A process is said to be adiabatic if heat neither enters nor leaves during the process. This is an important category of process.

Many real processes, especially rapid ones, may be approximated by the corresponding adiabatic process. For example the "correct" formula for the speed of sound in air was only devised when the assumption was made that the compressions and rarefactions of the sound waves were taking place adiabatically.

An "adiabat" is a line showing, for example, the relation between the pressure and the volume of a gas undergoing a reversible, adiabatic change. It contrasts with an "isothermal"

This process can be also expressed mathematically. For a such a process, ΔQ = 0.


0 = ΔU + ΔW

Any work done by the system is done at the expense of the internal energy. Any work done on the system serves to increase the internal energy.

For an ideal gas changing from conditions ( P1, V1, T1 ) to ( P1, V1, T1 ) is an adiabatic process,

P1V1γ = P2V2γ and T1V1γ-1 = T2V2γ-1

where *γ = cp / cn
*cp is just simply the specific heat of a gas at a constant pressure, and cv is just simply the specific heat at a constant volume. For more information, see Specific Heats of Gases.

Ad`i*a*bat"ic (#), a. [Gr. not passable; priv. + through + to go.] Physics

Not giving out or receiving heat.

-- Ad`i*a*bat`ic*al*ly, adv.

Adiabatic line or curve, a curve exhibiting the variations of pressure and volume of a fluid when it expands without either receiving or giving out heat.



© Webster 1913.

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