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Über dieses Buch

This book covers aspects of multiphase flow and heat transfer during phase change processes, focusing on boiling and condensation in microscale channels. The authors present up-to-date predictive methods for flow pattern, void fraction, pressure drop, heat transfer coefficient and critical heat flux, pointing out the range of operational conditions that each method is valid. The first four chapters are dedicated on the motivation to study multiphase flow and heat transfer during phase change process, and the three last chapters are focused on the analysis of heat transfer process during boiling and condensation. During the description of the models and predictive methods, the trends are discussed and compared with experimental findings.

Inhaltsverzeichnis

Frontmatter

Chapter 1. Introduction

Abstract
This chapter describes a short historical background concerning the literature focused on multiphase flow and heat transfer during phase change processes. It also addresses the advantages and challenges of modelling and analyzing processes of fluid flow and heat transfer with more than one phase.
Subsequently, the advantages and drawbacks of using microscale heat management devices are addressed along the chapter, showing that the same heat transfer rate can be dissipated or absorbed with much lower refrigerant mass and heat exchanger area, maintaining the pumping power.
The characteristics of typical working fluids, as well as fluids with potential to be used in these types of equipment, are also discussed.
After finishing this chapter, the student should be able to identify conditions where multiphase flows are present, and will have learned how to recognize the main aspects responsible for differing heat transfer with phase change from single-phase convection.
Fabio Toshio Kanizawa, Gherhardt Ribatski

Chapter 2. Fundamentals

Abstract
General aspects related to the fundamentals of two-phase flow and flow boiling and condensation, necessary for the development of the next chapters, are detailed in this chapter.
The main parameters related to two-phase flow are defined, focusing on conditions of liquid and vapor simultaneous flow, such as characterization and definition of flow patterns, and phases velocities and fractions.
A discussion about void fraction is also addressed, presenting the main predictive models and methods in a didactical way, finishing with a comparison among the methods.
This chapter also presents discussions about fundamental aspects of flow boiling and condensation, describing the flow topology evolution during the phase change process.
It also presents the methods to characterize channels according to its size as micro or macroscale according to distinct approaches.
After finishing this chapter, the student should be able to understand the main parameters that characterize multiphase flows, with and without heat transfer, as well as be able to select a proper method for void fraction estimation. Additionally, the reader should have a general idea of the variation of flow characteristics during flow boiling and condensation along a channel.
Fabio Toshio Kanizawa, Gherhardt Ribatski

Chapter 3. Flow Patterns

Abstract
This chapter addresses subjective and objective experimental methods for flow pattern classification usually adopted in experimental studies.
Subsequently, classical prediction methods for flow pattern transitions in conventional channels are presented since they are used as the basis for the development of predictive methods for microscale channels. This description comprises the classical methods of Taitel and Dukler (AIChE J 22(1):47–55, 1976) and Taitel, Barnea, and Dukler (AIChE J 26(3):345–354, 1980) for horizontal and vertical upward flows, respectively, as well as other methods.
In continuation to Sect. 2.​2, this chapter details the difference between flow pattern transition criteria in micro and macroscale conditions, and the flow pattern differences for in-tube convective boiling and condensation. Therefore, based on the highlighted differences, predictive methods for flow patterns during boiling and condensation are described, comprising conditions of macro and microscale channels.
After finishing this chapter, the student should be able to classify a flow pattern identification method as subjective or objective. Additionally, the student will be aware of the dominant mechanisms for flow pattern transition and will be able to select an appropriate predictive method for flow patterns (or flow pattern transitions) depending on the operational conditions.
Fabio Toshio Kanizawa, Gherhardt Ribatski

Chapter 4. Pressure Drop

Abstract
This chapter begins with the characterization of the pressure drop parcels during two-phase flow based on separated phase approaches, based on which it can be identified that void fraction is a very important parameter for estimation of accelerational and gravitational pressure drop parcels.
Despite this aspect, it is shown that estimating the frictional pressure drop parcel during two-phase flow by solving the fluid mechanic problem is very difficult, or even impossible in several cases; therefore, a discussion about trends for pressure drop during two-phase flow in macro and microscale channels is presented. In this discussion, the effects of distinct parameters, such as mass flux and vapor quality, are described.
Subsequently, the main predictive methods for the frictional pressure drop parcel are described, which comprises the homogeneous model, two-phase multiplier-based methods, empirical methods, and mechanistic methods.
After finishing this chapter, the student should be able to properly address all the pressure drop parcels and select appropriate predictive methods to estimate the frictional pressure drop parcel.
Fabio Toshio Kanizawa, Gherhardt Ribatski

Chapter 5. Flow Boiling

Abstract
This chapter addresses the analysis of flow boiling, which in turn depends on concepts of nucleate boiling. Hence, it begins with a discussion about the main mechanisms and phenomena during pool boiling, addressing the criteria for bubble nucleation and growth. Subsequently, the boiling curve is discussed, presenting the boiling regimes that can be observed during evaporation of liquid in contact with a surface.
Subsequently, the heat transfer coefficient characteristics during in-tube flow are discussed, inferring the expected trends according to distinct operational conditions.
Finally, predictive methods for the heat transfer coefficient during flow boiling are described, which comprises mostly methods that are based on the combination of nucleate boiling and convective effects. Nonetheless, methods using an approach similar to two-phase multipliers are also described, as well as a mechanistic methods, which are based on the prior identification of the local flow patterns, and then the heat transfer coefficient is modelled for each flow pattern. The chapter finishes describing a new approach to evaluate heat transfer coefficient during flow boiling under transient conditions of heat flux.
After finishing this chapter, the student should be able to identify the dominant mechanisms during flow boiling, as well as select proper predictive methods for heat transfer coefficient depending on the operational conditions.
Fabio Toshio Kanizawa, Gherhardt Ribatski

Chapter 6. Critical Heat Flux and Dryout

Abstract
The critical heat flux (CHF) was briefly introduced in Chap. 5, and in the present chapter, the analyses of studies concerning CHF is deepened.
Firstly, the classical hydrodynamic and macrolayer models are described, which includes the dominant mechanisms and resulting relationships for CHF. The predictions according to these models are valid for boiling conditions on horizontal surfaces exposed to stagnant liquid.
Then, models and methods to predict CHF during flow boiling are also addressed, including the classical Katto and Ohno (Int J Heat Mass Transf 27:1641–1648, 1984) method, as well as methods that were published more recently. Predictive methods focused on CHF estimation for flow boiling in microscale channels are also described.
After finishing this chapter, the student should be able to discuss the main mechanisms that lead to CHF inception, as well as be able to select CHF predictive methods depending on the operational conditions.
Fabio Toshio Kanizawa, Gherhardt Ribatski

Chapter 7. Condensation

Abstract
This chapter presents and discusses the heat transfer mechanisms during convective condensation inside conventional and microscale channels. It begins with the description of the vapor condensation process on an isothermal flat surface, which was first derived by Nusselt. This description is important by itself, but also to infer the main non-dimensional parameters related to gravitational parcel of heat transfer during flow condensation.
The effects of distinct operational parameters, such as mass flux, saturation temperature, wall and fluid temperature difference, and vapor quality on the heat transfer coefficient are also addressed. Heat transfer coefficient prediction methods for the heat transfer coefficient for condensations inside conventional and microscale channels are also presented and critically compared.
After finishing this chapter, the student should be able to infer the dominant mechanisms during convective condensation inside channels as well as select proper predictive methods depending on the operational conditions.
Fabio Toshio Kanizawa, Gherhardt Ribatski

Backmatter

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