Isobaric-isothermal flash calculations are at the heart of any process calculation. In this paper, we propose two new methods for flash calculations at a specified temperature and pressure. The governing equations derived can not only be solved rapidly but also converge correctly even very close to the critical point with the methods presented in this paper. The derived equations show that simplified equations have been used in the past by other workers. The use of full equations results in faster convergence. Two different approaches, the pressure and density-based, are presented in this work.

The density-based approach is particularly useful in reducing the computational time substantially in the case of multiparameter equations of state such as the PC-SAFT and the Helmholtz energy equations of state. Many examples are provided to demonstrate the efficacy of the methods. The methods presented have immediate use in process simulation software and thermodynamic programs.

等压-等温闪蒸计算是任何过程计算的核心。在本文中，我们提出了两种在指定温度和压力下进行闪蒸计算的新方法。用本文提出的方法不仅可以快速求解得到的控制方程，而且即使在非常接近临界点的情况下也可以正确收敛。推导的方程式表明，简化的方程式在过去已被其他工人使用。使用完整的方程式可以加快收敛速度​​。在这项工作中提出了两种不同的方法，即基于压力和基于密度的方法。

在多参数状态方程（例如PC-SAFT和Helmholtz能量状态方程）的情况下，基于密度的方法在减少计算时间方面特别有用。提供了许多实例来证明该方法的有效性。提出的方法可立即用于过程仿真软件和热力学程序中。