At least one parameter of at least one fluid in a
pipe is measured using a spatial array of acoustic pressure sensors placed at predetermined axial locations along the
pipe 12. The pressure sensors provide acoustic pressure signals, which are provided to a
signal processing system that determines the
speed of sound amix of the fluid (or mixture) in the
pipe 12 using acoustic spatial array
signal processing techniques. Numerous spatial
array processing techniques may be employed to determine the
speed of sound amix. The
speed of sound amix is provided to another logic
system that calculates the percent composition of the mixture, e.g.,
water fraction, or any other parameter of the mixture or fluid which is related to the sound speed amix. The
signal processing system may also determine the Mach number Mx of the fluid. The acoustic pressure signals measured are lower frequency (and longer
wavelength) signals than those used for ultrasonic flow meters, and thus are more tolerant to inhomogeneities in the flow. No
external source is required and thus may operate using passive listening. The invention will work with arbitrary sensor spacing and with as few as two sensors if certain information is known about the acoustic properties of the system.