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2018 | Buch

Ferrofluids: Composition and Physical Processes Kapitel lesen Erstes Kapitel lesen

Convection in Ferro-Nanofluids: Experiments and Theory

Physical Mechanisms, Flow Patterns, and Heat Transfer

verfasst von: Aleksandra A. Bozhko, Sergey A. Suslov

Verlag: Springer International Publishing

Buchreihe : Advances in Mechanics and Mathematics

Enthalten in: Springer Professional "Wirtschaft+Technik" , Springer Professional "Technik" , Springer Professional "Wirtschaft"

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SUCHEN

Über dieses Buch

This book covers the experimental and theoretical study of convection in non-isothermal ferro-nanofluids (FNFs). Since FNFs are not transparent and magnetic fields are very sensitive to the shape of the boundary between magnetic and nonmagnetic media, special flow visualization techniques based on the use of thermo-sensitive liquid crystal films, infrared cameras, as well as local and integral temperature sensors are discussed in the book.

This book considers several major configurations of convective chambers and the applied magnetic field. For each of them, the stability boundaries are determined theoretically and experimentally. The physical types of dominant instabilities and the characteristics of their interactions are subsequently established using linear and weakly non-linear hydrodynamic stability analyses and elements of bifurcation theory. The book also discusses the potential of using magnetically controlled ferro-nanofluids as a heat carrier in situations where heat removal by natural convection is not possible due to the lack of gravity (orbital stations) or extreme confinement (microelectronics).

Researchers and practitioners working in the areas of fluid mechanics, hydrodynamic stability, and heat and mass transfer will benefit from this book.

Inhaltsverzeichnis

Frontmatter
Chapter 1. Ferrofluids: Composition and Physical Processes
Abstract
A brief history and an overview of the current state of knowledge of ferrofluids (also known as ferrocolloids or ferro-nanofluids) are given. Applications of ferrofluids as advanced heat carrier media in heat management systems are emphasised. It is discussed that in the absence of a magnetic field, ferrofluids can be considered as a type of synthesised nanofluids or ordinary colloids. However, when they are placed in an external magnetic field, they behave as magneto-polarisable media, the magnetic susceptibility of which is several orders of magnitude larger than that of natural fluids and gases. Various physical mechanisms of heat and mass transfer in ferrofluids are identified. It is shown that the macroscopic behaviour of ferrofluids is strongly affected by their microstructure that depends on the way they are synthesised, stored and used.
Aleksandra A. Bozhko, Sergey A. Suslov
Chapter 2. Governing Equations
Abstract
In this chapter the equations describing flows of non-isothermal ferrofluids and the corresponding boundary conditions are summarised. The main physical assumptions under which these equations are valid are discussed, and references to further reading are given. The constitutive equations for ferrofluid magnetisation are also reviewed. It is emphasised that commonly used Langevin’s magnetisation law may be inaccurate in the case of non-isothermal ferrofluids, and thus the second-order modified mean-field model is preferred. Subsequently, the nondimensional form of equations is introduced, and the major governing nondimensional parameters in terms of which the results are presented throughout the manuscript are defined, and their physical meaning is identified.
Aleksandra A. Bozhko, Sergey A. Suslov
Chapter 3. Theory of Thermogravitational and Thermomagnetic Convection in an Infinite Vertical Layer of Homogeneous Ferrofluid
Abstract
The chapter discusses results of hydrodynamic stability analysis of non-isothermal ferrofluid flow arising between two parallel infinite plates maintained at different temperatures and placed in a uniform external magnetic field of various orientations. To distinguish between gravitational and magnetic buoyancy effects in the most straightforward way, the vertical layer configuration with the downward gravity is chosen while magnetic field is applied in the direction perpendicular to the layer or under a small angle with respect to the normal to the layer. In the absence of the gravity, such a configuration reduces to magnetic Rayleigh-Bénard problem. Comprehensive linear and weakly nonlinear stability results are presented. The existence of multiple three-dimensional convection patterns is demonstrated, and symmetry breaking effects of nonlinear fluid magnetisations are emphasised.
Aleksandra A. Bozhko, Sergey A. Suslov
Chapter 4. Experimental Methodology
Abstract
The methodology of experimental investigation of thermogravitational and thermomagnetic convection in ferrofluids is discussed. The necessary physical conditions for the observation of thermomagnetic convection in external uniform magnetic field are identified. The methods of registering heat fluxes and visualising convection flow patterns in nontransparent ferrofluids are discussed. Various designs of experimental chambers, sensors and measuring devices are presented, and the main features distinguishing the behaviour of magneto-polarisable fluids from that of their non-magnetic counterparts are highlighted. Specifically, the influence of the working chamber geometries, sizes and boundaries on the distribution of a magnetic field inside cavities and thus on the characteristics of the arising convective flows and heat transfer is emphasised.
Aleksandra A. Bozhko, Sergey A. Suslov
Chapter 5. Experimental Investigation of Thermogravitational Convection in Ferrofluids
Abstract
Specific features of thermogravitational instability and thermogravitational flows arising in ferrofluids are discussed. It is shown that in contrast to ordinary fluids, the characteristics of convection setting in ferrofluids depend on the history of its storage and the conditions of experiment. This is found to be due to a complex composition of ferrocolloids containing carrier fluid, solid particles, their aggregates and surfactant that make them essentially multiphase systems. The results of a comprehensive experimental study of convective heat transfer and flow patterns arising in such fluids when they are non-uniformly heated are presented. Spatially and temporally chaotic ferrofluid flows similar to those previously found in gases and binary mixtures are detected in close proximity of the convection onset. In particular, regimes are detected where convection sets and decays spontaneously drastically changing heat transfer across the domain occupied by the fluid. It is noted that the possibility of such a behavior of nanofluids must be taken into account to avoid malfunction of advanced heat exchangers make use of nanofluids as working media.
Aleksandra A. Bozhko, Sergey A. Suslov
Chapter 6. Experimental Investigation of Thermomagnetic Convection in Ferrofluids
Abstract
The thermomagnetic mechanism of convection is considered at various orientations of the applied uniform magnetic field with respect to the temperature gradient and of the fluid layer with respect to the gravity. Its interaction with the thermogravitational mechanism is discussed. Experimental maps of stability convection-free states are obtained. Heat transfer in a magnetic field is studied as a function of fluid properties and experimental control parameters. The dependence of spatio-temporal evolution of convection flows on the strength of the applied field, the magnitude of the temperature gradient and fluid layer inclination with respect to the gravity is investigated. The conditions leading to stabilisation and destabilisation of convection-free states in non-isothermal ferrofluids placed in a magnetic field are determined. Factors influencing the onset of convection and convection flows in finite enclosures filled with realistic ferrofluids are listed, and their overall effect that is currently beyond the reach of theoretical treatment is demonstrated experimentally.
Aleksandra A. Bozhko, Sergey A. Suslov
Chapter 7. Concluding Remarks
Abstract
A brief summary of the book is presented in this chapter.
Aleksandra A. Bozhko, Sergey A. Suslov
Backmatter
Metadaten
Titel
Convection in Ferro-Nanofluids: Experiments and Theory
verfasst von
Aleksandra A. Bozhko
Sergey A. Suslov
Copyright-Jahr
2018
Electronic ISBN
978-3-319-94427-2
Print ISBN
978-3-319-94426-5
DOI
https://doi.org/10.1007/978-3-319-94427-2