Mass fraction of species

A mass-transfer coefficient hm can be used to represent /A in terms of the difference between the inlet and surface mass fraction of species A,... 

Constant, defined as 2na/X A (Ofii Mass fraction of species A... 

Mole fraction of species T Mass fraction of species... 

In Eqs. (6) and (7) e represents the internal energy per unit mas, q the heat flux vector due to molecular transport, Sh the volumetric heat production rate, ta, the mass fraction of species i, Ji the mass flux vector of species i due to molecular transport, and 5, the net production rate of species i per unit volume. In many chemical engineering applications the viscous dissipation term (—t Vm) appearing in Eq. (6) can safely be neglected. For closure of the above set of equations, an equation of state for the density p and constitutive equations for the viscous stress tensor r, the heat flux vector q, and the mass flux vector 7, are required. In the absence of detailed knowledge on the true rheology of the fluid, Newtonian behavior is often assumed. Thus, for t the following expression is used ... 

Dynamic friction coefficient Kinematic viscosity, m /s Mass fraction of species i Mass fraction of species i in phase k Density, kg/m ... 

Consider a solid plane wall (medium B) of area A, thickness L, and density p. The wall is subjected on both sides to different concentrations of a species A to which it is permeable. The boundary surfaces at.t = 0 and x - L are located within the solid adjacent to the interfaces, and the mass fractions of A at those surfaces are maintained at and 2. respectively, at all times (Fig. 14-19). The mass fraction of species A in the wall varies in the. v-direction only and can be expressed as >v (.t). Therefore, mass transfer through the wall in this case can be modeled as steady and one-dimensional. Here we determine the rate of mass diffusion of species A through the wall using a similar approach to that used in Chapter 3 for heat conduction. 

It is often suitable to write the mass conservation equations in terms of mass fractions of species rather than molar concentrations, especially for flow processes, where properties of the fluid may vary with composition and temperatures. The mass conservation equation for species k can therefore be written (in vector symbolism) ... 

Sustained combustion requires a continuous supply of fresh reactants and a continuous removal of reaction products. This process is loosely known as mass transfer. Specifically, mass transfer is a consequence of three possible modes bulk fluid motion, molecular and turbulent diffusion, and reaction sources and sinks. Mass transfer due to bulk fluid motion is generally known as convection. It is similar to the convection heat transfer process. Mathematically, the rate of change for species / per unit volume, pYit via convection can be described as 3(pUjY ldxj, where p is fluid density, Yt is the mass fraction of species i, Uj is the / -component of the fluid velocity. 

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