56 terms

# Thermo Test 1 (Chapters 1-3)

#### Terms in this set (...)

Thermodynamics
The science of energy
Energy
The ability to cause change
1st Law of Thermodynamics
Conservation of energy
2nd Law of Thermodynamics
Energy has quality as well as quantity, and helps us determine which direction a process will occur (ex: coffee loses heat = less quality)
Primary Dimensions
Mass, length, time, and temperature
Secondary Dimensions
Velocity, energy, and volume
System
A quantity of matter (closed system) or region in space (open space) chosen for study
Boundary
The real or imaginary surface that separates the system and its surroundings, the mass or space outside the system. The boundary can be fixed or movable/deformable
Closed System
No mass is exchanged across the boundary separating the system and its surroundings
Open System
A region in space
Control Volumes
Used when mass flow is involved, such as in compressors, turbines, or nozzles. Both mass and energy can cross the boundary
Intensive Properties
Do not depend on the amount of mass in the system, such as temperature, pressure, and density
Extensive Properties
Depend on the size of the system, or how much mass is contained in the system, and include total mass, total volume, and total momentum
Mean Free Path
The average distance a molecule travels before bumping another molecule
Density
Mass per unit volume (kg/m^3)
Equilibrium
A balanced state with no unbalanced potentials, or drivers, causing macroscopic change in the system
Thermal Equilibrium
Temperature is the same throughout the entire system
Mechanical Equilibrium
When there is no change in pressure at any point in the system with time
Phase Equilibrium
When multi-phase system phase masses each equilibrium
State Postulate
The state of a simple compressible system is completely specified by two independent intensive properties
Simple Compressible System
Does not involve electrical, magnetic, gravitational, motion, and surface tension effects
Process
Any change that a system undergoes from on equilibrium state to another
Path
The series of states through which a system passes during a process
Quasi-Equilibrium Process
When a process proceeds in such a manner that the system remains infinitesimally close to an equilibrium state
Isothermal Process
Temperature remains constant
Isobaric Process
Pressure remains constant
Isochoric Process
Specific Volume remains constant
Cycle
Process where initial and final states are identical
No change with time
Where the fluid flows through a control volume (open system) steadily
Pressure
A normal force exerted by a fluid per unit area
Absolute Pressure
Actual pressure at a given position, it is measured relative vacuum (absolute zero pressure, void of any molecules)
Gage Pressure
Difference between the absolute pressure and the local atmospheric pressure; most pressure-measuring devices are calibrated to read zero in the atmosphere, so they indicate gage pressure
Vacuum Pressure
Pressures below atmospheric pressure
Pascal's Law
The pressure applied to a confined fluid increases the pressure throughout by the same amount
Macroscopic
Those forms a system possesses as a whole with respect to an outside reference frame, such as kinetic or potential energies
Microscopic
Those forms related to the molecular structure of a system of a system and to the degree of molecular activity, independent of outside reference frames
Internal Energy
Sum of all microscopic forms of energy
Kinetic Energy
Energy that a system possesses as a result of its motion relative to some outside reference frame
Potential Energy
Energy that a system possesses as a result of its elevation in a gravitational field
Sensible Energy
The portion of the internal energy of a system associated with the kinetic energy of the molcules
Latent Energy
The internal energy associated with the phase of a system
Heat Transfer and Work
The only 2 forms of energy interactions associated with a closed system
Mechanical Energy
The form of energy that can be converted to mechanical work completely and directly by an ideal mechanical device such as an ideal turbine
Heat
The form of energy that is transferred between two systems (or a system and its surroundings) driven by a temperature difference
No heat transfer
Conduction
Transfer of energy form energetic particles of a substance to the adjacent less energetic particles as a result of interaction (contact)
Convection
Transfer of energy between a solid surface and the adjacent fluid in motion, involving the combined effects of conduction and fluid motion (advection)
Transfer of energy due to the emission of electromagnetic waves (photons)
Work
The form of energy transfer associated with a force acting through a distance, such as rising piston, a rotating shaft, and electric wire crossing system boundaries
Power
The work done per unit time (kW)
Efficiency
Indicates how well an energy conversion or transfer process is accomplished

Performance = Desired Output/Required Input
Pure Substance
Has a fixed chemical composition throughout
Latent Heat
The amount of energy absorbed or released during a phase-change process
Latent Heat of Fusion
The amount of energy absorbed by melting, which is equivalent to the amount of energy released during freezing
Quality (x)
The ratio of mass of vapor to the total mass of mixture. Quality is between 0 and 1

x = m(vapor)/m(total)