All Free Chemical Engineering MCQs with Answers

• 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…

• 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.