Inertance

Inertance

Inertance is a measure of the pressure gradient in a fluid required to cause a change in flow-rate with time. The unit of inertance is Pa m-3 s2 and the usual symbol is I.

For a circular tube the inertance is given by:

:I = { ho cdot ell over A} ,

where:"ρ" is the density (in units of kg / m3) of the fluid:"ℓ" is the length (in units of meters) of the tube:"A" is the cross sectional area (in units of m2) of the tube

The pressure gradient is related to the change in flow-rate by the equation:

: Delta p = I cdot {dot Q} = I cdot {dQ over dt}

To some it may appear counterintuitive that an increase in cross sectional area of a tube reduces the inertance of the tube. However, for the same mass flow-rate, a lower cross sectional area implies a higher fluid velocity and therefore a higher pressure gradient to accelerate the fluid.

The equation assumes constant density, that all parts of the fluid undergo the same acceleration and that the flow is fully developed (turbulent) "plug flow". This precludes sharp bends, water hammer and so on.

In respiratory physiology Inertance (of air) is measured in cmH2O L-1 s2.

1 cmH2O L-1 s2 ≈ 98100 Pa m-3 s2.

Using small-signal analysis, an inertance can be represented as a fluid reactance through the relation:

: X = j omega I

where:omega = 2 pi f:f is the frequency in Hz.

References

*cite book | author= Massey, B.S. | title= Mechanics of Fluids | year = 1989 | | publisher=Chapman & Hall | id= ISBN-10: 0412342804


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  • inertance — [inɛʀtɑ̃s] n. f. ÉTYM. Mil. XXe; de inerte, et suff. ance, dans son emploi spécialisé en physique. ❖ ♦ Phys. En acoustique, Composante de la réactance acoustique d un milieu (avec la pulsation et la « raideur ») …   Encyclopédie Universelle

  • Inertance — Die Inertance ist eine Messgröße der Pneumologie und bezeichnet die Trägheit von Lunge und Thorax. Im klinischen Bereich hat sie kaum Relevanz.[1] Physikalische Betrachtungsweise Vereinfacht kann man die Inertance mit Hilfe eines Rohres erklären …   Deutsch Wikipedia

  • inertance — ]tən(t)s noun ( s) : acoustic inertance * * * /in err tns, i nerr /, n. Acoustics. the effect of inertia in an acoustic system, an impeding of the transmission of sound through the system. Also called acoustic inertance, acoustic mass. [INERT +… …   Useful english dictionary

  • inertance — /in err tns, i nerr /, n. Acoustics. the effect of inertia in an acoustic system, an impeding of the transmission of sound through the system. Also called acoustic inertance, acoustic mass. [INERT + ANCE] * * * …   Universalium

  • inertance — akustinė masė statusas T sritis fizika atitikmenys: angl. acoustic mass vok. akustische Masse, f rus. акустическая масса, f pranc. inertance, f; masse acoustique, f …   Fizikos terminų žodynas

  • inertance — nectarine …   Anagrams dictionary

  • inertance — in·ert·ance …   English syllables

  • acoustic inertance — noun or acoustic mass : the impeding effect of inertia upon the transmission of sound in a conduit, equal in a tubular conduit (as an organ pipe) to the mass of the vibrating medium divided by the square of the cross section : the acoustic… …   Useful english dictionary

  • acoustic inertance — Acoustics. inertance. Also called acoustic mass. * * * …   Universalium

  • nectarine — inertance …   Anagrams dictionary

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