4

# According to Stefan Boltzmann law, the total radiation from a black body per second per unit area is directly proportional to the

Absolute temperature

Square of the absolute temperature

Cube of the absolute temperature

Fourth power of the absolute temperature

D. Fourth power of the absolute temperature

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 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

# 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

4

# Film coefficient is defined as the ratio of

Thermal conductivity to the equivalent thickness of the film of fluid

Temperature drop through the films of fluids to the thickness of film of fluids

Thickness of film of fluid to the thermal conductivity

Thickness of film of fluid to the temperature drop through the films of fluids

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

# Fourier's law of heat conduction is valid for

One dimensional cases only

Two dimensional cases only

Three dimensional cases only

Regular surfaces having non-uniform temperature gradients

4

# Thermal conductivity of water in general with rise in temperature

Increases

Decreases

Remain constant

May increase or decrease depending on temperature

4

0.002

0.02

0.01

0.1

4

# A grey body is one whose absorptivity

Varies with temperature

Varies with the wave length of incident ray

Varies with both

Does not vary with temperature and wave length of the incident ray

4

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

Absolute temperature (T)

F

T

4

20°C

40°C

60°C

66.7°C

4

Emissivity

Transmissivity

Reflectivity

4

# Reynolds number is the ratio of

Energy transferred by convection to that by conduction

Kinematic viscosity to thermal diffusivity

Inertia force to viscous force

None of the above

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

4

# The rate of heat flow through a body is Q = [kA (T₁ - T₂)]/x. The term x/kA is known as

Thermal coefficient

Thermal resistance

Thermal conductivity

None of these

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

A.Cmin/U

U/A.Cmin

A.U.Cmin

A.U/Cmin

4

Stanton number

Nusselt number

Biot number

Peclet number

4

# According to Stefan Boltzmann law, the total radiation from a black body per second per unit area is directly proportional to the

Absolute temperature

Square of the absolute temperature

Cube of the absolute temperature

Fourth power of the absolute 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

Thermometer

Thermistor

Thermocouple

None of these

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

k. A. (dT/dx)

k. A. (dx/dT)

k. (dT/dx)

k. (dx/dT)

4

Conduction

Convection

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

Composition

Density

Porosity

All of the above

4

Watt/cm² °K

Watt/cm4 °K

Watt²/cm °K⁴

Watt/cm² °K⁴

4

K cal/kg m² °C

K cal m/hr m² °C

K cal/hr m² °C

K calm/hr °C

4

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

Face area

Time

Thickness

Temperature difference