A flowmeter for unsteady liquid flow measurements

An unsteady flowmeter was developed for implementation in the Inolivent-4 total liquid ventilator prototype. The proposed design consists of a symmetrical venturi tube comprising three pressure sensors and in which flow measurement is obtained by numerically solving a slightly modified version of the unsteady Bernoulli equation. A prototype was validated experimentally by applying zero-mean sinusoidal flows. Low-frequency characterization determined the venturi discharge coefficient as a function of the Reynolds number, and higher-frequency (≤4Hz) measurements determined the applicable bandwidth of the device. The velocity profiles were measured in the venturi by particle image velocimetry (PIV), and the device was calibrated experimentally by comparison with an ultrasonic flowmeter and measurements from a piston pump. Results showed that quasi-steady flows could be accurately measured in the 5–60 ml/s range, while low-amplitude (≤10ml/s) oscillatory flows were well-measured for frequencies below 3 Hz. Finally, PIV experiments showed that the flat velocity profile assumption required for a simple solution of the flowmeter equation was valid within the operating range.

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► We developed a liquid flowmeter for a biomedical application.
► We proposed a method for retrieving unsteady flowrate from differential pressure.
► The venturi discharge coefficient was determined as a function of Reynolds number.
► Unsteady characterization presented acceptable dynamic response up to 3 Hz.
► The device gives good performances for flow amplitudes from 5 to 60 ml/s.