Development of counter-current flow limitation model applicable to a sharp-edged liquid entrance
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Development of Counter-Current Flow Limitation Model Applicable to a Sharp-Edged Liquid Entrance Ji Hwan Jeong Dept. o f Environmental Management, Cheonan College of Foreign Studies, Anseo-dong, Cheonan, Choongnam 330-705, Korea (Received 22 Men, 2001 9 accepted 28 .hdy 200t)
Abstract-There are many industrial machines that fimction b5, operation of multi-pha~ fluids. Some of them take advantage of the charaeteristics of counter-currant two-phase flow. The maximum flow rates of gas and liquid phases which flow in opposite-directions t counter-current flow) are limited by a phenomenon known as a Counter-Current Flow Limitation (CCFL or floodingI. The mass and momentum con~rvation equations for two phases were established to build a system of first-order partial derivative equations (PDE), A new CCFL modeI was developed based on the characteristic equation of the first-order PDE system. The present model applies m the case in which a non-unitbnn flow is deveIoped around a square or sharp-edged entrance of liquid phase, The model can be used u) predict the operating-limit of components in which mass and heat transfer are taking place between liquid and gas phases. Key words: CCFL. Flooding, Counte>Current Flow. Hyperbolic System, Characteristic Equation
INTRODUCTION
Since this characteristic of the CCFL phenomenon sets an operation limit of chemical process plants in which heat and mass transfer occur between gas and liquid phases, chemical engineers began investigating this phenomenon around five decades ago. Nowadays, chemical engineers are interested in flooding since packed columns [Hart and Hong, 19981 and structured packings [Cho et al, 1995] have beeu widely adopted by the chemical and allied industries. Also, the CCFL phenomenon is of importance in the field of safety analysis of nuclear power plants (NPPs) as it prevents the emergency core cooling system (ECCS) of NPPs from performing its function successfully. CCFL phenomena have been investigated in analytical as well as experimental ways so that many models have been developed, The analytical models can be categorized in three groups as follows:
A laJge number of industrial systems adopt a countel:curreat twophase flow configuralion in which the gas phase flows upwards and the liquid phase downwards. In order to achieve maximum flow rates of counter-current two-phase flow with a fixed pumping power, each phase should flow separately, if a circular flow path is vertically installed, the dominant flow patlern would be an mnular flow regime. Let us assume an annular flow regime in which a water film flows dovmwards along the inside of a circular pipe and a gas slream flows upwards along the central region surrounded by the liquid film, With low gas and liquid flow rates, two separate fluids flow preserving annular flow regime. When gas flow rate increases, the interracial friction between two phases increases and waves are developed on the interface. Sine waves with small amplitude and various wavelengths are initially generated in the upper part of the t
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