4

Iron

Concrete

Wood

4

# The process of heat transfer from one particle of the body to another is called conduction, when the particles of the body

Move actually

Do not move actually

Affect the intervening medium

Does not affect the intervening medium

4

0.45

0.55

0.40

0.75

4

# The time constant of a thermocouple is

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

4

Stanton number

Biot number

Peclet number

Grashoff number

4

# According to Kirchoff's law, the ratio of emissive power to absorptivity for all bodies is equal to the emissive power of a

Grey body

Brilliant white polished body

Red hot body

Black body

4

# A steam pipe is to be insulated by two insulating materials put over each other. For best results

Better insulation should be put over pipe and better one over it

Inferior insulation should be put over pipe and better one over it

Both may be put in any order

Whether to put inferior OIL over pipe or the better one would depend on steam temperature

4

# A cube at high temperature is immersed in a constant temperature bath. It loses heat from its top, bottom and side surfaces with heat transfer coefficients of h₁, h₂ and h₃ respectively. The average heat transfer coefficient for the cube is

h₁ + h₂ + h₃

(h₁.h₂.h₃)1/3

1/h₁ + 1/h₂ + 1/h₃

None of these

4

Conduction

Convection

None of these

4

Composition

Density

Porosity

All of the above

4

# Thermal diffusivity of a substance is

Directly proportional to the thermal conductivity

Inversely proportional to density of substance

Inversely proportional to specific heat

All of the above

4

k. A. (dT/dx)

k. A. (dx/dT)

k. (dT/dx)

k. (dx/dT)

4

# 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

Conduction and convection

4

# In counter flow heat exchangers

Both the fluids at inlet (of heat exchanger where hot fluid enters) are in their coldest state

Both the fluids at inlet are in their hottest state

Both the fluids at exit are in their hottest state

One fluid is in hottest state and other in coldest state at inlet

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

Black body

Grey body

Opaque body

White body

4

# The amount of radiation mainly depends upon the

Nature of the body

Temperature of the body

Type of surface of the body

All of these

4

Iron

Concrete

Wood

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

# Heat transfer takes place as per

Zeroth law of thermodynamics

First law of thermodynamic

Second law of the thermodynamics

Kirchoff's law

4

One

Two

Three

Four

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

Conduction

Convection

None of these

4

# Thermal conductivity of non-metallic amorphous solids with decrease in temperature

Increases

Decreases

Remain constant

May increase or decrease depending on temperature

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

# The logarithmic mean temperature difference (tm) is given by (where Δt1 and Δt2 are temperature differences between the hot and cold fluids at entrance and exit)

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

4

# Joule sec is the unit of

Universal gas constant

Kinematic viscosity

Thermal conductivity

Planck's constant

4

Reflected

Refracted

Transmitted

Absorbed

4

# Kirchhoff's law states that

The total radiation from a black body per second per unit area is directly proportional to the fourth power of the absolute temperature

The wave length corresponding to the maximum energy is proportional to the absolute temperature

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

None of the above

4

Conduction

Convection