Ultrasonic flowmeters

Abstract

Recent accounts of ultrasonic flowmeters usually concentrate on either transit time or Doppler types. Although these are the most common types in use today, at least six other types exist. Part 1 of this two-part paper describes the physical principles of eight types of ultrasonic flowmeters, along with some general considerations (flow profile, accuracy, response time) applicable to any flowmeter. Part 2 deals mainly with single-path transit time ultrasonic flowmeters for liquids, but discusses in a more general sense ultrasonic propagation starting at the transmitting transducer, continuing across impedance mismatches and attenuating media, and including the effects of reflection, refraction and diffraction. Application of these ultrasonic propagation principles is illustrated by various flow cell designs such as the axial offset type for pipe diameters down to a few mm; the square-hole zigzag type for in-line area-averaging; clamp-on and wetted-transducer installations on conventional pipes; and special cells. Finally, the use of microprocessor technology is illustrated with respect to improving accuracy and reliability, and for calculating fluid-or flow-related parameters such as sound speed, temperature, density, viscosity, Reynolds number, Mach number, standard deviation of the flow velocity, and mass flow rate.