Stefan Boltzmann law is applicable for heat transfer by
Conduction
Convection
Radiation
Conduction and radiation combined
Correct Answer :
C. Radiation
Related Questions
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
Planck's law holds good for
Black bodies
Polished bodies
All coloured bodies
All of the above
When α is absorptivity, ρ is reflectivity and τ is transmissivity, then for a diathermanous body,
α = 1, ρ = 0 and τ = 0
α = 0, ρ = 1 and τ = 0
α = 0, ρ = 0 and τ = 1
α + ρ = 1 and τ = 0
In free convection heat transfer transition from laminar to turbulent flow is governed by the critical value of the
Reynold's number
Grashoff's number
Reynold's number, Grashoff's number
Prandtl number, Grashoff's number
Temperature of steam at around 540°C can be measured by
Thermometer
Thermistor
Thermocouple
None of these
Thermal conductivity of air at room temperature in kcal/m hr °C is of the order of
0.002
0.02
0.01
0.1
When heat is transferred from hot body to cold body, in a straight line, without affecting the intervening medium, it is referred as heat transfer by
Conduction
Convection
Radiation
Conduction and convection
Heat is closely related with
Liquids
Energy
Temperature
Entropy
The concept of overall coefficient of heat transfer is used in case of heat transfer by
Conduction
Convection
Radiation
Conduction and convection
Moisture would find its way into insulation by vapour pressure unless it is prevented by
High thickness of insulation
High vapour pressure
Less thermal conductivity insulator
A vapour seal
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.
Which of the following is the case of heat transfer by radiation?
Blast furnace
Heating of building
Cooling of parts in furnace
Heat received by a person from fireplace
The process of heat transfer from one particle of the fluid to another by the actual movement of the fluid particles caused by some mechanical means, is known as
Conduction
Free convection
Forced convection
Radiation
The critical thickness of insulation for a sphere is
k/h₀
2k/h₀
h₀/k
h₀/2k
Depending on the radiating properties, body will be transparent when
P = 0, x = 0 and a = 1
P=1, x = 0, and a = 0
P = 0, T= 1, and a = 0
X = 0, a + p = 1
In a shell and tube heat exchanger, baffles are provided on the shell side to
Improve heat transfer
Provide support for tubes
Prevent stagnation of shell side fluid
All of these
The time constant of a thermocouple is
The time taken to attain the final temperature to be measured
The time taken to attain 50% of the value of initial temperature difference
The time taken to attain 63.2% of the value of initial temperature difference
Determined by the time taken to reach 100°C from 0°C
Which of the following statement is correct?
A grey body is one which absorbs all radiations incident on it.
At thermal equilibrium, the emissivity and absorptivity are same.
The energy absorbed by a body to the total energy falling on it, is called emissivity.
A perfect body is one which is black in colour.
Which of the following is expected to have highest thermal conductivity?
Steam
Solid ice
Melting ice
Water
Depending on the radiating properties, a body will be opaque when
P = 0, x = 0 and a = 1
P=1, x = 0 and a = 0
P = 0, x = 1 and a = 0
X = 0, a + p = 1 Where a = absorptivity, p = reflectivity, X = transmissivity.
The process of heat transfer from one particle of the body to another is called conduction, when the particles of the body
Move actually
Do not move actually
Affect the intervening medium
Does not affect the intervening medium
Unit of thermal diffusivity is
m²/hr
m²/hr °C
kcal/m² hr
kcal/m. hr °C
The most commonly used method for the design of duct size is the
Velocity reduction method
Equal friction method
Static regains method
Dual or double method
Heat is transferred by all three modes of transfer, viz. conduction, convection and radiation in
Electric heater
Steam condenser
Boiler
Refrigerator condenser coils
The product of Reynolds number and Prandtl number is known as
Stanton number
Biot number
Peclet number
Grashoff number
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
In convection heat transfer from hot flue gases to water tube, even though flow may be turbulent, a laminar flow region (boundary layer of film) exists close to the tube. The heat transfer through this film takes place by
Convection
Radiation
Conduction
Both convection and conduction
Wiens law states that the wave length corresponding to ________ is proportional to the absolute temperature.
Minimum energy
Maximum energy
Both (A) and (B)
None of these
The unit of Stefan-Boltzmann constant is
Watt/mK
Watt/m²K²
Watt/m²K4
Watt/mK²
Which of the following has least value of conductivity?
Glass
Water
Plastic
Air