Heat is transferred by all three modes of transfer, viz. conduction, convection and radiation in
Electric heater
Steam condenser
Boiler
Refrigerator condenser coils
Correct Answer :
C. Boiler
Related Questions
Thermal conductivity of water at 20°C is of the order of
0.1
0.23
0.42
0.51
The heat transfer takes place according to
Zeroth law of thermodynamics
First law of thermodynamics
Second law of thermodynamics
Kirchhoff's law
According to Kirchoff's law, the ratio of emissive power to absorptivity for all bodies is equal to the emissive power of a
Grey body
Brilliant white polished body
Red hot body
Black body
The value of the wavelength for maximum emissive power is given by
Wien's law
Planck's law
Stefan's law
Fourier's law
Free convection flow depends on
Density
Coefficient of viscosity
Gravitational force
All of these
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
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
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
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
Heat conducted through per unit area and unit thick face per unit time when temperature difference between opposite faces is unity, is called
Thermal resistance
Thermal coefficient
Temperature gradient
Thermal conductivity
Upto the critical radius of insulation,
Added insulation will increase heat loss
Added insulation will decrease heat loss
Convective heat loss will be less than conductive heat loss
Heat flux will decrease
According to Prevost theory of heat exchange
It is impossible to transfer heat from low temperature source to t high temperature source
Heat transfer by radiation requires no medium
All bodies above absolute zero emit radiation
Heat transfer in most of the cases takes place by combination of conduction, convection and radiation
Stefan Boltzmann law is applicable for heat transfer by
Conduction
Convection
Radiation
Conduction and radiation combined
Fourier's law of heat conduction is (where Q = Amount of heat flow through the body in unit time, A = Surface area of heat flow, taken at right angles to the direction of heat flow, dT = Temperature difference on the two faces of the body, dx = Thickness of the body, through which the heat flows, taken along the direction of heat flow, and k = Thermal conductivity of the body)
k. A. (dT/dx)
k. A. (dx/dT)
k. (dT/dx)
k. (dx/dT)
Thermal conductivity of non-metallic amorphous solids with decrease in temperature
Increases
Decreases
Remain constant
May increase or decrease depending on temperature
Planck's law holds good for
Black bodies
Polished bodies
All coloured bodies
All of the above
Log mean temperature difference in case of counter flow compared to parallel flow will be
Same
More
Less
Depends on other factors
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
When heat is transferred by molecular collision, it is referred to as heat transfer by
Conduction
Convection
Radiation
Scattering
Thermal conductivity of water in general with rise in temperature
Increases
Decreases
Remain constant
May increase or decrease depending on temperature
According to Wien's law, the wavelength corresponding to maximum energy is proportion to
Absolute temperature (T)
I²
F
T
The ratio of surface convection resistance to the internal conduction resistance is known as
Grashoff number
Biot number
Stanton number
Prandtl number
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
Kirchhoff's law states that
The total radiation from a black body per second per unit area is directly proportional to the fourth power of the absolute temperature
The wave length corresponding to the maximum energy is proportional to the absolute temperature
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
None of the above
Which of the following is expected to have highest thermal conductivity?
Steam
Solid ice
Melting ice
Water
The transfer of heat by molecular collision is known as
Conduction
Convection
Radiation
None of these
Heat is closely related with
Liquids
Energy
Temperature
Entropy
According to Newton's law of cooling, the heat transfer from a hot body to a cold body is
Directly proportional to the surface area
Directly proportional to the difference of temperatures between the two bodies
Either (A) or (B)
Both (A) and (B)
Emissivity of a white polished body in comparison to a black body is
Higher
Lower
Same
Depends upon the shape of body
Fourier's law of heat conduction gives the heat flow for
Irregular surfaces
Nonuniform temperature surfaces
One dimensional cases only
Two dimensional cases only