Advantages, disadvantages and designs of Coriolis mass flow meters

Advantages:

– Principle of universal application for measuring flow rates of liquids and gases.

– Direct measurement of mass flow rate (does not require pressure and temperature compensation).

– The measurement principle does not depend on the density or viscosity of the fluid.

– The measurement accuracy is very high (typically ±0.1% vL).

– The sensor is multivariable: it measures mass flow rate, density, and temperature simultaneously.

– It is insensitive to changes in the speed profile.

– It does not require entrance and exit sections.

Disadvantages:

– The initial economic investment is relatively high.

– Installation costs can be considerable, depending on the model and manufacturer.

– The temperature range is limited: typically from -50 to +350 °C (-60 to +660 °F).

– Its use is restricted to fluids with low gas content and single-phase fluids.

– Some large models are very heavy.

Twin-tube metering systems

In most twin-tube flow meters, the measuring tubes oscillate out of phase; this arrangement effectively decouples the flow meter from the influence of external vibrations. There are several types of twin-tube flow meters. Regarding the geometric characteristics of the measuring tubes, each manufacturer offers different geometries, and straight, curved, or slightly arched tube models are available. The straight or slightly arched tubes used by E+H allow for the construction of compact and space-saving sensors (see figure below):

Fig.: E+H Coriolis mass flow meters (examples).

– Promass F (two left): Versatile standard sensor, also suitable for large flow rates.

– Promass A (top right): Single tube system for small flow volumes (DN 4, 1/24 to 1/6″).

– Promass I (center): Single tube measuring system designed for hygienic applications.

– Promass E (center, right): Measurement system with a lower acquisition cost of ownership compared to "traditional" measurement systems in comparable applications.

– Promass M (bottom left): Measuring system for process pressures up to 350 bar (5,000 psi).

-Promass H (bottom right): Special single-tube system for chemically aggressive fluids.

Single-tube metering systems

Single-tube metering systems offer several advantages over double-tube systems:

– They are easy to clean.

– Pressure losses are significantly lower.

– The stresses induced in the fluid are lower because they do not need a separating partition that divides the flow into two measuring tubes.

The drawback of this design – a single oscillating measuring tube – is that decoupling, an inherent characteristic of double-tube flow meters, is not immediately achievable. Therefore, care must be taken during the development stage to equip the flow meter with features that effectively decouple the system from external influences.

The "torsion balance" system:

E+H achieves this decoupling by combining the characteristic high resonant frequency with its patented Torsion Mode Balanced™ (TMB) system. In the case of the Promass I single-tube sensor, the balance required for accurate measurement is achieved by means of a pendulum mass mounted eccentrically on the measuring tube, which oscillates in the opposite direction to create a torsional effect (see figure below). Thanks to this integrated system balance, Promass I is as easy to install as any twin-tube system. No special vibration damping mounts are required upstream or downstream of the measuring sensor.

The Promass I measuring system allows even the determination of the "chain" viscosity, as one more parameter of the process.

Fig. 83: Vibration inhibition by the Promass I "torsional balancing" system.

This single-tube measuring system was introduced in 1997 by E+H and does not require any additional support or accessories whatsoever.

w = Angular velocity, m1 = Mass of the measuring tube plus the fluid, m2 = Pendulum mass,

v1 = Velocity of m1, v2 = Velocity of m2, p = Linear momentum