Which of the following property of air does not increase with rise in temperature?
Thermal conductivity
Thermal diffusivity
Density
Dynamic viscosity
Correct Answer :
C. Density
Related Questions
Thermal diffusivity of a substance is
Directly proportional to the thermal conductivity
Inversely proportional to density of substance
Inversely proportional to specific heat
All of the above
The heat transfer from a hot body to a cold body is directly proportional to the surface area and difference of temperatures between the two bodies. This statement is called
First law of thermodynamics
Newton's law of cooling
Newton's law of heating
Stefan's law
Radiation is the process of heat transfer in which heat flows from a ________, in a straight line, without affecting the intervening medium.
Cold body to hot body
Hot body to cold body
Smaller body to larger body
Larger body to smaller body
The ratio of the energy absorbed by the body to total energy falling on it is called
Absorptive power
Emissive power
Absorptivity
Emissivity
The heat of sun reaches to us according to
Conduction
Convection
Radiation
None of these
The ratio of the emissive power and absorptive power of all bodies is the same and is equal to the emissive power of a perfectly black body. This statement is known as
Kirchoffs law
Stefan's law
Wien' law
Planck's law
An ordinary passenger aircraft requires a cooling system of capacity.
2 TR
4 TR
8 TR
10 TR
Sensible heat factor is given by (where S.H. = Sensible heat, and L.H. = Latent heat)
S.H/(S.H + L.H)
(S.H + L.H) /S.H
(L.H - S.H)/S.H
S.H/(L.H - S.H)
Heat is transferred by all three modes of transfer, viz. conduction, convection and radiation in
Electric heater
Steam condenser
Boiler
Refrigerator condenser coils
Thermal diffusivity of a substance is given by (where h = Thermal diffusivity, ρ = Density of substance, S = Specific heat, and k = Thermal conductivity)
h = k/ ρS
h = ρS/k
h = S/ρk
h = kρ/S
Which of the following has least value of conductivity?
Glass
Water
Plastic
Air
Thermal conductivity of water at 20°C is of the order of
0.1
0.23
0.42
0.51
Total heat is the heat required to
Change vapour into liquid
Change liquid into vapour
Increase the temperature of a liquid or vapour
Convert water into steam and superheat it
Planck's law holds good for
Black bodies
Polished bodies
All coloured bodies
All of the above
Total emissivity of polished silver compared to black body is
Same
Higher
More or less same
Very much lower
A steam pipe is to be lined with two layers of insulating materials of different thermal conductivities. For the minimum heat transfer,
The better insulation must be put inside
The better insulation must be put outside
One could place either insulation on either side
One should take into account the steam temperature before deciding as to which insulation is put where
In free convection heat transfer, Nusselt number is function of
Grashoff number and Reynold number
Grashoff number and Prandtl number
Prandtl number and Reynold number
Grashoff number, Prandtl number and Reynold number
In case of liquids and gases, the heat transfer takes place according to
Conduction
Convection
Radiation
None of these
Which of the following statement is wrong?
The heat transfer in liquid and gases takes place according to convection.
The amount of heat flow through a body is dependent upon the material of the body.
The thermal conductivity of solid metals increases with rise in temperature
Logarithmic mean temperature difference is not equal to the arithmetic mean temperature difference.
The unit of overall coefficient of heat transfer is
W/m²K
W/m²
W/mK
W/m
Two plates spaced 150 mm apart are maintained at 1000°C and 70°C. The heat transfer will take place mainly by
Convection
Radiation
Forced convection
Free convection
The ratio of the emissive power and absorptive power of all bodies is the same and is equal to the emissive power of a perfectly black body. This statement is known as
Wien's law
Stefan's law
Kirchhoff's law
Planck's law
According to Dalton's law of partial pressures, (where pb = Barometric pressure, pa = Partial pressure of dry air, and pv = Partial pressure of water vapour)
Pb = pa - pv
Pb = pa + pv
Pb = pa × pv
Pb = pa/pv
The value of the wavelength for maximum emissive power is given by
Wien's law
Planck's law
Stefan's law
Fourier's law
A grey body is one whose absorptivity
Varies with temperature
Varies with the wave length of incident ray
Varies with both
Does not vary with temperature and wave length of the incident ray
Thermal conductivity of air with rise in temperature
Increases
Decreases
Remain constant
May increase or decrease depending on temperature
Heat transfer in liquid and gases takes place by
Conduction
Convection
Radiation
Conduction and convection
When absorptivity (α) = 1, reflectivity (ρ) = 0 and transmissivity (τ) = 0, then the body is said to be a
Black body
Grey body
Opaque body
White body
The thermal diffusivities for gases are generally
More than those for liquids
Less than those for liquids
More than those for solids
Dependent on the viscosity
The use of heat exchangers is made in
Radiators in automobile
Condensers and boilers in steam plants
Condensers and evaporators in refrigeration and air conditioning units
All of the above