EFFECT OF FINITE MEDIUM SPEED OF SOUND ON CORIOLIS MASSFLOWMETERS

M. Anklin, G. Eckert, S. Sorokin, A. Wenger

Abstract

A theory is presented for the interaction between a vibrating tube and the enclosed flowing fluid with finite speed of sound. From this the influence of the speed of sound on the massflow measurements is derived. This model is valid for compressible mediums and for flow velocities which may be quite high (~ 100 m/s) but still subsonic. Such velocities can easily be reached in a Coriolis mass flowmeter (CMF) for gas application. The exact theoretical calculation is complex and the results can not be written in a simple one line equation. Nevertheless, we approximate the exact formula to estimate the deviation between true mass flow and the CMF reading. This deviation can be described with mainly two terms:<BR />The first term is proportional to (<i>kd</i>)² = (2 &pi; <i>f</i> <i>d</i> / <i>c</i>)², with <i>f</i> being the resonant frequency, <i>c</i> being speed of sound of the medium, and <i>d</i> being the diameter of tube. This term contributes most to the observed deviation. The second term depends on density and velocity of fluid. A comparison of this model with experimental data shows a good agreement.

Keywords

eigenfrequency, speed of sound, phase shift, time lag, compressibility

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IMEKO TC

TC9 - Flow Measurement

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