Fluid Requirements for E+H Ultrasonic, Mass, Vortex, Magnetic, and Differential Pressure Flow Meters

The requirements of pipeline flow meters (including ultrasonic, Coriolis mass, vortex, magnetic, and differential pressure types) for fluid flow conditions (laminar / turbulent flow) are fully determined by their measurement principles. The core difference lies in whether they rely on stable disturbances formed by turbulent flow or only require a uniform flow velocity distribution. Each flow meter type is explained separately below:

Must operate under turbulent flow conditions. Measurement is based on the Karman vortex street effect: when fluid passes a vortex shedder, regular vortices form downstream, and the vortex frequency is proportional to flow velocity. Stable, identifiable vortex signals can only be generated under fully developed turbulent flow (Reynolds number Re typically in the range of 10⁴ to 10⁶).

Under laminar or transitional flow, vortices become disordered, frequency signals are distorted, and measurement accuracy degrades significantly. In engineering applications, sufficient straight pipe sections must be ensured: 10D–40D upstream and 5D downstream to eliminate disturbances and maintain a uniform flow field.

Suitable for both laminar and turbulent flow; no strict flow regime limits. Based on the law of electromagnetic induction: conductive fluid cutting through a magnetic field generates an induced electromotive force, whose magnitude is proportional to the average cross-sectional flow velocity. The flow meter accurately integrates to obtain average flow velocity regardless of laminar flow (parabolic velocity distribution) or turbulent flow (more uniform velocity distribution), and is insensitive to flow regime.

Only avoid empty pipes, large amounts of bubbles, or high-concentration solid particles (to prevent electrode abrasion). Straight pipe requirements are low, generally 5D upstream and 2D downstream.

Completely independent of flow regime; laminar, turbulent, and transitional flow all applicable. Using the Coriolis force effect, mass flow rate is measured directly by detecting changes in inertial force of fluid inside vibrating measuring tubes, independent of velocity distribution or flow regime.

High accuracy is maintained even for laminar flow of high-viscosity media or complex flow conditions with gas or solid inclusions, as long as the measuring tubes are full. There are almost no straight pipe requirements, and the meter is insensitive to disturbances from upstream pipe fittings.

Flow regime requirements vary by measurement principle:

• Transit-time method (mostly for large pipe diameters, clean fluids) Suitable for both laminar and turbulent flow. Flow velocity is calculated by measuring the difference in ultrasonic transit time in forward and reverse flow directions, reflecting average flow velocity with low straight pipe requirements.
• Doppler method (mostly for fluids containing particles / bubbles) More suitable for turbulent flow or moderately disturbed flow regimes. It relies on particles / bubbles in the fluid to reflect ultrasonic signals. Under laminar flow, uneven particle distribution tends to weaken signals and reduce accuracy.

E+H’s PMD75 is mainly used for liquid level, volume or mass measurement of liquids, differential pressure monitoring, and flow measurement (volumetric or mass flow) of gases, steam and liquids. Flow measurement requires auxiliary devices such as orifice plates and Pitot tubes.

Fully developed turbulent flow is mandatory. A pressure difference is generated via a throttling device, and the pressure difference is proportional to the square of flow rate. Fully turbulent flow above the critical Reynolds number (e.g., Re > 10⁵ for standard orifice plates) must be achieved; otherwise, nonlinear errors in the pressure difference-flow rate relationship will increase sharply.

Extremely high uniformity of flow velocity is required, with upstream straight pipe sections of 5D–40D depending on the throttling element. Insufficient straight pipes cause distorted velocity distribution and distorted differential pressure measurement. Normal measurement is not possible under laminar flow, with large pressure difference fluctuations that are difficult to correct via algorithms.