/sci/ - Science & Math

[op No.4191865]

Hello /sci/, I'd appreciate your help on this.

I'm doing my PhD in engineering, and my project involves microfluidics. I just designed a new process to remove bubbles, and need a vacuum to do it. My device needs to be inside a special room and it doesn't have access to the house vacuum (for those unfamiliar, a little nozzle labeled "Vac" common in most labs).

I don't need much pressure, just about -100 kPa, or roughly 12 psi if I remember the conversion correctly. It does need to be a fairly consistent pressure though.

So, I'm looking for a small device capable of creating a light vacuum, and it can be of ANY design so long as it's consistent, small, and cheap. I'd prefer not to spend more than $300 of my adviser's money on this, especially if my idea doesn't work and I will not be able to build something from various parts.

[op No.4191879]

I forgot that it needs to be fairly clean and quiet too. I don't want this contaminating everything and pissing other people off who work inside the same room.

I already have a few ideas, but I'm hoping some of you will have other that ideas that could take me in different directions.

[Anonymous No.4191892]

>>4191865
>>4191879
Why not use an ordinary vacuum pump, like the ones that evacuate refirgerant systems?

[Anonymous No.4191897]

Does it need to run continuously?

[op No.4191904]

>>4191892
Are these quiet, and do you have some links? I literally have no experience with this whatsoever.

>>4191897
Yes, I would like it to stand alone. It will run for a few weeks at a time.

[Anonymous No.4191913]

can you use a hobby pump? fish tanks and such

[Anonymous No.4191915]

compressed air brake bleeder?

[op No.4191929]

>>4191915
>>4191913
Looking into it now. If you guys can give photos it would be really helpful, but no problem. I'll check both out and see if they could work.

[op No.4191943]

>>4191929
I need to do more research on compressed air brake bleeders, but for now the hobby pump looks nice except for the fact that I may not be able to control the vacuum pressure. I'll need to convert gallons per minute of output into psi.

[op No.4191957]

Hmm, about 50-60 gallons per hour should work for me on those fish tank pumps. That's about 12 psi.

[Anonymous No.4191991]

If you want to have consistent pressure, you could make a little PID loop.

Pressure sensor, op-amps, and small control valve

[op No.4192004]

>>4191991
Control valve is a great idea. It might be obvious, but again this is my first time using a vacuum that I need to control. So far, here is my idea:

Use a hobby pump, get a larger output than I need. Buy a regulator / control valve from a reputable scientific store like Cole Parmer. I'll look for cheaper options in the mean time.

[Anonymous No.4192018]

here's a homemade vacuum pump, detailed video, but no control valve
http://www.youtube.com/watch?v=uyG2_-QNjZY

[op No.4192023]

>>4192018
Thanks for the info.

[Anonymous No.4192034]

Actually, a vacuum regulator would be fine. It is its own contained feedback loop.

[op No.4192061]

I'm a little confused now. I need about 12-14 psi, which I thought was pretty small. This is about 83-100 kPa. It might even be a good idea to go double that because I can use two lines simultaneously.

I'm confused because few pumps offer pressures that high. I'm using pretty small tubing. Do I need to see what tubing the psi values are calculated with, and correct based on the tubing I will be using? I'd assume so, since smaller tubing will result in greater suction.

For example, these big aquarium pumps hardly go to 14 psi. I have this little 1 mm thick membrane I want to vacuum pump, and I can't imagine a pump like that not being able to deliver.

Can someone tell me how these pressure values are calculated?

[Anonymous No.4192076]

For a rough guess, use Bernoulli's.

Also, draw me a schematic.

[op No.4192110]

>>4192076
Here's a very rough schematic. Imagine water with bubbles, contained in glass. There's a patch of air permeable material on the top. A port is on top of this patch. Small tubing is connected to the port, and the tubing is connected to a vacuum pump.

[op No.4192118]

It's also possible to put larger tubing around the entire port, which is about 1/4 inch in diameter in case the smaller tubing cannot attach to a vacuum pump.

[op No.4192128]

The paper says, "The bubble trap was first connected to a vacuum source (house vacuum, -98 kPa relative to atmospheric pressure)".

This means that I need 98 kPa of suction, right? Or did I interpret this statement wrong. For some of you, I'm sure this is not a big deal but I am out of my comfort zone.

[Anonymous No.4192181]

>>4192128

-98KPa is almost a perfect vacuum.

You're understanding the definition of vacuum and negative pressures incorrectly.

[op No.4192191]

>>4192181
Thanks for clarifying. Based on that passage, which is all I have, are you able to calculate how much pressure I need to get my bubbles through the gas permeable membrane?

[Anonymous No.4192193]

>>4192181
>You're
>Fuck

0Pa = Perfect vacuum

[Anonymous No.4192328]

>I'd assume so, since smaller tubing will result in greater suction.
Smaller tubes will give you LESS suction. If the air is being sucked out through a small tube, it will move slower.
The air leaving your water will increase the pressure and you'll need to pump it away to keep the pressure low. Thicker tubing will let the air move to the pump faster. I'm not sure how many air bubbles you have, though, it may not be a problem.

>I'm doing my PhD in engineering
You're surrounded all day by experts in nearly all fields that exist. One of them is bound to know something about vacuum. If not, go to the physics department and find someone working with experimental surface physics (or possibly laser physics). They frequently work with pressures down to 10^-12 mbar (=10^-10 Pa). They can tell you all you need to know about all sorts of pumps, piping and regulation.

>>4192128
>(house vacuum, -98 kPa relative to atmospheric pressure)
You can get this with any kind of piston or membrane pump (look them up on wiki). Atmospheric pressure is 101325 Pa, so the pressure used is 3.3 kPa.

[Anonymous No.4192396]

>>4192181
-98 kpa is low vacuum as the net pressure is still measured in Pascalles. "Vacuumness" is a logarithmic scale, with ultrahigh vacuum, the best we can get, being measured in picopascal.

[op No.4192445]

>>4192328
Wonderful, so I can use a very small pump then. Thanks very much. I know that I'm surrounded by experts, but I've been designing a complicated process all vacation and this simple problem is all that's standing in my way.

I could wait and ask some professionals when I get back, but if I can involve /sci/ and get an answer sooner, why not? I also got some alternative ideas for pumps (like the hobby pump) which are useful.

3.3 kPa is much more reasonable too. I can't imagine needing such a strong pump on such thin membrane, when the membrane itself is highly gas permeable.

[Anonymous No.4192454]