Heat Transfer

401. The Stefan-Boltzmann constant depends on the

1. Medium
2. Temperature
3. Surface
4. None of these

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402. The sum of reflectivity and absorptivity for an opaque body is equal to

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

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403. The thermal boundary layer at NPr > 1

1. Is thicker than hydrodynamic boundary layer
2. Is thinner than hydrodynamic boundary layer
3. And the hydrodynamic boundary layers are identical
4. Disappears

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404. The thermal efficiency of a reversible heat engine operating between two given thermal reservoirs is 0.4. The device is used either as a refrigerator or as a heat pump between the same reservoirs. Then the coefficient of performance as a refrigerator (COP)_R and the co-efficient of performance as a heat pump (COP)HP are

1. (COP)_R = (COP)_HP = 0.6
2. (COP)_R = 2.5; (COP)_HP = 1.5
3. (COP)_R = 1.5; (COP)_HP = 2.5
4. (COP)_R = (COP)_HP = 2.5

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405. The thermal radiation emitted by a body is proportional to Tⁿ, where T is its absolute temperature. The value of 'n' is exactly 4 for

1. Black painted bodies only
2. All bodies
3. Polished bodies only
4. A black body

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406. The thermal radiative flux from a surface of emissivity = 0.4 is 22.68 kW/m². The approximate surface temperature (K) is (Stefan-Boltzmann constant = 5.67 × 10^-8 W/m².K4)

1. 1000
2. 727
3. 800
4. 1200

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407. The thickness of condensate layer in filmwise condensation depends on the

1. Condensation rate
2. Surface configuration
3. Liquid flow rate from the surface
4. All (A), (B) and (C)

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408. The type of liquor circulation system to be ' employed in evaporators (viz. natural or forced circulation) is determined mainly by the _________ of the liquid.

1. Viscosity
2. Density
3. Thermal conductivity
4. Corrosive nature

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409. The unit of conductance in SI unit is

1. W/m
2. W/m²
3. W/°K
4. W/m°K

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410. The unit of heat transfer co-efficient in SI unit is

1. J/m²°K
2. W/m²°K
3. W/m°K
4. J/m°K

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