Combinations of PFRs Configurational Effects

The volume of the recycle PFR may be obtained by a material balance for A around the differential control volume dV. Equating molar flow input and output, for steady-state operation, we have 

The volume V calculated by means of equation 15.2-2 may be arranged into any l/D ratio and any series or parallel arrangement, provided  

For point (1), the value of Re (= DGIfx, where G is the mass rate of flow per unit area, mlAc, and fi is viscosity) may sometimes be used as a guide. For cylindrical geometry, 

Equation 15.4-2 states that, for given m and /x, Re oc ) 1 15.4-3 states that, for given m, ji, and V, Re oc L1/2 , and 15.4-4 states that, for given m, /jl, V, and D, Re L/D. This last may be used to determine the minimum ratio, (L/D)min, based on Remin for PF in an empty vessel, as illustrated in the next example. Equation 15.4-3 is more useful for 

Devise a procedure for determining L and D for PF in an empty cylindrical vessel with a specified value of V. 

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