Applicability of equations of state for modeling helium systems

Proper design of helium systems with large number of components and involved configurations such as helium liquefiers/refrigerators requires the use of tools like process simulators. The accuracy of the simulation results, to a great extent, depends on the accuracy of property data. For computation of thermodynamic properties of helium, the 32-parameter MBWR equation of state proposed by McCarty and Arp [1] is widely used. However, it is computationally involved, makes the simulation process more time-consuming and sometimes leads to computational difficulties such as numerical oscillations, divergence in solution especially, when the process operates over a wide thermodynamic region and is constituted of many components. Substituting MBWR EOS by simpler equations of state (EOS(s)) at selected thermodynamic planes, where the simpler EOS(s) have the similar accuracy as that of MBWR EOS may enhance ease of computation. In the present paper, the methodology to implement this concept has been elucidated with examples of steady state and dynamic simulation of helium liquefier/refrigerator based on Collins cycle. The above concept can be applied to thermodynamic analysis of other process cycles where computation of fluid property is involved.

► Highly non-linear MBWR EOS causes divergence in simulation and increases computational complexities.
► Alternatives suggested for the involved MBWR equations of state (EOS) for helium in simulations.
► Based on accuracy, applicability of each EOS in specific thermodynamic regions identified.
► Proposed the concept of using more than one EOS for helium in a single simulation.
► Implications of accuracy of computation showed by steady state and dynamic simulations.