Abstract

On this paper the authors present a unified EOS for Helium 4 below its liquidation and towards absolute zero. While such EOS’s exist in the literature, they are divided to different region depending on temperatures and pressures, but in this work an overall equation has been created using all the available data and different methods. Thus, the provided equations offer a solid point of reference for any cryogenic engineering applications as they cover to a very high accuracy all the known data and combine them in a ready to use form for any application. Additionally, because of the availability and continuity of the equations covering the entire Fluid, Superfluid and Lambda spectrum thermodynamic maps can now be created for both Helium 4, giving the tools to directly study thermodynamic cycles on maps as done in higher temperatures. The equations that describe the thermodynamic characteristics are offered in two different forms, one of high accuracy with large number of terms, and one with lesser but adequate accuracy with less terms to be used for quicker calculations. Overall, this set of equations can be used to describe the working medium in any cryogenic application using Helium 4 without the need to differentiate one’s models and equations depending on the temperature and pressure regions, meaning that the same model can be used to describe even different phases of Helium 4 in the same application.

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