point of tracer measurement, the variance for open-open system is: (3) Where, (4) which represents the ratio of rate of transport by convection to rate of transport by diffusion or dispersion. = characteristic length (m) = effective dispersion coefficient ( m2/s) = superficial velocity (m/s) based on empty cross-section Vessel dispersion number is defined as: The variance of a continuous distribution measured at a finite number of equidistant locations is given by: (5) Where mean residence time τ is given by: (6) (7) Thus (σθ)2 can be evaluated from the experimental data on C vs. t and for known values of , the dispersion number can be obtained from eq. (3) as: (8) Thus axial dispersion coefficient DL can be estimated (L = packed height) As mentioned before, there are also other boundary conditions that can be applied to the dispersion model giving different relationships for the dispersion number. Advantages From the safety technical point of view the PFTR has the advantages that It operates in a steady state It is well controllable Large heat transfer areas can be installed Concerns The main problems lies in difficult and sometimes critical start-up and shut down operations. Applications Plug flow reactors are used for some of the following applications: Large-scale production Fast reactions Homogeneous or heterogeneous reactions Continuous production High-temperature reactions See also Flow chemistry Continuous stirred-tank reactor Laminar flow reactor Microreactor Oscillatory baffled reactor Reference and sources Chemical reactors