Thermodynamics: Fundamentals, Pure Substances, and Power Cycles

Comprehensive practice flashcards detailing fundamental definitions, thermodynamic properties, systems, laws, ideal gas processes, pure substance phase behaviors, and power plant cycle components.

Thermodynamics

Derived from the Greek words "therme" (heat) and "dynamis" (power); a branch of physical sciences that treats various phenomena of energy and related properties of matter, especially laws governing heat transformation into other energy forms and vice versa.

Intensive Property

Properties of a system that are independent of mass, such as temperature, pressure, and density.

Extensive Property

Properties whose values depend on the size or extent of the system, such as total mass and total volume.

Gage Pressure

The pressure reading obtained from a pressure gage instrument, which can be higher or lower than local atmospheric pressure.

Vacuum Pressure

A negative pressure reading indicating a pressure that is less than atmospheric pressure.

Absolute Pressure

The true pressure measured above a perfect vacuum, calculated as $P_{abs} = P_{g} + P_{atm}$.

Barometer

An instrument specifically used to measure atmospheric pressure.

Absolute Zero

The theoretical temperature at which all molecular motion ceases, equivalent to $-273\,^\circ\text{C}$.

Specific Volume

The ratio of the volume occupied by a substance to its mass ($v = \frac{V}{m}$), expressed in units such as $m^3/kg$.

Specific Weight

Also called weight density; the weight of a substance per unit volume ($\gamma = \rho g$).

Specific Gravity

Also known as relative density; the ratio of the density of a substance to the density of water at standard temperature.

Internal Energy

The thermal energy stored within a substance due to microscopic molecular motion and activity governed by its temperature.

Flow Work

The work required to push fluid into or out of a thermodynamic system, defined as the product of pressure and volume ($W_f = P(V_2 - V_1)$ or $W_f = P(v_2 - v_1)$).

Enthalpy

The total heat energy of a substance during a constant pressure process, defined as the sum of internal energy and flow work ($h = u + Pv$).

Entropy

A thermodynamic property that quantifies the amount of energy in a substance that is unavailable to perform useful work ($S = \frac{q}{T}$).

Open System

A thermodynamic system across whose boundaries both mass and energy can flow; interchangeably referred to as a control volume.

Closed System

A thermodynamic system in which energy may cross the boundary as heat or work, but no mass enters or leaves.

Isolated System

A system completely shielded from its surroundings across whose boundaries neither mass nor energy (heat or work) can cross.

Control Volume

A designated fixed region in space selected for thermodynamic analysis of mass and energy balance.

Control Surface

The physical or imaginary boundary enclosing a control volume.

Steady State

A condition in a control volume where there is no accumulation of mass or energy over time.

Mechanical Equilibrium

A state of balance within a system wherein there is no change in pressure at any point with time.

Thermal Equilibrium

A state of balance achieved when the temperature is uniform throughout the entire system.

Chemical Equilibrium

A state of balance achieved when the chemical composition of a system does not change over time, indicating no chemical reactions occur.

Simple Compressible System

A thermodynamic system that is completely free from electrical, magnetic, gravitational, motion, and surface tension effects.

Quasi-Equilibrium Process

A process that proceeds so slowly that the system remains infinitesimally close to an equilibrium state at all times.

Thermodynamic Cycle

A sequence of processes through which a system passes that ultimately returns the system to its initial state.

Pure Substance

A substance with a fixed, homogeneous chemical composition throughout, regardless of phase coexistence.

Compressed Liquid

A liquid state in which the prevailing pressure is greater than the saturation pressure at the existing temperature.

Subcooled Liquid

A liquid state in which the actual temperature is lower than the saturation temperature at the prevailing pressure.

Saturated Liquid

A pure liquid substance that is at the threshold of vaporizing without containing any vapor.

Saturated Vapor

A pure gaseous substance that is at the threshold of condensing without containing any liquid droplets.

Saturated Liquid–Vapor Mixture

A two-phase state in which saturated liquid and saturated vapor coexist in thermodynamic equilibrium.

Superheated Vapor

A vapor whose existing temperature is higher than the saturation temperature at the given pressure, meaning it is not on the verge of condensing.

Degrees of Superheat

The temperature difference by which a superheated vapor exceeds its saturation temperature at a given pressure ($^\circ\text{SH} = T_{\text{given}} - T_{\text{sat}}$).

Degrees Subcooled

The temperature difference by which the saturation temperature exceeds the actual temperature of a subcooled liquid ($^\circ\text{SC} = T_{\text{sat}} - T_{\text{given}}$).

Quality

The mass fraction of saturated vapor relative to the total mass of a saturated liquid-vapor mixture ($x = \frac{m_v}{m_T}$).

Percent Moisture

The mass fraction of saturated liquid relative to the total mass of a wet mixture ($y = \frac{m_L}{m_T}$), related to quality by $x + y = 1$.

Critical Point

The unique thermodynamic point at which the saturated liquid and saturated vapor states become identical.

Sensible Heat

Heat added to or removed from a substance that causes an observable change in temperature without changing its phase.

Latent Heat

The amount of thermal energy absorbed or released by a substance during an isothermal phase-change process.

First Law of Thermodynamics

The principle of conservation of energy asserting that energy cannot be created or destroyed, only converted from one form to another.

Second Law of Thermodynamics

States that it is impossible to construct a cyclic heat engine that receives heat from a high-temperature reservoir and performs an equivalent amount of work.

Third Law of Thermodynamics

States that the absolute entropy of a pure crystalline substance in complete internal equilibrium is identically zero at absolute zero.

Zeroth Law of Thermodynamics

States that when two bodies are separately in thermal equilibrium with a third body, they are also in thermal equilibrium with each other.

Ideal Gas

A hypothetical substance whose physical behavior is completely defined by the equation of state $PV = mRT$ or $PV = nRT$.

Isometric Process

An internally reversible constant-volume thermodynamic process ($V_1 = V_2$) during which non-flow boundary work is zero ($W_n = 0$).

Isobaric Process

An internally reversible constant-pressure thermodynamic process ($P_1 = P_2$) wherein heat transfer equals the change in enthalpy ($q = \Delta h$).

Isothermal Process

An internally reversible constant-temperature process ($T_1 = T_2$), governed by Boyle's law ($P_1V_1 = P_2V_2$) for an ideal gas.

Isenthalpic Process

A constant-enthalpy process ($h_1 = h_2$), such as the expansion occurring across a throttling valve.

Isentropic Process

A reversible adiabatic process characterized by zero heat transfer ($q = 0$) and constant entropy ($s_1 = s_2$).

Polytropic Process

A general reversible thermodynamic process described by the pressure-volume relation $PV^n = C$, where $n$ is the polytropic exponent.

Carnot Heat Engine

A hypothetical engine operating on the reversible Carnot cycle consisting of two isothermal and two isentropic processes, representing the maximum theoretical efficiency between two reservoirs.

Boiler

A closed pressure vessel in which water is heated to high temperatures to generate high-pressure steam for power or heating applications.

Steam Turbine

A rotary mechanical device that extracts thermal energy from expanding high-pressure steam to produce rotating shaft work.

Surface Condenser

A shell-and-tube heat exchanger that converts exhaust steam from a turbine into liquid water at sub-atmospheric pressure via circulating cooling water.

Cooling Tower

A specialized heat-rejection device that cools a circulating warm water stream by bringing it into direct contact with ambient air via partial evaporation.

Crossflow Cooling Tower

A cooling tower design where incoming air travels horizontally across the downward stream of falling water.

Counterflow Cooling Tower

A cooling tower configuration where incoming air travels vertically upward directly against the downward-flowing water.

Hyperbolic Cooling Tower

A large chimney-style natural draft cooling tower that utilizes natural air buoyancy without requiring mechanical fans.

Induced Draft Cooling Tower

A mechanical draft cooling tower that utilizes motorized fans to draw air upward through the fill surface.

Passive Draft Cooling Tower

A natural draft tower that couples the upward thermal draft of heated air with a tall chimney structure to move air without mechanical assistance.

Feedwater Pump

A high-pressure pump used in a steam cycle to pressurize and deliver liquid condensate from the condenser into the steam boiler.

Back Work Ratio

The ratio of pump work required to the work produced by the turbine in a power cycle ($\text{BWR} = \frac{W_P}{W_T}$).

Open Feedwater Heater

A direct-contact heat exchanger in a regenerative cycle where extracted turbine steam mixes directly with feedwater at an intermediate pressure.

Closed Feedwater Heater

A shell-and-tube heat exchanger in which extracted turbine steam condenses on the shell side to heat high-pressure feedwater flowing inside tubes without direct contact.

Deaeration

The process of venting non-condensable dissolved gases (such as oxygen) from boiler feedwater to prevent corrosion in the power plant piping and boiler.

Steam Trap

An automatic valve that allows condensed liquid water to pass through to a region of lower pressure while preventing the loss of vaporous steam.