The amount of heat flow through a body by conduction is
Directly proportional to the surface area of the body
Directly proportional to the temperature difference on the two faces of the body
Dependent upon the material of the body
All of the above
Correct Answer :
D. All of the above
Related Questions
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
Thermal conductivity of glass wool varies from sample to sample because of variation in
Composition
Density
Porosity
All of the above
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 heat transfer by conduction through a thick cylinder (Q) is given by (where T₁ = Higher temperature, T₂ = Lower temperature, r₁ = Inside radius, r₂ = Outside radius, l = Length of cylinder, and k = Thermal conductivity)
Q = [2πlk (T₁ - T₂)]/2.3 log (r₂/r₁)
Q = 2.3 log (r₂/r₁)/[2πlk (T₁ - T₂)]
Q = [2π (T₁ - T₂)]/2.3 lk log (r₂/r₁)
Q = = 2πlk/2.3 (T₁ - T₂) log (r₂/r₁)
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
Sensible heat is the heat required to
Change vapour into liquid
Change liquid into vapour
Increase the temperature of a liquid of vapour
Convert water into steam and superheat it
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
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
The heat is transferred by conduction, convection and radiation in
Melting of ice
Boiler furnaces
Condensation of steam in condenser
None of these
The emissive power of a body depends upon its
Temperature
Wave length
Physical nature
All of the above
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
Fourier's law of heat conduction gives the heat flow for
Irregular surfaces
Nonuniform temperature surfaces
One dimensional cases only
Two dimensional cases only
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
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
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
In a heat exchanger with one fluid evaporating or condensing, the surface area required is least in
Parallel flow
Counter flow
Cross flow
All of these
A grey body is one whose absorptivity
Varies with temperature
Varies with wavelength of the incident ray
Is equal to its emissivity
Does not vary with temperature and. wavelength of the incident ray
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 value of the wavelength for maximum emissive power is given by
Wien's law
Planck's law
Stefan's law
Fourier's law
Heat is transferred by all three modes of transfer, viz. conduction, convection and radiation in
Electric heater
Steam condenser
Boiler
Refrigerator condenser coils
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 amount of radiation mainly depends upon the
Nature of the body
Temperature of the body
Type of surface of the body
All of these
Cork is a good insulator because it has
Free electrons
Atoms colliding frequency
Low density
Porous 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 critical thickness of insulation for a sphere is
k/h₀
2k/h₀
h₀/k
h₀/2k
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
The critical radius is the insulation radius at which the resistance to heat flow is
Maximum
Minimum
Zero
None of these
The ratio of the energy absorbed by the body to total energy falling on it is called
Absorptive power
Emissive power
Absorptivity
Emissivity
A cube at high temperature is immersed in a constant temperature bath. It loses heat from its top, bottom and side surfaces with heat transfer coefficients of h₁, h₂ and h₃ respectively. The average heat transfer coefficient for the cube is
h₁ + h₂ + h₃
(h₁.h₂.h₃)1/3
1/h₁ + 1/h₂ + 1/h₃
None of these
Which of the following would lead to a reduction in thermal resistance?
In conduction, reduction in the thickness of the material and an increase in thermal conductivity.
In convection, stirring of the fluid and cleaning the heating surface.
In radiation, increasing the temperature and reducing the emissivity.
All of the above