Although a Coriolis flow meter inherently measures mass flow, the continuous measurement of fluid density enables it. The meter for volumetric flow calculation is the preferred means of expressing fluid flow. The relationship between mass flow (W), volume flow (Q), and mass density (ρ) are effortless.
All the flow meter’s computer must do to output a volumetric flow measurement is to take the mass flow measurement value and divide it by the measured density of the fluid. A simple dimensional analysis exercise (done with metric measurement units) validates this concept for both forms of the above equation:
Coriolis mass flow meters are very accurate and reliable. They are also entirely immune to swirl and other fluid disturbances, which means they may be located nearly anywhere in a piping system with no need for straight-run pipe lengths upstream or downstream of the meter.
Their natural ability to measure accurate mass flow and their characteristic linearity and accuracy make them ideally suited for custody transfer applications (where fluid flow represents a product being bought and sold).
Perhaps the most significant disadvantage of Coriolis flow meters is their high initial cost, especially for large pipe sizes. Coriolis flow meters are also more limited in operating temperature than other flow meters and may have difficulty measuring low-density fluids (gases), and mixed-phase (liquid/vapor) flows.
Bent tubing used to detect process flow can also trap process fluid inside to the point where it becomes unacceptable for hygiene.
Straight Coriolis tube flow meter designs and designs where the angle of the tubes is lightweight are better in this respect than the traditional U-tube Coriolis flow meter design.
However, a disadvantage of straight tubes is that they are stiffer than U-shaped tubes, so straight-tube Coriolis flow meters tend to be less sensitive to low flow rates than their U-tube counterparts.
Benefits of Coriolis Mass Flow Meters
- True mass flow measurement.
- Other temperature and density measurements
- Mass flow measurements are highly accurate
- High precision density measurement
- Insensitive to pressure, temperature, and viscosity
- No entry and exit sections are required.
- Works in both flow directions (forward and return).
- Measurement range settings can be optimized for flow and density
Flow meters with a Coriolis design have the following disadvantages:
- Affected by Gas Inclusions.
- Sensitive to vibrations if installed incorrectly.
- Limited choice of materials.
- Nominal diameter limited at the top.