Basic Thermodynamics – Key Vocabulary

Vocabulary flashcards summarizing essential terms and definitions from Basic Thermodynamics lecture notes.

Thermodynamics

Branch of science that studies energy, its conversion between forms and its effects on matter.

Continuum Concept

Assumption that matter is continuous and properties like temperature, pressure, and density vary smoothly without molecular discontinuities.

Entropy

Property that measures the disorder of a system and the portion of energy unavailable for work.

Internal Energy

Total microscopic kinetic and potential energy contained within a system.

First Law of Thermodynamics

Energy cannot be created or destroyed; for a system, Q = ΔU + W.

Boyle’s Law

For a fixed mass of gas at constant temperature, pressure is inversely proportional to volume (PV = constant).

Charles’s Law

For a fixed mass of gas at constant pressure, volume is directly proportional to absolute temperature (V/T = constant).

Gay-Lussac’s Law

For a fixed mass of gas at constant volume, pressure is directly proportional to absolute temperature (P/T = constant).

Combined Gas Law

Relationship combining Boyle’s, Charles’s, and Gay-Lussac’s laws: PV/T = constant for a fixed mass.

Zeroth Law of Thermodynamics

If two systems are each in thermal equilibrium with a third, they are in equilibrium with each other.

Dia-thermal Boundary

System boundary that permits heat transfer between system and surroundings.

Adiabatic Boundary

Boundary that does not allow any heat transfer between system and surroundings.

PMM-1 (Perpetual Motion Machine of First Kind)

Hypothetical device that produces work indefinitely without energy input; violates First Law.

Coefficient of Performance (COP)

Efficiency measure for refrigerators/heat pumps: desired output ÷ required work input.

PMM-2 (Perpetual Motion Machine of Second Kind)

Hypothetical device that converts heat completely into work with no other effect; violates Second Law.

Boiler

Component of a thermal power plant that converts water to high-pressure steam.

Steam Turbine

Machine that converts thermal energy of steam into mechanical shaft work.

Condenser

Device that condenses exhaust steam to water by rejecting heat to a cooling medium.

Feedwater Pump

Pump that raises condensate pressure before it re-enters the boiler.

Economizer

Heat exchanger that preheats boiler feedwater using flue-gas heat.

Superheater

Section of boiler that raises steam temperature above saturation.

Carnot Theorem

No engine operating between two reservoirs is more efficient than a reversible Carnot engine.

Specific Heat (c)

Heat required to raise temperature of unit mass of a substance by one degree Celsius or Kelvin.

Heat Engine

Cyclic device that converts heat from a high-temperature source into mechanical work while rejecting heat to a sink.

Air-Standard Efficiency

Idealized thermal efficiency of an internal-combustion cycle assuming air behaves as a perfect gas with reversible processes.

Power Plant

Industrial facility that converts primary energy sources into electrical power.

Heat Pump

Device that transfers heat from low to high temperature using mechanical work.

Otto Cycle

Ideal cycle for spark-ignition engines: isentropic compression, constant-volume heat addition, isentropic expansion, constant-volume heat rejection.

Diesel Cycle

Ideal cycle for compression-ignition engines: isentropic compression, constant-pressure heat addition, isentropic expansion, constant-volume heat rejection.

Thermal Efficiency (Otto Cycle)

η = 1 − 1/r^(γ−1), where r is compression ratio and γ is specific-heat ratio.

Thermal Efficiency (Diesel Cycle)

η = 1 − (1/r^(γ−1))·[(rc^γ −1)/(γ(rc −1))], with cut-off ratio r_c.

System (Thermodynamic)

Selected quantity of matter or region in space chosen for study.

Open System

System that allows both mass and energy to cross its boundary.

Closed System

System that allows energy but not mass to cross its boundary.

Isolated System

System that allows neither mass nor energy exchange with surroundings.

Homogeneous System

System with uniform physical structure and chemical composition throughout.

Heterogeneous System

System composed of two or more phases with different compositions or structures.

Thermodynamic Equilibrium

State where a system is in thermal, mechanical, chemical, and phase equilibrium simultaneously.

Mechanical Equilibrium

Condition of uniform pressure within a system; no unbalanced forces.

Thermal Equilibrium

Uniform temperature throughout a system; no heat flow occurs.

Chemical Equilibrium

No net chemical reaction progress; composition remains constant over time.

Fixed Boundary

System boundary whose size and shape remain constant during interaction.

Movable Boundary

Boundary that changes size or shape (e.g., piston surface) during interaction.

Real Boundary

Physical surface that clearly separates system from surroundings.

Imaginary Boundary

Conceptual surface drawn to define a control volume (e.g., flow through a pipe).

Characteristic Gas Equation

Ideal-gas relation PV = nRT (or Pv = RT for unit mass).

Swept Volume

Volume displaced by a piston between top and bottom dead centers.

Compression Ratio (r)

Ratio of total cylinder volume to clearance volume in an engine cylinder.

Specific-Heat Relation

For an ideal gas, Cp − Cv = R, where R is the gas constant.

Steady-Flow Energy Equation (SFEE)

Energy balance for control volumes under steady conditions: Q̇ + ṁ(h1 + V1²/2 + gz1) = Ẇ + ṁ(h2 + V2²/2 + gz2).

Kelvin-Planck Statement

No cyclic device can convert heat from a single reservoir entirely into work.

Clausius Statement

Heat cannot spontaneously flow from colder to hotter body without external work.

Carnot Cycle

Reversible cycle with two isothermal and two adiabatic processes; establishes maximum possible efficiency.

Rankine Cycle

Ideal vapor-power cycle involving pump, boiler, turbine, and condenser; models steam power plants.

Exergy

Maximum useful work obtainable as a system reaches equilibrium with its environment.

Calorific Value

Heat released per unit quantity of fuel upon complete combustion.

Higher Heating Value (HHV)

Calorific value that includes heat of condensation of combustion water vapor.

Lower Heating Value (LHV)

Calorific value excluding heat recovered from condensing water vapor.

Isothermal Process

Thermodynamic process that occurs at constant temperature.

Isobaric Process

Process that occurs at constant pressure.

Adiabatic (Isentropic) Process

Process with no heat transfer; for ideal reversible case, entropy remains constant (PV^γ = constant).

P–V Diagram

Graph of pressure versus volume; illustrates work and processes in thermodynamic cycles.

T–S Diagram

Graph of temperature versus entropy; helpful for visualizing heat transfers and efficiencies.

Air Standard Cycle

Ideal engine cycle using air as working fluid with simplified, reversible processes.

Cut-off Ratio (r_c)

For Diesel cycle, ratio of cylinder volume after combustion to volume before combustion at constant pressure phase.

Heat Rejection

Quantity of heat expelled by a system to a low-temperature sink.

Heat Input

Heat absorbed from a high-temperature source by a heat engine or power plant.

Specific Heat at Constant Pressure (Cp)

Heat required to raise temperature of unit mass one degree at constant pressure.

Specific Heat at Constant Volume (Cv)

Heat required to raise temperature of unit mass one degree at constant volume.

Extensive Property

Property that depends on system mass, e.g., volume or internal energy.

Intensive Property

Property independent of system mass, e.g., temperature or pressure.