Q.1
When absorptivity (α) = 1, reflectivity (ρ) = 0 and transmissivity (τ) = 0, then the body is said to be a
Q.2
Upto the critical radius of insulation,
Q.3
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)
Q.4
In counter current flow heat exchanger, the logarithmic temperature difference between the fluids is ________ as compared to parallel flow heat exchanger.
Q.5
In counter flow heat exchangers
Q.6
The energy distribution of an ideal reflector at higher temperatures is largely in the range of
Q.7
In regenerator type heat exchanger, heat transfer takes place by
Q.8
Heat flows from one body to other when they have
Q.9
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
Q.10
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
Q.11
Which of the following would lead to a reduction in thermal resistance?
Q.12
Heat transfer in liquid and gases takes place by
Q.13
Which of the following statement is correct?
Q.14
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
Q.15
In free convection heat transfer, Nusselt number is function of
Q.16
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
Q.17
Thermal conductivity of glass wool varies from sample to sample because of variation in
Q.18
Two plates spaced 150 mm apart are maintained at 1000°C and 70°C. The heat transfer will take place mainly by
Q.19
According to Stefan Boltzmann law, ideal radiators emit radiant energy at a rate proportional to
Q.20
The critical radius is the insulation radius at which the resistance to heat flow is
Q.21
Film coefficient is defined as the ratio of
Q.22
The highest thermal diffusivity is of
Q.23
The rate of energy transferred by convection to that by conduction is called
Q.24
Thermal conductivity of water _________ with rise in temperature.
Q.25
Which of the following property of air does not increase with rise in temperature?
Q.26
Unit of thermal diffusivity is
Q.27
Temperature of steam at around 540°C can be measured by
Q.28
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.
Q.29
The use of heat exchangers is made in
Q.30
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
0 h : 0 m : 1 s