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A porous medium consists of a solid structure with void spaces that are in general complicated and distributed throughout the structure. The void spaces can be interconnected or not. The pores are identifiable regions that serve as elements for the void space. The traditional view of porous media was inspired by porous structures found in nature, for example, packed sand saturated with water that...
We now turn our attention to the results that constitute the core of modern research on convective heat and mass transfer through porous media. Our objective is not only to organize the compact presentation of these results, but also to explain their origin. We want to show the student how to anticipate these results and the results for related problems. This is why we begin with methodology. We emphasize...
The energy crisis of the 1970s and the continuing emphasis on efficiency (the conservation of fuel resources) has led to a complete overhaul of the way in which power systems are analyzed and improved thermodynamically. The new methodology is exergy analysis and its optimization component is known as thermodynamic optimization, or entropy generation minimization (EGM). This new approach is based on...
Realistic models of energy systems demand the treatment of installations and their flowing surroundings together, more so when the installations are large and their spheres of impact greater. The interface between energy systems and the environment is formed by flows, environmental flows. In the opening sections of this chapter we review the fundamentals of some of the most important types of flows...
In this chapter we discuss a series of developments that point in the direction of applying porous media concepts to the description, simulation, and optimization of compact systems with complex flow structures. Compact and miniaturized heat exchangers are primary examples of this trend. Other examples are chemical reactors, fiber filters, brush seals, and the modeling of microsegregation during the...
The development of complex cellular systems such as the vertebrates requires the availability of large amounts of oxygen for the metabolic needs of the cells. The respiratory and circulatory systems are the specialized and hierarchically organized flow systems that meet this need. The respiratory system carries oxygen from the air to the pulmonary veins, whereas in the circulatory system oxygen is...
Drying is the process of thermally removing volatile substances (e.g., moisture) to yield a solid product. Mechanical methods for separating a liquid from a solid are not considered drying. When a wet solid is subjected to thermal drying, two processes occur simultaneously: transfer of energy (mostly as heat) from the surrounding environment to evaporate the surface moisture, and transfer of internal...
The void spaces of a porous structure can be interconnected or not. In the latter case the void spaces are disconnected “inclusions” that do not allow a flow to permeate through the porous structure. When the inclusions are large, the flow inside each fluid-filled inclusion may play an important role in the global transport of heat and mass through the structure. This is especially true in coarse...
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