The terms appearing in this equation have similar significance to those of the individual species equations, that is, the first term represents accumulation, the second represents the contribution of convection and the third term represents the sum of volumetric sources of all the components. For single-phase flow processes, the summation of sources of all the components will be zero (since there cannot be net generation or destruction of mass).

The performance equations of ideal reactors, which are well known to any reactor engineer, are just the limiting cases of these general mass conservation equations. Possible simplifications of these equations are discussed later in the chapter after discussing all the governing equations and their dimensionless forms.

2.1.2. Conservation of Momentum

Application of the law of conservation of momentum yields a basic set of equations governing the motion of fluids, which are used to calculate velocity and pressure fields. Details of the derivation of momentum transport equations may be obtained from such textbooks as Bird et al. (1960), Brodkey and Hershey (1988) or Deen (1998). The governing equations can be written:

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