Centrifugal Pump Shear Rate Estimation?

[TiCl4]

Does anyone have a reference to a means to calculate the maximum shear rate of a liquid being pumped through a centrifugal pump? We currently are looking at replacing a Sulzer pump with a different brand (Summit), and while the pump curves are very closely aligned and within the process needs, I need to figure out if the shear rate is different. The fluid being handled is acrylic/styrene acrylic polymers, which can be sensitive to shear. The current pump is a Sulzer APT-33 with half-open impeller design. The level of shear with the pump is acceptable, as no product destabilization occurs. However, I need to figure out if the alternative pump being offered is of substantially the same shear rate, and I don't know of any general correlations or calculations for estimating that.

Can anyone point me in the right direction?

 

[EdStainless]

Start with impeller diameter and speed, this specific speed is proportional to shear if the impeller design is similar.

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P.E. Metallurgy, consulting work welcomed

 

[pierreick]

Hi,

https://pumpschool.com/applications/Shear.pdf

My experience with latex was to use peristaltic pump diaphragm type and/or pressure push to prevent degradation of the product.

Pierre

 

[TiCl4]

Ed,

I had wondered if impeller tip speed was the most critical factor, but I admit some ignorance as to the design of centrifugal pump internals; for example, I know that they have some level of internal recirculation flow while operating, but don't know if different levels of internal recirc flow affect shear rate.

Do you know how impeller type (open, half-open, etc) affects shear rate?

Pierre,

We use AODD pumps elsewhere for low-shear pumping, but this application requires continuous flow at higher flow rates (1,200-1,500 gpm), and the current use of a centrifugal pump is acceptable for product stability.

 

[EdStainless]

An open impeller generally has more recirculation so slightly lower shear rates.
Impeller radius x speed is a good rough estimate of the shear levels, if the impellers are similar.
If they are of different styles and blade counts then it gets more complicated.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[Latexman]

TiCl4,

About 30 years ago, I asked my megacorp's fluid flow expert the same question, "What is the effective shear rate in a centrifugal pump?".

He told me to use:

Shear rate (sec^-1) = 10 x RPM/60 or 10 x RPS.

This equation has worked well for me ever since. There was also a lot of engineers in our business that used impeller tip speed with good success, as recommended by Ed Stainless. As you probably know, this area is not an exact science. We rely a lot on using similar impellers and tip speeds to what we know works.

We have used certain centrifugal pumps in several latex services (vinyl acrylic, all acrylic, styrene acrylic, and styrene butadiene latexes). The one I'm most familiar/comfortable with is a recessed impeller centrifugal that was used historically in a lot of pulp and paper mills.

If your wallet is fat, consider Discflo or Tesla Disk Pumps, they are based on Nikola Tesla's bladeless centripetal flow turbine!

Good Luck,
Latexman

 

[pierreick]

Hi,
Another technology suitable for your application is

https://www.psgdover.com/mouvex/products/eccentric-disc-pumps

Note: I used this technology to transfer monomers emulsion prior to polymerization.

https://iqs.co.th/wp-content/uploads/2020/07/Mouvex-General-Product-Brochure.pdf

Pierre

 

[georgeverghese]

Pumping hydraulic eff also has an effect on shear rate - the lower the e, the greater the power spent in needless fluid internal recirculation.

 

[TiCl4]

Thanks for the input all. Our vendor suggested Discflo as an option, but cautioned that motor HP will be much higher (lower efficiency, I guess).

The current pump isan APT-33 with what is called a "special open" impeller. I'm not sure that extreme measures for low-shear are necessary, as this looks like a standard semi-open impeller with fewer vanes for larger passages. Looking at the design, does anything pop out to anyone?

 

[georgeverghese]

From Petrowiki, Shell guideline for low shear applications is to operate at Ns < 700 (specific speed).
Would also suggest another derived parameter, given isentropic pumping power is near zero, that
z = P.(1-e)/M, where M = mass rate though pump in kg/sec, P = pumping power at pump shaft in W
be another parameter to compare with.

Parameter z will vary over the operating flow range, so you may want to compare the area under the curve if you plot z on the y axis against operating mass rate.

 

[pierreick]

Hi,
You may want to drop an email to this guy:

https://instockpump.com/wp-content/uploads/2020/11/Liquid-Shear.pdf

Pierre