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Description
Thermo-acoustic oscillations (Taconis oscillations) are the characteristic phenomenon for the cryogenic systems, where one end of the pipe is in continuous contact with the extremely cold process fluid and the second end of the pipe is directly exposed to the warm ambient temperature. As warmer fluid has the smaller density and therefore arises, the warm end is normally placed at the top and the cold end at the bottom. The reason behind is that in that way the fluid mixing is limited, and convection heat is reduced. However, under several specific conditions the layers of fluid can start to oscillate between warm and cold end, bringing an enormous heat load to the cold system (up to 1000 times larger than without oscillations). This phenomenon is very undesirable as it not only affects the cryogenic process due to heat input, but also causes the freezing of the external surfaces of the installation.
Systems operating with supercritical liquid or superfluid helium are the most vulnerable to the occurrence of thermo-acoustic oscillations, as the driving force for the phenomenon is the warm-cold end temperature ratio. Other factors that have a decisive role if oscillations appear or not, are: the ratio of warm-to-cold space of the pipeline, the volume occupied by the fluid inside (in particular the diameter-length combination), the length of the pipeline itself, the operating parameters of the fluid and its properties. It should be emphasized, that the mentioned factors favor the occurrence of thermo-acoustic oscillations but do not indicate conclusively whether it will in fact occur or not; from this reason the designer of the cryogenic installation should assess the risk of the oscillations on a case-by-case basis.
Cryogenic valves in combination with unfavorable operating conditions are vulnerable to the occurrence of thermo-acoustic oscillations. However, undertaking the appropriate precautions can reduce or completely abolish the probability of their appearance. This publication illustrates different possibilities to avoid or reduce the risk of thermo-acoustic oscillations in the plant.
| Submitters Country | Switzerland |
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