Advances in Multiphase Flow and Heat Transfer

The interfacial area concentration is an important parameter to characterize the interfacial transport of mass, momentum and energy. The dynamic modeling approach of interfacial area, namely, the Interfacial Area Transport Equation (IATE) is thus indispensable for an accurate prediction of twophase flows using the two-fluid model. This article reviews the theoretical development of the IATE from two aspects: formulation of the transport equation and modeling of the closures. The first approach to arrive at the IATE is based on the statistical description of a large number of particles using the Boltzmann transport equation. This approach is straightforward to obtain the macroscopic equation of the interfacial area concentration. However, for flows with continuous interface such as annular flow, one has to resort to the second approach, the local instantaneous formulation to derive the macroscopic transport equation. The source and sink terms in the IATE are required to close the problem and they are divided into volume change term, phase change term and particle interaction term. Details on formulating IATE using both approaches and modeling of the closures are discussed.

The study of a single droplet impact and spread on a heated surface is motivated by its strong relevance to spray cooling technology. The generic view on the study of the spray cooling process exhibits the synthesis of fluid mechanics, heat transfer and surface thermodynamics. Due to the complex phenomena involved, no comprehensive theoretical models are available. The few works that appeared in the literature so far have been largely empirical; the applicability of several correlations proposed is limited. This book chapter reports an experimental study of fundamental aspects of the dynamic characteristics of a single droplet impacting on a heated surface. In this experiment, the entire dynamic process of a droplet from the moment of collision with the substrate surface including the rebound was visualized and analyzed using a high-speed CCD camera. The experimental study focused mainly on the spread of a liquid droplet under the influences of substrate temperature varying from 26°C to 240°C, the inclination angle of substrates at 0°, 30°, and 60°, the wettability of substrates with contact angles from 30° to 90°, the viscosity of liquids ranging from 0.00089 up to 0.9161 kg/m.s, and surfactants of different concentrations.

More and more attentions have been paid to better understanding of the mechanisms of multiphase flow and interphase mass transfer on the mesoscale (particle scale), namely about solid particles, bubbles and drops. The behavior of particle swarms and effects of surfactant are subsequently studied to approximate real industrial processes. Besides, the sub-particle scale Marangoni effect, induced by interphase mass transfer, is also studied for seeking measures of mass transfer enhancement. The computational fluid dynamics and computational transport principles are being developed into reliable and efficient tools for improving the macroscopic performances of unit operations and process equipments.

Multiphase flows are very common in the petroleum, chemical, and nuclear industries, oftentimes involving harsh media, strict safety regulations, access difficulties, long distances, and aggressive surroundings; accordingly, there is a need to determine the dispersed phase holdup using noninvasive fast responding techniques. Moreover, knowledge of the flow structure is essential for the assessment of the transport processes involved. The ultrasonic technique fulfills these requirements and could have the capability to provide the information required. In this chapter, the current status of the ultrasonic technique in the context of multiphase flow metering (MFM) is thoroughly reviewed; the focus is on multiphase flows of interest in the oil industry. Specific aspects involving the application of the technique to gas-liquid and gas-liquid-solid flows as well as dispersions and slurries are addressed. It is expected that this chapter will provide the reader with a clear view of what is already known about the application of ultrasonics to multiphase flows, its potential, and the research needs so that the technique could be effectively brought to the field.

Direct Contact Condensation (DCC) is a special mode of condensation where condensation occurs on the interface between steam and water. The condensation of steam injected into water is one of the least studied forms of condensation. Nevertheless, there is a range of devices which rely heavily on effective use of DCC, such as steam driven jet pumps, steam ejectors and safety valves in nuclear reactors. Therefore, correct prediction and modelling of DCC behaviour are crucial to obtain an optimised design of such devices. In this chapter the process of the DCC of steam injected into water is described in details, where different regions of the process will be presented. The process is compared with other modes of condensation and is described as one of the multi-phase flows. In addition, an analytical model for DCC is presented. Furthermore, the chapter focuses on the behaviour of injected steam, commonly termed as a regime. Different regimes of DCC are presented in details and parameters that determine the DCC regime are discussed. A three dimensional condensation regime diagram is presented, where the DCC regime is shown as a function of steam inflow rate, temperature of the water subcooling and steam injector diameter size. After that, the penetration distance of steam into water or a steam plume length is discussed and a two dimensional steam plume length diagram is presented. The diagram shows the length of the steam plume in relation to the steam Reynolds number and the condensation potential.

Addition of small amount of surfactants or polymeric additives may reduce the drag in multiphase flow systems. This chapter presents an overview on the available studies of drag reduction with surfactants and polymeric additives in multiphase flow including gas-liquid two-phase flow, liquid-liquid two-phase flow and gas-liquid-liquid three-phase flow. First, the research background of drag reduction technologies with additives is presented. Then, basic knowledge of drag reduction surfactants and polymeric additives is briefly described. Measured physical properties of surfactant and polymer solutions such as surface tension and viscosity are shown. Next, the drag reduction mechanisms of polymer and surfactant solutions are discussed. The, comprehensive review on the available studies on drag reduction with polymers and surfactants in multiphase flow is presented. The mechanisms are also reviewed. Based on the present review, future research needs are discussed and recommended.

A comparison of the performance of 54 void fraction correlations based on unbiased experimental data set of 3385 data points. A comprehensive literature search was undertaken for the available void fraction correlations and experimental void fraction data for upward and downward vertical and horizontal two-phase flows. The performance of the correlations in correctly predicting the diverse data set was evaluated. Comparisons between the correlations were made and appropriate recommendations were drawn. The analysis showed that most of the correlations developed are very restricted in terms of handling a wide variety of data sets. Based on this analysis void fraction correlations with the best predictive capability are highlighted.