Analysis of a cantilever coriolis mass flowmeter concept

A new flowmeter concept which simultaneously measures density, mean velocity, and mass flowrate has been conceived, analyzed, and experimentally verified. The concept is based on the dissipative effect of Coriolis inertial forces present in a vibrating hydroelastic cantilever. The concept also demonstrates: (1) the use of dynamic governing equations as a basis of measurement and, (2) the value of microprocessor algorithm implementation.

The cantilever Coriolis flowmeter concept was analyzed using literature associated with hydroelastic system stability as a basis. The governing equation is a fourth-order non-self-adjoint partial differential equation for which no closed-form solution is known. The boundary value problem associated with the cantilever geometry was solved numerically. Approximate single-mode analytical solutions were obtained using perturbation theory and a related simplified technique. In the range of interest, all three solutions agreed very well.

The theoretical analysis showed that the dynamic response of the cantilever flow sensor with static deflection motion excitation is essentially a second-order damped response in which the decay constant and frequency of vibration are dependent on the flowing fluid density and mean velocity. For this form of motion excitation, the cantilever Coriolis flowmeter operates as a sampled-data sensor. The analytical results were used to develop algorithms which transform the recorded transient waveform decay and frequency characteristics into fluid density, mean velocity, and mass flowrate.

A proof of principle experiment was performed to verify the analytical results. Using a microprocessor-based data acquisition and computation system three cantilever flow sensors were evaluated over a range of 0 to 1000 kg/h using a simple water circulation loop, cantilever Coriolis flowmeter was compared against an industrial thermal Each flowmeter. Thin wall tubing sensors worked best inspite of difficulties with multimodal response characteristics. The mass flow measurement tracking between the cantilever Coriolis and the thermal flowmeters was good with relative linearity in the range +5% to +10%. Density measurement results between the Coriolis density calculation and the known water density were +1% to +5%. Follow-on work will include prototypic experimentation and evaluation of several enhancements