from the book (Reference_Heat Transfer (Cengel) 2nd ed) Flashcards
is the transfer of energy from the more energetic particles of a
substance to the adjacent, less energetic ones as a result of interactions between the particles.
conduction
is the mode of heat transfer between a solid
surface and the adjacent liquid or gas that is in motion, and it involves the
combined effects of conduction and fluid motion.
convection
is the energy
emitted by matter in the form of electromagnetic waves (or photons) as a result of the changes in the electronic configurations of the atoms or molecules.
radiation
the form of energy that
can be transferred from one system to another as a result of temperature difference.
heat
The science that deals with the determination of the rates of such energy transfers is
heat transfer
what law of thermodynamics requires that the rate of
energy transfer into a system be equal to the rate of increase of the energy of
that system
first law or the conservation of energy
law of thermodynamics that requires that heat be transferred in the direction
of decreasing temperature
second law or the state of entropy
The basic requirement for heat transfer is the presence of a
temperature difference
is the driving force for heat
transfer,
temperature difference
the temperature difference per unit length or the rate of change of temperature
temperature gradient
NOTE
The larger the temperature gradient, the higher
the rate of heat transfer.
The heat transfer problems
encountered in practice can be considered in two groups:
(1) rating and
(2) sizing problems.
The forms of energy
related to the molecular structure of a system and the degree of the molecular
activity are referred to as the
microscopic energy
The sum of all microscopic
forms of energy is called the _________ of a system, and is denoted by
U (or u on a unit mass basis).
internal energy
portion of the internal energy of a system associated with the kinetic energy of the molecules is called_______
sensible energy or
sensible heat.
The internal energy associated with the phase of
a system is called ______
latent energy or latent heat.
The internal energy associated with the atomic bonds in
a molecule is called _______
chemical (or bond) energy
the internal energy
associated with the bonds within the nucleus of the atom itself is called _____
nuclear energy.
in this equation
h=u +Pv
Pv represents the _______
flow energy of the fluid (also called the flow work)
in this equation
h=u +Pv
The internal energy u represents the microscopic energy of a _______
nonflowing fluid
in this equation
h=u +Pv
the enthalpy h represents the microscopic energy of a _______.
flowing fluid
is defined as the energy required to
raise the temperature of a unit mass of a substance by one degree
specific heat
The specific heats of a substance, in general, depend on two independent
properties such as _____
temperature and pressure.
ideal gas depend on
temperature only
A substance whose specific volume (or density) does not change with temperature or pressure is called an
incompressible substance
Work done per unit time is called ____-, and is denoted
by W
·
.
power
In daily life, we frequently refer to the sensible and latent forms of internal
energy as ______
heat
The amount of heat transferred
per unit time is called
heat transfer rate
The rate of heat transfer per unit area normal to the direction of heat transfer
is called
heat flux
A large number of engineering devices such as water heaters and car radiators
involve mass flow in and out of a system, and are modeled as
control volumes
steady means
no change with time
The amount of mass flowing through a cross section of a flow device per
unit time is called the
mass flow rate
h is the slope of the temperature curve on a T-x diagram (the
rate of change of T with x), at location x
temperature gradient
the rate of heat transfer through a unit thickness of the material per unit area per unit
temperature difference.
thermal conductivity
is the mode of energy transfer between a solid surface and the
adjacent liquid or gas that is in motion, and it involves the combined effects of
conduction and fluid motion.
convection
Convection is called _______ if the fluid is forced to flow over
the surface by external means such as a fan, pump, or the wind
forced convection
convection is called_______if the fluid motion is caused
by buoyancy forces that are induced by density differences due to the variation of temperature in the fluid
natural (or free) convection
the rate of convection heat transfer is also reffered to as
newton’s law of cooling
is the energy emitted by matter in the form of electromagnetic
waves (or photons) as a result of the changes in the electronic configurations
of the atoms or molecules.
radiation
NOTE
Unlike conduction and convection, the transfer of
energy by radiation DOES NOT REQUIRE the presence of an intervening medium
NOTE
Most heat transfer problems encountered in practice are transient in nature,
but they are usually analyzed under some presumed steady conditions since
steady processes are easier to analyze, and they provide the answers to our
questions.
