All Free Chemical Engineering MCQs with Answers

• A. Asymptotic
• B. Hyperbolic
• C. Parabolic
• D. Linear

Explanation: For steady one-dimensional conduction through a plane wall with constant thermal conductivity and no heat generation, the heat flux is…

• A. 1
• B. 10
• C. 20
• D. 30

Explanation: Tube-side water velocity is commonly kept near 1 m/s as an upper practical value in heat exchangers to limit erosion, vibration, and…

• A. Yellow paint
• B. White paint
• C. Black paint
• D. Grey paint

Explanation: Black surfaces absorb the greatest fraction of incident solar radiation because they have high absorptivity.

• A. Saving of steam
• B. Realisation of multiple effect economy in a single effect
• C. None of these
• D. Both A. and B.

Explanation: Thermo-compression recompresses the vapour so it can serve again as the heating medium, reducing fresh-steam consumption.

• A. All A., B. and C.
• B. Flow velocity
• C. Turbulence of shell side fluid
• D. Rate of heat transfer

Explanation: Transverse baffles force the shell-side fluid across the tubes, increasing its velocity and turbulence.

• A. Conduction
• B. Radiation
• C. Forced convection
• D. Natural convection

Explanation: Radiation transfers energy through electromagnetic waves and can occur through a vacuum, unlike conduction and convection, which require…

• A. Temperature gradient of the wall to that across the entire pipe
• B. Heat flux at the wall to that across the entire pipe
• C. Temperature difference to the temperature gradient at the wall
• D. None of these

Explanation: The Nusselt number, Nu = hL/k, compares convective heat flux at a wall with the conductive heat flux through the fluid over the…

• A. Mass diffusivity × Momentum diffusivity
• B. Thermal diffusivity × Momentum
• C. Thermal diffusivity × Mass diffusivity
• D. Thermal diffusivity/Momentum diffusivity

Explanation: Prandtl number is the ratio of momentum diffusivity to thermal diffusivity, Pr = ν/α.

• A. < 1
• B. > 1
• C. 1
• D. Between 1 & 2

Explanation: The LMTD correction factor accounts for the departure of a multipass exchanger from ideal countercurrent flow and is normally less than…

• A. Decreases
• B. Increases
• C. Remains unchanged
• D. May increase or decrease; depends on the gas

Explanation: At low gas density, gas molecules travel relatively freely between collisions, and their thermal conductivity generally increases as…

• A. Remain same
• B. Decreases
• C. Increases
• D. May increase or decrease depending on the type of gas

Explanation: Gas molecules move faster at higher temperature, increasing the transport of molecular energy and hence thermal conductivity.

• A. None of these
• B. Arithmetic mean area
• C. Geometric mean area
• D. Logarithmic mean area

Explanation: Radial heat flow through a cylinder occurs over an area that changes with radius, so the appropriate equivalent area is the logarithmic…

• A. Shape and porosity of the body
• B. Surface temperature of the body
• C. Nature of the surface
• D. Wavelength of radiation

Explanation: Radiation emission depends on wavelength, surface temperature and surface nature or emissivity.

• A. Constant overall heat transfer co-efficient.
• B. Constant rate of fluid flow
• C. Constant specific heat
• D. No partial phase change in the system

Explanation: The LMTD derivation assumes a constant flow rate, but density and therefore volumetric flow can change substantially as a fluid is heated…

• A. (r1 - r2)/-ln(r1/r2)
• B. (r1 - r2)/ln(r2/r1)
• C. (r2 - r1)/ln(r1/r2)
• D. (r1 - r2)/ln(r1/r2)

Explanation: The logarithmic mean is obtained by dividing the difference of the two values by the logarithm of their ratio: (r1 − r2)/ln(r1/r2).

• A. 4.36
• B. 2.36
• C. 120.36
• D. Dependent on NRe only

Explanation: For fully developed laminar flow in a circular tube with constant wall heat flux, the standard Nusselt number is Nu = 4.36.

• A. Average
• B. Sum
• C. Product
• D. Geometric mean

Explanation: In series, heat passes successively through each resistance, so the temperature drops add.

• A. n = 0.4 is used for heating
• B. n = 0.3 is used for cooling
• C. Reynolds number for the flow involved is < 2100
• D. Reynolds number for the flow involved is > 10000

Explanation: The Dittus-B​oelter correlation is intended for turbulent flow, typically with Reynolds number above about 10,000.

• A. Pe = Nu.Re
• B. Pe = Re/Pr
• C. Pe = Pr/Re
• D. Pe = Re.Pr

Explanation: For heat transfer, the Peclet number compares convective transport with thermal diffusion and is Pe = Re × Pr.

• A. Thermal conductivity
• B. Thermal diffusivity
• C. Heat transfer co-efficient
• D. Stefan-Boltzmann constant

Explanation: Fourier’s law is q = −kA(dT/dx), where k is the thermal conductivity. Thermal diffusivity instead measures the rate at which temperature…