Prediction of Nitrogen Thermophysical Property Change under Transcritical Condition in Venturi Tube

Abstract

Radical changes in fluid properties occur near the critical point, which could trigger flow instability in cryogenic fluid machinery for a hydrogen energy-based society. Therefore, more detailed investigations are necessary to understand this instability phenomenon. In this investigation, we conducted CFD analysis of nitrogen flow in a Venturi tube simulating the experimental apparatus that could perform a flow test under transcritical and supercritical conditions. Physical properties of nitrogen were extrapolated by the dataset based on the Helmholtz energy equation of states. In addition, the grid resolution was carefully investigated to grasp fluid properties change in the modeled Venturi tube. In the simulation, we simulated the flow using a coupled solver for compressible CFD simulation for several conditions: Liquid, Supercritical, and Transcritical conditions. Moreover, we also used a segregated solver for the Transcritical condition for the comparison assumed the incompressibility. The simulation results of the Transcritical conditions indicated a more radical change in density and other physical properties than the other conditions, suggesting a flow instability near the critical point. Compared with the incompressible simulation, a temperature diffusion was observed near the critical point, supposed to be induced by sudden changes in specific heat. This research enabled us to establish a simulation method for predicting abrupt changes in physical properties near the critical point.