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Total Questions : 448 | Page 32 of 45 pages
Question 311. Reynolds number (RN) is given by (where h = Film coefficient, l = Linear dimension, V = Velocity of fluid, k = Thermal conductivity, t = Temperature, ρ = Density of fluid, cp = Specific heat at constant pressure, and μ = Coefficient of absolute viscosity)
  1.    RN = V²/t.cp
  2.    RN = μ cp/k
  3.    RN = hl/k
  4.    RN = ρ V l /μ
 Discuss Question
Answer: Option D. -> RN = ρ V l /μ
Question 312. Two long parallel surfaces each of emissivity 0.7 are maintained at different temperatures and accordingly have radiation heat exchange between them. It is desired to reduce 75% of the radiant heat transfer by inserting thin parallel shields of emissivity 1 on both sides. The number of shields should be
  1.    Two
  2.    Three
  3.    Four
  4.    One
 Discuss Question
Answer: Option B. -> Three
Question 313. A cube at high temperature is immersed in a constant temperature bath. It loses heat from its top, bottom and side surfaces with heat transfer coefficients of h₁, h₂ and h₃ respectively. The average heat transfer coefficient for the cube is
  1.    1/h₁ + 1/h₂ + 1/h₃
  2.    h₁ + h₂ + h₃
  3.    None of these
  4.    (h₁.h₂.h₃)1/3
 Discuss Question
Answer: Option A. -> 1/h₁ + 1/h₂ + 1/h₃
Question 314. Radiation is the process of heat transfer in which heat flows from a ________, in a straight line, without affecting the intervening medium.
  1.    Larger body to smaller body
  2.    Smaller body to larger body
  3.    Cold body to hot body
  4.    Hot body to cold body
 Discuss Question
Answer: Option D. -> Hot body to cold body
Question 315. Moisture would find its way into insulation by vapour pressure unless it is prevented by
  1.    High vapour pressure
  2.    High thickness of insulation
  3.    A vapour seal
  4.    Less thermal conductivity insulator
 Discuss Question
Answer: Option C. -> A vapour seal
Question 316. Which of the following is a case of steady state heat transfer?
  1.    I.C. engine
  2.    None of these
  3.    Heating of building in winter
  4.    Air preheaters
 Discuss Question
Answer: Option B. -> None of these
Question 317. The ratio of surface convection resistance to the internal conduction resistance is known as
  1.    Biot number
  2.    Grashoff number
  3.    Stanton number
  4.    Prandtl number
 Discuss Question
Answer: Option A. -> Biot number
Question 318. Fourier's law of heat conduction gives the heat flow for
  1.    One dimensional cases only
  2.    Irregular surfaces
  3.    Nonuniform temperature surfaces
  4.    Two dimensional cases only
 Discuss Question
Answer: Option A. -> One dimensional cases only
Question 319. The process of heat transfer from one particle of the fluid to another by the actual movement of the fluid particles due to difference of density caused by temperature of the particle is known as
  1.    Conduction
  2.    Forced convection
  3.    Free convection
  4.    Radiation
 Discuss Question
Answer: Option C. -> Free convection
Question 320. If the energy radiated per second per sq. cm. of the surface for wave lengths lying between λ, and λ + dλ is represented by (eλ.dλ), then eλ is called
  1.    Emissive power
  2.    Absorptive power
  3.    Emissivity
  4.    None of these
 Discuss Question
Answer: Option A. -> Emissive power

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