Electromagnetic Flowmeters

Overview

Engineering reference data for Electromagnetic Flowmeters in fluid mechanics.

Key Formulas

Reynolds Number

$Re = \frac{\rho v D}{\mu}$

Ratio of inertial to viscous forces — determines flow regime.

Bernoulli's Equation

$P + \frac{1}{2}\rho v^2 + \rho g h = \text{const}$

Conservation of energy for steady, inviscid, incompressible flow.

Continuity Equation

$A_1 v_1 = A_2 v_2$

Conservation of mass for incompressible flow.

Darcy-Weisbach

$\Delta P = f \frac{L}{D} \frac{\rho v^2}{2}$

Pressure drop due to friction in a pipe.

Variables

Working Principles

Electromagnetic flowmeters operate on Faraday's Law of Electromagnetic Induction. When an electrically conductive fluid flows through a magnetic field generated by the meter, a voltage is induced. This voltage is directly proportional to the average velocity of the fluid.

Key operational conditions:

• The fluid must be electrically conductive (typical threshold > 5 µS/cm).
• The pipe must be completely filled with fluid.
• The lining and electrodes must be compatible with the process fluid.

Selection Considerations

• Lining Material: Selection depends on fluid corrosivity, abrasion, and temperature. Common options include PTFE, hard rubber, and ceramic.
• Electrode Material: Must resist corrosion and erosion. Options include stainless steel, Hastelloy C, titanium, and platinum-iridium.
• Size and Range: The meter size should match the pipe size to avoid constriction. Ensure the expected flow rate falls within the specified flow range (typically turndown ratio of 10:1 to 20:1).

Common Applications

• Water and wastewater treatment
• Chemical processing and dosing
• Food and beverage production (sanitary versions available)
• Pulp and paper manufacturing
• Mining and mineral processing slurry metering

References

• Original Source