4

# In heat exchangers, degree of approach is defined as the difference between temperatures of

Cold water inlet and outlet

Hot medium inlet and outlet

Hot medium outlet and cold water inlet

Hot medium outlet and cold water outlet

D. Hot medium outlet and cold water outlet

4

k/h₀

2k/h₀

h₀/k

h₀/2k

4

Wien's law

Stefan's law

Kirchhoff's law

Planck's law

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 use of heat exchangers is made in

Condensers and boilers in steam plants

Condensers and evaporators in refrigeration and air conditioning units

All of the above

4

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

Increases

Decreases

Remain constant

May increase or decrease depending on temperature

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

# The automobile radiator is a heat exchanger of

Parallel flow type

Counter flow type

Cross flow type

Regenerator type

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

kcal/m²

kcal/hr °C

kcal/m² hr °C

kcal/m hr °C

4

Hr (time)

Sq. m (area)

°C (temperature)

K.cal (heat)

4

-1/3

-2/3

1

-1

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

Liquids

Energy

Temperature

Entropy

4

Stanton number

Nusselt number

Biot number

Peclet number

4

Stanton number

Biot number

Peclet number

Grashoff number

4

# Sensible heat is the heat required to

Change vapour into liquid

Change liquid into vapour

Increase the temperature of a liquid of vapour

Convert water into steam and superheat it

4

One

Two

Three

Four

4

# Film coefficient is defined as Inside diameter of tube

Equivalent thickness of film

Thermal conductivity Equivalent thickness of film Specific heat × Viscosity

Thermal conductivity Molecular diffusivity of momentum Thermal diffusivity

Film coefficient × Inside diameter Thermal conductivity

4

K cal/kg m² °C

K cal m/hr m² °C

K cal/hr m² °C

K calm/hr °C

4

All of these

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

# 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

# Metals are good conductors of heat because

Their atoms collide frequently

Their atoms are relatively far apart

They contain free electrons

They have high density

4

W/m²K

W/m²

W/mK

W/m

4

h = k/ ρS

h = ρS/k

h = S/ρk

h = kρ/S

4

# The most commonly used method for the design of duct size is the

Velocity reduction method

Equal friction method

Static regains method

Dual or double method

4

Moisture

Density

Temperature

All of the above

4

# Thermal diffusivity is a

Function of temperature

Physical property of a substance

Dimensionless parameter

All of these

4

# The expression Q = ρ AT4 is called

Fourier equation

Stefan-Boltzmann equation

Newton Reichmann equation

Joseph-Stefan equation