Basic Engineering Thermodynamics

A set of vocabulary flashcards covering key definitions, laws, properties, governing equations, and cycle concepts from basic engineering thermodynamics.

Engineering Thermodynamics

The branch of engineering studying energy, heat, and work, how they convert and transfer across systems, and the application of thermodynamic laws to power plants, engines, turbines, and refrigeration systems.

Thermodynamic System

The specific part of the universe selected for study or thermodynamic analysis (e.g., a gas inside a piston-cylinder device).

Surroundings

Everything located outside the boundary of a thermodynamic system.

Boundary

The real or imaginary surface that separates a thermodynamic system from its surroundings.

Intensive Property

A thermodynamic property that is independent of the size or mass of the system, such as temperature ($T$) and pressure ($P$).

Extensive Property

A thermodynamic property that depends directly on the size or extent of the system, such as total mass ($m$) and total volume ($V$).

Thermodynamic Process

A transformation or change that takes a thermodynamic system from one state of equilibrium to another.

Thermodynamic Cycle

A sequence of thermodynamic processes that begins and ends at the identical state, returning the working fluid to its initial conditions.

Pure Substance

Matter that has a homogeneous and invariable chemical composition throughout; it can exist in a single phase or as a multi-phase mixture (e.g., water, ice, air, or carbon dioxide).

Enthalpy ($H$)

A thermodynamic property representing the total energy content of a system, expressed in units of energy such as Joules ($\text{J}$) or kilojoules ($\text{kJ}$), calculated as $H = mh$.

Specific Enthalpy ($h$)

The total enthalpy per unit mass of a substance, expressed in units of $\text{J/kg}$ or $\text{kJ/kg}$.

First Law of Thermodynamics

The law of energy conservation stating that energy can neither be created nor destroyed; for a closed system, the change in internal energy equals net heat added minus work done: $\Delta U = Q - W$.

Constant-Volume Specific Heat ($C_v$)

The energy required to raise the temperature of $1\,\text{kg}$ of a substance by $1\,^\circ\text{C}$ in an isochoric process, mathematically defined as $C_v = \left(\frac{\partial u}{\partial T}\right)_v$.

Boundary Work

The mechanical work done by or on a system during expansion or compression against a moveable boundary, defined by $W_{\text{out}} = p\Delta V$.

Polytropic Process

An expansion or compression process involving heat transfer characterized by the pressure-volume relationship $PV^n = \text{constant}$ or $Pv^n = \text{constant}$, where $n$ is the polytropic exponent.

Isobaric Process

A constant-pressure thermodynamic process, corresponding to a polytropic exponent of $n = 0$ where $P = \text{constant}$.

Isothermal Process

A constant-temperature thermodynamic process, corresponding to a polytropic exponent of $n = 1$ for an ideal gas where $Pv = \text{constant}$.

Isochoric Process

A constant-volume thermodynamic process, corresponding to a polytropic exponent of $n = \infty$ where $v = \text{constant}$.

Control Volume

An open thermodynamic system with fixed or moving boundaries that permits mass transfer across its boundary, along with possible energy transfers via heat and work.

Constant-Pressure Specific Heat ($C_p$)

The energy required to raise the temperature of $1\,\text{kg}$ of a substance by $1\,^\circ\text{C}$ in an isobaric process, mathematically defined as $C_p = \left(\frac{\partial h}{\partial T}\right)_p$.

Mass Flow Rate ($\dot{m}$)

The amount of fluid mass passing through a cross-sectional area per unit time, given by $\dot{m} = \rho \dot{V} = \rho V_{\text{avg}, n} A$, measured in $\text{kg/s}$.

Supercritical Fluid

A substance at a state with temperature and pressure exceeding its critical point ($T_c$ and $P_c$), characterized by the absence of distinct liquid and gas phases.

Saturated Liquid-Vapour Region

The two-phase coexistence region located beneath the vapor dome between the saturated liquid line and the saturated vapour line on a $T\text{-}v$ or $P\text{-}v$ diagram.

Turbine (Steady-Flow Model)

A device that converts the thermal energy and enthalpy of a high-energy fluid into useful shaft work; for an insulated steady-flow device, shaft power is $\dot{W}_{\text{shaft}} = \dot{m}(h_i - h_e)$.

Compressor (Steady-Flow Model)

A mechanical device that consumes external shaft power to raise the pressure and enthalpy of a gas or vapor, with shaft power given by $\dot{W}_{\text{shaft}} = \dot{m}(h_e - h_i)$.

Throttling Valve

A flow-restricting device used in vapor-compression refrigeration systems that creates a pressure drop, reducing saturation temperature and causing partial phase change without doing work.

Indirect Heat Exchanger

A device (such as a shell-and-tube heat exchanger) that transfers heat between two flowing fluids at different temperatures without allowing the fluids to mix.

Heat Engine

A continuously operating cyclic device that absorbs thermal energy from a high-temperature source ($T_H$), produces net work ($\dot{W}_{\text{net,out}}$), and rejects waste heat to a low-temperature sink ($T_L$).

Thermal Efficiency ($\eta_{\text{th}}$) of a Heat Engine

The dimensionless ratio of net mechanical work produced to total heat supplied to the heat engine: $\eta_{\text{th}} = \frac{\dot{W}_{\text{net,out}}}{\dot{Q}_H} = 1 - \frac{\dot{Q}_L}{\dot{Q}_H}$.

Rankine Cycle

The ideal thermodynamic cycle for steam power plants consisting of four processes: isentropic pumping, isobaric heat addition in a boiler, isentropic expansion in a turbine, and isobaric heat rejection in a condenser.

Entropy ($S$)

A thermodynamic property that measures the microscopic disorder of a system and represents the amount of thermal energy unavailable to perform useful mechanical work.

Coefficient of Performance for Cooling ($\text{COP}_R$)

An efficiency metric for refrigerators and air conditioners defined as the rate of heat removed from the refrigerated space divided by the required work input: $\text{COP}_R = \frac{\dot{Q}_L}{\dot{W}_{\text{in}}} = \frac{\dot{Q}_L}{\dot{Q}_H - \dot{Q}_L}$.

Coefficient of Performance for Heating ($\text{COP}_{\text{HP}}$)

An efficiency metric for heat pumps defined as the rate of heat delivered to the heated high-temperature space divided by the required work input: $\text{COP}_{\text{HP}} = \frac{\dot{Q}_H}{\dot{W}_{\text{in}}} = \frac{\dot{Q}_H}{\dot{Q}_H - \dot{Q}_L}$.

Seasonal Coefficient of Performance (SCOP)

A realistic efficiency metric assessing heat pump and air conditioner performance over an entire heating season, incorporating weather variations, part-load performance, and defrost cycles.

Entropy Transfer via Work

A zero-quantity interaction based on the Second Law of Thermodynamics: work transfer across a system boundary does not transfer any entropy.