4

Conduction

Convection

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

Solids

Liquids

Gases

None of these

4

Pb = pa - pv

Pb = pa + pv

Pb = pa × pv

Pb = pa/pv

4

Reflected

Refracted

Transmitted

Absorbed

4

# Pick up the wrong case. Heat flowing from one side to other depends directly on

Face area

Time

Thickness

Temperature difference

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

# In a shell and tube heat exchanger, baffles are provided on the shell side to

Improve heat transfer

Provide support for tubes

Prevent stagnation of shell side fluid

All of these

4

Wien's law

Stefan's law

Kirchhoff's law

Planck's law

4

k/h₀

2k/h₀

h₀/k

h₀/2k

4

Absorptive power

Emissive power

Absorptivity

Emissivity

4

h = k/ ρS

h = ρS/k

h = S/ρk

h = kρ/S

4

# Heat transfer by radiation mainly depends upon

Its temperature

Nature of the body

Kind and extent of its surface

All of the above

4

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

Absolute temperature (T)

F

T

4

0.002

0.02

0.01

0.1

4

Temperature

Thickness

Area

Time

4

Thermometer

Thermistor

Thermocouple

None of these

4

A.Cmin/U

U/A.Cmin

A.U.Cmin

A.U/Cmin

4

# 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

4

Parallel flow

Counter flow

Cross flow

All of these

4

# Two plates spaced 150 mm apart are maintained at 1000°C and 70°C. The heat transfer will take place mainly by

Convection

Forced convection

Free convection

4

Black body

Grey body

Opaque body

White body

4

Minimum energy

Maximum energy

Both (A) and (B)

None of these

4

Grashoff number

Biot number

Stanton number

Prandtl number

4

Temperature

Wave length

Physical nature

All of the above

4

# A steam pipe is to be lined with two layers of insulating materials of different thermal conductivities. For the minimum heat transfer,

The better insulation must be put inside

The better insulation must be put outside

One could place either insulation on either side

One should take into account the steam temperature before deciding as to which insulation is put where

4

1 : 1

2 : 1

1 : 2

4 : 1

4

# Absorptivity of a body will be equal to its emissivity

At all temperatures

At one particular temperature

When system is under thermal equilibrium

At critical temperature

4

Wien's law

Planck's law

Stefan's law

Fourier's law

4

# The insulation ability of an insulator with the presence of moisture would

Increase

Decrease

Remain unaffected

May increase/decrease depending on temperature and thickness of insulation