Pick up the wrong case. Heat flowing from one side to other depends directly on
Face area
Time
Thickness
Temperature difference
Correct Answer :
C. Thickness
Related Questions
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.Cmin/U
U/A.Cmin
A.U.Cmin
A.U/Cmin
In free convection heat transfer, Nusselt number is function of
Grashoff number and Reynold number
Grashoff number and Prandtl number
Prandtl number and Reynold number
Grashoff number, Prandtl number and Reynold number
If the temperature of a solid surface changes from 27°C to 627°C, then its emissive power changes in the ratio of
6
9
27
81
In regenerator type heat exchanger, heat transfer takes place by
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
Moisture would find its way into insulation by vapour pressure unless it is prevented by
High thickness of insulation
High vapour pressure
Less thermal conductivity insulator
A vapour seal
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
1 : 1
2 : 1
1 : 2
4 : 1
Log mean temperature difference in case of counter flow compared to parallel flow will be
Same
More
Less
Depends on other factors
Depending on the radiating properties, a body will be opaque when
P = 0, x = 0 and a = 1
P=1, x = 0 and a = 0
P = 0, x = 1 and a = 0
X = 0, a + p = 1 Where a = absorptivity, p = reflectivity, X = transmissivity.
The ratio of surface convection resistance to the internal conduction resistance is known as
Grashoff number
Biot number
Stanton number
Prandtl number
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
20°C
40°C
60°C
66.7°C
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
Heat flows from one body to other when they have
Different heat contents
Different specific heat
Different atomic structure
Different temperatures
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
Conduction
Convection
Radiation
Conduction and convection
Heat conducted through per unit area and unit thick face per unit time when temperature difference between opposite faces is unity, is called
Thermal resistance
Thermal coefficient
Temperature gradient
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)
h = k/ ρS
h = ρS/k
h = S/ρk
h = kρ/S
According to Stefan Boltzmann law, ideal radiators emit radiant energy at a rate proportional to
Absolute temperature
Square of temperature
Fourth power of absolute temperature
Fourth power of temperature
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 value of the wavelength for maximum emissive power is given by
Wien's law
Planck's law
Stefan's law
Fourier's law
In free convection heat transfer transition from laminar to turbulent flow is governed by the critical value of the
Reynold's number
Grashoff's number
Reynold's number, Grashoff's number
Prandtl number, Grashoff's number
Thermal conductivity of water at 20°C is of the order of
0.1
0.23
0.42
0.51
Which of the following is a case of steady state heat transfer?
I.C. engine
Air preheaters
Heating of building in winter
None of the above
Which of the following is expected to have highest thermal conductivity?
Steam
Solid ice
Melting ice
Water
Heat is transferred by all three modes of transfer, viz. conduction, convection and radiation in
Electric heater
Steam condenser
Boiler
Refrigerator condenser coils
Which of the following property of air does not increase with rise in temperature?
Thermal conductivity
Thermal diffusivity
Density
Dynamic viscosity
In case of liquids and gases, the heat transfer takes place according to
Conduction
Convection
Radiation
None of these
Depending on the radiating properties, body will be transparent when
P = 0, x = 0 and a = 1
P=1, x = 0, and a = 0
P = 0, T= 1, and a = 0
X = 0, a + p = 1
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 highest thermal diffusivity is of
Iron
Lead
Concrete
Wood
The radiation emitted by a black body is known as
Black radiation
Full radiation
Total radiation
All of these
The ratio of the energy absorbed by the body to total energy falling on it is called
Absorptive power
Emissive power
Absorptivity
Emissivity