Why is the choice of piping important for thermal mass flow meters?

Deviation in measurement of the thermal mass flow meter

Deviation in the measurement data can be caused by using a too short pipe length, because the pipe length is a parameter for the gas temperature. For an optimal performance we advise to avoid excessive temperature fluctuations during commissioning and process operation as much as possible, especially in a process with thermal mass flow meters and controllers. If you use mass flow meters based on the Coriolis principle, temperature fluctuations have no influence on the measurement data, as this measurement principle has been based on measurement of real mass.

Frozen pipes

Another effect which I encounter in the field is frozen pipes. How do frozen pipes occur?
When a cooled gas flows with a high velocity through the piping, the temperature of the piping will lower, especially when restrictions in the piping are used, such as narrowing of pipe diameter or the use of (shut-off) valves in the piping. As a result, the piping will attract moisture. If the ambient temperature lowers beneath zero degrees, the moisture will freeze.

Not only can your pipes freeze on the outside, it can also happen within the pipe when the medium (gas) contains moisture. In this case, you can avoid freezing by using a refrigeration dryer to dry the gas in the pipes. Solution to make sure the gas which is used in the process is dry, to avoid freezing as well.

Where can you encounter deviation in measurement and frozen pipes?

The two effects discussed here are very common in all kinds of processes with high gas flow rates (>500 l/min), such as:

• Plasma vapour deposition technique; used to provide rotor blades with a coating to make them suitable for high temperatures
• Blast furnaces; to make stainless steel out of conventional steel