July 2013, Vol. 240 No. 7
TechNotes
New Technology For Gas Flow, Composition
Quantitech has launched an in-pipe, gas-flow monitoring technology that also offers the ability to measure gas composition or purity.
When the speed of sound (SoS) in a gas is measured along a path in both directions simultaneously, the difference in the measured velocities is proportional to the gas velocity along the pipe. If gas temperature is expected to fluctuate, an automatic compensation is applied.
If the gas is at a pressure below ambient, then it is only the volume of the sound that would limit the measurement capability. Measurements at 100 mbar are feasible and flow rates between 0.01 l/min and 200 l/min are possible in pipes up to 200 mm in diameter. Running from a 24 Vdc supply, the meters respond rapidly and output data in variety of formats.
When qualitatively monitoring of single gases, any change in the SoS measurement will indicate that the purity of the gas has changed.
For mixtures of two gases, SoS is a combination of the two main gas components, so there is a simple calculation to derive the proportion of each component. For example, the SoS for pure carbon dioxide (CO-2) is 259 m/s, and for methane (CH-4) it is 430 m/s. So, if the SoS measurement is 401 m/s, the gas composition is 83% methane and 17% carbon dioxide.
“Unlike other methods, this measurement is not affected by the gas composition, temperature, density, viscosity or pressure, and there is no obstruction at the measurement point,” said sales director Dominic Duggan.
In another example, the SoS in hydrogen is about 1250 m/sec, two to three times higher than most other gases, so any gas that dilutes hydrogen flow will produce a significant reduction in the measured SoS to warn instantly that the fuel is diluted. Similarly, the SoS for helium is 970 m/sec, so the measurement of helium purity is also a good application for the Voxtrac device.
For further information, visit www.quantitech.co.uk .
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