Adiabatic process
Some chemical and physical processes occur too rapidly for energy to enter or leave the system as heat, allowing a convenient "adiabatic approximation".The assumption of adiabatic isolation is useful and often combined with other such idealizations to calculate a good first approximation of a system's behaviour.The transfer of energy as work into an adiabatically isolated system can be imagined as being of two idealized extreme kinds.In nature, this ideal kind occurs only approximately because it demands an infinitely slow process and no sources of dissipation.This finds practical application in diesel engines which rely on the lack of heat dissipation during the compression stroke to elevate the fuel vapor temperature sufficiently to ignite it.Adiabatic expansion occurs in the Earth's atmosphere with orographic lifting and lee waves, and this can form pilei or lenticular clouds.[10] Such temperature changes can be quantified using the ideal gas law, or the hydrostatic equation for atmospheric processes.where P is pressure, V is volume, and γ is the adiabatic index or heat capacity ratio defined asOur initial conditions being 100 kPa of pressure, 1 L volume, and 300 K of temperature, our experimental constant (nR) is:This is why a high-compression engine requires fuels specially formulated to not self-ignite (which would cause engine knocking when operated under these conditions of temperature and pressure), or that a supercharger with an intercooler to provide a pressure boost but with a lower temperature rise would be advantageous.A diesel engine operates under even more extreme conditions, with compression ratios of 16:1 or more being typical, in order to provide a very high gas pressure, which ensures immediate ignition of the injected fuel.Since this process does not involve any heat transfer or work, the first law of thermodynamics then implies that the net internal energy change of the system is zero.Any work (δW) done must be done at the expense of internal energy U, since no heat δQ is being supplied from the surroundings.Using the ideal gas law and assuming a constant molar quantity (as often happens in practical cases),The change in internal energy of a system, measured from state 1 to state 2, is equal to At the same time, the work done by the pressure–volume changes as a result from this process, is equal to Since we require the process to be adiabatic, the following equation needs to be true By the previous derivation, Rearranging (c4) givesUsing the ideal gas law and assuming a constant molar quantity (as often happens in practical cases),These properties may be read from the classical behaviour of ideal gases, except in the region where PV becomes small (low temperature), where quantum effects become important.The Greek word ἀδιάβατος is formed from privative ἀ- ("not") and διαβατός, "passable", in turn deriving from διά ("through"), and βαῖνειν ("to walk, go, come").Energy can enter or leave a thermodynamic system enclosed by walls that prevent mass transfer only as heat or work.[21] The reason is that calorimetry presupposes a type of temperature as already defined before the statement of the first law of thermodynamics, such as one based on empirical scales.Rather, the definition of absolute thermodynamic temperature is best left till the second law is available as a conceptual basis.[22] In the eighteenth century, the law of conservation of energy was not yet fully formulated or established, and the nature of heat was debated.One approach to these problems was to regard heat, measured by calorimetry, as a primary substance that is conserved in quantity.The view that eventually established itself, and is currently regarded as right, is that the law of conservation of energy is a primary axiom, and that heat is to be analyzed as consequential.On the one hand, in quantum theory, if a perturbative element of compressive work is done almost infinitely slowly (that is to say quasi-statically), it is said to have been done adiabatically.While the occupation numbers are unchanged, nevertheless there is change in the energy levels of one-to-one corresponding, pre- and post-compression, eigenstates.Thus a perturbative element of work has been done without heat transfer and without introduction of random change within the system.Recent research[26] suggests that the power absorbed from the perturbation corresponds to the rate of these non-adiabatic transitions.This corresponds to the classical process of energy transfer in the form of heat, but with the relative time scales reversed in the quantum case.The strong irreversibility of the change, due to viscosity or other entropy production, does not impinge on this classical usage.
- The isotherms are the red curves and the adiabats are the black curves.
- The adiabats are isentropic.
- Volume is the horizontal axis and pressure is the vertical axis.
adiabatic theoremThermodynamicsCarnot heat engineClassicalStatisticalChemicalQuantum thermodynamicsEquilibriumNon-equilibriumZerothSecondSystemsClosed systemIsolated systemEquation of stateIdeal gasReal gasState of matterPhase (matter)Control volumeInstrumentsProcessesIsobaricIsochoricIsothermalIsentropicIsenthalpicQuasistaticPolytropicFree expansionReversibilityIrreversibilityEndoreversibilityCyclesHeat enginesHeat pumpsThermal efficiencySystem propertiesConjugate variablesProperty diagramsIntensive and extensive propertiesProcess functionsFunctions of stateTemperatureEntropyintroductionPressureVolumeChemical potentialParticle numberVapor qualityReduced propertiesMaterial propertiesProperty databasesSpecific heat capacityCompressibilityThermal expansionEquationsCarnot's theoremClausius theoremFundamental relationIdeal gas lawMaxwell relationsOnsager reciprocal relationsBridgman's equationsTable of thermodynamic equationsPotentialsFree energyFree entropyInternal energyEnthalpyHelmholtz free energyGibbs free energyGeneralGas laws"Perpetual motion" machinesPhilosophyEntropy and timeEntropy and lifeBrownian ratchetMaxwell's demonHeat death paradoxLoschmidt's paradoxSynergeticsCaloric theoryVis viva ("living force")Mechanical equivalent of heatMotive powerKey publicationsAn Inquiry Concerning theSource ... FrictionOn the Equilibrium ofHeterogeneous SubstancesReflections on theMotive Power of FireMaxwell's thermodynamic surfaceEntropy as energy dispersalBernoulliBoltzmannBridgmanCarathéodoryCarnotClapeyronClausiusde Dondervon HelmholtzKelvinMassieuMaxwellvon MayerNernstOnsagerPlanckRankineSmeatonThompsonvan der WaalsWaterstonNucleationSelf-assemblySelf-organizationOrder and disorderAncient Greekthermodynamic processthermodynamic systemenvironmentisothermal processfirst law of thermodynamicsadiabatic flame temperature