Fundamentals of Heat & Mass Transfer
Solution Manual | All 14 Chapters
Questions With Correct and Verified
Answers
Equilibrium - ANSWER-A state of balance
heat transfer - ANSWER-the movement of energy from a warmer object to a cooler
object
thermal energy - ANSWER-The total energy of motion in the particles of a substance
Conduction - ANSWER-The direct transfer of heat from one substance to another
substance that it is touching.
conductor - ANSWER-A material that allows heat and electricity to pass through it.
Insulator - ANSWER-A material that does not allow heat or electrons to move through it
easily.
Convection - ANSWER-Process by which, in a fluid or gas being heated, the warmer
part of the mass will rise and the cooler portions will sink.
Radiation - ANSWER-Energy that is radiated or transmitted in the form of rays or waves
or particles.
mechanical energy - ANSWER-Kinetic or potential energy associated with the motion or
position of an object
electrical energy - ANSWER-The energy of electric charges
Under what conditions may the lumped capacitance method be used to predict the
transient response of a solid to a change in its thermal environment? - ANSWER-The
assumption can be made if the thermal resistance of the solid is small compared to the
resistance between the solid and its surroundings
What is the physical interpretation of the Biot number? - ANSWER-The biot number is
the measure of the temperature drop in the solid relative to the temperature difference
between the solid's surface and the fluid. It can also be thought of as the conductive
resistance over the convective resistance
,Is the lump capacitance method of analysis likely to be more applicable for a hot solid
being cooled by forced convection in air or in water? By forced convection in air or
natural convection by air? - ANSWER-It is more applicable for forced convection in air
as opposed to water and natural convection as opposed to forced convection. This is
due to the assumption that the solid has uniform temperature. That assumption requires
the thermal resistance inside the solid to be much smaller than the thermal conduction
between the solid and the fluids. In the examples, I selected the situations that resulted
in larger thermal resistances between the solid and fluid.
Is the lumped capacitance method of analysis likely to be more applicable for cooling of
a hot solid made of copper or aluminum? For silicon nitrite or glass? - ANSWER-
What parameters determine the time constant associated with the transient thermal
response of a lumped capacitance solid? Is this response accelerated or decelerated by
an increase in the convection coefficient? By an increase in the density or specific heat
of the solid? - ANSWER-The thermal time constant is directly proportional to the thermal
resistance and lumped thermal capacitance.
Increasing convection coefficient decreases thermal resistance and will accelerate its
response.
Increasing density or specific heat will decelerate its response.
For one-dimensional, transient conduction in a plane wall, a long cylinder, or a sphere
with surface convection, what dimensionless parameters may be used to simplify the
representation of thermal conditions? How are these parameters defined? - ANSWER-
Why is the semi-infinite solution applicable to any geometry at early times? - ANSWER-
What is the physical interpretation of the Fourier number? - ANSWER-
What requirement must be satisfied for use of a one-term approximation to determine
the transient thermal response of a plane wall, a long cylinder, or a sphere experiencing
one-dimensional conduction due to a change in surface conditions? At what stage of a
transient process is the requirement not satisfied? - ANSWER-
What does transient heating or cooling of a plane wall with equivalent convection
conditions at opposite surfaces have in common with a plane wall heated or cooled by
convection at one surface and well insulated at the other surface? - ANSWER-
How may a one-term approximation be used to determine the transient thermal
response of a plane wall, long cylinder, or a sphere subjected to a sudden change in
surface temperature? - ANSWER-
,For one-dimensional, transient conduction, what is implied by the idealization be applied
to a plane wall? A long cylinder? A sphere? An object of arbitrary geometry? -
ANSWER-
What differentiates an explicit, finite-difference solution to a transient conduction
conduction problem from an implicit solution? - ANSWER-
What is meant by characterization of the implicit finite-difference method as
unconditionally stable? What constraint is placed on the explicit method to ensure a
stable solution? - ANSWER-
What are the physical mechanisms associated with heat transfer by conduction,
convection, and radiation? - ANSWER-Conduction: The transfer of energy between
objects that are in physical contact. Thermal conductivity is the property of a material to
conduct heat and evaluated primarily in terms ofFourier's Law for heat conduction.
Convection: The transfer of energy between an object and its environment, due to fluid
motion. The average temperature, is a reference for evaluating properties related to
convective heat transfer.
Radiation: The transfer of energy from the movement of charged particles within atoms
is converted to electromagnetic radiation.
What is the driving potential for heat transfer? What are analogs to this potential and to
heat transfer itself for the transport of electric charge and fluid flow? - ANSWER-The
driving potential for heat transfer is temperature difference.
Electric charge: Electrons flow in a wire due to the potential difference between the two
terminals.
Fluid flow: The fluid always flows from high head to low head regions.
What is the difference between a heat flux and a heat rate? What are their units
(explain)? - ANSWER-Heat flux is the heat rate per unit area.
Heat flux - W/m^2 (W=J/s)
Heat rate - J/s
What is a temperature gradient? What are its units? What is the relationship of heat flow
to a temperature gradient? - ANSWER-The rate of change of temperature with respect
to length (dT/dx).
Units are temp over length K/m or C/m.
What is thermal conductivity? What are its units? What roles does it play in heat
transfer? - ANSWER-The heat energy transferred per unit time and per unit surface
area, divided by the temperature difference.
, Units are W/mK or W/mC.
Applied in the law of conduction.
What is Fourier's Law? Write the equation. - ANSWER-The time rate of heat transfer
through a material is proportional to the negative gradient in the temperature and to the
area through which the heat flows.
qx = -k(dT/dx)
If heat transfer by conduction through a medium occurs under steady-state conditions,
will the temperature at a particular instant vary with location in the medium? Will the
temperature at a particular location vary with time? - ANSWER-qx = -k(dT/dx) under SS
conditions, thus temperature varies with respect to location and not time.
What is the difference between natural convection and forced convection? - ANSWER-
Natural: Flow induced by buoyancy forces, which are due to density differences caused
by temp variations in the fluid
Forced: Flow induced by external means (fan, pump, atm winds, etc)
What conditions are necessary for the development of a hydrodynamic boundary layer?
A thermal boundary layer? What varies across a hydrodynamic boundary layer? Across
a thermal boundary layer? - ANSWER-For both, the conditions consist of convection
heat transfer between a fluid in motion and a bounding surface when the two are at
different temperatures.
Hydrodynamic - velocity varies from zero at the surface to a finite value u-infinity
associated with the flow
Thermal - temperature varies from Ts at y=0 to T-infinity in the outer flow
If convection heat transfer for flow of a liquid or a vapor is not characterized by
liquid/vapor phase change, what is the nature of the energy being transferred? What is
it if there is such a phase change? - ANSWER-Sensible, latent
What is Newton's law of cooling? - ANSWER-States that the rate of change of
temperature of an object is proportional to the difference between its own temperature
and the ambient temperature.
Q = hA(T-Tamb)
What role is played by the convection heat transfer coefficient in Newtons law of
cooling? What are its units? - ANSWER-Correlates the properties of the boundary layer,
surface geometry, and nature of the fluid motion to heat transfer
Solution Manual | All 14 Chapters
Questions With Correct and Verified
Answers
Equilibrium - ANSWER-A state of balance
heat transfer - ANSWER-the movement of energy from a warmer object to a cooler
object
thermal energy - ANSWER-The total energy of motion in the particles of a substance
Conduction - ANSWER-The direct transfer of heat from one substance to another
substance that it is touching.
conductor - ANSWER-A material that allows heat and electricity to pass through it.
Insulator - ANSWER-A material that does not allow heat or electrons to move through it
easily.
Convection - ANSWER-Process by which, in a fluid or gas being heated, the warmer
part of the mass will rise and the cooler portions will sink.
Radiation - ANSWER-Energy that is radiated or transmitted in the form of rays or waves
or particles.
mechanical energy - ANSWER-Kinetic or potential energy associated with the motion or
position of an object
electrical energy - ANSWER-The energy of electric charges
Under what conditions may the lumped capacitance method be used to predict the
transient response of a solid to a change in its thermal environment? - ANSWER-The
assumption can be made if the thermal resistance of the solid is small compared to the
resistance between the solid and its surroundings
What is the physical interpretation of the Biot number? - ANSWER-The biot number is
the measure of the temperature drop in the solid relative to the temperature difference
between the solid's surface and the fluid. It can also be thought of as the conductive
resistance over the convective resistance
,Is the lump capacitance method of analysis likely to be more applicable for a hot solid
being cooled by forced convection in air or in water? By forced convection in air or
natural convection by air? - ANSWER-It is more applicable for forced convection in air
as opposed to water and natural convection as opposed to forced convection. This is
due to the assumption that the solid has uniform temperature. That assumption requires
the thermal resistance inside the solid to be much smaller than the thermal conduction
between the solid and the fluids. In the examples, I selected the situations that resulted
in larger thermal resistances between the solid and fluid.
Is the lumped capacitance method of analysis likely to be more applicable for cooling of
a hot solid made of copper or aluminum? For silicon nitrite or glass? - ANSWER-
What parameters determine the time constant associated with the transient thermal
response of a lumped capacitance solid? Is this response accelerated or decelerated by
an increase in the convection coefficient? By an increase in the density or specific heat
of the solid? - ANSWER-The thermal time constant is directly proportional to the thermal
resistance and lumped thermal capacitance.
Increasing convection coefficient decreases thermal resistance and will accelerate its
response.
Increasing density or specific heat will decelerate its response.
For one-dimensional, transient conduction in a plane wall, a long cylinder, or a sphere
with surface convection, what dimensionless parameters may be used to simplify the
representation of thermal conditions? How are these parameters defined? - ANSWER-
Why is the semi-infinite solution applicable to any geometry at early times? - ANSWER-
What is the physical interpretation of the Fourier number? - ANSWER-
What requirement must be satisfied for use of a one-term approximation to determine
the transient thermal response of a plane wall, a long cylinder, or a sphere experiencing
one-dimensional conduction due to a change in surface conditions? At what stage of a
transient process is the requirement not satisfied? - ANSWER-
What does transient heating or cooling of a plane wall with equivalent convection
conditions at opposite surfaces have in common with a plane wall heated or cooled by
convection at one surface and well insulated at the other surface? - ANSWER-
How may a one-term approximation be used to determine the transient thermal
response of a plane wall, long cylinder, or a sphere subjected to a sudden change in
surface temperature? - ANSWER-
,For one-dimensional, transient conduction, what is implied by the idealization be applied
to a plane wall? A long cylinder? A sphere? An object of arbitrary geometry? -
ANSWER-
What differentiates an explicit, finite-difference solution to a transient conduction
conduction problem from an implicit solution? - ANSWER-
What is meant by characterization of the implicit finite-difference method as
unconditionally stable? What constraint is placed on the explicit method to ensure a
stable solution? - ANSWER-
What are the physical mechanisms associated with heat transfer by conduction,
convection, and radiation? - ANSWER-Conduction: The transfer of energy between
objects that are in physical contact. Thermal conductivity is the property of a material to
conduct heat and evaluated primarily in terms ofFourier's Law for heat conduction.
Convection: The transfer of energy between an object and its environment, due to fluid
motion. The average temperature, is a reference for evaluating properties related to
convective heat transfer.
Radiation: The transfer of energy from the movement of charged particles within atoms
is converted to electromagnetic radiation.
What is the driving potential for heat transfer? What are analogs to this potential and to
heat transfer itself for the transport of electric charge and fluid flow? - ANSWER-The
driving potential for heat transfer is temperature difference.
Electric charge: Electrons flow in a wire due to the potential difference between the two
terminals.
Fluid flow: The fluid always flows from high head to low head regions.
What is the difference between a heat flux and a heat rate? What are their units
(explain)? - ANSWER-Heat flux is the heat rate per unit area.
Heat flux - W/m^2 (W=J/s)
Heat rate - J/s
What is a temperature gradient? What are its units? What is the relationship of heat flow
to a temperature gradient? - ANSWER-The rate of change of temperature with respect
to length (dT/dx).
Units are temp over length K/m or C/m.
What is thermal conductivity? What are its units? What roles does it play in heat
transfer? - ANSWER-The heat energy transferred per unit time and per unit surface
area, divided by the temperature difference.
, Units are W/mK or W/mC.
Applied in the law of conduction.
What is Fourier's Law? Write the equation. - ANSWER-The time rate of heat transfer
through a material is proportional to the negative gradient in the temperature and to the
area through which the heat flows.
qx = -k(dT/dx)
If heat transfer by conduction through a medium occurs under steady-state conditions,
will the temperature at a particular instant vary with location in the medium? Will the
temperature at a particular location vary with time? - ANSWER-qx = -k(dT/dx) under SS
conditions, thus temperature varies with respect to location and not time.
What is the difference between natural convection and forced convection? - ANSWER-
Natural: Flow induced by buoyancy forces, which are due to density differences caused
by temp variations in the fluid
Forced: Flow induced by external means (fan, pump, atm winds, etc)
What conditions are necessary for the development of a hydrodynamic boundary layer?
A thermal boundary layer? What varies across a hydrodynamic boundary layer? Across
a thermal boundary layer? - ANSWER-For both, the conditions consist of convection
heat transfer between a fluid in motion and a bounding surface when the two are at
different temperatures.
Hydrodynamic - velocity varies from zero at the surface to a finite value u-infinity
associated with the flow
Thermal - temperature varies from Ts at y=0 to T-infinity in the outer flow
If convection heat transfer for flow of a liquid or a vapor is not characterized by
liquid/vapor phase change, what is the nature of the energy being transferred? What is
it if there is such a phase change? - ANSWER-Sensible, latent
What is Newton's law of cooling? - ANSWER-States that the rate of change of
temperature of an object is proportional to the difference between its own temperature
and the ambient temperature.
Q = hA(T-Tamb)
What role is played by the convection heat transfer coefficient in Newtons law of
cooling? What are its units? - ANSWER-Correlates the properties of the boundary layer,
surface geometry, and nature of the fluid motion to heat transfer
