All Free Chemical Engineering MCQs with Answers
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6,983 questions · page 246 of 350
4901. The heat flux in the nucleate boiling regimes is proportional to (where, ΔT = excess temperature) ?
- A. (ΔT)3
- B. (ΔT)4
- C. (ΔT)2
- D. √(ΔT)
Explanation: In the nucleate-boiling region, empirical boiling correlations commonly give heat flux approximately proportional to the cube of excess…
Correct answer: (ΔT)3- A. Oily
- B. Coated
- C. Clean & smooth
- D. Dirty
Explanation: A clean, smooth surface is readily wetted by the condensate, allowing a continuous liquid film to form, which is film condensation.
Correct answer: Clean & smooth- A. Nucleate
- B. None of these
- C. Low pressure
- D. Pool
Explanation: Pool boiling occurs when a submerged heated surface boils a relatively stagnant liquid, allowing bubbles to rise and become absorbed into…
Correct answer: Pool4904. The separation of liquid droplets from the vapor is done by a/an _____________ in the evaporators?
- A. Entrainment separator
- B. Steam ejector
- C. Compressor
- D. Vacuum pump
Explanation: An entrainment separator, also called a vapor-liquid separator or demister, removes liquid droplets carried along with evaporator vapor.
Correct answer: Entrainment separator- A. 3
- B. 0.33
- C. 1
- D. 1.33
Explanation: With the same total heat-transfer area and terminal temperature conditions, the total temperature driving force is distributed among the…
Correct answer: 1- A. αT
- B. α T4
- C. α × 1/T
- D. Independent of T
Explanation: Wien's displacement law states that the wavelength of maximum black-body emission is inversely proportional to absolute temperature: λmaxT…
Correct answer: α × 1/T- A. More
- B. Unpredictable
- C. Same
- D. Less
Explanation: Equivalent diameter is four times the flow area divided by the wetted perimeter.
Correct answer: Less- A. 0
- B. ∞
- C. Equal to the difference between hot and cold fluids inlet temperature
- D. Equal to the difference between hot fluid inlet temperature and cold fluid outlet temperature
Explanation: For concurrent flow, one terminal temperature difference is the difference between the two outlet temperatures.
Correct answer: 0- A. Elastic
- B. Viscous
- C. Inertial
- D. None of these
Explanation: The Grashof number compares buoyancy effects caused by density variation with viscous resistance in natural convection.
Correct answer: Viscous- A. Hyperbolic
- B. Parabolic
- C. Linear
- D. Logarithmic
Explanation: For one-dimensional steady conduction through a plane wall with constant thermal conductivity, the temperature gradient is constant, so…
Correct answer: Linear- A. Open pan
- B. Long tube
- C. None of these
- D. Agitated film
Explanation: Agitated-film evaporators provide rapid heat transfer with short residence time, making them suitable for viscous or heat-sensitive…
Correct answer: Agitated film- A. 1/V̅ -0.8
- B. V̅ -0.8
- C. V̅ -2
- D. 1/ V̅ -2
Explanation: For flow inside condenser tubes, the film coefficient commonly varies approximately as V̅^0.8.
Correct answer: 1/V̅ -0.8- A. Higher condensing film co-efficient is desired
- B. Condensate is corrosive in nature
- C. Lower pressure drop through the exchanger is desired
- D. Temperature of the incoming vapor is very high
Explanation: A corrosive condensate is placed inside the tubes so the expensive corrosion-resistant material is limited to the tube side and cleaning…
Correct answer: Condensate is corrosive in nature- A. Cube
- B. Plate
- C. Sphere
- D. All will cool at the same rate
Explanation: For equal mass and material, the sphere has the smallest surface-area-to-volume ratio.
Correct answer: Sphere- A. Increases the rate of condensation
- B. Decreases thermal resistance
- C. Is desirable to increase the film co-efficient
- D. None of these
Explanation: A non-condensing gas accumulates near the condensing surface and adds mass-transfer and heat-transfer resistance.
Correct answer: None of these- A. Grashoff number
- B. Peclet number
- C. Reynolds number
- D. Prandtl number
Explanation: Natural convection is driven by buoyancy caused by density differences, and its relative strength is measured by the Grashof number.
Correct answer: Grashoff number- A. BTU/hr. °F. ft
- B. BTU/hr. ft2°F
- C. BTU/hr. °F
- D. BTU/hr. ft
Explanation: The heat-transfer coefficient relates heat flux to temperature difference, so its units are energy divided by time, area, and temperature…
Correct answer: BTU/hr. ft2°F- A. Finned tube heat exchanger with air inside and steam outside
- B. Shell and tube heat exchanger with air inside tubes and steam on shell side
- C. Finned tube heat exchanger with air outside and steam inside
- D. Shell and tube heat exchanger with air on shell side and steam inside tubes
Explanation: Air has a much lower heat-transfer coefficient than condensing steam, so fins should be placed on the air side to increase its effective…
Correct answer: Finned tube heat exchanger with air outside and steam inside- A. W/m.k
- B. W/m
- C. None, 'a' is just a number
- D. W/m.k2
Explanation: Since K has units W/(m·K) and T has units K, the coefficient a in K = K0 + aT must have units W/(m·K²).
Correct answer: W/m.k2- A. 0.6 to 120
- B. 0.001 to 1
- C. 0.5 to 5
- D. 120 to 400
Explanation: The Colburn heat and mass transfer analogy is commonly applied over approximately 0.6 < Pr < 120.
Correct answer: 0.6 to 120