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1. Introduction
Subcooled boiling flows are encountered in many industrial applications such as boilers, nuclear reactors, and the new generation of electronic and computer systems. There have been many efforts to understand and model subcooled boiling flow. In the field of nuclear Engineering, subcooled boiling flows have been studied as an important issue in the optimum design and safety of nuclear systems because the presence of vapor bubbles has a large effect on the heat transfer characteristics of a nuclear system as well as pressure drops, flow nstability, etc. However, subcooled boiling flow is very difficult to understand due to the complex behavior of bubbles with heat and mass transfer through the bubble interface. Therefore, in order to understand subcooled boiling flow, which is a challenging problem, it is essential to acquire thorough knowledge on condensing bubbles.

1 引言

过冷沸腾流是在许多工业应用，如锅炉，遇到的核反应堆，以及电子和计算机系统的新一代。已经有很多的努力去了解和模型的过冷流动沸腾。在核工程领域，过冷沸腾流动进行了研究，为优化设计和核系统安全的一个重要问题是由于气泡的存在以及压力下降，流量nstability，等。然而在核系统的传热特性有很大的影响，是理解通过过冷流动沸腾气泡界面的传热传质泡沫的复杂的行为很难。因此，为了了解过冷流动沸腾，这是一个具有挑战性的问题，它是对冷凝泡沫获得透彻的知识本质。

There have been many experimental analyses on bubble behavior. In these experimental studies, bubble behavior regarding the bubble size, shape, velocity and moving trajectory was investigated in various conditions. However, it has been impossible to obtain complete information about the bubble behavior due to the existence of the bubble interface between the vapor and liquid phases. The shape and the area of the varying interface, which governs the behavior of each phase, are very complex and thus difficult to measure. Moreover, in subcooled boiling flow, bubble condensation significantly affects the change of interface so this complicates the analysis of the behavior of condensing bubbles even more. Therefore, it is necessary to carry out numerical simulations for bubble behavior as a complement to experiments. Such numerical simulations may contribute to a better physical understanding of complex phenomena regarding the behavior of condensing bubbles.

One of the numerical methods for bubble simulation is the volume of fluid (VOF) model proposed by Hirt and Nichols (1981) . It can deal with immiscible fluids with clearly defined interface; the direct simulation of the varying interface is possible. Many numerical studies have analyzed bubble behavior in terms of the bubble size, bubble shape, rise trajectory and bubble velocity using the VOF model. Tomiyama et al. (1991a ), Wachem and Schouten (2002) , L ¨orstad and Fuchs (2004), and Gopala and Wachem (2008)examined the applicability of the VOF model to the analysis of a single rising bubble in liquid. These examinations confirmed that the VOF model can yield good predictions of the bubble shape and terminal velocity. The VOF model also has been used to analyze the following: the effect of a channel wall on bubble shapes and terminal velocities (Tomiyama et al., 1991b); the velocity distribution and the distribution of the local wall shear stress in slug flow (Taha and Cui, 2006); the effect of the liquid velocity field on bubble motion in a linear shear flow (Tomiyama et al. 1993); the traj本论文由英语论文网提供整理，提供论文代写，英语论文代写，代写论文，代写英语论文，代写留学生论文，代写英文论文，留学生论文代写相关核心关键词搜索。