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)

A. Q = [2πlk (T₁ - T₂)]/2.3 log (r₂/r₁)

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

Universal gas constant

Kinematic viscosity

Thermal conductivity

Planck's constant

Conduction

Convection

Radiation

None of these

Conduction

Free convection

Forced convection

Radiation

Different heat contents

Different specific heat

Different atomic structure

Different temperatures

Nature of body

Temperature of body

Type of surface of body

All of the above

K cal/kg m² °C

K cal m/hr m² °C

K cal/hr m² °C

K calm/hr °C

Varies with temperature

Varies with wavelength of the incident ray

Is equal to its emissivity

Does not vary with temperature and. wavelength of the incident ray

Iron

Lead

Concrete

Wood

Absolute temperature

Square of the absolute temperature

Cube of the absolute temperature

Fourth power of the absolute temperature

Grashoff number

Biot number

Stanton number

Prandtl number

Cold water inlet and outlet

Hot medium inlet and outlet

Hot medium outlet and cold water inlet

Hot medium outlet and cold water outlet

Zeroth law of thermodynamics

First law of thermodynamics

Second law of thermodynamics

Kirchhoff's law

Fourier equation

Stefan-Boltzmann equation

Newton Reichmann equation

Joseph-Stefan equation

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

-1/3

-2/3

1

-1

A grey body is one which absorbs all radiations incident on it.

At thermal equilibrium, the emissivity and absorptivity are same.

The energy absorbed by a body to the total energy falling on it, is called emissivity.

A perfect body is one which is black in colour.

Directly proportional to the thermal conductivity

Inversely proportional to density of substance

Inversely proportional to specific heat

All of the above

Melting of ice

Boiler furnaces

Condensation of steam in condenser

None of these

k. A. (dT/dx)

k. A. (dx/dT)

k. (dT/dx)

k. (dx/dT)

Temperature

Thickness

Area

Time

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 = 0 Where a = absorptivity, p = reflectivity, X = transmissivity.

Thermal resistance

Thermal coefficient

Temperature gradient

Thermal conductivity

Change vapour into liquid

Change liquid into vapour

Increase the temperature of a liquid or vapour

Convert water into steam and superheat it

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

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

20°C

40°C

60°C

66.7°C

Density

Coefficient of viscosity

Gravitational force

All of these

_{1} r_{2} (T_{1} - T_{2})/ (r_{2} - r_{1})

_{1} r_{2} (T_{1} - T_{2})/ (r_{2} - r_{1})

_{1} r_{2} (T_{1} - T_{2})/ (r_{2} - r_{1})

_{1} r_{2} (T_{1} - T_{2})/ (r_{2} - r_{1})

Composition

Density

Porosity

All of the above