Abstract In this work, we have incorporated a crossover equation of state into the pseudopotential multiphase Lattice Boltzmann model (LBM) to improve the prediction of thermodynamic properties of fluids and their flow in near-critical and supercritical regions. Modeling carbon dioxide (CO2) properties in these regions is of increasing interest for industrial processes such as CO2 storage and heat transfer where CO2 is used as a working fluid. Despite the importance of accurately modeling near-critical and supercritical fluids, popular classical cubic equations of state (EoS) are not accurate. The proposed crossover EoS is a proven hybrid equation which uses the original classical EoS far from the critical point where it is valid, and near the critical point, it asymptotically switches to using non-analytic scaling laws. It also transforms into the ideal gas EoS as the density approaches zero. In order to demonstrate the validity and versatility of the crossover approach in the prediction accuracy of LBM in near-critical flows, this formulation was incorporated into the Peng-Robinson (P-R) EoS. First, 2D static droplets of CO2 and water at vapor-liquid equilibrium were modeled using both P-R EoS and its crossover formulation, and the numerically predicted results were then compared against the experimental data. The results demonstrate that the model accuracy in representing the thermodynamic behavior of the fluid in near-critical region is improved after adopting the crossover formulation with respect to the classical analytical EoS. The crossover P-R EoS was further applied to study several two-phase CO2 flows in mini-channels at near-critical temperatures. The flow patterns showed a good qualitative agreement with the experimental data in the near-critical region. The study is further extended to multi-component multiphase systems, specifically to water droplet penetration into porous media filled with CO2.

中文翻译：

---

近/超临界 CO2 流的格子 Boltzmann 模拟具有状态方程的交叉公式

摘要 在这项工作中，我们在赝势多相格子玻尔兹曼模型 (LBM) 中加入了一个交叉状态方程，以改进对近临界和超临界区域中流体及其流动的热力学性质的预测。对这些区域中的二氧化碳 (CO2) 特性进行建模，对于使用 CO2 作为工作流体的 CO2 储存和传热等工业过程越来越感兴趣。尽管准确模拟近临界和超临界流体很重要，但流行的经典三次状态方程 (EoS) 并不准确。提出的交叉 EoS 是一个经过验证的混合方程，它使用原始经典 EoS 远离其有效的临界点，并在临界点附近渐近地切换到使用非解析缩放定律。当密度接近零时，它也会转变为理想的气体 EoS。为了证明交叉方法在近临界流中 LBM 预测精度方面的有效性和通用性，该公式被纳入 Peng-Robinson (PR) EoS。首先，使用 PR EoS 及其交叉公式对处于汽液平衡状态的 CO2 和水的二维静态液滴进行建模，然后将数值预测结果与实验数据进行比较。结果表明，在采用相对于经典分析 EoS 的交叉公式后，表示近临界区域流体热力学行为的模型精度得到了提高。交叉 PR EoS 进一步应用于研究接近临界温度下微型通道中的几种两相 CO2 流动。流动模式与近临界区域的实验数据显示出良好的定性一致性。该研究进一步扩展到多组分多相系统，特别是水滴渗透到充满 CO2 的多孔介质中。