Some issues related to the modeling of interfacial areas in gas–liquid flows I. The conceptual issues

Jean-Marc Delhaye
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引用次数: 19

Abstract

Two-phase flow modeling has been under constant development for the past forty years. Actually there exists a hierarchy of models which extends from the homogeneous model valid for two-phase flows where the phases are strongly coupled to the two-fluid model valid for two-phase flows where the phases are a priori weakly coupled. However the latter model has been used extensively in computer codes because of its potential in handling many different physical situations.

The two-fluid model is based on the balance equations for mass, momentum and energy, averaged in a certain sense and expressed for each phase and for the interface between the phases. The difficulty in using the two-fluid model stems from the closure relations needed to arrive at a complete set of partial differential equations describing the flow. These closure relations should supply the information lost during the averaging of the balance equations and should specify in particular the interactions of mass, momentum and energy between the phases. Another requirement for the interaction terms is that they should satisfy the interfacial balance equations. Some of these terms such as the added mass term or the lift force term do not depend on the interfacial area but some others do, such as the mass transfer term, the drag term or the heat flux term. It is then necessary to model the interfacial area in order to evaluate the corresponding fluxes. Another benefit resulting from the modeling of the interfacial area would be to replace the usual static flow pattern maps which specify the flow configuration by a dynamic follow-up of the flow pattern. All these reasons explain why so much effort has been put during the past twenty years on the modeling and measurement of the interfacial area in two-phase flows.

This article contains two parts. The first one deals with the conceptual issues and has the following objectives:

    1.

    to give precise definitions of the interfacial area concentrations;

    2.

    to explain the origin of the interfacial area concentration transport equation suggested by M. Ishii in 1975;

    3.

    to explain some paradoxical behaviors encountered when calculating the interfacial area concentration transport velocity.

气液流动界面区域建模的若干问题1 .概念问题
两相流模型在过去的四十年里得到了不断的发展。实际上存在一个层次的模型,从适用于相强耦合的两相流的均匀模型延伸到适用于相先验弱耦合的两相流的双流体模型。然而,后一种模型由于其处理许多不同物理情况的潜力而在计算机代码中广泛使用。双流体模型基于质量、动量和能量的平衡方程,在一定意义上进行平均,并对每个相和相之间的界面表示。使用双流体模型的困难之处在于,要得到一套完整的描述流动的偏微分方程所需要的闭合关系。这些闭合关系应提供平衡方程平均过程中丢失的信息,并应特别说明各相之间质量、动量和能量的相互作用。对相互作用项的另一个要求是它们应满足界面平衡方程。其中一些项,比如附加质量项,或者升力项,不依赖于界面面积,但是其他一些项,比如传质项,阻力项,或者热通量项。为了计算相应的通量,有必要对界面面积进行建模。界面区域建模的另一个好处是用动态跟踪流型来取代通常的静态流型图,后者指定了流型的配置。所有这些原因都解释了为什么在过去的二十年中,人们在两相流界面面积的建模和测量方面付出了如此多的努力。本文分为两部分。第一阶段涉及概念问题,目标如下:给出界面面积浓度的精确定义;2 .解释1975年M. Ishii提出的界面面积浓度输运方程的起源;解释了计算界面浓度输运速度时遇到的一些矛盾行为。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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