4

Grashoff number

Biot number

Stanton number

Prandtl number

B. Biot number

4

Conduction

Convection

None of these

4

Conduction

Convection

None of these

4

# Fouling factor is used

In heat exchanger design as a safety factor

In case of Newtonian fluids

When a liquid exchanges heat with a gas

None of the above

4

# A grey body is one whose absorptivity

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

4

Steam

Solid ice

Melting ice

Water

4

# When heat is transferred from hot body to cold body, in a straight line, without affecting the intervening medium, it is referred as heat transfer by

Conduction

Convection

Conduction and convection

4

1 : 1

2 : 1

1 : 2

4 : 1

4

# Upto the critical radius of insulation,

Added insulation will increase heat loss

Added insulation will decrease heat loss

Convective heat loss will be less than conductive heat loss

Heat flux will decrease

4

# Log mean temperature difference in case of counter flow compared to parallel flow will be

Same

More

Less

Depends on other factors

4

# Heat flows from one body to other when they have

Different heat contents

Different specific heat

Different atomic structure

Different temperatures

4

Iron

Concrete

Wood

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

Wien's law

Stefan's law

Kirchhoff's law

Planck's law

4

m²/hr

m²/hr °C

kcal/m² hr

kcal/m. hr °C

4

# In convection heat transfer from hot flue gases to water tube, even though flow may be turbulent, a laminar flow region (boundary layer of film) exists close to the tube. The heat transfer through this film takes place by

Convection

Conduction

Both convection and conduction

4

kcal/m²

kcal/hr °C

kcal/m² hr °C

kcal/m hr °C

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

# Heat transfer by radiation mainly depends upon

Its temperature

Nature of the body

Kind and extent of its surface

All of the above

4

# Which of the following would lead to a reduction in thermal resistance?

In conduction, reduction in the thickness of the material and an increase in thermal conductivity.

In convection, stirring of the fluid and cleaning the heating surface.

In radiation, increasing the temperature and reducing the emissivity.

All of the above

4

# Depending on the radiating properties, a body will be opaque when

P = 0, x = 0 and a = 1

P=1, x = 0 and a = 0

P = 0, x = 1 and a = 0

X = 0, a + p = 1 Where a = absorptivity, p = reflectivity, X = transmissivity.

4

Pb = pa - pv

Pb = pa + pv

Pb = pa × pv

Pb = pa/pv

4

0.002

0.02

0.01

0.1

4

Grashoff number

Nusselt number

Weber number

Prandtl number

4

# Unit of thermal conductivity in S.I. units is

J/m² sec

J/m °K sec

W/m °K

Option (B) and (C) above

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

20°C

40°C

60°C

66.7°C

4

# Heat transfer takes place as per

Zeroth law of thermodynamics

First law of thermodynamic

Second law of the thermodynamics

Kirchoff's law

4

# LMTD in case of counter flow heat exchanger as compared to parallel flow heat exchanger is

Higher

Lower

Same

Depends on the area of heat exchanger

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