The Coriolis effect was discovered by physicist Gustave Gaspard Coriolis during the 1830s, and is described as "the inertial force exerted on an object as a result of movement relative to a rotating frame of reference". The use of the Coriolis effect as a technique for liquid and gas mass flow measurement was firmly established over 20 years ago.
The Rheonik range of Coriolis mass flowmeters is characterised by its unique and patented Omega tube element which has a torsional or swinging movement rather than the bending motion traditionally associated with Coriolis meters. The torsional motion of the Omega tube is relatively easy to stimulate and requires only a small amount of energy to keep the tubes moving. Rheonik claim that the unique mechanical arrangement of the Omega tube meter allows the use of tubing with heavier wall thickness giving higher pressure ratings, combating abrasion and erosion and eliminating the requirement for the secondary pressure containment found with conventional designs. The tube thickness usually reaches the same schedule as the process pipeline and meters are manufactured right up to 300 mm line size and capable of a flow rate of 1500 tons per hour. This facilitates custody transfer of large pipe mass-flow utilising direct mass measurement as opposed to the conversion of volumetric readings into a mass value.
The flexibility of the Rheonik range in terms of application is due to the patented mechanical arrangement of the meter. Each flowmeter has two measuring tubes parallel to one another and formed into the unique Omega shape. These oscillate in opposing directions. The oscillating system is driven with two high mass crossbars mounted on vertical torsion rods:
* The high mass crossbars stabilise the torsional movement, either eliminating or greatly reducing interference from external vibration and providing continued, reliable operation with the presence of oscillation dampening factors such as entrained gas bubbles or non-homogeneity in the process stream.
* The torsion rods minimise stress on the tubing, guide the tube movement and help 'energise' the torsional motion. This rugged mechanical arrangement is energy conserving and requires very little power input (typically less than 300 mW) to maintain oscillation amplitude. The design provides for an exceptionally well balanced mechanism that approaches perpetual motion once energised.
These meters achieve a turndown ratio of 50:1 and are available in a wide variety of sizes, from extremely low flows of 0,001 kg/min up to 25 000 kg/min. The physical construction of the meters makes them suitable for applications where excessive process conditions are involved with temperatures as low as
-200°C and in excess of 400°C and pressure up to 890 bar. Approvals include EEXia IIC, EEx de IIC (ATEX and CSA) and Fiscal (OIML R117), and models are available in exotic materials such as hastelloy, monel and tantalum to solve the most challenging applications.
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