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Electromagnetic Flowmeters

Reference data and engineering information about electromagnetic flowmeters for fluid mechanics applications.

electromagneticflowmeters

Overview

Engineering reference data for Electromagnetic Flowmeters in fluid mechanics.

Key Formulas

Reynolds Number

Re=ρvDμRe = \frac{\rho v D}{\mu}

Ratio of inertial to viscous forces — determines flow regime.

Bernoulli's Equation

P+12ρv2+ρgh=constP + \frac{1}{2}\rho v^2 + \rho g h = \text{const}

Conservation of energy for steady, inviscid, incompressible flow.

Continuity Equation

A1v1=A2v2A_1 v_1 = A_2 v_2

Conservation of mass for incompressible flow.

Darcy-Weisbach

ΔP=fLDρv22\Delta P = f \frac{L}{D} \frac{\rho v^2}{2}

Pressure drop due to friction in a pipe.

Variables

Symbol Description Unit
ReRe Reynolds number —
ρ\rho Fluid density kg/m³
vv Flow velocity m/s
DD Characteristic dimension m
μ\mu Dynamic viscosity Pa·s
PP Pressure Pa
ff Darcy friction factor —

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