Heat, Mass, and Momentum Transfer
Life depends on heat and mass transfer between organisms and their surroundings. Such processes as carbon dioxide exchange between leaves and the atmosphere, oxygen uptake by microorganisms, oxygen and carbon dioxide exchange in the lungs of animals, or convective heat loss from the surfaces of animal coats are fundamental to the existence of living organisms. A thorough understanding of these exchange processes is therefore a necessary part of the study of physical ecology. In this chapter we will first discuss molecular diffusion. It is by this process that heat and mass are transported in still air or water, as they are in parts of the lungs of animals, in soils, and in the substomatal cavities of leaves. Molecular diffusion is also important in convective heat and mass transfer between surfaces and fluids flowing over them since a thin boundary layer is always formed near the surface through which transport is by diffusion. After diffusion processes are discussed, we will then present convective heat and mass transfer theory as it applies to fluids moving over plates, cylinders, and spheres. Finally, we will discuss momentum exchange and the force of moving fluids on objects in them.
KeywordsHeat Transfer Nusselt Number Momentum Transfer Free Convection Molecular Diffusion
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