Abstract

A mass flow meter includes a body having a cylindrical bore and an elongated cylindrical piston positioned in the bore concentrically therewith. An elongated annular fluid flow channel of uniform depth is bounded by a cylindrical surface of the piston and a surface of the bore. Fluid flows laminafly through the channel. First and second concentric ferrules are located at first and second end portions of the piston to precisely position and hold the piston concentrically in the bore, by elastically expanding in response to longitudinal forces on the first and second end portions of the piston to symmetrically engage a wall of the bore. A first pressure measuring probe in fluid communication with an upstream equalization chamber measure fluid pressure in the upstream equalization chamber, and a second differential pressure transducer in fluid communication between the upstream equalization chamber and a downstream equalization chamber measures differential fluid pressure between the two equalization chambers. The difference between the pressures measured in the two equalization chambers represents the mass flow of the fluid through the channel. The simple, near-ideal geometric shapes of the bore, piston, and ferrules permits simple, accurate mathematical modeling of corrections to account for changes in pressure, temperature, and thermal gradient.