Heat Transfer

291. Overall heat transfer co-efficient of a particular tube is U₁. If the same tube with some dirt deposited on either side has coefficient U₂, then

1. U₁ = U₂
2. U₂ > U₁
3. U₁ > U₂
4. U₁ = dirt factor - U₂

292. Overall thermal resistance for conductive heat transfer through a series of flat resistances is equal to the

1. Maximum resistance in the series
2. Sum of all resistances
3. Average of all resistances
4. Minimum resistance presents in the series

293. Peclet number (Pe) is given by

1. Pe = Re.Pr
2. Pe = Re/P_r
3. P_e = P_r/R_e
4. Pe = Nu.Re

294. Pick out the correct equation.

1. jH = (St)(Pr)^2/3 = f/2
2. jH = (St)(Pr)^1/3 = f/2
3. jH = (St)^2/3(Pr) = f/2
4. jH = (St)^1/3(Pr) = f/2

295. Pick out the correct statement.

1. 1 kcal/hr.m.°C is equal to 1 BTU/hr. ft.°F
2. In steady state heat conduction, the only property of the substance which determines the temperature distribution, is the thermal conductivity
3. In unsteady state heat conduction, heat flows in the direction of temperature rise
4. In heat transfer by forced convection, Grashoff number is very important

296. Pick out the wrong statement.

1. Heat transfer from a hot body to cold body by the emission of heat waves is called radiation
2. Filmwise condensation takes place on non-wettable surfaces
3. The boiling point of a solution is affected by liquid head as well as boiling point elevation
4. None of these

297. Pick out the wrong statement:

1. With change in temperature, the radiant energy emitted by a black body remains unchanged
2. Absorptivity of a body approaches unity in case of diffuse reflection
3. Absorptivity of a perfectly black body is unity
4. Value of Stefan-Boltzmann constant is 4.876 × 10^-8 KCal/m².hr.°K⁴

298. Planck's distribution law is valid for _________ bodies.

1. Black
2. White
3. Coloured
4. All (A), (B) & (C)

299. Prandtl and Reynold's analogies are identical for Prandtl number value of

1. 0
2. 0.5
3. 1
4. 5

300. Prandtl and Reynolds analogy are same, when Prandtl number is

1. 0.5
2. 1
3. > 2
4. 1.5