When heat is transferred by molecular collision, it is referred to as heat transfer by
Conduction
Convection
Radiation
Scattering
Correct Answer :
B. Convection
Related Questions
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 highest thermal diffusivity is of
Iron
Lead
Concrete
Wood
In case of liquids and gases, the heat transfer takes place according to
Conduction
Convection
Radiation
None of these
The process of heat transfer from one particle of the body to another by the actual motion of the heated particles, is called
Conduction
Convection
Radiation
None of these
According to Stefan Boltzmann law, the total radiation from a black body per second per unit area is directly proportional to the
Absolute temperature
Square of the absolute temperature
Cube of the absolute temperature
Fourth power of the absolute temperature
Thermal diffusivity is
A dimensionless parameter
Function of temperature
Used as mathematical model
A physical property of the material
The heat transfer takes place according to
Zeroth law of thermodynamics
First law of thermodynamics
Second law of thermodynamics
Kirchhoff's law
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
The thickness of thermal and hydrodynamic boundary layer is equal if Prandtl number is
Equal to one
Greater than one
Less than one
Equal to Nusselt number
Heat transfer in liquid and gases takes place by
Conduction
Convection
Radiation
Conduction and convection
The energy distribution of an ideal reflector at higher temperatures is largely in the range of
Shorter wavelength
Longer wavelength
Remain same at all wavelengths
Wavelength has nothing to do with it
The value of the wavelength for maximum emissive power is given by
Wien's law
Planck's law
Stefan's law
Fourier's law
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
In counter flow heat exchangers
Both the fluids at inlet (of heat exchanger where hot fluid enters) are in their coldest state
Both the fluids at inlet are in their hottest state
Both the fluids at exit are in their hottest state
One fluid is in hottest state and other in coldest state at inlet
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
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)
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
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 natural convection air cooled condensers are used in
Domestic refrigerators
Water coolers
Room air conditioners
All of these
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 heat of sun reaches to us according to
Conduction
Convection
Radiation
None of these
The transfer of heat by molecular collision is smallest in
Solids
Liquids
Gases
None of these
The emissive power of a body depends upon its
Temperature
Wave length
Physical nature
All of the above
Thermal conductivity of non-metallic amorphous solids with decrease in temperature
Increases
Decreases
Remain constant
May increase or decrease depending on temperature
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 emissivity for a black body is
0
0.5
0.75
1
Fouling factor is used
In heat exchanger design as a safety factor
In case of Newtonian fluids
When a liquid exchanges heat with a gas
None of the above
The rate of energy transferred by convection to that by conduction is called
Stanton number
Nusselt number
Biot number
Peclet number
The value of Prandtl number for air is about
0.1
0.3
0.7
1.7
Reynolds number (RN) is given by (where h = Film coefficient, l = Linear dimension, V = Velocity of fluid, k = Thermal conductivity, t = Temperature, ρ = Density of fluid, cp = Specific heat at constant pressure, and μ = Coefficient of absolute viscosity)
RN = hl/k
RN = μ cp/k
RN = ρ V l /μ
RN = V²/t.cp