Preface

Multiphase flow and heat transfer have been found a wide range of applications in nearly all aspects of engineering and science fields such as mechanical engineering, chemical and petrochemical engineering, nuclear engineering, energy engineering, material engineering, ocean engineering, mineral engineering, electronics and micro-electronics engineering, information technology, space technology, micro- and nano-technologies, bio-medical and life science etc. With the rapid development of various relevant technologies, the research of multiphase flow and heat transfer is growing very fast nowadays than ever before. It is highly the time to provide a vehicle to present the state-of-the-art knowledge and research in this very active field.

To facilitate the exchange and dissemination of original research results and state-of-the-art reviews pertaining to multiphase flow and heat transfer efficiently, we have proposed the eBook series entitled Advances in Multiphase Flow and Heat Transfer to present state-of-the-art reviews/technical research work in all aspects of multiphase flow and heat transfer fields by inviting renowned scientists and researchers to contribute chapters in their respective research interests. The eBook series have now been launched and two volumes have been planned to be published per year since 2009. The e-books provide a forum specially for publishing these important topics and the relevant interdisciplinary research topics in fundamental and applied research of multiphase flow and heat transfer. The topics include multiphase transport phenomena including gas-liquid, liquid-solid, gas-solid and gas-liquid-solid flows, phase change processes such as flow boiling, pool boiling, and condensation etc, nuclear thermal hydraulics, fluidization, mass transfer, bubble and drop dynamics, particle flow interactions, cavitation phenomena, numerical methods, experimental techniques, multiphase flow equipment such as multiphase pumps, mixers and separators etc, combustion processes, environmental protection and pollution control, phase change materials and their applications, macro-scale and micro-scale transport phenomena, micro- and nano-fluidics, micro-gravity multiphase flow and heat transfer, energy engineering, renewable energy, electronic chips cooling, data-centre cooling, fuel cell, multiphase flow and heat transfer in biological and life engineering and science etc. The eBook series do not only present advances in conventional research topics but also in new and interdisciplinary research fields. Thus, frontiers of the interesting research topics in a wide range of engineering and science areas are timely presented to readers.

In volume 4, there are seven chapters on various topics relevant to multiphase flow and heat transfer.

Chapter 1 deals with modeling of interfacial area transport in two-phase flows. 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 two-phase flows using the two-fluid model. This chapter 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.

Chapter 2 presents an experimental study on dynamic behavior of liquid droplet impacting on heated surfaces. 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 eBook 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.

Chapter 3 deals with numerical simulation of multiphase flow and interface mass transfer on particle scale. 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.

Chapter 4 deals with the use of the ultrasonic technique for the study and online monitoring of multiphase Flows.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.

Chapter 5 presents a topic on direct contact condensation (DCC) of steam injected into water – new developments in condensation regime and steam plume length prediction. 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.

Chapter 6 presents a comprehensive review on drag reduction with surfactants and polymeric additives in multiphase flow. 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.

Chapter 7 deals with an investigation on void fraction and flow patterns of two-phase flow in upward and downward vertical and horizontal pipes. 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.

As the founding editors of the eBook series, we are very happy to see that the e-books have been available to our readers since 2009 (two volumes per year). All the chapters have been reviewed by experts in the relevant areas. We are very much grateful to the authors who have contributed to the chapters and the reviewers who took their time and energy for their review. It is our great wishes if the eBook series are able to provide useful knowledge for our community and to facilitate the progress of the research in the field of multiphase flow and heat transfer.

We would like to express our gratitude to our families for their great support to our work on the eBook series.