Liquid-Liquid Two-Phase Flow Systems
Flows of two immiscible liquids are encountered in a diverse range of processes and equipments. In particular in the petroleum industry, where mixtures of oil and water are transported in pipes over long distances. Accurate prediction of oil-water flow ch
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General Description of Liquid-Liquid Flows: Flow Patterns
Flows of two immiscible liquids are encountered in a diverse range of processes and equipments. In particular in the petroleum industry, where mixtures of oil and water are transported in pipes over long distances. Accurate prediction of oil-water flow characteristics, such as flow pattern, water holdup and pressure gradient is important in many engineering applications. However, despite of their importance, liquid-liquid flows have not been explored to the same extent as gas-liquid flows. In fact, gas-liquid systems represent a very particular extreme of two-fluid systems characterized by low-density ratio and low viscosity ratio. In liquid-liquid systems the density difference between the phases is relatively low. However, the viscosity ratio encountered extends over a range of many orders of magnitude. Table 1.1 summarizes experimental studies reported in the literature on horizontal oil-water pipe flows, while studies on inclined and vertical systems are summarized in Table 1.2 and 1.3. (The tables can be found at the end of the end of this article before the bibliography). These tables reflect the wide range of physical properties encountered. Moreover, oils and oil-water emulsions may show a Newtonian or non-Newtonian rheological behavior. Therefore, the various concepts and results related to gas-liquid two-phase flows cannot be readily applied to liquid-liquid systems. Diverse flow patterns were observed in liquid-liquid systems. In most of the reported studies the identification of the flow pattern is based on visual observations, photographic/video techniques, or on abrupt changes in the average system pressure drop. In some recent studies, the visual observation and pressure drop measurements are backedup by conductivity measurements, high frequency impedance probes or Gamma densitometers for local holdup sampling, or local pressure fluctuations and average holdup measurements (see Tables 1.1 to 1.3). The flow patterns can be classified into four basic prototypes: Stratified layers with either smooth or wavy interface; Large slugs, elongated or spherical, of one liquid in the other; A dispersion of relatively fine drops of one liquid in the other; Annular flow, where one of the liquids forms the core and the other liquid flows in the annulus. In many cases, however, the flow pattern consists of a combination of these basic prototypes. Sketches of various possible flow patterns observed in horizontal systems are given in Figure 1.1. Stratified flow with a complete separation of the liquids may prevail for some limited range of relatively low flow rates where the stabilizing gravity force due to a finite density difference is dominant (Figure 1.1a). It is possible that one of the layers is discontinuous, and the flow structure is stratified layers of a free liquid and a dispersion of the other liquid (Figure 1.1c-d). With increasing the flow rates, the interface displays a wavy V. Bertola (ed.), Modelling and Experimentation in Two-Phase Flow ©
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