25 mm
40 mm
160 mm
800 mm
A. 25 mm
Quantity of heat flowing in one second through one cm cube of material when opposite faces ^re maintained at a temperature difference of 1°C
Quantity of heat flowing in one second through a slab of the material of area one cm square, thickness 1 cm when its faces differ in temperature by 1°C
Heat conducted in unit time across unit area through unit thickness when a temperature difference of unity is maintained between opposite faces
All of the above
Thermal coefficient
Thermal resistance
Thermal conductivity
None of these
tm = (Δt1 - Δt2)/ loge (Δt1/Δt2)
tm = loge (Δt1/Δt2)/ (Δt1 - Δt2)
tm = tm = (Δt1 - Δt2) loge (Δt1/Δt2)
tm = loge (Δt1 - Δt2)/ Δt1/Δt2
Change vapour into liquid
Change liquid into vapour
Increase the temperature of a liquid of vapour
Convert water into steam and superheat it
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
Radiant heat is proportional to fourth power of absolute temperature
Emissive power depends on temperature
Emissive power and absorptivity are constant for all bodies
Ratio of emissive power to absorptive power for all bodies is same and is equal to the emissive power of a perfectly black body.
Conduction
Convection
Radiation
None of these
I.C. engine
Air preheaters
Heating of building in winter
None of the above
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 = 0 Where a = absorptivity, p = reflectivity, X = transmissivity.
20°C
40°C
60°C
66.7°C
0.002
0.02
0.01
0.1
Radiators in automobile
Condensers and boilers in steam plants
Condensers and evaporators in refrigeration and air conditioning units
All of the above
Remain same
Decreases
Increases
May increase or decrease depending upon temperature
Grashoff number
Nusselt number
Weber number
Prandtl number
Watt/cm² °K
Watt/cm4 °K
Watt²/cm °K⁴
Watt/cm² °K⁴
Direct mixing of hot and cold fluids
A complete separation between hot and cold fluids
Flow of hot and cold fluids alternately over a surface
Generation of heat again and again
Irregular surfaces
Nonuniform temperature surfaces
One dimensional cases only
Two dimensional cases only
Higher
Lower
Same
Depends upon the shape of body
Is black in colour
Reflects all heat
Transmits all heat radiations
Absorbs heat radiations of all wave lengths falling on it
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
Free electrons
Atoms colliding frequency
Low density
Porous body
Convection
Radiation
Forced convection
Free convection
2 TR
4 TR
8 TR
10 TR
Increases
Decreases
Remain constant
May increase or decrease depending on temperature
S.H/(S.H + L.H)
(S.H + L.H) /S.H
(L.H - S.H)/S.H
S.H/(L.H - S.H)
Increases
Decreases
Remain constant
May increase or decrease depending on temperature
A dimensionless parameter
Function of temperature
Used as mathematical model
A physical property of the material
Stanton number
Biot number
Peclet number
Grashoff number
Function of temperature
Physical property of a substance
Dimensionless parameter
All of these
α = 1, ρ = 0 and τ = 0
α = 0, ρ = 1 and τ = 0
α = 0, ρ = 0 and τ = 1
α + ρ = 1 and τ = 0