INFRASON : industrial boilers soot cleaning by infrasound, low frequency sound

SOUND

PHYSICAL VARIABLES :

A sound is an elastic disturbance of the media where it travels ; this media can be either :

a gas
a liquid
a solid

A pure sound is a sinusoidal oscillation of each element around its nominal position, amplitude of this oscillation is called x, its velocity is u and its frequency f.

In a fluid without viscosity, pressure around the average pressure is called acoustic pressure and can be described as :

P= Pm sin wt
where w =2 Pf

This pressure variation involves a volume mass variation according to the thermodynamic equations.

These variations are generally considered as "small" compare to the nominal values.

SOUND VELOCITY

The velocity of the disturbance depend of the media characteristics and can be written as

C= ( E/P0)1/2 = ( aRT/M)1/2
weherein E = = volumic elastic module
P0 = avarage pressure of the gas
a = 1.41 (for air )
R = perfect gas constant ( 8.314 MKS )
M = molaire mass
T = absolute temperature ( °c + 273 )

To be simple, we can consider :

C = 20( T) 1/2

Impedance of the media :

If we consider a single wave moving forward in only one direction (ox, flat wave) :

p and u are only dependent on ct - x
p and u are in phase
Z, the impedance is a real terme :

Z = p / u

Z = r0C

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