In a heat exchanger with one fluid evaporating or condensing, the surface area required is least in
In a heat exchanger with one fluid evaporating or condensing, the surface area required is least in
When absorptivity (α) = 1, reflectivity (ρ) = 0 and transmissivity (τ) = 0, then the body is said to be a
When absorptivity (α) = 1, reflectivity (ρ) = 0 and transmissivity (τ) = 0, then the body is said to be a
In heat exchangers, degree of approach is defined as the difference between temperatures of
In heat exchangers, degree of approach is defined as the difference between temperatures of
If the energy radiated per second per sq. cm. of the surface for wave lengths lying between λ, and λ + dλ is represented by (eλ.dλ), then eλ is called
If the energy radiated per second per sq. cm. of the surface for wave lengths lying between λ, and λ + dλ is represented by (eλ.dλ), then eλ is called
Thermal conductivity of solid metals with rise in temperature normally
Thermal conductivity of solid metals with rise in temperature normally
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)
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)
According to Newton's law of cooling, the heat transfer from a hot body to a cold body is
According to Newton's law of cooling, the heat transfer from a hot body to a cold body is
The thickness of thermal and hydrodynamic boundary layer is equal if Prandtl number is
The thickness of thermal and hydrodynamic boundary layer is equal if Prandtl number is
Thermal conductivity of air with rise in temperature
Thermal conductivity of air with rise in temperature
In counter flow heat exchangers
In counter flow heat exchangers
The heat of sun reaches to us according to
The heat of sun reaches to us according to
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)
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)
The concept of overall coefficient of heat transfer is used in heat transfer problems of
The concept of overall coefficient of heat transfer is used in heat transfer problems of
Pick up the wrong case. Heat flowing from one side to other depends directly on
Pick up the wrong case. Heat flowing from one side to other depends directly on
Reynolds number is the ratio of
Reynolds number is the ratio of
The critical temperature is the temperature
The critical temperature is the temperature
An ordinary passenger aircraft requires a cooling system of capacity.
An ordinary passenger aircraft requires a cooling system of capacity.
Heat is closely related with
Heat is closely related with
Unit of thermal conductivity in M.K.S. units is
Unit of thermal conductivity in M.K.S. units is
Absorptivity of a body will be equal to its emissivity
Absorptivity of a body will be equal to its emissivity
The value of the wavelength for maximum emissive power is given by
The value of the wavelength for maximum emissive power is given by
The unit of Stefan Boltzmann constant is
The unit of Stefan Boltzmann constant is
The energy distribution of an ideal reflector at higher temperatures is largely in the range of
The energy distribution of an ideal reflector at higher temperatures is largely in the range of
The unit of Stefan-Boltzmann constant is
The unit of Stefan-Boltzmann constant is
The insulation ability of an insulator with the presence of moisture would
The insulation ability of an insulator with the presence of moisture would
According to Stefan Boltzmann law, the total radiation from a black body per second per unit area is directly proportional to the
According to Stefan Boltzmann law, the total radiation from a black body per second per unit area is directly proportional to the
A steam pipe is to be lined with two layers of insulating materials of different thermal conductivities. For the minimum heat transfer,
A steam pipe is to be lined with two layers of insulating materials of different thermal conductivities. For the minimum heat transfer,
Metals are good conductors of heat because
Metals are good conductors of heat because
Radiation is the process of heat transfer in which heat flows from a ________, in a straight line, without affecting the intervening medium.
Radiation is the process of heat transfer in which heat flows from a ________, in a straight line, without affecting the intervening medium.
The logarithmic mean temperature difference (tm) is given by (where Δt1 and Δt2 are temperature differences between the hot and cold fluids at entrance and exit)
The logarithmic mean temperature difference (tm) is given by (where Δt1 and Δt2 are temperature differences between the hot and cold fluids at entrance and exit)
If the temperature of a solid surface changes form 27°C to 627°C, then its emissive power changes in the ratio of
If the temperature of a solid surface changes form 27°C to 627°C, then its emissive power changes in the ratio of
The thermal diffusivities for gases are generally
The thermal diffusivities for gases are generally
A heat exchanger with heat transfer surface area A and overall heat transfer coefficient U handles two fluids of heat capacities Cmax and Cmin. The number of transfer units (NTU) used in the analysis of heat exchanger is specified as
A heat exchanger with heat transfer surface area A and overall heat transfer coefficient U handles two fluids of heat capacities Cmax and Cmin. The number of transfer units (NTU) used in the analysis of heat exchanger is specified as
The process of heat transfer from one particle of the body to another by the actual motion of the heated particles, is called
The process of heat transfer from one particle of the body to another by the actual motion of the heated particles, is called
The ratio of Nusselt number and the product of Reynold's number and Prandtl number is equal to
The ratio of Nusselt number and the product of Reynold's number and Prandtl number is equal to
Thermal conductivity of non-metallic amorphous solids with decrease in temperature
Thermal conductivity of non-metallic amorphous solids with decrease in temperature
Cork is a good insulator because it has
Cork is a good insulator because it has
Thermal conductivity of air at room temperature in kcal/m hr °C is of the order of
Thermal conductivity of air at room temperature in kcal/m hr °C is of the order of
The transfer of heat by molecular collision is smallest in
The transfer of heat by molecular collision is smallest in
Fourier's law of heat conduction gives the heat flow for
Fourier's law of heat conduction gives the heat flow for
The product of Reynolds number and Prandtl number is known as
The product of Reynolds number and Prandtl number is known as
The natural convection air cooled condensers are used in
The natural convection air cooled condensers are used in
Two long parallel surfaces each of emissivity 0.7 are maintained at different temperatures and accordingly have radiation heat exchange between them. It is desired to reduce 75% of the radiant heat transfer by inserting thin parallel shields of emissivity 1 on both sides. The number of shields should be
Two long parallel surfaces each of emissivity 0.7 are maintained at different temperatures and accordingly have radiation heat exchange between them. It is desired to reduce 75% of the radiant heat transfer by inserting thin parallel shields of emissivity 1 on both sides. The number of shields should be
Fourier's law of heat conduction is valid for
Fourier's law of heat conduction is valid for
The value of the wave length for maximum emissive power is given by
The value of the wave length for maximum emissive power is given by
Fouling factor is used
Fouling factor is used
The emissivity for a black body is
The emissivity for a black body is
Kirchhoff's law states that
Kirchhoff's law states that
In counter current flow heat exchanger, the logarithmic temperature difference between the fluids is ________ as compared to parallel flow heat exchanger.
In counter current flow heat exchanger, the logarithmic temperature difference between the fluids is ________ as compared to parallel flow heat exchanger.
Thermal conductivity of water at 20°C is of the order of
Thermal conductivity of water at 20°C is of the order of
A designer chooses the values of fluid flow rates and specific heats in such a manner that the heat capacities of the two fluids are equal. A hot fluid enters the counter flow heat exchanger at 100°C and leaves at 60°C. A cold fluid enters the heat exchanger at 40°C. The mean temperature difference between the two fluids is
A designer chooses the values of fluid flow rates and specific heats in such a manner that the heat capacities of the two fluids are equal. A hot fluid enters the counter flow heat exchanger at 100°C and leaves at 60°C. A cold fluid enters the heat exchanger at 40°C. The mean temperature difference between the two fluids is
The heat transfer by conduction through a thick sphere is given by
The heat transfer by conduction through a thick sphere is given by
An electric cable of aluminium conductor (k = 240 W/mK) is to be insulated with rubber (k = 0.15 W/mK). The cable is to be located in air (h = 6 W/m²). The critical thickness of insulation will be
An electric cable of aluminium conductor (k = 240 W/mK) is to be insulated with rubber (k = 0.15 W/mK). The cable is to be located in air (h = 6 W/m²). The critical thickness of insulation will be
According to Stefan's law, the total radiation from a black body per second per unit area is proportional to
According to Stefan's law, the total radiation from a black body per second per unit area is proportional to
Upto the critical radius of insulation,
Upto the critical radius of insulation,
Which of the following is a case of steady state heat transfer?
Which of the following is a case of steady state heat transfer?
Emissivity of a white polished body in comparison to a black body is
Emissivity of a white polished body in comparison to a black body is
Thermal conductivity of water in general with rise in temperature
Thermal conductivity of water in general with rise in temperature
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
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
Thermal diffusivity of a substance is
Thermal diffusivity of a substance is
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
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
The ratio of surface convection resistance to the internal conduction resistance is known as
The ratio of surface convection resistance to the internal conduction resistance is known as
Moisture would find its way into insulation by vapour pressure unless it is prevented by
Moisture would find its way into insulation by vapour pressure unless it is prevented by
In a shell and tube heat exchanger, baffles are provided on the shell side to
In a shell and tube heat exchanger, baffles are provided on the shell side to
