Segmental orifice plates and the emulation of the 90°-bend

The 90 ° - bend represents the most common structural element in piping systems and can have a significant impact on the measuring accuracy of flow meters installed downstream. Within the type-approval procedure of water meters, its impact is emulated by means of a segmental orifice plate with a segment area of 7 % (SOP7). In research and development, coverage rates of 33 % (SOP33) or more are sometimes used as an alternative. The purpose of this study is to evaluate the comparability of the flow conditions and their influence on the measurement deviation of flow meters, which is the basic requirement for using SOPs as a substitute for the 90°- bend. We present laser Doppler measurements downstream of an SOP33 and a 90°- bend and describe the flow development in a distance range from 2 to 30 diameters. Besides a quantitative comparison with performance indicators, the measurements are used to model the response of an ultrasonic and electromagnetic flow meter, including recent investigations of an SOP7. The results demonstrate the consistently poor agreement between the SOP7 and the 90°- bend, whereas the SOP33 provides similar flow conditions starting at a distance of 10 diameters. Further studies are necessary to develop a disturbance generator emulating the near-field range.

The Influence of Admixtures to the Signal of an Electromagnetic Flow Meter

Measurement error in an electromagnetic flow meter appears if magnetic and electric properties of admixtures are different from that of the fluid. Expressions of the error, which depends on volume concentration, permeability, and electric conductivity of particles were obtained by approximating the particles’ shape as an ellipsoid. Components of the error, which appear inside particles and outside particles in active zone of flow meter, with any canal form are investigated. Expressions of the error are presented assuming that particles are oriented in various directions with respect of the flow direction and are spinning. Different cases of magnetic and electric admixtures properties are discussed. Error expression obtained for flows with nonconductive and nonmagnetic particles coincides with experimental and modelling results obtained by other explorers for flows with air bubbles. Magnetic particles with high electric conductivity are especially dangerous. Extra measurement error in this case greatly depends on the shape of the particle. Measurement error increases if particle shape differs from a sphere. The complementary measurement error can exceed the volume concentration of particles by ten times if the ratio between the longest and the shortest axes of ellipsoid exceeds 3.

Gauging flow velocity in 2 positions for discharge calculation in pipes

ABSTRACT This paper utilizes the maximum entropy model to calculate discharges in pipes. The proposed model requires the flow velocities to be gauged in just two positions along the pipe radius to calculate the discharge of any given pipe with circular cross-section regardless its diameter size. A genetic algorithm is used to determine the two parameters of the entropy equation for pipe flow. Three water mains are assessed. The discharge values achieved by the maximum entropy model coupled to the genetic algorithm for two water mains are compared to those achieved by a calibrated AquaProbe ABB electromagnetic flow meter and remain within the device accuracy (± 2%), as reported by its manufacturer. A Cole type Pitot tube in series with a Venturi tube are used to respectively define three velocity profiles and gauge three different discharges for the third water main. The three discharge values obtained by the maximum entropy model are compared to the ones obtained by the Venturi tube and remain within the presented uncertainties (3.3%, 3.1% and 2.8%) for each discharge gauged by the Venturi tube. The discharge calculation in any given pipe is facilitated by the presented method.