Dispersion in coiled tubular reactors: A CFD and experimental analysis on the effect of pitch

Mixing Efficiency and Residence Time Distributions of a Side-Injection Tubular Reactor Equipped with Static Mixers

“…The dimensionless time is defined as θ = t / t̅ , where t is time and t̅ is the mean residence time, which corresponds to the first moment of the distribution E θ . The analytical solutions of the tanks-in-series model (TISM) and the axial-dispersion model (ADM) were used to observe whether the determined RTDs resemble those of a PFR (or a tubular reactor with low dispersion). In particular, the number of equivalent CSTRs in series, N CSTRs (for the TISM), and the dispersion number, Θ = 1/ Pe (for the ADM, where Pe is the Peclet number, defined as the ratio between the advective transport rate and the diffusive transport rate, , where L is the characteristic length, v is the flow velocity, and is the mass diffusion coefficient), were determined to measure the similarity of the system to a PFR.…”

“…8,9 Therefore, a plug-flow (PF) behavior can only be achieved in an empty tube if the reactor is extremely long 9,10 or if the tube is bent or coiled to reduce axial dispersion. 11,12 Alternatively, the process can be carried out in a series of CSTRs, but with a very large investment cost, as theoretically a PFR performance is reached with an infinite series of CSTRs. 9 Another solution is the use of active mixers in tubular reactors, such as ultrasonic micromixers and pulse- flow mixers.…”

“…On the other hand, turbulent flow requires large velocities, thus this solution can be adopted only for fast reactions which require small residence times in the reactor (which is usually not the case in the pharmaceutical and polymer industries). Instead, empty reactors in laminar regime have to rely on molecular diffusion to even out radial gradients. , Therefore, a plug-flow (PF) behavior can only be achieved in an empty tube if the reactor is extremely long , or if the tube is bent or coiled to reduce axial dispersion. , Alternatively, the process can be carried out in a series of CSTRs, but with a very large investment cost, as theoretically a PFR performance is reached with an infinite series of CSTRs . Another solution is the use of active mixers in tubular reactors, such as ultrasonic micromixers and pulse-flow mixers.…”

Influence of Buoyancy Effects on the Mixing Process and RTD in a Side-Injection Reactor Equipped with Static Mixers

“…13 Considering an empty tube, a plug flow behavior can be obtained only if the tube is extremely long with respect to its diameter 15,16 and it possibly follows a coiled geometry. 17,18 Alternatively, active mixers such as ultrasonic micromixers and pulse-flow mixers can be employed, but their efficiency is hindered by their high cost, difficulty of maintenance, and high failure rate. 19 only the energy derived from the flow momentum itself.…”

“…In these cases, the mixing process among the streams of reactant is based only on diffusion, , and often, the resulting mixing times are too large, causing undesirable situations in terms of process planning, productivity levels, and product quality control . Considering an empty tube, a plug flow behavior can be obtained only if the tube is extremely long with respect to its diameter , and it possibly follows a coiled geometry. , …”