thermo chapter 2 Flashcards
conservation of the
quality of energy, not the quantity
Energy Conservation
which is of the highest quality of energy, for
example, can always be converted to an equal amount of
thermal energy (also called heat).
Electricity,
Energy can exist in numerous
forms such as thermal,
mechanical, kinetic, potential,
electric, magnetic, chemical,
and nuclear, and their sum
constitutes the
total energy E
Thermodynamics provides no
information about the absolute
value of the total energy. It deals
only with the
change of the total
energy,
of energy
are those a system possesses
as a whole with respect to some
outside reference frame, such as
kinetic and potential energies
macroscopic forms
of energy are those
related to the molecular structure of a system
and the degree of the molecular activity, and
they are independent of outside reference
frame
microscopic forms
The sum of all the
microscopic forms of energy. Denoted by U
internal energy
energy that a system
possesses as a result of its motion relative
to some reference frame
kinetic energy (KE)
the energy that a
system possesses as a result of its elevation
in a gravitational field
potential energy (PE)
The magnetic, electric, and surface tension effects are
significant in some specialized cases only and are usually
ignored
total energy of a system
closed systems whose velocity and elevation of the center of gravity remains constant during a process are often referred to as
stationary systems
the amount of mass flowing through a cross section
mass flow rate
which is the volume of a fluid flowing through a cross section per unit time
volume flow rate
- the form of
energy that can be converted to
mechanical work completely and
directly by an ideal mechanical
device such as an ideal turbine
Mechanical Energy
Kinetic and potential energies are the
familiar forms of
mechanical energy.
the pressure of a flowing fluid is also associated with its
mechanical energy pressure unit Pa is equivalent to
Mechanical Energy
pressure itself is not a form of energy, but a
pressure force acting on a fluid through a distance
produces work,
flow work,
Energy can cross the boundary of a
closed system in two distinct forms:
heat and work
is defined as the form of
energy that is transferred between
two systems (or a system and its
surroundings) by virtue of a
temperature difference
Heat
is energy in transition. It is
recognized only as it crosses the
boundary of a system
Heat
A process during which there is no
heat transfer is called
adiabatic
process
Heat transfer per unit mass of a system is denoted
q
the amount of heat being transferred per unit time
rate of the heat transfer
heat transfer is denoted by
.Q
it is also a form of energy that is being transferred by heat
work
have inexact differentials designated
by the symbol δ. differential amount of heat or work
is represented by δQ or δW, respectively, instead
of dQ or dW
Path functions
For a specified constant torque, the work done
during n revolutions is determined as follows: A
force F acting through a moment arm r generates a
torque T of
SHAFT WORK
are point functions (i.e., they depend
on the state only, and not on how a system
reaches that state), and they have exact
differentials designated by the symbol d. A small
change in volume, for example, is represented by
dV, and the total volume change during a process
between states 1 and 2 is
Properties
The net change (increase or decrease) in the
total energy of the system during a process is equal
to the difference between the total energy entering
and the total energy leaving the system during that
process
ENERGY BALANCE
The determination of the energy change of a system
during a process involves the evaluation of the
energy of the system at the beginning and at the end
of the process, and taking their difference
ENERGY CHANGE OF A SYSTEM
Heat transfer to a system (heat
gain) increases the energy of the molecules and
thus the internal energy of the system
Heat Transfer, Q
An energy interaction that is
not caused by a temperature difference between
a system and its surroundings is work
Work Transfer, W
Mass flow in and out of the
system serves as an additional mechanism of
energy transfer. When mass enters a system,
the energy of the system increases because
mass carries energy with it
Mass Flow, m
is defined as the ratio of the energy
delivered to the house by hot
water to the energy supplied to
the water heater
efficiency of a water heater
which is the ratio of the
electrical power output to the mechanical power input
Generator efficiency
is usually defined
as the ratio of the net shaft work output of the turbine
to the heat input to the working fluid
thermal efficiency of a power plant
as the ratio of the
net electrical power output to the rate of fuel energy
input
overall efficiency for the power plant
defined as
the amount of light output in
lumens per W of electricity
consumed
lighting efficacy
can be defined as
the ratio of the useful energy
transferred to the food to the
energy consumed by the
appliance
efficiency of a cooking
appliance
