Acoustic resistance values for capillaries
Leak effect/capillary tube: an acoustical resistance is found in a capillary tube or a thin slit of length
,small relative to the wave length
of the acoustic signal (
). This resistance is mainly due to the friction between the fluid and the wall. It is called viscous resistance.
The acoustic resistance
is expressed in
. It depends on the dynamic viscosity coefficient of the fluid
(
). This unit,
, is also called the Poiseuille.In a capillary tube of radius
and length
, the acoustical resistance is
.In the case of a rectangular slit of width
, height
and length
, the acoustical resistance is
In the case where the channel geometry is unknown, the acoustical resistance cannot be analytically calculated. In this case, we generally use a model with an equivalent acoustic resitance. The value of this resitance is estimated by comparing experimental values with theoretical ones. This can be done by mesuring the acoustical impedance of the element under study.
