Thermodynamics & Refrigeration Cycles Flashcards
What is thermodynamics the study of?
The study of energy, its transformations, and its relation to states of matter.
What are the methods used to calculate thermodynamic properties?
The First and Second law of thermodynamics.
What are two common refrigeration cycle methods of thermal energy transfer?
Compression and Absorption Refrigeration Cycles.
What is a thermodynamic system?
A region in space or a quantity of
matter bounded by a closed surface.
What is the surroundings?
Everything external to the system.
What separates the system from the surroundings?
The system boundary.
Does the system boundary have to be real or imaginary?
The system boundary can be both real or imaginary.
Can the system boundary be movable or fixed?
The system boundary can be either movable or fixed.
What is entropy?
It measures the molecular disorder of the system.
What forms can energy be categorized into when producing an effect?
Stored or transient forms.
What are the types of stored energy?
Thermal (Internal), Potential, Kinetic, Chemical, and Nuclear Energy.
What is internal energy?
Energy caused by the motion of molecules
and/or intermolecular forces.
What is potential energy?
Energy caused by attractive forces existing
between molecules, or the elevation of the system.
What is kinetic energy?
Energy caused by the velocity of molecules.
What is chemical energy?
Energy caused by the arrangement of atoms composing the molecules.
What is nuclear energy?
Derives from the cohesive forces holding
protons and neutrons together as the atom’s nucleus.
What are the types of transient energy?
Heat, Work, Mechanical or Shaft Work, and Flow Work.
What is heat?
The mechanism that transfers energy across the boundaries of systems with differing temperatures.
In what direction does heat always go?
Always toward the lower temperature.
When is heat considered positive?
When energy is added to the system.
What is work?
The mechanism that transfers energy across the boundaries of systems with differing pressures (or force of any kind).
In what direction does work always go?
Always toward the lower pressure.
When is work considered positive?
When energy is removed from the system or the system does work on the surroundings.
What is the shaft work?
The energy delivered or absorbed by a mechanism, such as a turbine, air compressor, or internal combustion engine.
What is flow work?
The work done by the fluid just outside the system on the adjacent fluid entering the system to force or push it into the system.
When does flow work occur?
When fluid is entering or exiting the system.
What is a property of the system?
An observable characteristic of the system.
What is the state of the system?
Specifying the minimum set of independent properties.
What are the most common thermodynamic properties?
Temperature, pressure, specific volume, density.
What are other used thermodynamic properties?
Entropy, enthalpy, and stored forms of energy.
What is enthalpy equal to?
The sum of internal energy and flow work.
What’s a process?
A change in state that can be defined as any change in the properties of a system.
How is a process described?
A process is described by specifying the initial and final equilibrium states, the path (if identifiable), and the interactions that take place across system boundaries during the process.
What is a cycle?
A process or a series of processes wherein the initial and final states of the system are identical.
What do the values at the conclusion and at the beginning of a cycle have in common?
At the conclusion of a cycle, all the properties have the same value they had at the beginning.
What is a pure substance?
A homogeneous and invariable chemical composition.
If the phase changes in a pure substance does the composition change?
It can exist in more than one phase, but the chemical composition is the same in all phases.
What is a subcooled liquid?
If the temperature of the liquid is lower than the saturation temperature for the given pressure.
What is a compresses liquid?
The pressure is greater than the saturation pressure for the given temperature.
What is a saturated liquid?
If a substance is liquid at the saturation temperature and pressure.