Deiters Ulrich K, Bell Ian H
Institute of Physical Chemistry, University of Cologne, Köln, Germany.
Applied Chemicals and Materials Division, National Institute of Standards and Technology, Boulder, Colorado.
AIChE J. 2019;65. doi: 10.1002/aic.16730.
Two-dimensional cross-sections of the phase envelopes of fluid mixtures-in particular isotherms, isobars, and isopleths-are often computed point-by-point by incrementing a so-called marching variable and solving the equilibrium conditions at each step. The marching variable is usually pressure, temperature, or a mole fraction, depending on the application. These isolines, however, can have rather complicated shapes, so that a simple unidirectional "sweep" of the marching variable often gives merely a part of the desired isoline. It is then necessary to restart the sweep with different initial values, or to switch to another marching variable. This, however, makes it difficult to compute complete isolines automatically, without human interference. We propose here a new marching technique through which it is possible to follow isolines of arbitrary shape and thus to compute complete isolines, as long as they are contiguous.
流体混合物相包络的二维横截面——特别是等温线、等压线和等组成线——通常通过增加一个所谓的步进变量并在每一步求解平衡条件来逐点计算。根据应用情况，步进变量通常是压力、温度或摩尔分数。然而，这些等值线可能具有相当复杂的形状，以至于对步进变量进行简单的单向“扫描”通常只能得到所需等值线的一部分。然后有必要用不同的初始值重新开始扫描，或者切换到另一个步进变量。然而，这使得在没有人工干预的情况下自动计算完整的等值线变得困难。我们在此提出一种新的步进技术，通过该技术可以跟踪任意形状的等值线，从而计算完整的等值线，只要它们是连续的。
