4 replies to this topic

[NRMO]

Hello all,

 

I am working on some calculations for scaling up a mixing tank.  I believe that I am fine with calculations concerning energy and tank dimensions, but I am unsure about the mixing calculations.  I know that a simple calculation shows that less speed is needed when scaling up, and as a result, I am assuming that the shear stress will be the about same. However, I feel that I am not considering other fluid mechanics calculations.  I also wonder if there is a direct correlation between the number of mixing blades with the mixing speed.  The smaller tank had a mixer attached with five equally sized blades (paddles) with two flow-through holes on each side of the blade, and it was suggested that the scaled up tank should have a mixer with three blades, two with six flow through holes and a smaller one with four flow through holes.  From the diagram, the mixer is designed for radial flow as the blades are not pitched. Is there more that I need to consider when scaling up the mixing?  What are some calculations?

[latexman]

No diagram attached.  What physical or chemical (or both) task is the mixer doing?  Two dimensioned and labelled sketch/drawings (small tank and big tank) would be useful.  Especially to explain these flow through holes, which I am not familiar with.  What is the baffle situation?  What reference are your calcs following?  Oldshue, Perry, other?  Established references are great to ensure all the important variables are being looked at.  It appears due diligence to the technology is lacking.

Edited by latexman, 28 December 2018 - 05:48 AM.

[breizh]

Hi,

What about talking to the vendor of the existing equipment ? It should be able to give you pointers .......

 

Attached a few tips about mixing .

 

good luck

Breizh

Edited by breizh, 29 December 2018 - 02:26 AM.

[NRMO]

Hello again!

 

I appreciate the responses.  Thank you for the files Breizh; I will read them soon.  For any future responses, I can only upload a crude hand drawn diagram just to be sure that I do not accidentally release anything proprietary.  To make 58 kg of a liposomal suspension, we use a jacketed 60L tank, and it is almost filled to the brim in the process.  The current tank has no baffles.  It has 5 blades/paddles with holes on the agitator (see left figure in attached file).  The blades are not pitched.  The goal is to scale up to 230 kg.  I can use thermodynamic and heat transfer equations to size up the tank, but I am struggling with the mixing aspect.  The solution has low viscosity, and I believe it is a Newtonian fluid.  I am assuming that many of the mixing properties will be the same when I scale up, but I am not sure if I am correct in doing this. I am using this equation to determine the final speed (in RPM) for the larger tank:  N2 = N1*(D1/D2)^n where n = 1.  

 

It was suggested the new agitator in the larger tank have 3 blades with the second blade perpendicular to the first and third (see the right figure in attached file).  Does decreasing the number of blades decrease the speed?  Does anyone know the reason for the holes in the blades in the first place?

 

Thanks!

Attached Files

•  basic_diagram010319.pdf   8.9KB   41 downloads

[breizh]

Hi ,

In addition to my previous reply you will find  a course about agitation, mixing and scale up .

Why not asking vendors like LIGHTNIN or CHEMINEER  (LEWA)) or others their thoughts about your existing equipment ?

 

http://www.postmixing.com/

 

hope this is going to help you.

Breizh

Edited by breizh, 07 January 2019 - 01:41 AM.