Thermodynamics: Introduction and Basic Concepts Study Notes

Thermodynamics

The science of energy and its transformations, particularly between heat, work, and the properties of matter.

First Law of Thermodynamics

The principle of conservation of energy stating that energy cannot be created or destroyed, only changed in form ($\Delta E = E_{\text{in}} - E_{\text{out}}$).

Second Law of Thermodynamics

The law asserting that energy possesses quality as well as quantity, and natural processes proceed only in the direction of decreasing quality of energy.

Zeroth Law of Thermodynamics

States that if two bodies are each in thermal equilibrium with a third body, they are in thermal equilibrium with each other; serves as the basis of temperature measurement.

Classical Thermodynamics

A macroscopic approach that evaluates the overall behavior of a system without requiring detailed knowledge of individual particles.

Statistical Thermodynamics

A microscopic approach based on evaluating the average statistical behavior of large groups of individual atoms or molecules.

Closed System (Control Mass)

A thermodynamic system with a fixed amount of mass where no mass can cross the boundary, though energy may cross as heat or work.

Open System (Control Volume)

A selected region in space where both mass and energy can flow across the boundary surface.

Isolated System

A system whose boundary prevents any exchange of mass or energy with its surroundings.

Intensive Property

A system characteristic that is independent of system size or mass, such as temperature ($T$), pressure ($P$), or density ($\rho$).

Extensive Property

A system characteristic that depends directly on the size or extent of the system, such as total mass ($m$), total volume ($V$), or total energy ($E$).

Specific Property

An extensive property expressed per unit mass, converting it into an intensive value (e.g., specific volume $v = \frac{V}{m}$).

Continuum

The idealization of matter as continuous and evenly distributed rather than empty space with tiny molecules, valid for ordinary engineering scales.

Specific Gravity ($SG$)

The dimensionless ratio of a substance's density to that of pure water at $4^\circ\text{C}$ ($\rho_{\text{H}_2\text{O}} = 1000\,\text{kg/m}^3$): $SG = \frac{\rho}{\rho_{\text{H}_2\text{O}}}$. Substances with $SG < 1$ float in water.

Thermodynamic Equilibrium

A state of balance where no driving forces exist, requiring simultaneous thermal, mechanical, phase, and chemical equilibrium.

State Postulate

The principle stating that the thermodynamic state of a simple compressible system is completely specified by two independent, intensive properties.

Quasi-equilibrium Process

An idealized process occurring slowly enough that the system remains infinitesimally close to thermodynamic equilibrium at all points, providing the maximum theoretical work output.

Isothermal Process

A thermodynamic process during which temperature remains constant ($T = \text{constant}$).

Isobaric Process

A thermodynamic process during which pressure remains constant ($P = \text{constant}$).

Isochoric (Isometric) Process

A thermodynamic process during which specific volume remains constant ($v = \text{constant}$).

Steady-Flow Process

A process in which a fluid flows steadily through a control volume such that conditions at any fixed position do not change with time.

Absolute Pressure ($P_{\text{abs}}$)

The actual pressure measured relative to absolute vacuum ($0\,\text{Pa}$).

Gage Pressure ($P_{\text{gage}}$)

The pressure relative to local atmospheric pressure: $P_{\text{gage}} = P_{\text{abs}} - P_{\text{atm}}$. Most measurement gages read zero at atmospheric pressure.

Vacuum Pressure ($P_{\text{vac}}$)

The pressure measured below atmospheric pressure: $P_{\text{vac}} = P_{\text{atm}} - P_{\text{abs}}$.

Hydrostatic Pressure with Depth

The linear increase of pressure with fluid depth due to fluid weight above: $P = P_{\text{atm}} + \rho g h$.

Pascal's Principle

The principle stating that an externally applied pressure is transmitted equally throughout an entire confined fluid: $\frac{F_1}{A_1} = \frac{F_2}{A_2}$.

Barometer

An instrument used to measure atmospheric pressure by balancing it against an inverted column of fluid: $P_{\text{atm}} = \rho g h$.

Manometer

A U-tube containing one or more dense fluids used to measure small to moderate pressure differences.