Thermo Final Exam Definitions Flashcards
The branch of physical science that deals with the relations between heat and other forms of energy, and of the relationships between all forms of energy.
Thermodynamics
Whatever we want to study.
System
Everything external to the system.
Surroundings
Distinguishes a system from its surroundings.
Boundary
A system that always contains the same matter. No mass transfer across its boundary can occur.
Closed System
Special type of closed system that does not interact in any way with its surroundings.
Isolated System
A given region of space through which mass flows. Mass may cross the boundary.
Control Volume
Characterizes by statistical means the average behavior of the particles making up a system.
Microscopic Approach
Describes the system behavior in terms of the gross effects of the particles making up the system, specifically effects that can be measured with instruments.
Macroscopic Approach
The condition of a system as described by its properties.
State
A transformation from one state to the other.
Process
Property that depends on the size or extent of a system.
Extensive Property
Property that’s independent of the size or extent of a system.
Intensive Property
Pressure with respect to the zero pressure of a complete vacuum.
Absolute Pressure
When the system pressure is greater than the atmospheric pressure.
Gage Pressure
When the atmospheric pressure is greater than the system pressure.
Vacuum Pressure
Physical property that determines whether two objects are in thermal equilibrium.
Temperature
If object A is in thermal equilibrium with object B, and object B is in thermal equilibrium with object C, then object C is also in thermal equilibrium with object A.
0th Law of Thermodynamics
The rate of energy transfer by work.
Power
A process that undergoes a sequence of equilibrium states during the process.
Quasi-Equilibrium Process
A process involving no heat transfer.
Adiabatic Process
The transfer of energy from more energetic particles of a substance to less energetic adjacent particles due to interactions between them (Fourier’s Law).
Conduction
Energy transfer between a solid surface and an adjacent gas or liquid by the combined effects of conduction and bulk flow within the gas or liquid (Newton’s Law of Cooling).
Convection
Energy transported by electromagnetic waves (Stefan-Boltzman Law).
Thermal Radiation
Energy can be neither created nor destroyed during a process, it can only change forms.
1st Law of Thermodynamics
Sequence of processes that begins and ends at the same state.
Thermodynamic Cycle
The change in the amount of energy contained within a system is equal to the net amount of energy transferred in across the system boundary by heat transfer minus the net amount of energy transferred out across the system boundary by work.
Closed System Energy Balance
Projection of the P - v - T surface onto the pressure - temperature plane.
Phase Diagram
Designates the temperature at which a phase change takes place at a given pressure.
Saturation Temperature
Designates the pressure at which a phase change takes place at a given temperature.
Saturation Pressure
Chart that shows that at states where the pressure p is small relative to the critical pressure pc (where pR is small), the compressibility factor Z is approximately 1.
Generalized Compressibility Chart
Time rate of change of mass contained within the control volume at time t is equal to the time rate flow of mass in across the inlet i at time t minus the time rate flow of mass out across exit e at time t.
Mass Rate Balance
Time rate of change of the energy contained within the control volume at time t, is equal to the net rate at which energy is being transferred in by heat transfer at time t, minus the net rate at which energy is being transferred out by work at time t, plus the net rate of energy transfer into the control volume accompanying mass flow.
Energy Rate Balance
A flow passage of varying cross-sectional area in which the velocity of a gas or liquid increases in the direction of flow.
Nozzle
A flow passage of varying cross-sectional area in which the velocity of a gas or liquid decreases in the direction of flow.
Diffuser
A device in which power is developed as a result of a gas or liquid passing through a set of blades attached to a shaft free to rotate.
Turbine
Device in which work is done on a gas flowing through to change the state (increase pressure / elevation).
Compressor
Device in which work is done on a liquid flowing through to change the state (increase pressure / elevation).
Pump
A mixing chamber in which hot and cold streams are mixed directly.
Direct Contact Heat Exchanger
A gas or liquid stream is separated from another gas or liquid by a wall through which energy is conducted. Heat transfer occurs from hot stream to the cold stream as the streams flow in opposite directions.
Tube-Within-a-Tube Counterflow Heat Exchanger
A device that achieves a significant reduction in pressure by introducing a restriction into a line through which a gas or liquid flows.
Throttling Device
It is impossible for any system to operate in such a way that the sole result would be an energy transfer by heat from a cooler to a hotter body.
Clausius Statement
A system that always remains at constant temperature even though energy is added or removed by heat transfer.
Thermal Reservoir
It is impossible for any system to operate in a thermodynamic cycle and deliver a net amount of energy by work to its surroundings while receiving energy by heat transfer from a single thermal reservoir.
Kelvin-Planck Statement
It is impossible for a system to operate in a way that entropy is destroyed.
Entropy Statement
A process where the system and all parts of its surrounding cannot be exactly restored to their initial states after the process has occurred.
Irreversible Process
A process where no irreversibilities are present within the system and its surroundings.
Reversible Process
A process where no irreversibilities are present within the system, but irreversibilities are present within the surroundings.
Internally Reversible Process
The thermal efficiency of an irreversible power cycle is always less than the thermal efficiency of a reversible power cycle when each operates between the same two thermal reservoirs. All reversible power cycles operating between the same two reservoirs have the same thermal efficiency.
Carnot Corollaries
Constant-entropy process.
Isentropic Process
The change in the amount of entropy contained within the system during some time interval is equal to the net amount of entropy transferred across the system boundary accompanying heat transfer plus the amount of entropy produced within the system.
Entropy Balance
The ratio of actual turbine work to the maximum theoretical work, each per unit of mass flowing.
Isentropic Turbine Efficiency
The ratio of minimum theoretical work input to the actual work input, each per unit of mass flowing.
Isentropic Compressor Efficiency
Provides the heat transfer of energy needed to vaporize water circulating in Subsystem B.
Subsystem A
Water vapor expands through the turbine, developing power. Water then condenses and returns to the boiler.
Subsystem B
Power developed by the turbine drives an electric generator.
Subsystem C
Removes energy by heat transfer arising from steam condensing in Subsystem B.
Subsystem D
Rankine cycle modification that increases vapor temperature to a superheated state at the turbine inlet.
Superheat
Rankine cycle modification where after passing through the turbine, the steam enters a steam generator where it is reheated before passing through another turbine.
Reheat
Rankine cycle modification where steam generation occurs at a pressure greater than the critical pressure of water.
Supercritical
A mixture of fuel and air is ignited by a spark plug.
Spark Ignition Combustion Engine
Air is compressed to a high pressure and temperature. Combustion occurs spontaneously when fuel is injected.
Compression Ignition Combustion Engine
Volume swept by the piston when it moves from top dead center to bottom dead center.
Displacement Volume
Volume at bottom dead center divided by volume at top dead center.
Compression Ratio (r)
Four strokes of the piston for every two revolutions of the crankshaft.
Four-Stroke Cycle
With the intake valve open, piston stroke draws a fresh charge into the cylinder.
Intake Stroke
The gas mixture expands and work is done one the piston as it returns to bottom dead center.
Power Stroke
The burned gasses are purged from the cylinder through the open exhaust valve.
Exhaust Stroke
Two strokes of the piston for every one revolution of the crankshaft.
Two-Stroke Cycle
With both valves closed, piston compresses charge, raising the pressure and temperature, and requiring work input from the piston to the cylinder.
Compression Stroke
