. and C.
• C. Is the ratio of thermal conductivity to thermal capacity
• D. Is defined as K/ρ . Cp

Explanation: Thermal diffusivity is α = k/(ρCp), with units m²/s, and represents how rapidly temperature disturbances spread through a material.

• A. Temperature difference
• B. Heat flux
• C. None of these
• D. That across the entire pipe

Explanation: The Nusselt number compares the temperature gradient at the wall with the characteristic temperature gradient across the fluid, often…

• A. Kcal/hr.m.°C
• B. Kcal/hr. m2 °C
• C. Kcal/hr.m
• D. Kcal/hr. °C

Explanation: Thermal conductivity relates heat-transfer rate to area, temperature difference, and length, giving units of heat/(time × length ×…

• A. Both the tube sheets floating
• B. Both the tube sheets fixed
• C. The top tube sheet floating and bottom tube sheet fixed
• D. The top tube sheet fixed and the bottom tube-sheet floating

Explanation: In a conventional calandria evaporator, the tube bundle is secured between fixed upper and lower tube sheets.

• A. 0
• B. 1
• C. 0.5
• D. 0.90

Explanation: A black body absorbs all incident radiation and emits the maximum possible radiation at a given temperature.

• A. Watt/m4. °K
• B. Watt/m2. °K
• C. Watt/m2. °K
• D. Watt/m.°K

Explanation: Thermal conductivity relates heat flux to temperature gradient, so its SI unit is W/(m·K).

• A. Forced convection and conduction
• B. Forced convection only
• C. Conduction only
• D. Free and forced convection

Explanation: Heat first crosses the stationary fluid layer next to the wall by conduction, then is carried through the moving liquid by forced…

• A. Thermal conductivity
• B. Thickness
• C. Temperature difference
• D. Heat transfer area

Explanation: Fourier's law gives heat-transfer rate as proportional to area, thermal conductivity, and temperature difference, but inversely…

• A. Increase
• B. Decrease
• C. Either increase or decrease; depends on the coolant flow rate
• D. Remain unchanged

Explanation: With condensing steam, the hot-side temperature is essentially constant, so reversing the coolant inlet and outlet temperatures only…

• A. Planck's law
• B. Kirchhoff's law
• C. Wien's law
• D. Stefan-Boltzmann law

Explanation: Planck's law gives the spectral, or monochromatic, emissive power as a function of wavelength and temperature.

• A. 1 and 0
• B. 0 and 1
• C. 1 and ∞
• D. 0 and 0.5

Explanation: A perfect black body absorbs all incident radiation and reflects none, so its absorptivity is 1 and reflectivity is 0.

• A. Low density
• B. Abundance & high heat capacity
• C. Low viscosity
• D. High fluidity

Explanation: Water is widely used because it is inexpensive and abundant and has a high specific heat, allowing it to remove substantial heat with a…