4

Heat flows from one body to other when they have

Different heat contents

Different specific heat

Different atomic structure

Different temperatures

D. Different temperatures

4

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

4

2 TR

4 TR

8 TR

10 TR

4

Stanton number

Biot number

Peclet number

Grashoff number

4

According of Kirchhoff's law

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.

4

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.

Equal to

Directly proportional to

Inversely proportional to

None of these

4

According to Wien's law, the wavelength corresponding to maximum energy is proportion to

Absolute temperature (T)

F

T

4

The amount of heat flow through a body by conduction is

Directly proportional to the surface area of the body

Directly proportional to the temperature difference on the two faces of the body

Dependent upon the material of the body

All of the above

4

The thermal diffusivities for gases are generally

More than those for liquids

Less than those for liquids

More than those for solids

Dependent on the viscosity

4

Thermal diffusivity of a substance is

Directly proportional to thermal conductivity

Inversely proportional to density of substance

Inversely proportional to specific heat

All of the above

4

0

0.5

0.75

1

4

0.45

0.55

0.40

0.75

4

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

First law of thermodynamics

Newton's law of cooling

Newton's law of heating

Stefan's law

4

According to Prevost theory of heat exchange

It is impossible to transfer heat from low temperature source to t high temperature source

Heat transfer by radiation requires no medium

All bodies above absolute zero emit radiation

Heat transfer in most of the cases takes place by combination of conduction, convection and radiation

4

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)

Q = [2πlk (T₁ - T₂)]/2.3 log (r₂/r₁)

Q = 2.3 log (r₂/r₁)/[2πlk (T₁ - T₂)]

Q = [2π (T₁ - T₂)]/2.3 lk log (r₂/r₁)

Q = = 2πlk/2.3 (T₁ - T₂) log (r₂/r₁)

4

Log mean temperature difference in case of counter flow compared to parallel flow will be

Same

More

Less

Depends on other factors

4

Aluminium

Steel

Brass

Copper

4

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

4

According to Newton's law of cooling, the heat transfer from a hot body to a cold body is

Directly proportional to the surface area

Directly proportional to the difference of temperatures between the two bodies

Either (A) or (B)

Both (A) and (B)

4

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

4

Fouling factor is used

In heat exchanger design as a safety factor

In case of Newtonian fluids

When a liquid exchanges heat with a gas

None of the above

4

The heat transfer by conduction through a thick sphere is given by

Q = 2πkr1 r2 (T1 - T2)/ (r2 - r1)

Q = 4πkr1 r2 (T1 - T2)/ (r2 - r1)

Q = 6πkr1 r2 (T1 - T2)/ (r2 - r1)

Q = 8πkr1 r2 (T1 - T2)/ (r2 - r1)

4

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

Thermal conductivity

4

Watt/cm² °K

Watt/cm4 °K

Watt²/cm °K⁴

Watt/cm² °K⁴

4

A perfect black body is one which

Is black in colour

Reflects all heat

Absorbs heat radiations of all wave lengths falling on it

4

Thermal conductivity of solid metals with rise in temperature normally

Increases

Decreases

Remain constant

May increase or decrease depending on temperature

4

Total heat is the heat required to

Change vapour into liquid

Change liquid into vapour

Increase the temperature of a liquid or vapour

Convert water into steam and superheat it

4

h = k/ ρS

h = ρS/k

h = S/ρk

h = kρ/S

4

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

4

Temperature

Thickness

Area

Time