All Free Chemical Engineering MCQs with Answers

• A. Free convection
• B. Mixed convection (both free and forced)
• C. Entry length problem in laminar forced conduction (developing thermal boundary layer)
• D. Forced convection

Explanation: The ratio Gr/Re² compares buoyancy effects with forced-flow effects. When it is approximately one, both mechanisms are important, so the…

• A. J.m-2.K-1
• B. J.m-1.K-1
• C. W.m-2.K-1
• D. W-1m2K

Explanation: Thermal resistance is defined as temperature difference divided by heat-transfer rate, giving units K/W, equivalent to W⁻¹m²K for an…

• A. None of these
• B. Decreased
• C. No effect on
• D. Increased

Explanation: With hot feed in a multiple-effect evaporator, forward feeding generally improves economy because the feed enters at a relatively high…

• A. Temperature of the heating surface is more than the boiling point of the liquid
• B. Temperature of the heating surface is less than the boiling point of the liquid
• C. Bubbles from heating surface are absorbed by the mass of the liquid
• D. Very large vapour space is necessary

Explanation: In sub-cooled boiling, the bulk liquid is below its saturation temperature, while the heating surface must be above the local boiling…

• A. Between two bodies in physical contact with each other
• B. Between two bodies not in physical contact with each other
• C. From one part of a body to the another part of the same body
• D. Both B & C

Explanation: Conduction requires molecular or electronic interaction across a material interface, so two bodies must be in physical contact.

• A. Condensation rate
• B. Surface configuration
• C. All A., B. and C.
• D. Liquid flow rate from the surface

Explanation: The condensate-film thickness is governed by the condensate flow produced by condensation and by the surface geometry, such as a vertical…

• A. Greater than
• B. Half
• C. Is same as
• D. Lower than

Explanation: Dropwise condensation exposes much more of the cold surface directly to fresh condensate-free regions, giving a higher heat-transfer…

• A. 1
• B. > 1
• C. < 1
• D. Between 0 and 1

Explanation: Steam economy is the kilograms of water evaporated per kilogram of steam supplied.

• A. Viscosity of liquid is highest in first effect
• B. Transfer from effect to effect is done by pumps
• C. None of these
• D. No pump is required to withdraw the product from the last effect

Explanation: In forward feed, liquid flows from one effect to the next because of the pressure difference, without inter-effect pumps.

• A. Glazed
• B. Smooth
• C. Coated
• D. Oily

Explanation: Dropwise condensation requires a non-wetting surface so that condensate forms separate droplets rather than a continuous film.

• A. Density
• B. Pressure
• C. Viscosity
• D. Corrosiveness & fouling characteristics

Explanation: Fluid routing depends strongly on corrosiveness, fouling tendency, pressure and viscosity because these affect material selection…

• A. 6.12 x 10^5
• B. 3.06 x 10^5
• C. 7.24 x 10^5
• D. 9.08 x 10^5

Explanation: Salt in the feed is 300(0.20) = 60 kg/min, so the concentrated product is 60/0.30 = 200 kg/min and water evaporated is 100 kg/min.

• A. Lower economy
• B. A lower capacity
• C. A higher capacity
• D. None of these

Explanation: For a cold, viscous feed, backward feed sends the more concentrated liquid to the hotter effect, where its viscosity decreases and heat…

• A. Mass transfer between a gas and a liquid
• B. Absorption with chemical reaction
• C. Heat transfer in turbulent flow
• D. Heat transfer in laminar flow

Explanation: The Graetz number characterizes developing heat or mass transfer in internal flow, and in this context it is especially associated with…

• A. W/m
• B. W/°K
• C. W/m2
• D. W/m°K

Explanation: Thermal conductance is heat-transfer rate per unit temperature difference, so its SI unit is W/K, written here as W/°K.

• A. Transformer oil
• B. Water
• C. Molten sodium (a coolant used in fast breeder reactor)
• D. Dilute H2SO4

Explanation: The Prandtl number is the ratio of momentum diffusivity to thermal diffusivity.

• A. Is inversely proportional to the resistance across which the drop occurs
• B. None of these
• C. And the wall is not related
• D. And the wall are proportional to individual resistances

Explanation: For resistances in series, the heat rate is the same through each resistance and the temperature drop is ΔT = qR.

• A. Solution has an elevation of boiling point
• B. Evaporators operate under vacuum
• C. Evaporators operate at atmospheric pressure
• D. None of these

Explanation: A solution's boiling-point elevation reduces the effective temperature difference available in each effect, so the double-effect capacity…

• A. Grashoff
• B. Biot
• C. Stanton
• D. Reynolds

Explanation: Natural-convection heat transfer depends mainly on buoyancy and fluid-property effects, represented by the Grashof and Prandtl numbers, so…

• A. 0°C
• B. 0°K
• C. 100°C
• D. Room temperature

Explanation: Thermal radiation is emitted by matter at every temperature above absolute zero, although the intensity increases strongly with…