1. Consider the following statements with reference to dropwise condensation during heat and mass transfer:
1. Vapour condenses on the surface in the form of drops, and consequently a large part of cooling surface is always bare to vapour for undergoing condensation
2. The rate of heat transfer is many times larger than what is achieved in film condensation
3. It occurs on a non-wettable cooling surface where the liquid condensate drops do not spread
2. The rate of heat transfer is many times larger than what is achieved in film condensation
3. It occurs on a non-wettable cooling surface where the liquid condensate drops do not spread
Which of the above statements are correct?
(a) 1 and 2 only
(b) 1 and 3 only
(c) 2 and 3 only
(d) 1, 2 and 3
(a) 1 and 2 only
(b) 1 and 3 only
(c) 2 and 3 only
(d) 1, 2 and 3
Answer: (d)
2. Consider the following statements regarding heat transfer coefficient for laminar flow:
1. When the buoyancy forces are in the same direction as the external forces, they increase the rate of heat transfer
2. When the external and buoyancy forces act in opposite directions, the heat transfer is increased
1. When the buoyancy forces are in the same direction as the external forces, they increase the rate of heat transfer
2. When the external and buoyancy forces act in opposite directions, the heat transfer is increased
Which of the above statements is/are correct?
(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1nor 2
(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1nor 2
Answer: (a)
3. Consider the following statements regarding velocity distribution in turbulent flow through pipe:
1. No fundamental theory is yet available to determine the velocity distribution
2. Empirical and semi-empirical relations are used to correlate the velocity field in turbulent flow
1. No fundamental theory is yet available to determine the velocity distribution
2. Empirical and semi-empirical relations are used to correlate the velocity field in turbulent flow
Which of the above statement is/are correct?
(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1 nor 2
(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1 nor 2
Answer: (c)
4. A very thin layer at the wall where viscous shear stress dominates is known as:
(a) Buffer sublayer
(b) Viscous sublayer
(c) Turbulent sublayer
(d) Buffer layer
(a) Buffer sublayer
(b) Viscous sublayer
(c) Turbulent sublayer
(d) Buffer layer
Answer: (b)
5. Consider the following statements regarding rotating cylinders in heat and mass transfer:
1. Heat transfer by convection between a rotating body and a surrounding fluid is of importance in the thermal analysis of flywheels, turbine rotors and other rotating components of various machines
2. With the heat transfer, a critical velocity is reached when the circumferential speed of the cylinder surface becomes approximately equal to the upward natural convection velocity at the side of heated stationary cylinder
3. At speeds greater than critical the peripheral speeds Reynolds number becomes the un-controlling parameter
1. Heat transfer by convection between a rotating body and a surrounding fluid is of importance in the thermal analysis of flywheels, turbine rotors and other rotating components of various machines
2. With the heat transfer, a critical velocity is reached when the circumferential speed of the cylinder surface becomes approximately equal to the upward natural convection velocity at the side of heated stationary cylinder
3. At speeds greater than critical the peripheral speeds Reynolds number becomes the un-controlling parameter
Which of the above statements are correct?
(a) 1, 2 and 3
(b) 1 and 3 only
(c) 1 and 2 only
(d) 2 and 3 only
(a) 1, 2 and 3
(b) 1 and 3 only
(c) 1 and 2 only
(d) 2 and 3 only
Answer: (c)
6. When X-ray diffraction pattern consists of sharply defined rings, the solid is
(a) Monocrystalline
(b) Amorphous
(c) Polycrystalline
(d) None of these
Answer: (c)
7. The number of atoms per unit cell in a simple cubic, FCC and BCC unit cells is, respectively
(a) 2, 1 and 4
(b) 1, 4 and 2
(c) 2, 4 and 1
(d) 1, 2 and 4
Answer: (b)
8. No Bragg reflection of X-rays from a crystal will be observed if
is smaller than(a) 𝜆/4
(b) 𝜆/3
(c) 𝜆/2
(d) 𝜆
Answer: (c)
9. CaO and NaCl have similar crystal structures and approximately same ionic radii. If U is the lattice energy of NaCl, the lattice energy of CaO is nearly
(a) 0.5𝑈
(b) 𝑈
(c) 2𝑈
(d) 4𝑈
Answer: (d)
10. For which of the following process is inter system crossing (ISC) essential?
(a) Chemiluminescence
(b) Fluorescence
(c) Phosphorescence
(d) Radioactive decays
Answer: (c)
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