•
Brayton cycle- A thermodynamic cycle that
describes gas turbine engines. Inlet gas is brought to high pressure through a
compressor, after which it is heated in a combustion chamber and expanded
through a turbine for energy extraction. It is an "open" system, in
that the working fluid is not recycled.
•
Rankine cycle- Also referred to as the
steam cycle, the Rankine cycle utilizes the evaporation-condensation properties
of a working fluid to drive a turbine. Water vapor, or steam, is often used as
the working fluid for these processes. A pump is used to circulate the fluid
through a boiler, where it is heated (or boiled) at a constant pressure into
steam, after which it is expanded through a turbine for energy
extraction. It is a "closed" system, in that the working fluid
is recycled.
•
Combined cycle (CC)- A combined cycle
system utilizes two or more thermodynamic cycles to recover energy from hot
exhaust gas streams. These cycles often combine Brayton and Rankine cycles in
series, through the use of a "heat recovery steam generator" or HRSG.
This device is a large heat exchanger used to extract heat from exhaust gases
to boil water in a Rankine cycle.
•
Combined heat and power (CHP)- Similar to
a combined cycle process, CHP cycles are used to generate steam for functions
beyond generating electricity. These functions can include space heating,
process heating, or direct steam use.
•
Turbine- A rotor-machine that is used to
extract energy from high pressure, high temperature fluids via expansion across
the turbine blades.
•
Heat Recovery Steam Generator (HRSG)- A
specialized heat exchanger often used in power generation. These devices will
produce steam for a specific process or to drive a steam turbine.
•
Heat rate - A ratio of incoming fuel
energy (in BTU) to outgoing electrical energy (in kWh). Heat rates are a
convenient way to assess the efficiency of a power plant. These rates will be
larger than one (normally around the magnitude of 10,000) and indicate increases
in effiency as the number goes down.
•
Hybrid electric vehicle (HEV)- Features a
parallel drivetrain architechture, with a battery-driven electric motor and an
internal combustion engine coupled into the same transmission. Usually features
energy recovery technology to recharge the battery during operation
•
Plug-in hybrid electric vehicle (PHEV)-
Similar to HEVs, PHEVs utilize a two-way transmission to couple a gas burning
engine with a battery-driven motor. Battery packs can be recharged using
external power from a wall outlet.
•
Battery electric vehicles (BEV)- Electric
vehicles driven purely by an electric motor. The BEV battery pack must be
charged using external power from a wall outlet.
•
Torque-speed plots- A graphical plot used
to characterize the performance of engines and motors. These plots are related
to the power output of the engine or motor.
•
Natural gas vehicles (NGV)-Vehicles
driven by natural gas instead of liquid gasoline. Traditional internal
combustion engines can be adapted to burn natural gas, with a large part of the
converstion stemming from different fuel storage requirements.
The mass (m) of a
body is the measure of the amount of material present in that body.
The weight (wt) of a
body is the force exerted by that body when its mass is accelerated in a
gravitational field.
The specific volume (
ν ) of a substance is the total volume (V) of that substance
divided by the total mass (m) of that substance (volume per unit mass).
The density ( ) of a
substance is the total mass (m) of that substance divided by the total ρ volume
(V) occupied by that substance (mass per unit volume).
Specific gravity
(S.G.) is a measure of the relative density of a substance as compared to the
density of water at a standard temperature
Humidity is the
amount of moisture (water vapor) in the air.
Absolute humidity is
the mass of water vapor divided by a unit volume of air (grams of water/cm3 of air)
Relative humidity is
the amount of water vapor present in the air divided by the maximum amount that
the air could contain at that temperature. Relative humidity is expressed as a
percentage.
An intensive property
is independent of the amount of mass.
Extensive properties
are those that vary directly with the mass.
Temperature is a
measure of the molecular activity of a substance. The greater the movement of molecules,
the higher the temperature.
The absolute
temperature scale that corresponds to the Celsius scale is called the Kelvin
(K) scale.
The absolute scale
that corresponds to the Fahrenheit scale is called the Rankine (R) scale.
Pressure is a measure
of the force exerted per unit area on the boundaries of a substance (or
system). It is caused by the collisions of the molecules of the substance with
the boundaries of the system.
When pressure is
measured relative to a perfect vacuum, it is called absolute pressure (psia).
When pressure is
measured relative to atmospheric pressure (14.7 psi), it is called gauge
pressure (psig).
Energy is defined as
the capacity of a system to perform work or produce heat.
Potential energy (PE)
is defined as the energy of position.
Kinetic energy (KE)
is the energy of motion.
The specific internal
energy (u) of a substance is its internal energy per unit mass.
Specific enthalpy (h)
is defined as h=u+Pν, where u is the specific internal energy
(Btu/lbm) of the system being studied, P is the pressure of the system (lbf/ft2 ), and ν
is the specific volume (ft3 /lbm) of the system.
Work is defined for
mechanical systems as the action of a force on an object through a distance.
A positive value for
work indicates that work is done by the system on its surroundings; a negative
value indicates that work is done on the system by its surroundings.
A positive value for
heat indicates that heat is added to the system by its
surroundings
The heat added to or
removed from a substance to produce a change in its temperature is called
sensible heat.
Latent heat is the
amount of heat added to or removed from a substance to produce a change in
phase.
Latent heat of fusion
is the amount of heat added or removed to change phase between solid and
liquid.
Latent heat of
vaporization is the amount of heat added or removed to change phase between
liquid and vapor.
The ratio of the heat
(Q) added to or removed from a substance to the change in temperature (∆T) produced is called the heat capacity (Cp) of the substance.
The heat capacity of
a substance per unit mass is called the specific heat(cp) of the substance.
Power is defined as
the time rate of doing work. It is equivalent to the rate of the energy
transfer.
Entropy is sometimes
referred to as a measure of the inability to do work for a given heat
transferred.
A system in
thermodynamics is nothing more than the collection of matter that is being
studied.
An isolated system is
one that is not influenced in any way by the surroundings. This means that no
energy in the form of heat or work may cross the boundary of the system. In
addition, no mass may cross the boundary of the system.
A closed system has
no transfer of mass with its surroundings, but may have a transfer of energy
(either heat or work) with its surroundings.
An open system is one
that may have a transfer of both mass and energy with its surroundings.
A control volume is a
fixed region in space chosen for the thermodynamic study of mass and energy
balances for flowing systems. The boundary of the control volume may be a real
or imaginary envelope.
The control surface
is the boundary of the control volume.
Steady state is that
circumstance in which there is no accumulation of mass or energy within
thecontrol volume, and the properties at any point within the system are
independent of time.
The path of the
succession of states through which the system passes is called the
thermodynamic process.
When a system in a
given initial state goes through a number of different changes in state (going
through various processes) and finally returns to its initial values, the
system has undergone a cyclic process or cycle.
A reversible process
for a system is defined as a process that, once having taken place, can be
reversed, and in so doing leaves no change in either the system or
surroundings.
An irreversible
process is a process that cannot return both the system and the surroundings to
their original conditions.
An adiabatic process
is one in which there is no heat transfer into or out of the system. The system
can be considered to be perfectly insulated.
Isentropic Process
An isentropic process
is one in which the entropy of the fluid remains constant. This will be true if
the process the system goes through is reversible and adiabatic. An isentropic
process can also be called a constant entropy process.
Polytropic Process
When a gas undergoes
a reversible process in which there is heat transfer, the process frequently
takes place in such a manner that a plot of the Log P (pressure) vs. Log V
(volume) is a straight line. Or stated in equation form PVn
= a constant. This
type of process is called a polytropic process.
A throttling process
is defined as a process in which there is no change in enthalpy from state one
to state two, h1 =h2 ; no work is done, W = 0; and the process is
adiabatic, Q = 0
First Law of Thermodynamics :
Energy can neither be created nor destroyed, only altered in
form.
Second Law of Thermodynamics :
It is impossible to construct a device that operates in a
cycle and produces no effect other than the removal of heat from a body at one
temperature and the absorption of an equal quantity of heat by a body at a
higher temperature.
Critical Point:- The temperature and pressure above which
there is no distinction between the liquid and vapor phases.
Triple point - the temperature and pressure at which all
three phases can exist in equilibrium .
Sublimation - change of phase from solid to vapor
Vaporization - change of phase from liquid to vapor
Condensation - change of phase from vapor to liquid
Fusion or melting - change of phase from solid to liquid
Boyle's Law
The pressure of a gas expanding at constant temperature
varies inversely to the volume.
Charles' Law
The pressure of a gas
varies directly with temperature when the volume is held constant, and the
volume varies directly with temperature when the pressure is held constant.
1 ft-lbf = 1.286 x 10-3 Btu = 3.766 x 10-7kW-hr
1 Btu = 778.3 ft-lbf
= 2.928 x 10-4kW-hr
1 kW-hr = 3.413 x 103Btu = 2.655 x 106 ft-lbf
The term saturation
defines a condition in which a mixture of vapor and liquid can exist together
at a given temperature and pressure.
The temperature at which vaporization (boiling) starts to
occur for a given pressure is called the
saturation temperature or boiling point.
The pressure at which vaporization (boiling) starts to occur
for a given temperature is called the
saturation pressure.
The graphical representation of this relationship between
temperature and pressure at saturated
conditions is called the vapor pressure curve.
When a substance exists as part liquid and part vapor at
saturation conditions, its quality (x) is
defined as the ratio of the mass of the vapor to the total mass
of both vapor and liquid.
If the temperature of the liquid is lower than the saturation
temperature for the existing pressure,
it is called either a subcooled liquid (implying that the
temperature is lower than the saturation
temperature for the given pressure) or a compressed liquid
(implying that the pressure is greater
than the saturation pressure for the given temperature).
The moisture content of a substance is the opposite of its
quality. Moisture (M) is defined as
the ratio of the mass of the liquid to the total mass of both
liquid and vapor.
If a substance exists entirely as vapor at saturation
temperature, it is called saturated vapor.
When the vapor is at a temperature greater than the
saturation temperature, it is said to exist as
superheated vapor.
Property Diagrams: The phases of a substance and the
relationships between its properties are most commonly shown on property
diagrams. There are six different types of commonly encountered property
diagrams. These are: Pressure- Temperature (P-T) diagrams, Pressure-Specific
Volume (P-ν) diagrams, Pressure-Enthalpy (P-h) diagrams, Enthalpy-Temperature
(h-T) diagrams, Temperature-entropy (T-s) diagrams, and Enthalpy-Entropy (h-s)
or Mollier diagrams.
The line that separates the solid and vapor phases is called
the sublimation line.
The line that separates the solid and liquid phases is called
the fusion line.
The line that separates the liquid and vapor phases is called
the vaporization line.
The point where the three lines meet is called the triple
point. The triple point is the only point at which all three phases can exist
in equilibrium.
The point where the vaporization line ends is called the
critical point.
The Mollier diagram can be used to determine various
properties of a fluid.
Mollier diagram is an h versus s
plot.
Can only be used when quality is
greater than 50% and for superheated steam.
Contains a series of constant
temperature, constant pressure, constant moisture content, and constant
superheat lines.
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