Heat Transfer

411. The unit of heat transfer co-efficient is

1. BTU/hr. ft₂°F
2. BTU/hr. °F. ft
3. BTU/hr. °F
4. BTU/hr. ft

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412. The units of resistance to heat transfer is

1. J.m^-2.K^-1
2. J.m^-1.K^-1
3. W.m^-2.K^-1
4. W^-1m²K

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413. The value of Stefan-Boltzmann constant in SI unit is

1. 5.6697 × 10^-8W/m².°K4
2. 0.1714 × 10^-8W/m².°K4
3. 5.6697 × 10^-8kcal/m². °K4
4. 0.1714 × 10^-8kcal/m². °K4

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414. The variation of thermal conductivity of a metal with temperature is often correlated using an expression of the form K = K₀ + at, where, K is the thermal conductivity and T is the temperature (in °K). The units of 'a' in SI system will be

1. W/m.k
2. W/m
3. W/m.k²
4. None, 'a' is just a number

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415. The wavelength at which the maximum monochromatic emissive power occurs for a black body, is (where, T = absolute temperature of the black body).

1. αT
2. α × 1/T
3. α T⁴
4. Independent of T

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416. Thermal conductivities of most of the liquids _________ with rise in temperature.

1. Increases
2. Decreases
3. Remains unchanged
4. May increase or decrease; depends on the liquid

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417. Thermal conductivity of a conducting solid material depends upon its

1. Temperature
2. Porosity
3. Both (A) & (B)
4. Neither (A) nor (B)

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418. Thermal conductivity of a gas at low density, _________ with increase in temperature.

1. Decreases
2. Increases
3. Remains unchanged
4. May increase or decrease; depends on the gas

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419. Thermal diffusivity is given by

1. k/ρCp
2. ρCp/k
3. μCp/a
4. μ/hCp

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420. Thermal diffusivity is the most important in heat transfer by

1. Conduction
2. Radiation
3. Condensation
4. Natural convection

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