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1999 | Buch | 2. Auflage

Convection in Porous Media

verfasst von: Donald A. Nield, Adrian Bejan

Verlag: Springer New York

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Über dieses Buch

Papers on convection in porous media continue to be published at the rate of over 100 per year. This indication of the continued importance of the subject, together with the wide acceptance of the first edition, has encouraged us to prepare an expanded second edition. We have retained the basic structure and most of the text of the first edition. With space considerations in mind, we have been selective in our choice of references, but nevertheless there are over 600 new references. We also made an effort to highlight new conceptual developments and engineering applications. In the introductory material, we judged that Chapters 2 and 3 needed little alteration (though there is a new Section 2.6 on other approaches to the topic), but our improved understanding of the basic modeling of flow through a porous medium has led to a number of changes in Chapter 1, both within the old sections and by the addition of a section on turbulence in porous media, and a section on fractured media, deformable media, and complex porous structures. In Chapter 4, on forced convection, we have added major new sections on compact heat exchangers, on heatlines for visualizing convection, and on constructal tree networks for the geometric minimization of the resistance to volume-to-point flows in heterogeneous porous media.

Inhaltsverzeichnis

Frontmatter
1. Mechanics of Fluid Flow Through a Porous Medium
Abstract
By a porous medium we mean a material consisting of a solid matrix with an interconnected void. We suppose that the solid matrix is either rigid (the usual situation) or it undergoes small deformation. The interconnectedness of the void (the pores) allows the flow of one or more fluids through the material. In the simplest situation (“single-phase flow”) the void is saturated by a single fluid. In “two-phase flow” a liquid and a gas share the void space.
Donald A. Nield, Adrian Bejan
2. Heat Transfer Through a Porous Medium
Abstract
In this chapter we focus on the equation that expresses the first law of thermodynamics in a porous medium. We start with a simple situation in which the medium is isotropic, and where radiative effects, viscous dissipation, and the work done by pressure changes are negligible. Very shortly we shall assume that there is local thermal equilibrium so that T s = T f = T, where T s and T f are the temperatures of the solid and fluid phases, respectively. More complex situations will be considered in Section 6.5. Here we also assume that heat conduction in the solid and fluid phases takes place in parallel so that there is no net heat transfer from one phase to the other.
Donald A. Nield, Adrian Bejan
3. Mass Transfer in a Porous Medium: Multicomponent and Multiphase Flows
Abstract
The term “mass transfer” is used here in a specialized sense, namely the transport of a substance that is involved as a component (constituent, species) in a fluid mixture. An example is the transport of salt in saline water. As we shall see below, convective mass transfer is analogous to convective heat transfer.
Donald A. Nield, Adrian Bejan
4. Forced Convection
Abstract
The fundamental question in heat transfer engineering is to determine the relationship between the heat transfer rate and the driving temperature difference. In nature, many saturated porous media interact thermally with one another, and with solid surfaces that confine them or are embedded in them. In this chapter we analyze the basic heat transfer question by looking only at forced convection situations, in which the fluid flow is caused (forced) by an external agent unrelated to the heating effect. First we discuss the results that have been developed based on the Darcy flow model, and later we address the more recent work on the non-Darcy effects. We end this chapter with a review of current engineering applications of the method of forced convection through porous media.
Donald A. Nield, Adrian Bejan
5. External Natural Convection
Abstract
Numerical calculation from the full differential equations for convection in an unbounded region is expensive, and hence approximate solutions are important. For small values of the Rayleigh number Ra, perturbation methods are appropriate. At large values of Ra thermal boundary layers are formed, and boundary layer theory is the obvious method of investigation. This approach forms the subject of much of this chapter. We follow, to a large extent, the discussion by Cheng (1985a).
Donald A. Nield, Adrian Bejan
6. Internal Natural Convection: Heating from Below
Abstract
We start with the simplest case, that of zero flow through the fluid-saturated porous medium.For an equilibrium state the momentum equation is satisfied if
$$- \nabla P + \rho fg = 0$$
(6.1)
.
Donald A. Nield, Adrian Bejan
7. Internal Natural Convection: Heating from the Side
Abstract
Enclosures heated from the side are most representative of porous systems that function while oriented vertically, as in the insulations for buildings, industrial cold-storage installations, and cryogenics. As in the earlier chapters, we begin with the most fundamental aspects of the convection heat transfer process when the flow is steady and in the Darcy regime. Later, we examine the special features of flows that deviate from the Darcy regime, flows that are time-dependent, and flows that are confined in geometries more complicated than the two-dimensional rectangular space shown in Fig. 7.1.
Donald A. Nield, Adrian Bejan
8. Mixed Convection
Abstract
Since we have dealt with natural convection and forced convection in some detail, our treatment of mixed convection can be brief. It is guided by the review paper by Lai et al. (1991a). We start with a treatment of boundary layer flow on heated plane walls inclined at some nonzero angle to the horizontal.
Donald A. Nield, Adrian Bejan
9. Double-Diffusive Convection
Abstract
In this chapter we turn our attention to processes of combined (simultaneous) heat and mass transfer that are driven by buoyancy. The density gradients that provide the driving buoyancy force are induced by the combined effects of temperature and species concentration nonuniformities present in the fluid saturated medium. The present chapter is guided by the review of Trevisan and Bejan (1990), which began by showing that the conservation statements for mass, momentum, energy, and chemical species are the equations that have been presented here in Chapters 1–3. The new feature is that beginning with Eq. (3.26) the buoyancy effect in the momentum equation is represented by two terms, one due to temperature gradients, and the other to concentration gradients.
Donald A. Nield, Adrian Bejan
10. Convection with Change of Phase
Abstract
In the examples of forced and natural convection discussed until now, the fluid that flowed through the pores did not experience a change of phase, no matter how intense the heating or cooling effect. In the present chapter we turn our attention to situations in which a change of phase occurs, for example, melting or evaporation upon heating, and solidification or condensation upon cooling. These convection problems constitute a relatively new and active area in the field of convection in porous media.
Donald A. Nield, Adrian Bejan
11. Geophysical Aspects
Abstract
Most of the studies of convection in porous media published before 1970 were motivated by geophysical applications, and many published since have geophysical ramifications; see, for example, the reviews bys Cheng (1978, 1985b). On the other hand, geothermal reservoir modeling involves several features which are outside the scope of this book. Relevant reviews include those by Donaldson (1982), Grant (1983), O’Sullivan (1985a), Bodvarsson et al. (1986), Bjornsson and Stefansson (1987), Lai et al. (1994), and McKibbin (1998). In this chapter we discuss a number of topics which involve additional physical processes or which led to theoretical developments beyond those which we have already covered.
Donald A. Nield, Adrian Bejan
Backmatter
Metadaten
Titel
Convection in Porous Media
verfasst von
Donald A. Nield
Adrian Bejan
Copyright-Jahr
1999
Verlag
Springer New York
Electronic ISBN
978-1-4757-3033-3
Print ISBN
978-1-4757-3035-7
DOI
https://doi.org/10.1007/978-1-4757-3033-3