When α is absorptivity, ρ is reflectivity and τ is transmissivity, then for a diathermanous body,
When α is absorptivity, ρ is reflectivity and τ is transmissivity, then for a diathermanous body,
The automobile radiator is a heat exchanger of
The automobile radiator is a heat exchanger of
Unit of thermal conductivity in S.I. units is
Unit of thermal conductivity in S.I. units is
Joule sec is the unit of
Joule sec is the unit of
Heat flows from one body to other when they have
Heat flows from one body to other when they have
The highest thermal diffusivity is of
The highest thermal diffusivity is of
Wien’s law states that the wave length corresponding to ________ is proportional to the absolute temperature.
Wien’s law states that the wave length corresponding to ________ is proportional to the absolute temperature.
The critical thickness of insulation for a sphere is
The critical thickness of insulation for a sphere is
Which of the following is the case of heat transfer by radiation?
Which of the following is the case of heat transfer by radiation?
The unit of overall coefficient of heat transfer is
The unit of overall coefficient of heat transfer is
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
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
Total emissivity of polished silver compared to black body is
Total emissivity of polished silver compared to black body is
Two plates spaced 150 mm apart are maintained at 1000°C and 70°C. The heat transfer will take place mainly by
Two plates spaced 150 mm apart are maintained at 1000°C and 70°C. The heat transfer will take place mainly by
The most commonly used method for the design of duct size is the
The most commonly used method for the design of duct size is the
The emissive power of a body depends upon its
The emissive power of a body depends upon its
According of Kirchhoff's law
According of Kirchhoff's law
Stefan Boltzmann law is applicable for heat transfer by
Stefan Boltzmann law is applicable for heat transfer by
Depending on the radiating properties, a body will be white when
(Where a = absorptivity, p = reflectivity, x = transmissivity)
Depending on the radiating properties, a body will be white when
(Where a = absorptivity, p = reflectivity, x = transmissivity)
According to Stefan Boltzmann law, ideal radiators emit radiant energy at a rate proportional to
According to Stefan Boltzmann law, ideal radiators emit radiant energy at a rate proportional to
Film coefficient is defined as the ratio of
Film coefficient is defined as the ratio of
The rate of energy emission from unit surface area through unit solid angle, along a normal to the surface, is known as
The rate of energy emission from unit surface area through unit solid angle, along a normal to the surface, is known as
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)
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)
The amount of heat flow through a body by conduction is
The amount of heat flow through a body by conduction is
LMTD in case of counter flow heat exchanger as compared to parallel flow heat exchanger is
LMTD in case of counter flow heat exchanger as compared to parallel flow heat exchanger is
The thermal diffusivities for solids are generally
The thermal diffusivities for solids are generally
The total emissivity power is .defined as the total amount of radiation emitted by a black body per unit
The total emissivity power is .defined as the total amount of radiation emitted by a black body per unit
Heat transfer in liquid and gases takes place by
Heat transfer in liquid and gases takes place by
A perfect black body is one which
A perfect black body is one which
Unit of thermal diffusivity is
Unit of thermal diffusivity is
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
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
All radiations in a black body are
All radiations in a black body are
The rate of heat flow through a body is Q = [kA (T₁ - T₂)]/x. The term x/kA is known as
The rate of heat flow through a body is Q = [kA (T₁ - T₂)]/x. The term x/kA is known as
Free convection flow depends on
Free convection flow depends on
The expression Q = ρ AT4 is called
The expression Q = ρ AT4 is called
40% of incident radiant energy on the surface of a thermally transparent body is reflected back. If the transmissivity of the body be 0.15, then the emissivity of surface is
40% of incident radiant energy on the surface of a thermally transparent body is reflected back. If the transmissivity of the body be 0.15, then the emissivity of surface is
Planck’s law holds good for
Planck’s law holds good for
The ratio of the thickness of thermal boundary layer to the thickness of hydrodynamic boundary layer is equal to (Prandtl number) n, where n is equal to
The ratio of the thickness of thermal boundary layer to the thickness of hydrodynamic boundary layer is equal to (Prandtl number) n, where n is equal to
The heat is transferred by conduction, convection and radiation in
The heat is transferred by conduction, convection and radiation in
In heat transfer, conductance equals conductivity (kcal/hr/sq.m/°C/cm) divided by
In heat transfer, conductance equals conductivity (kcal/hr/sq.m/°C/cm) divided by
The critical radius is the insulation radius at which the resistance to heat flow is
The critical radius is the insulation radius at which the resistance to heat flow is
Which of the following is expected to have highest thermal conductivity?
Which of the following is expected to have highest thermal conductivity?
Depending on the radiating properties, a body will be opaque when
Depending on the radiating properties, a body will be opaque when
Unit of thermal conductivity in M.K.S. units is
Unit of thermal conductivity in M.K.S. units is
Which of the following property of air does not increase with rise in temperature?
Which of the following property of air does not increase with rise in temperature?
Heat transfer by radiation mainly depends upon
Heat transfer by radiation mainly depends upon
In case of liquids and gases, the heat transfer takes place according to
In case of liquids and gases, the heat transfer takes place according to
Heat conducted through per unit area and unit thick face per unit time when temperature difference between opposite faces is unity, is called
Heat conducted through per unit area and unit thick face per unit time when temperature difference between opposite faces is unity, is called
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
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
The transfer of heat by molecular collision is known as
The transfer of heat by molecular collision is known as
The concept of overall coefficient of heat transfer is used in case of heat transfer by
The concept of overall coefficient of heat transfer is used in case of heat transfer by
In convection heat transfer from hot flue gases to water tube, even though flow may be turbulent, a laminar flow region (boundary layer of film) exists close to the tube. The heat transfer through this film takes place by
In convection heat transfer from hot flue gases to water tube, even though flow may be turbulent, a laminar flow region (boundary layer of film) exists close to the tube. The heat transfer through this film takes place by
Thermal conductivity of glass wool varies from sample to sample because of variation in
Thermal conductivity of glass wool varies from sample to sample because of variation in
Heat transfer takes place as per
Heat transfer takes place as per
Which of the following has maximum value of thermal conductivity?
Which of the following has maximum value of thermal conductivity?
A non-dimensional number generally associated with natural convection heat transfer is
A non-dimensional number generally associated with natural convection heat transfer is
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
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
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
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
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)
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)
A grey body is one whose absorptivity
A grey body is one whose absorptivity
According to Prevost theory of heat exchange
According to Prevost theory of heat exchange
Total heat is the heat required to
Total heat is the heat required to
Film coefficient is defined as Inside diameter of tube
Film coefficient is defined as Inside diameter of tube
In regenerator type heat exchanger, heat transfer takes place by
In regenerator type heat exchanger, heat transfer takes place by
The radiation emitted by a black body is known as
The radiation emitted by a black body is known as
The value of Prandtl number for air is about
The value of Prandtl number for air is about
Sensible heat factor is given by (where S.H. = Sensible heat, and L.H. = Latent heat)
Sensible heat factor is given by (where S.H. = Sensible heat, and L.H. = Latent heat)
Thermal conductivity of a material may be defined as the
Thermal conductivity of a material may be defined as the
Which of the following would lead to a reduction in thermal resistance?
Which of the following would lead to a reduction in thermal resistance?
A steam pipe is to be insulated by two insulating materials put over each other. For best results
A steam pipe is to be insulated by two insulating materials put over each other. For best results
When heat is transferred by molecular collision, it is referred to as heat transfer by
When heat is transferred by molecular collision, it is referred to as heat transfer by
In free convection heat transfer transition from laminar to turbulent flow is governed by the critical value of the
In free convection heat transfer transition from laminar to turbulent flow is governed by the critical value of the
Log mean temperature difference in case of counter flow compared to parallel flow will be
Log mean temperature difference in case of counter flow compared to parallel flow will be
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
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
Thermal diffusivity is
Thermal diffusivity is
Depending on the radiating properties, body will be transparent when
(Where a = absorptivity, p = reflectivity, x = transmissivity)
Depending on the radiating properties, body will be transparent when
(Where a = absorptivity, p = reflectivity, x = transmissivity)
Thermal conductivity of water _________ with rise in temperature.
Thermal conductivity of water _________ with rise in temperature.
Conduction is a process of heat transfer
Conduction is a process of heat transfer
The rate of energy transferred by convection to that by conduction is called
The rate of energy transferred by convection to that by conduction is called
Sensible heat is the heat required to
Sensible heat is the heat required to
Thermal diffusivity of a substance is given by (where h = Thermal diffusivity, ρ = Density of substance, S = Specific heat, and k = Thermal conductivity)
Thermal diffusivity of a substance is given by (where h = Thermal diffusivity, ρ = Density of substance, S = Specific heat, and k = Thermal conductivity)
According to Wien's law, the wavelength corresponding to maximum energy is proportion to
According to Wien's law, the wavelength corresponding to maximum energy is proportion to
When heat is transferred from hot body to cold body, in a straight line, without affecting the intervening medium, it is referred as heat transfer by
When heat is transferred from hot body to cold body, in a straight line, without affecting the intervening medium, it is referred as heat transfer by
Which of the following statement is correct?
Which of the following statement is correct?
The use of heat exchangers is made in
The use of heat exchangers is made in
The time constant of a thermocouple is
The time constant of a thermocouple is
The process of heat transfer from one particle of the body to another is called conduction, when the particles of the body
The process of heat transfer from one particle of the body to another is called conduction, when the particles of the body
The heat transfer takes place according to
The heat transfer takes place according to
Which of the following statement is wrong?
Which of the following statement is wrong?
Thermal conductivity of wood depends on
Thermal conductivity of wood depends on
Temperature of steam at around 540°C can be measured by
Temperature of steam at around 540°C can be measured by
The total radiation from a black body per second per unit area is ________ fourth power of the absolute temperature. This statement is known as Stefan Boltzmann law.
The total radiation from a black body per second per unit area is ________ fourth power of the absolute temperature. This statement is known as Stefan Boltzmann law.
According to Kirchoff's law, the ratio of emissive power to absorptivity for all bodies is equal to the emissive power of a
According to Kirchoff's law, the ratio of emissive power to absorptivity for all bodies is equal to the emissive power of a
Heat is transferred by all three modes of transfer, viz. conduction, convection and radiation in
Heat is transferred by all three modes of transfer, viz. conduction, convection and radiation in
The amount of radiation mainly depends on
The amount of radiation mainly depends on
Depending on the radiating properties, a body will be black when
(Where a = absorptivity, p = reflectivity, X = transmissivity.)
Depending on the radiating properties, a body will be black when
(Where a = absorptivity, p = reflectivity, X = transmissivity.)
Thermal diffusivity is a
Thermal diffusivity is a
In free convection heat transfer, Nusselt number is function of
In free convection heat transfer, Nusselt number is function of
The amount of radiation mainly depends upon the
The amount of radiation mainly depends upon the
The ratio of the energy absorbed by the body to total energy falling on it is called
The ratio of the energy absorbed by the body to total energy falling on it is called
Which of the following has least value of conductivity?
Which of the following has least value of conductivity?
