Internally-nonprotruding one-port ultrasonic flow sensors for air and some other gases

A pair of recessed or flush-mounted transducers, if isolated acoustically from one another by attenuating O-rings and displaced axially by approximately 50 to 100 mm within a given port, may be used to measure by the contrapropagation method, the flow of air and some other noncombustible gases. In an alternate one-port configuration, the transducers are displaced circumferentially in order to measure swirl. The O-ring isolation method presented is relatively inexpensive, but it is limited in the sense that not all gases can be sealed reliably and safely with the available O-ring materials at all temperatures and pressures of interest. Fortunately, silicone and some other O-ring materials provide the designer with some options for dealing with many "ordinary" gases at "ordinary" conditions.