Fundamental Heat and Mass Transport Processes

The conventional parameterizations used describing molecular transport of mass, energy and momentum are the Fick s law (mass diffusion), Fourier s law (heat diffusion or conduction) and Newton s law (viscous stresses). The mass diffusivity, Dc, the kinematic viscosity, i/, and the thermal diffusivity, a, all have the same units (m /s). The way in which these three quantities are analogous can be seen from the following equations for the fluxes of mass, momentum, and energy in one-dimensional systems [13, 135]  

Note that these analogies are less obvious in two- and three dimensional problems, however, because o is a tensor quantity with nine components, whereas jc and q are vectors with three components. 

The situation is much the same in liquids, although the molecules are more closely spaced and the molecular interactions are stronger and more frequent. Similarly, in a solid, conduction may be attributed to atomic activity in the form of lattice vibrations. The modern view is to ascribe the energy transfer to lattice waves induced by atomic motions. In a non-conductor, the energy transfer is exclusively via these waves, in a conductor it is also due to the translational motion of the free electrons. 

In reaction engineering the ordinary diffusion processes taking place close to an interface have been analyzed in two ways. First, as just mentioned, the interfacial transport fluxes can be described in a fundamental manner adopting the Fourier s and Fick s laws which are expressed in terms of the transport coefficients known as conductivity and diffusivity. Second, the interfacial 

This section contains a simple introduction to steady state and unsteady species mole (mass) diffusion in dilute binary mixtures. First, the physical interpretations of these diffusion problems are given. Secondly, the physical problem is expressed in mathematical terms relating the concentration profiles to the diffusion fluxes. Emphasis is placed on two diffusion problems that form the basis for the interfacial mass transfer modeling concepts used in reaction engineering. 

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