Tubular axial dispersion estimation

Water at room temperature is flowing through a 1.0-in i.d. tubular reactor at Re= 1000. What is the minimum tube length needed for the axial dispersion model to provide a reasonable estimate of reactor performance What is the Peclet number at this minimum tube length Why would anyone build such a reactor ... 

In stirred tanks, the power input to agitate the tank will depend on the physical properties of the liquid. In tubular reactors, the axial dispersion in empty tubes may be estimated [e.g., Wen in Petho and Noble (eds.), Residence Time Distribution Theory in Chemical Engineering, Verlag Chemie, 1982] as... 

For the design of tubular reactors an a priori estimation of the axial dispersion is indispensable. The dispersion in tubular reactors depends on the flow regime, characterized by the Reynolds number. Re, and the physical properties of the fluid, characterized by the Schmidt number. Sc. In addition, the presence of internal packings influences the flow behavior and, in consequence, the axial dispersion of the fluid. 

Table 3.2 Estimation of axial dispersion in tubular reactors [6].

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