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
Correct Answer :
D. Does not vary with temperature and wave length of the incident ray
Related Questions
A perfect black body is one which
Is black in colour
Reflects all heat
Transmits all heat radiations
Absorbs heat radiations of all wave lengths falling on it
According to Wien's law, the wavelength corresponding to maximum energy is proportion to
Absolute temperature (T)
I²
F
T
Heat is transferred by all three modes of transfer, viz. conduction, convection and radiation in
Electric heater
Steam condenser
Boiler
Refrigerator condenser coils
Film coefficient is defined as Inside diameter of tube
Equivalent thickness of film
Thermal conductivity Equivalent thickness of film Specific heat × Viscosity
Thermal conductivity Molecular diffusivity of momentum Thermal diffusivity
Film coefficient × Inside diameter Thermal conductivity
Thermal diffusivity of a substance is
Directly proportional to thermal conductivity
Inversely proportional to density of substance
Inversely proportional to specific heat
All of the above
Fourier's law of heat conduction gives the heat flow for
Irregular surfaces
Nonuniform temperature surfaces
One dimensional cases only
Two dimensional cases only
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
When heat is transferred from one particle of hot body to another by actual motion of the heated particles, it is referred to as heat transfer by
Conduction
Convection
Radiation
Conduction and convection
Which of the following property of air does not increase with rise in temperature?
Thermal conductivity
Thermal diffusivity
Density
Dynamic viscosity
The amount of radiation mainly depends upon the
Nature of the body
Temperature of the body
Type of surface of the body
All 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
Wien's law
Stefan's law
Kirchhoff's law
Planck's law
The rate of energy transferred by convection to that by conduction is called
Stanton number
Nusselt number
Biot number
Peclet number
Heat transfer in liquid and gases takes place by
Conduction
Convection
Radiation
Conduction and convection
Two balls of same material and finish have their diameters in the ratio of 2: 1 and both are heated to same temperature and allowed to cool by radiation. Rate of cooling by big ball as compared to smaller one will be in the ratio of
1 : 1
2 : 1
1 : 2
4 : 1
The rate of energy emission from unit surface area through unit solid angle, along a normal to the surface, is known as
Emissivity
Transmissivity
Reflectivity
Intensity of radiation
Conduction is a process of heat transfer
From one particle of the body to another without the actual motion of the particles
From one particle of the body to another by the actual motion of the heated particles
From a hot body to a cold body, in a straight line, without affecting the intervening medium
None of the above
Fourier's law of heat conduction is valid for
One dimensional cases only
Two dimensional cases only
Three dimensional cases only
Regular surfaces having non-uniform temperature gradients
When heat is transferred by molecular collision, it is referred to as heat transfer by
Conduction
Convection
Radiation
Scattering
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
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
An ordinary passenger aircraft requires a cooling system of capacity.
2 TR
4 TR
8 TR
10 TR
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
LMTD in case of counter flow heat exchanger as compared to parallel flow heat exchanger is
Higher
Lower
Same
Depends on the area of heat exchanger
The ratio of the energy absorbed by the body to total energy falling on it is called
Absorptive power
Emissive power
Absorptivity
Emissivity
According to Stefan's law, the total radiation from a black body per second per unit area is proportional to
Absolute temperature
T²
T⁵
T
The rate of heat flow through a body is Q = [kA (T₁ - T₂)]/x. The term x/kA is known as
Thermal coefficient
Thermal resistance
Thermal conductivity
None of these
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
The unit of overall coefficient of heat transfer is
W/m²K
W/m²
W/mK
W/m
Heat transfer takes place as per
Zeroth law of thermodynamics
First law of thermodynamic
Second law of the thermodynamics
Kirchoff's law
Thermal conductivity of water ________ with rise in temperature.
Remain same
Decreases
Increases
May increase or decrease depending upon temperature