Thermodynamics
The science of energy
Energy
The ability to cause changes
Conservation of energy principle
Energy can change from one form to another but the total amount of energy remains constant; Energy cannot be created or destroyed
The first law of thermodynamcis
An expression of the conservation of energy principle; asserts that energy is a thermodynamic property
The second law of thermodynamics
Energy has quality as well as quantity, and actual processes occur in the direction of decreasing quality of energy
Classical thermodynamics
A macroscopic approach to the study of thermodynamics that does not require a knowledge of the behavior of individual particles
Statistical thermodynamics
A microscopic approach, based on the average behavior of large groups of individual particles.
Heat movement
Heat flows in the direction of decreasing temperature
Application areas of thermodynamics
All activities in nature involve some interaction between energy and matter
Examples of areas that use thermodynamics
Human body, cars, wind turbines, food processing, piping network
Dimensions
Any physical quantity
Units
The magnitudes assigned to the dimensions
Primary/Fundamental dimensions
basic dimensions such as mass m, length L, time t, and temperature T
Secondary/derived dimenstions
basic dimensions based on primary dimensions such as velocity V, energy E, volume V
Metric SI system
A simple and logical system based on a decimal relationship between the various units.
English system
It has no apparent systematic numerical base, and various units in this system are related to each other rather arbitrarily.
Dimensional Homogeneity
All equations must be dimensionally homogeneous
Unity Conversion Ratios
All nonprimary units (secondary units) can be formed by combinations of primary units
System
A quantity of matter or a region in space chosen for study
Surroundings
The mass or region outside the system
Boundary
The real or imaginary surface that separates the system from its surroundings
The boundary of a system can be
fixed or movable
Systems may be considered
closed/open
Closed system (control mass)
A fixed amount of mass, and no mass can cross its boundary
Open system (control volume)
A properly selected region in space. Both mass and energy can cross the boundary
Control surface
The boundaries of a control volume. It can be real or imaginary
Property
Any characteristic of a system
Intensive properties
Those that are independent of the mass of a system, such as temperature, pressure, and density
Extensive properties
Those whose values depend on the size - or extent - of the system
Specific properties
Extensive properties per unit mass
Density
is mass per unit volume
Specific volume
* volume per unit mass
* inverse of density
Specific gravity
The ratio of the density of a substance to the density of some standard substance at a specific temperature (usually water at 4C)
Specific Weight
The weight of a unit volume of a substance
Equilibrium
A state of balance
Thermal Equilibrium
If the temperature is the same throughout the entire system
Mechanical Equilibrium
If there is no change in pressure at any point of the system with time
Phase equilibrium
If a system involves two phases and when the mass of each phase reaches an equilibrium level and stays there
Chemical equilibrium
If the chemical composition of a system does not change with time, that is, no chemical reaction occurs
The State Postulate
The state of a simple compressible system is completely specified by two independent intensive properties
Simple compressible system
If a system involves no electrical, magnetic, gravitational, motion, and surface tension effects
Process
Any change that a system undergoes from one equilibrium state to another
Path
The series of states through which a system passes during a process
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
Isothermal process
A process during which the temperature T remains constant
Isobaric process
A process during which the pressure P remains constant
Isochoric (or isometric) process
A process during which the specific volume v remains constant
Cycle
A process during which the initial and final states are identical
The Steady-Flow Process
A process during which a fluid flows through a control volume steadily
Pressure
A normal force exerted by a fluid per unit area
Absolute Pressure
The actual pressure at a given position. It is measured relative to absolute vacuum
Gage pressure
The difference between the absolute pressure and the local atmospheric pressure.
Vacuum pressure
Pressures below atmospheric pressure
Hydrostatic conditions
The pressure is the same at all points on a horizontal plane in a given fluid regardless of geometry, provided that the points are interconnected by the same fluid
Barometer
A device used to measure atmospheric pressure
Barometric pressure
another name for atmospheric pressure
Standard atmosphere (atm)
a unit of pressure, the pressure produced by a column of mercury 760 mm in height at 0C under standard gravitational acceleration
Manometer
Commonly used to measure small and moderate pressure differences