Thermodynamics Flashcards
Energy is…(two things)
- When work is done on or by the system
- When heat is added to or removed from the system
Define a system
A quantity of matter or a region in space chosen for study
Define Surroundings
The mass or region outside the system
Define Boundary
The real or imaginary surface that separates the system from its surroundings
Can the boundary of a system be fixed or movable?
Yes
Systems may be considered to be…(2 things)
Close or open
Define Property
Any characteristic of a system
Properties are considered to be…(2 things)
Intensive or extensive
Define Intensive properties
Those that are independent of the mass of a system, such as temperature, pressure, and density
Define extensive properties
Those whose values depend on the size - or extent - of the system.
Define specific properties
Extensive properties per unit mass
Define Equilibrium
A state of balance. In an equilibrium state there are no unbalanced potentials (or driving forces) within the system.
Define thermal equilibrium
If the temperature is the same throughout the entire system
Define Mechanical equilibrium
If there is no change in pressure at any point of the system with time.
Define Phase equilibrium
If a system involves two phases and when the mass of each phase reaches an equilibrium level and stays there.
Define Chemical equilibrium
If the chemical composition of a system does not change with time, that is, no chemical reactions occur
Define State postlude
The state of a simple compressible system is completely specified by two Independent, intensive properties
Define Simple compressible system
If a system involves no electrical, magnetic, gravitational, motion, and surface tension effects
Define Process
Any change that a system undergoes from one equilibrium state to another
Define Path
The series of states through which a system passes during a process
How do you describe the process completely?
Specify the initial and final states, as well as the path it follows, and the interactions with the surroundings
What is a Quasistatic or quasi-equilibrium process
When a process proceeds in such a manner that the system remains infinitesimally close to an equilibrium state at all times.
Define Isothermal process
A process during which the temperature T remains constant
Define Isobaric process
A process during which the pressure P remains constant
Define Isochoric process
A process during which the specific volume v remains constant
Define a cycle
A process during which the initial and final states are identical
What is the Zeroth law of Thermodynamics?
If two bodies are in thermal equilibrium with a third body, they are also in thermal equilibrium with each other
Or…
The zeroth law can be restated as two bodies are in thermal equilibrium if both have the same temperature reading even if they are not in contact.
Temperature Scale
Define Ice point : A mixture of ice and water that is in equilibrium with air saturated with vapor at 1 atm pressure (0°C)
Define Steam point: A mixture of liquid water and water vapor (with no air) in equilibrium at 1 atm pressure (100°C)
What is a Thermodynamic temperature scale?
A temperature scale that is independent of the properties of any substance
Define Absolute pressure
The actual pressure at a given position. It is measured relative to absolute vacuum (i.e., absolute zero pressure)
Define Gage pressure
The difference between the absolute pressure and the local atmospheric pressure. Most pressure-measuring devices are calibrated to read zero in the atmosphere, and so they indicate gage pressure
Define Vacuum pressures
Pressures below atmospheric pressure
Define Macrosopic forms of energy
Those a system possesses as a whole with respect to some outside reference frame, such as kinetic and potential energies
Define Microscopic forms of energy
Those related to the molecular structure of a system and the degree of the molecular activity
Define Internal engery, U
The sum of all the microscopic forms of energy
Define Kinetic energy, KE
The energy that a system possesses as a result of its motion relative to some reference frame
Define Potential energy, PE
The energy that a system possesses as a result of its elevation in a gravitational field
Define Sensible energy
The portion of the internal energy of a system associated with the kinetic energies of the molecules
Define Latent energy
The internal energy associated with the phase of a system
Define chemical energy
The internal energy associated with the atomic bonds in a molecule
Define Nuclear energy
The tremendous amount of energy associated with the strong bonds within the nucleus of the atom itself
Define Heat
The form of energy interaction between two systems or a system and its surroundings due to temperature difference
Is this true?
Energy can cross the boundaries of a closed system in the form of heat and work
Yes
Define Work
The energy transfer associated with a force acting through a distance
Heat transfer to a system and work done by a system are…
- Positive?
- Negative?
- Positive
Heat transfer from a system and work done on a system are
- Positive?
- Negative?
- Negative
Heat and work are associated with a ____, not a ____
Heat and work are associated with a process**, not a **state
Heat or work has no meaning at a ____?
State
Heat and work are ____ ____ (define this)
Heat and work are path functions (their magnitudes depend on the path followed during a process as well as the end states)
What are the two requirements for a work interaction between a styem and it’s surroundings to exist?
- there must be a force acting on the boundary
- the boundary must move
Shaft work equation
Spring work equation
Work done on elastic solid bars equation
Work done to raise or to accelerate a body
(Main one)
Define Electrial work
The generalized force is the voltage (the electrical potential) and the generalized displacement is the electrical charge
(Don’t worry too much about this)
What is the equation for Electrical work
(Don’t worry too much about this)
Define Magnetic work
The generalized force is the magnetic field strength and the generalized displacement is the total magnetic dipole moment
(Don’t worry too much about this)
Define Electrical polarization work
The generalized force is the electric field strength and the generalized displacement is the polarization of the medium
(Don’t worry too much about this)
What is the first law of thermodynamics?
Energy can be neither created nor destroyed during a process; it can only change forms.
The first law:…
For all adiabatic processes between two specified states of a closed system, the net work done is the same regardless of the nature of the closed system and the details of the process.
Energry balance?
Energy change of the system:
What does efficiency indercate?
Indicates how well an energy conversion or transfer process is accomplished.
Performance = ?
Performance = Desired output / Required input
Combustion efficiency? And what is the symbol?
What is the Mechanical efficiency of an Nmech and an Nmotor
What is a Pure substance and example?
A substance that has a fixed chemical composition throughout
Air is a mixture of several gases, but it is considered to be a pure substance.
Define compresses liquid
A substance that is not about to vaporize
Deinfe saturated liquid
A liquid that is about to vaporize
Define saturated vapour
A vapour that is about to condense
Define Saturated liquid–vapour mixture
The state at which the liquid and vapour phases coexist in equilibrium
Define Superheated vapour
A vapour that is not about to condense (i.e., not a saturated vapour)
Define Saturation temperature Tsat
The temperature at which a pure substance changes phase at a given pressure
Define Saturation pressure Psat
The pressure at which a pure substance changes phase at a given temperature
Define Latent heat
The amount of energy absorbed or released during a phase-change process
Define Latent heat of fusion
The amount of energy absorbed during melting. It is equivalent to the amount of energy released during freezing
Define Latent heat of vaporization
The amount of energy absorbed during vaporization and it is equivalent to the energy released during condensation
Define the critical point in a property diagram
The point at which the saturated liquid and saturated vapour states are identical
What does a property diagram of a T-v pure substance look like?
What is Quality, x?
The ratio of the mass of vapor to the total mass of the mixture
Quality is between _ and _, where 0 is ____ ____, 1 is ____ ____
Quality is between 0 and 1, where 0 is sat. liquid, 1 is sat. vapour
What is the equation for Enthalpy?
Define the Equation of state
Any equation that relates the pressure, temperature, and specific volume of a substance
Pv = ZRT what is Z?
The farther away Z is from ____, the more the gas deviates from ____-____ ____
The farther away Z is from unity, the more the gas deviates from ideal-gas behaviour
Gases behave as an ideal gas at…?
…low densitites (i.e. low pressure, high temperature)
Reduced pressure
PR = ?
Reduced Temperature
TR = ?
What is the equation for the Pseudo-reduced specific volume
Define Moving boundary work
The expansion and compression work in a pistoncylinder device
Wb positive for…?
Wb is negative for…?
…expansion
…compression
Wb = ?
Wb = ∫ P dv
What is the Quasi-equilibrium process?
A process during which the system remains nearly in equilibrium at all times
What is the net work done during a cycle?
The net work done during a cycle is the difference between the work done by the system and the work done on the system
Area = A = ∫ ? = ∫ ?
Area = A = ∫ dA = ∫ P dV
The area under the process curve on a P-V diagram represents the…?
…boundary work
If n = 1 then it’s a…?
Isothermal process
Heat input and work output are…?
…positive
Heat output and work input are…?
…negative
∆U = ?
∆U = Q - W
What is the E equation for all systems?
E = KE + PE + U
Define Specific heat at constant volume, cv
The energy required to raise the temperature of the unit mass of a substance by one degree as the volume is maintained constant
Define Specific heat at constant pressure, cp
The energy required to raise the temperature of the unit mass of a substance by one degree as the pressure is maintained constant
cv and cp are ______.
cv is related to the changes in ___\_____\__ and cp
to the changes in ______
cv and cp are properties.
cv is related to the changes in internal energy and cp
to the changes in enthalpy
A common unit for specific heats is…?
[kJ/(kg·°C)] or [kJ/(kg·K)].
For ideal gases, u, h, cv, and cp vary with ____ only
Temperature only
At low pressures, all real gases approach…?
…ideal-gas behaviour
What are the three ways of calculating ∆u and ∆h?
- By using tabulated u and h data
- By using cv or cp relations (from tables) as a functoin of temperature and performing the intergations
- By using average specific heats
Specific heat ratio for monatomic gases such as helium or argon is….
And for diatomic gases like air is…
Monatomic gases = 1.667
Diatomic gases = 1.4 at room temperature
Define the conversation of mass
Mass cannot be created or destroyed during a process. Mass is conserved even during chemical reactions
Define Closed systems
The mass of the system remains constant during a process
Define control volumes
Mass can cross the boundaries, and so we must keep track of the amount of mass entering and leaving the control volume
Mass m and energy E can be converted to each other according to…?
E = mc2
𝑚̇<em>in</em> = ?
𝑚̇<em>in </em>= 𝑚̇out
What is Flow work or Flow energy?
The work (or energy) required to push the mass into or out of the control volume
Wflow = ?
Wflow = Pv
Equation for a non-flowing fluid
Equation for a flowing fluid
When the kinetic and potential energies of a fluid stream are negligible…(equation)
Emass = mh
Energy balance equation
What is a nozzle?
A nozzle is a device that increases the velocity of a fluid at the expense of pressure
What is a diffuser?
A diffuser is a device that increases the pressure of a fluid by slowing it down.
The ____-____ ____ of a nozzle ____ in the flow direction for subsonic flows and ____ for supersonic flows. The reverse is true for ____
The cross-sectional area of a nozzle decreases in the flow direction for subsonic flows and increases for supersonic flows. The reverse is true for diffusers
???
What is a Turbine?
Turbine drives the electric generator in steam, gas, or hydroelectric power plants. As the fluid passes through the turbine, work is done against the blades, which are attached to the shaft. As a result, the shaft rotates, and the turbine produces work.
What is a compressor?
Compressors, as well as pumps and fans, are devices used to increase the pressure of a fluid. Work is supplied to these devices from an external source through a rotating shaft.
What is a pump?
Pumps work very much like compressors except that they handle liquids instead of gases.
So…?
What is a Throttling valve?
Throttling valves are any kind of flow-restricting devices that cause a significant pressure drop in the fluid
The pressure drop in the fluid is often accompanied by a large drop in ____, and for that reason throttling devices are commonly used in ____ __ __-____ ____
…temperature, and for that reason throttling devices are commonly used in refrigeration and air-conditioning applications
Internal energy + flow energy = ?
Internal energy + flow energy = constant
During a throttling process, the enthalpy of a fluid remains ____. But internal and flow energies may be ____ to each other.
During a throttling process, the enthalpy of a fluid remains constant. But internal and flow energies may be converted to each other.
The section where the mixing process takes place is commonly referred to as a…?
…mixing chamber
What are heat exchangers?
Heat exchangers are devices where two moving fluid streams exchange heat without mixing
What is the uniform-flow process?
Uniform-flow process:
The fluid flow at any inlet or exit is uniform and steady, and thus the fluid properties do not change with time or position over the cross section of an inlet or exit.
If they do, they are averaged and treated as constants for the entire process.
What is an Adiomatic process?
When there is no heat transfer
Boundary work can…?
…move up or down
In an Isothermal process, T = ?
T = 0
In an Isobaric process, P = ?
P = constant
In an Isobaric process, ____ and ____ goes to ____
In an Isobaric process, heat** and **work goes to zero
∆u = q - w represents an ____ process
∆u = q - w represents an audiobatic process
In a turbine, if V1 = __ then there’s no need for ____ ____
In a turbine, if V1 = V2 then there’s no need for kinetic** **energy
In a turbine, if Z = _ then there’s no need for ____ ____
In a turbine, if Z = 0 then there’s no need for potential energy
m·h1 = Wout + m·h2 represents a…?
…turbine
m·h2 = Win + m·h1 represents a…?
…compressor
