# Thermodynamics Topics

1.38062e-23JK-1
Boltzmanns constant.
5.67e-8Wm-2K-4
Stefan-Boltzmann constant.
8.314 JK-1mol-1
Molar gas constant.
Absolute Humidity
The total mass of water vapour present in the air per unit volume, generally given in g/m3.
Absolute Pressure
Pressure measured from a starting point of 0 in perfect vacuum.
Absolute Temperature
Temperature measured on a scale that sets absolute zero as zero.
Absolute Temperature Scale
A temperature scale based upon the value zero as the lowest possible value.
Absolute Vacuum
A volume which contains no matter.
Absolute Zero
At this temperature atoms have no energy.
Adiabatic Compression
Compressing a gas without removing or adding heat.
Adiabatic Cooling
A method in which paramagnetic salts are pre-cooled, and then demagnetized, thereby producing further cooling.
Adiabatic Efficiency
The efficiency with which work is done with respect to heat gains or losses.
Adiabatic Expansion
The expansion of a gas, vapour, or liquid stream from a higher pressure to a lower pressure, with no change in enthalpy.
Adiabatic Line
A line on an indicator diagram that represents an adiabatic process.
Adiabatic Process
A process in which the system does not exchange heat with the surroundings.
Adiabatic Saturation Process
A process to determine absolute or relative humidity.
Aerodynamic Heating
The heating of a body produced by passage of air or other gases over the body.
Aerothermodynamic
A branch of thermodynamics relating to the heating effects associated with the dynamics of a gas.
Aerothermodynamic Border
An altitude at about 100 miles, above which the atmosphere is so rarefied that the skin of an object moving through it at high speeds generates no significant heat.
Aerothermoelasticity
The study of the response of elastic structures to the combined effect of aerodynamic heating and loading.
Air Cooling System
Air passes over cooling fins to remove the heat from the system.
Air Source Heat Pump
These extract heat directly from the outside air and transfer it to water or air inside the building.
Antoine Equation
A simple 3-parameter fit to experimental vapour pressures measured over a restricted temperature range.
Average Bond Enthalpy
Average enthalpy change per mole when the same type of bond is broken in the gas phase for many similar substances.
Baudelot Cooler
Heat exchanger in which water flows by gravity over the outside of the tubes or plates.
Bomb Calorimeter
A bomb calorimeter measures the enthalpy of combustion.
Bond Enthalpy
Enthalpy change per mole when a bond is broken in the gas phase for a particular substance.
Brake Thermal Efficiency
This is the ratio of Brake Power to Heat of Fuel for a heat engine.
Brayton Thermodynamic Cycle
The thermodynamic cycle of the gas turbine engine. Sometimes known as the Joule Cycle.
Carnot Cycle
An idealized reversible thermodynamic cycle.
Carnot Engine
An idealized reversible heat engine working in a Carnot cycle.
Carnot Limit
A theoretical limit on the efficiency of an engine based on the flow of heat between two reservoirs.
Carnot's theorems
No engine can be more efficient than a reversible engine working between the same limits of temperature. All reversible engines working between the same two limits of temperature have the same efficiency.
CCHP
Abbreviation of Combined Cooling Heat and Power.
Change of State
The change in a substance between solid and liquid or between liquid and gas.
Choroisotherm
A line representing equal temperature in time.
CHP
Abbreviation of Combined Heat and Power.
Chu
Abbreviation of centigrade heat unit.
Clausius, Rudolph Julius Emmanuel
German mathematical physicist; restated the second law of thermodynamics; coined the term "entropy".
Clausius statement
No process is possible whose sole result is the transfer of heat from a colder to a hotter body.
Clausius-Clapeyron Equation
Predicts the temperature dependence of vapour pressures of pure liquids or solids.
clo
A unit of thermal insulation used for clothing.
Coefficient of Performance
The ratio of cooling or heating to energy consumption.
Combined Cooling Heat and Power
Utilises the waste heat from a fuel cell or engine with absorption chillers to provide air conditioning and hot or cold water alongside electricity.
Combined Heat and Power
Electrical power generator set where the waste heat is used to heat water for building heat supply or for industrial processes.
Combined Water and Power
Similar to CHP, but in this instance the waste heat is used to produce potable water.
Combustion Engine
An engine that uses the heat from the combustion of a fuel to operate, fundamentally split into Internal and External combustion engines.
Compressed
Pressed into less space.
Condensation
The process by which vapour molecules reform a liquid.
Condensation Coefficient
The ratio of condensation rate to impingement rate.
Condensation Nucleus
A particle, either liquid or solid, upon which condensation of vapour begins.
Condensation Rate
The number per square metre per second at which molecules condense on a surface.
Conduction
This is the process by which heat flows from the hotter region of a substance to the colder region without there being any net flow of the material itself.
Conductive
Having the property or capability of conducting.
Convection
The heat is transfered from the solid or liquid by the surrounding gas.
Cooling System
System that extracts heat from a machine and ejects it to the surrounding world.
CoP
Abbreviation of Coefficient of Performance.
Critical Constant
Any of three constants associated with the critical point of a pure element or compound: critical density, critical pressure, critical temperature.
Critical Cooling Rate
The minimum rate of continuous cooling just sufficient to prevent undesired transformations.
Critical Density
The density of a pure element or compound at a critical point.
Critical Point
The temperature or pressure at which a change in crystal structure, phase or physical properties occurs.
Critical Pressure
The pressure at the critical point.
Critical State
The state of a pure element or compound when it is at a critical point.
Critical Temperature
The temperature at the critical point.
Critical Volume
The volume occupied by a certain mass, usually one gram molecule of a liquid or gaseous substance at its critical point.
Cryogenic Liquefaction
The process through which gases such as nitrogen, hydrogen, helium, and natural gas are liquefied under pressure at very low temperatures.
Cryohydrate
A mixture of ice and another substance in definite proportions such that a minimum melting or freezing point is attained.
CWP
Abbreviation of Combined Water and Power.
Dalton′s Law of Partial Pressures
The total pressure of a mixture of gases, which do not interact chemically, is equal to the sum of the partial pressures.
Delta T
A reference to a temperature difference. It is used to describe the difference in temperature of a heating or cooling fluid as it enters and as it leaves a system.
Differential Thermal Analysis
A technique that is often used to analyze materials that react or decompose at higher temperatures.
Dulong-Petit Law
The molar heat capacity is approximately equal to the three times the ideal gas constant.
Empirical Temperature
A property that is the same for any two systems that are in thermodynamic equilibrium with each other.
Energy Balance
The difference between the total incoming and total outgoing energy.
Energy Efficiency
Ratio of energy output of a conversion process or of a system to its energy input.
Enthalpy
Change in heat.
Enthalpy of Atomization
The change in enthalpy that occurs when one mole of a compound is converted into gaseous atoms.
Enthalpy of Combustion
The amount of energy released in burning completely an amount of substance.
Enthalpy of Formation
The enthalpy change when 1 mole of a substance is formed from the elements in their standard states.
Enthalpy of Fusion
The enthalpy change that occurs to melt a solid at its melting point.
Enthalpy of Hydration
The enthalpy change associated with placing gaseous molecules or ions in water.
Enthalpy of Neutralization
The heat released by an acid-base neutralization reaction running at constant pressure.
Enthalpy of Reaction
The heat absorbed or released by a chemical reaction running at constant pressure.
Enthalpy of Solution
The enthalpy change associated with dissolving a solute in a solvent.
Enthalpy of Sublimation
The change in enthalpy when one mole of solid vaporizes to form one mole of gas.
Enthalpy of Vaporization
The change in enthalpy when one mole of liquid evaporates to form one mole of gas.
Entropy
Measure of the disorder of a system.
External Combustion Engine
An engine that burns the fuel outside of the engine, such as a steam engine or stirling engine.
Fin
A fixed vertical aerodynamic surface or part of a cooling system.
First Law of Thermodynamics
ΔU = ΔW + ΔQ
Forced Heat Convection
If the flow of gas away from a hot object starts by itself it is called natural convection. However, if the gas is forced past the object it is called forced convection.
Fourier′s Law
Empirical relationship between the conduction rate in a material and the temperature gradient in the direction of energy flow.
Fourth State of Matter
Plasma are sometimes referred to as the fourth state of matter.
Freezing Point
The temperature at which the vapour pressure of a liquid is equal to the vapor pressure of the corresponding solid form.
Freezing Point Depression
The freezing point of a solution is always lower than the freezing point of the pure solvent.
Gas Laws
The thermodynamic laws applying to perfect gases.
Gas Turbine Efficiency
For a simple cycle gas turbine the efficiency is determined by the pressure ratio of the compressor.
Grashof Number
A nondimensional parameter used in the theory of heat transfer.
Ground Source Heat Pump
The heat is collected using a fluid that flows through pipes laid in the ground.
Heat
If a temperature difference exists between two points heat will flow from the point at the higher temperature to the point at the lower temperature. This flow will continue until equilibrium has been reached. The transmission of heat may be due to three different processes.
Heat Balance
A tabulation showing the percentages of the heat developed by combustion in the engine cylinder that are (1) delivered in the form of power at the crankshaft, (2) lost in friction, (3) lost to the cooling water, and (4) lost in the exhaust gases.
Heat Capacity
The amount of heat required to raise the temperature of a body through 1K.
Heat Content
The SI unit for heat content is the Joule per cubic metre.
Heat Engine
A device for converting heat into mechanical work.
Heat Exchanger
Device built for efficient heat transfer from one medium to another.
Heat Flow Rate
The SI unit of heat flow rate or power is the watt.
Heat of Combustion
The amount of energy released in burning completely an amount of substance.
Heat of Condensation
The heat liberated by a unit mass of gas at its boiling point as it condenses to a liquid. Equal to the heat of vaporization.
Heat of Fusion
The enthalpy change that occurs to melt a solid at its melting point.
Heat of Hydration
The enthalpy change associated with placing gaseous molecules or ions in water.
Heat of Neutralization
The heat released by an acid-base neutralization reaction running at constant pressure.
Heat of Reaction
The heat absorbed or released by a chemical reaction running at constant pressure.
Heat of Solution
The enthalpy change associated with dissolving a solute in a solvent.
Heat of Sublimation
The change in enthalpy when one mole of solid vaporizes to form one mole of gas.
Heat of Vaporization
The energy required to vaporize one mole of a liquid at a pressure of one atmosphere.
Heat Pipe
A device that can transfer large amounts of heat with a small difference in temperature between the hot and cold interface.
Heat Pump
A reversible heat engine that acts as a furnace in winter and an air conditioner in summer.
Heat Radiation
This is the electromagnetic radiation emitted by a body as a function of its temperature.
Heat Transfer
Movement of heat from one body or substance to another. Heat may be transferred by radiation, conduction, convection or a combination of these three methods.
Heating Curve
A plot of temperature verses time for a substance where energy is added at a constant rate.
Heating Value
The amount of heat produced by combustion of a unit quantity of a fuel.
Heating Ventilation and Air Conditioning
Lists all Heating Ventilation and Air Conditioning topics in the Encyclopaedia
HHV
Abbreviation of Higher Heating Value.
Higher Heating Value
The standard measure of the energy released during combustion of a fuel, assuming the product water is in the liquid state.
Insulation
A material used to prevent the leakage of electricity from a conductor and to provide mechanical spacing or support as protection against accidental contact with the conductor.
Insulator
A material that does not allow the passage of electric charge or is a poor conductor of thermal energy.
Integral Enthalpy of Solution
The heat absorbed or released when a solute is dissolved in a definite amount of solvent.
Inversion Temperature
The temperature above which a gas gains heat in expansion.
Irreversible Process
Any real process; when a system undergoes the changes State 1 -> State 2 -> State 1 by any real pathway, the universe is different that before the cyclic process took place in the system.
Isentrope
A line of equal or constant entropy.
Isentropic
Of equal or constant entropy with respect to either space or time.
Isobar
A contour line that corresponds to values measured at identical pressures.
Isotherm
A contour line that corresponds to values measured at identical temperatures.
Isothermal
Constant temperature.
Isothermal Expansion
The expansion or compression of a gas at constant temperature.
Joule Cycle
The thermodynamic cycle of the gas turbine engine.
Kelvin
The kelvin is the unit of thermodynamic temperature.
Kelvin-Planck statement
No process is possible whose sole result is the absorption of heat from a reservoir and the conversion of all of this heat into work.
Latent Heat
The amount of heat required to melt (or vapourize) 1 kilogram of a substance.
Latent Heat of Evaporation
The amount of heat required to vapourize 1 kilogram of a substance.
Latent Heat of Fusion
The amount of heat required to melt 1 kilogram of a substance.
LHV
Abbreviation of Lower Heating Value.
Linear Thermal Expansion
Most substances expand when heated and contract when cooled.
Lower Heating Value
The standard measure of the energy released during combustion of a fuel, assuming the product water is in the gaseous state.
Maxwellian Distribution
The velocity distribution, as computed in the kinetic theory of gases, of the molecules of a gas in thermal equilibrium.
Miller Cycle
A combustion process for the four stroke internal combustion engine where the intake valve is left open longer than it would be in an Otto cycle engine.
Molar Heat Capacity
The amount of heat required to raise the temperature of 1mol of a substance through 1K.
Natural Convection
Movement of a fluid caused only by temperature differences.
Natural Heat
A term that has generally referred to the heat produced within the body, usually the heat produced by the heart and the circulatory system.
Natural Heat Convection
If the flow of gas away from a hot object starts by itself it is called natural convection. However, if the gas is forced past the object it is called forced convection.
Noncondensable Gas
A gas whose temperature is above its critical temperature, so that it cannot be liquefied by increase of pressure alone.
Nusselt Number
A number expressing the ratio of convective to conductive heat transfer between a solid boundary and a moving fluid.
Otto Cycle
An idealized reversible cycle of four operations occurring in a perfect four-stroke petrol engine.
Peclet Number
A dimensionless number that is the ratio of heat advection to heat diffusion.
Perfect Fluid
A fluid chiefly characterized by lack of viscosity and, usually, by incompressibility.
Poisson Constant
The ratio of the gas constant to the specific heat of a gas at constant pressure.
Polytropic Process
A non-adiabatic reversible process characterized by the equation of path, pv = constant.
Rankine Cycle
A mathematical model that is used to predict the performance of steam engines. The Rankine cycle is an idealised thermodynamic cycle of a heat engine that converts heat into mechanical work. The heat is supplied externally to a closed loop, which usually uses water as the working fluid.
Ratio of Specific Heats
The ratio of molar heat capacity at constant pressure to molar heat capacity at constant volume.
Real Gas Effects
A gas behavior or phenomena resulting from the interactions of gas molecules.
Relative Temperature
The difference between the measured temperature value and an arbitrarily selected value, such as the freezing point of water.
R-Value
Under uniform conditions it is the ratio of the temperature difference across an insulator and the heat flux.
Sankey Diagram
A specific type of flow diagram, in which the width of the arrows is shown proportionally to the flow quantity.
Second Law of Thermodynamics
Clausius states: No process is possible whose sole result is the transfer of heat from a colder to a hotter body.
Simple Cycle Gas Turbine
Cycle consisting only of compression, combustion and expansion.
Soil Heat Flux
The amount of heat flowing into a cross-sectional area of soil per unit time.
Specific Heat Capacity
The amount of heat required to raise the temperature of 1kg of a substance through 1K.
Stagnation Enthalpy
The total energy or heat content of a system generated when the flow is brought to rest isentropically at a stagnation point.
Standard Enthalpy Change
A change in enthalpy associated with a reaction or transformation involving substances in their standard states.
Standard Enthalpy of Formation
The change in enthalpy when one mole of compound is formed from its elements in their most stable form and in their standard states.
Standard Enthalpy of Reaction
A change in enthalpy associated with a reaction involving substances in their standard states.
Standard State
A set of conditions defined to allow convenient comparison of thermodynamic properties.
State of Matter
There are three common states of matter: gases, liquids, and solids.
State Property
A state property is a quantity that is independent of how the substance was prepared.
Steady State
A condition devoid of transient effects.
Steam
The gas phase of water.
Super Heated Steam
Steam heated above its saturation temperature.
Super Heating
The heating of a liquid above its boiling temperature without the formation of the gaseous phase.
Superheated Vapour
Vapour at a temperature which is higher than the saturation temperature at the existing pressure.
Surroundings
In thermodynamics, the surroundings refer to the universe outside the system.
Thermal Conduction
The transfer of thermal energy by collisions of the atoms or molecules within a substance.
Thermal Conductivity
A measure of the ability of a material to conduct heat.
Thermal Cycling
Subjecting a product to pre-determined temperature changes, between hot and cold extremes.
Thermal Diffusivity
The ratio of heat conducted to the heat stored per unit volume.
Thermal Efficiency
Quantity of heat produced in relation to fuel input.
Thermal Electromotive Force
The electromotive force generated in a circuit containing two dissimilar metals when one junction is at temperature different from that of the other.
Thermal Energy
The internal energy in substances, the vibration of atoms and molecules within substances.
Thermal Energy Storage
The storage of thermal energy in a system such as molten salt.
Thermal Equilibrium
Two objects are in thermal equilibrium if there is no energy flow from one to the otherand both are at the same temperature.
Thermal Expansion
The change in length of a material with change in temperature.
Thermal Gradient
The rate at which the temperature changes with position.
Thermal Growth
Movement of the machine parts associated with a change in machinery temperature between the static and operating conditions.
Thermal Inertia
A bulk material property related to thermal conductivity and volumetric heat capacity.
Thermal Insulation
The materials and methods used to reduce heat transfer.
Thermal Resistance
The property of a material, device or system that impedes the flow of heat.
Thermal Runaway
A conduction that exists when heat causes more electron-hole pairs to be generated, which, in turn, causes more heat and which may eventually cause diode destruction.
Thermal Shock
Stresses induced in a material because of a rapid temperature change or a thermal gradient.
Thermodynamic Equilibrium
A system is at thermodynamic equilibrium if the energy it gains from its surroundings is exactly balanced by the energy it loses, no matter how much time is allowed to pass.
Thermodynamic Free Energy
The energy in a physical system that can be converted to do work.
Thermodynamic Properties
Basic qualities used in defining the condition of a substance, such as temperature, pressure, volume, enthalpy, entropy.
Thermodynamics Books
Lists all Books in the Encyclopaedia
Thermodynamics Calculations
Lists all Calculations in the Encyclopaedia
Thermodynamics Conversions
Lists all Conversions in the Encyclopaedia
Thermodynamics Weblinks
Lists all Weblinks in the Encyclopaedia
Third Law of Thermodynamics
For changes involving only perfect crystalline solids at absolute zero, the change of the total entropy is zero.
Ton Refrigeration Unit
Unit which removes same amount of heat in 24 hours as melting of 1 ton of ice.
Translation Energy
The energy associated with random straight line motion of gas molecules.
Vapour Pressure
The partial pressure of a gas in equilibrium with a condensed form (solid or liquid) of the same substance.
Vital Heat
A term that has generally referred to the heat produced within the body, usually the heat produced by the heart and the circulatory system.
Volume Thermal Expansion
Relative change in volume due to temperature change.
Water Cooling System
Water passes through the system or through a water cooling jack, this is then sent to a radiator where air is passed over the radiator to remove the heat from the water before it is sent back to the system to be cooled.
Working Fluid
A fluid used as the medium for the transfer of energy.
Zero Absolute Pressure
A total vacuum. Zero on the absolute pressure scale.
Zero Kelvin
At this temperature atoms have no energy.
Zero-Point Pressure
The pressure contributed by degenerate electrons, which do not come to rest even at absolute zero.
Zeroth Law of Thermodynamics
If two bodies are each in thermal equilibrium with a third body, then all three bodies are in thermal equilibrium with each other.

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