Lakshya Education MCQs

Question: For concentrating an aqueous solution of a material like anhydrous Na₂SO₄, whose solubility decreases with rise in temperature, the most suitable evaporator is a __________ evaporator.
Options:
A.High pressure
B.Vacuum
C.Backward feed
D.None of these
Answer: Option B

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Question 1. The purpose of providing a 'catchall' in the vapor line of an evaporator is to
  1.    Create vacuum
  2.    Regulate the vapor flow
  3.    Vent the non-condensible gases
  4.    Arrest the entrained liquid
Answer: Option D
Question 2. A dilute aqueous solution is to be concentrated in an evaporator system. High pressure steam is available. Multiple effect evaporator system is employed, because
  1.    Total heat transfer area of all the effects is -less than that in a single effect evaporator system
  2.    Total amount of vapor produced per Kg of feed steam in a multiple effect system is much higher than in a single effect
  3.    Boiling point elevation in a single effect system is much higher than that in any effect in a multieffect system
  4.    Heat transfer co-efficient in a single effect is much lower than that in any effect in a multieffect system
Answer: Option B
Question 3. A metal ball of radius 0.1 m at a uniform temperature of 90°C is left in air at 30°C. The density and the specific heat of the metal are 3000 kg/m³ and 0.4 kJ/kg.K respectively. The heat transfer co-efficient is 50 W/m².K Neglecting the temperature gradients inside the ball, the time taken (in hours) for the ball to cool to 60°C is
  1.    555
  2.    55.5
  3.    0.55
  4.    0.15
Answer: Option D
Question 4. __________ heat exchanger is used for chilling oil to be dewaxed.
  1.    U-tube
  2.    Double pipe
  3.    Fixed tube
  4.    Floating head
Answer: Option B
Question 5. Which area is used in case of heat flow by conduction through a cylinder?
  1.    Logarithmic mean area
  2.    Arithmetic mean area
  3.    Geometric mean area
  4.    None of these
Answer: Option A
Question 6. In Fourier's law, the proportionality constant is called the
  1.    Heat transfer co-efficient
  2.    Thermal diffusivity
  3.    Thermal conductivity
  4.    Stefan-Boltzman constant
Answer: Option C

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