A design of experiment (DoE) approach to optimize the inner geometry - - PowerPoint PPT Presentation

Louisa Ejim (Loughborough University) Supervisor: Dr. Nuno Reis 2nd Supervisor: Prof. Chris D. Rielly

A design of experiment (DoE) approach to optimize the inner geometry of baffled meso-scale tubes for continuous crystallization

Baffle spacing (l) Orifice diameter (do) Inner tube diameter (𝑒 = 10 𝑛𝑛)

A B C D E F G H I J

Smooth edged baffle type (SPC) Sharp edged baffle type (SEPC)

Figure 1

Aim & Objectives

• To determine the optimal

geometry

• By characterising the tubes using

solid-liquid residence time distribution (RTD)

• DoE approach to investigate the

effect of baffle spacing (𝑚), orifice diameter (𝑒𝑝) and baffle type on RTD

• PVC particles are used because
• f their similarities in flow

properties to crystals.

Glass tubes;

Batch Suspension Studies (critical amplitude: centre-to-peak)

Conclusions:

• Increased oscillation frequency

provides a lower critical amplitude required to suspend particles

• Sharp edged-baffles of the same

dimensions proved to require higher critical amplitude

• Tube A (𝑚 = 30 mm, 𝑒𝑝= 3.5 mm)

proved to require the lowest amplitude for suspension.

Continuous Liquid-solid RTD

Conclusions:

Smooth-edged baffle type:

• Gives lower energy input

requirement (e.g critical amplitude)

• Narrower RTD (close to plug

flow behaviour)

• Uniform mixing

Sharp- edged baffle type:

• Chaotic mixing
• Broader RTD
• Bubble retention/trapping.

𝐺 𝑢 = 1 − 𝑋 𝑢 , 𝑋 𝑢 =

𝐷𝑝𝑣𝑢(𝑢) 𝐷0

, 𝜄 =

𝑢 𝑢 0.0 0.2 0.4 0.6 0.8 1.0 1.2 0.0 1.0 2.0 3.0 4.0

F(Ө) Ө [-] SPC

A B C D E

a

0.0 0.2 0.4 0.6 0.8 1.0 1.2 0.0 1.0 2.0 3.0 4.0

F(Ө) Ө [-] SEPC

F G H I J

b

Plug flow with axial dispersion (D/uL)

Fitting parameters:

• Superficial velocity (m/s)
• Axial dispersion

coefficient (m2/s).

0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 A B C D E F G H I J

D/uL [-] Tube geometry

Smooth edged baffles (SPC) Sharp edged baffles (SEPC)

• Levenspiel Open- Open

boundary condition:

Conclusion

• The open baffle area,  identified as the dominant design parameter in controlling solids backmixing and

batch suspension of particles, with small values of  = 0.12 resulting in minimised axial dispersion

• Strong eddy vortices generated at lower values of , that presumably led to trapping of particles, an effect

not previously observed in OFRs

• Tube A (l/d = 3.0) showed clear flow characteristic advantages over the other meso-tubes studied.

Plug flow with axial dispersion DoE plots

Thank You!