Calculating CFM requirement with leakage

[Justaddaservo]

Hello,

We are designing a machine utilizing a vacuum suction cup disc for holding 32 glass vials rotating at 18.75rpm, with centripetal acceleration of 8.6 m/s^2. When the machine initially starts, there are no vials in the cups so they are all in free flow. Unfortunately we can't use check valves because of the vacuum requirements of our cups and the centripetal acceleration of our system. How could we calculate the cfm requirement accounting for this leakage?

 

[Heaviside1925]

Are the suction cups oriented facing the center of the centrifuge or the outer wall? I suspect the former from my limited experience with centrifuges like this. If so, then the suction would only be required to maintain the vials initial positions and would not be resisting the centrifugal acceleration, if this were the case, I would see only a slight vacuum requirement to hold the vials. What sort of piping and pump arrangements are you considering?

 

[Justaddaservo]

I attached a reference image to show the orientation.

The suction cups will be mounted to holes/pockets drilled into the side of the disc. The holes will lead to a cross hole drilled on the bottom of the disc. The disc will rotate above a fixed plate with vacuum channels. When the cross hole is within the channel, vacuum will be supplied to the suction cups. There is a small zone where the cups will have no vacuum after they transfer the vials to another wheel and before they pick up the next. So actually a maximum of 28 cups will leak at a time. In normal operation, all 28 active cups will have vials present. THe high cfm would only be needed to overcome the initial startup.


[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1722525385/tips/Pharma.App_o2lmjb.pdf[/url]

 

[Heaviside1925]

8.6 m/s^2

So, less than 1g. If this is correct than you would only need enough vacuum to essentially hold the vial's weight. Surface area, vacuum pressure = F that is greater than the vials weight. Then your CFM would be whatever your orifice can pass at that delta P. Probably easiest to works backwards from the pump. Do you have an idea of the pump you are going to use and its pump curve?

 

[Justaddaservo]

The suction cups I planned for have a 11mm diameter.

Most likely this pump.

https://www.gastmfg.com/products/1423/1423-101q-g625

https://www.gastmfg.com/sites/default/files/2019-08/std243.pdf

 

[Heaviside1925]

Do you have a spec on the suction cups? Thier orifice diameter, CV air?
Do you know the approximate weight of the vial and contents?

 

[Justaddaservo]

Here is the cup.

https://www.schmalz.com/en-us/vacuu...on-cups-fsga-1-5-folds-302818/10.01.06.00076/

 

[Heaviside1925]

So, you need to calculate choked flow for each cup (numerous free calcs and spreadsheets online or get out your Perry's). I think you could use the hose diameter of 2mm. The holding force is 3.8N @ -.6bar, so how much does your vial and contents weigh, F=MA?
Example: If choked flow is 1 cfm for a 2mm hose / inlet pressure 0barg outlet / -.6barg and you have 28 cups, you'll need a vacuum pump capable of 28CFM at -.6bar.
You may not need 3.8N of holding force which is why I asked the weight, if you need less a smaller capacity pump could work.