Performance evaluation of equations of state for typical cryogens two-phase simulation by pseudopotential lattice Boltzmann method

The pseudopotential lattice Boltzmann (LB) method has significant advantages in the simulation of liquid-vapor two-phase flow and phase-transition behavior of cryogenic fluids. However, prior research on multiphase flows employing the LB method primarily utilizes the cubic Peng-Robinson equation of state, which has limited accuracy in predicting thermodynamic properties of fluids, in particular for cryogens. This study presents a thermodynamic perspective on the performance of different equations of state in LB simulations, including high-precision equations of state such as those in Helmholtz energy form and the modified Benedict-Webb-Rubin equation of state. The performance of various equations of state within the entire two-phase region, ranging from the triple-point temperature to the critical-point temperature, is comparatively evaluated. It is found that the two-phase region characteristics of equations of state, which are often overlooked in traditional thermodynamics, significantly impact simulation stability. The feasibility and superiority of high-precision equations of state in simulating cryogenic fluids are further substantiated through analysis in three key aspects: liquid-vapor coexistence density, surface tension, and spurious velocity.