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
Correct Answer :
D. All of the above
Related Questions
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 amount of radiation mainly depends upon the
Nature of the body
Temperature of the body
Type of surface of the body
All of these
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
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
A composite slab has two layers of different materials with thermal conductivities k₁ and k₂. If each layer has the same thickness, then the equivalent thermal conductivity of the slab will be
k₁ k₂
(k₁ + k₂)
(k₁ + k₂)/ k₁ k₂
2 k₁ k₂/ (k₁ + k₂)
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
Thermal conductivity of water ________ with rise in temperature.
Remain same
Decreases
Increases
May increase or decrease depending upon temperature
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 critical radius is the insulation radius at which the resistance to heat flow is
Maximum
Minimum
Zero
None of these
Depending on the radiating properties, a body will be white when
P = 0, x = 0 and a = 1
P=1, T = 0 and a = 0
P = 0, x = 1 and a = 0
X = 0, a + p = 1 Where a = absorptivity, p = reflectivity, x = transmissivity
Which of the following is expected to have highest thermal conductivity?
Steam
Solid ice
Melting ice
Water
The product of Reynolds number and Prandtl number is known as
Stanton number
Biot number
Peclet number
Grashoff number
Temperature of steam at around 540°C can be measured by
Thermometer
Thermistor
Thermocouple
None of these
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 heat of sun reaches to us according to
Conduction
Convection
Radiation
None of these
Free convection flow depends on
Density
Coefficient of viscosity
Gravitational force
All of these
Thermal diffusivity of a substance is given by (where h = Thermal diffusivity, ρ = Density of substance, S = Specific heat, and k = Thermal conductivity)
h = k/ ρS
h = ρS/k
h = S/ρk
h = kρ/S
Thermal conductivity of solid metals with rise in temperature normally
Increases
Decreases
Remain constant
May increase or decrease depending on temperature
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
In heat transfer, conductance equals conductivity (kcal/hr/sq.m/ °C/cm) divided by
Hr (time)
Sq. m (area)
°C (temperature)
K.cal (heat)
Metals are good conductors of heat because
Their atoms collide frequently
Their atoms are relatively far apart
They contain free electrons
They have high density
The process of heat transfer from one particle of the fluid to another by the actual movement of the fluid particles due to difference of density caused by temperature of the particle is known as
Conduction
Free convection
Forced convection
Radiation
Which of the following has least value of conductivity?
Glass
Water
Plastic
Air
Absorptivity of a body will be equal to its emissivity
At all temperatures
At one particular temperature
When system is under thermal equilibrium
At critical temperature
Log mean temperature difference in case of counter flow compared to parallel flow will be
Same
More
Less
Depends on other factors
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
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
The value of Prandtl number for air is about
0.1
0.3
0.7
1.7
Which of the following property of air does not increase with rise in temperature?
Thermal conductivity
Thermal diffusivity
Density
Dynamic viscosity