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Author Topic: Aspirator ==> High Vacuum?  (Read 154 times)

no1uno

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Aspirator ==> High Vacuum?
« on: December 17, 2011, 09:49:49 PM »
I've been thinking on this, the "apparent" restriction upon the vacuum attainable with an Aspirator is the vapor pressure of the motive liquid/gas...

An aspirator runs on essentially the same principles as the oil diffusion pump.

What if an aspirator were run on recirculating liquid that had minimal vapour pressure? Water has a nominal vapour pressure of 2,333Pa, while ethylene glycol has a vapour pressure of 10.66Pa and 1,4-Butanediol has a vapour pressure of 1Pa. There are, of course, liquids with substantially better numbers than that, but ethylene glycol is not precisely hard to find and would prove or disprove the theory.

It would also open the door to high-vacuum in a space limited, low energy type application.
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Vesp

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Re: Aspirator ==> High Vacuum?
« Reply #1 on: December 17, 2011, 11:48:41 PM »
I do not know if it would reach that high of vacuum just because of mechanical imperfections or something along those lines. However the strength of the vacuum it can pull is determined by its vapour pressure, so if you had something like cold ethylene glycol blasting through it - it would indeed pull a much higher vacuum.
Of course, be sure to make sure it is pure, anhydrous, and so on.
If there were little amounts of water in it, you'd defeat the purpose.. I bet.
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Wizard X

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Re: Aspirator ==> High Vacuum?
« Reply #2 on: December 17, 2011, 11:49:51 PM »
Quote from: no1uno on December 17, 2011, 09:49:49 PM
I've been thinking on this, the "apparent" restriction upon the vacuum attainable with an Aspirator is the vapor pressure of the motive liquid/gas...

An aspirator runs on essentially the same principles as the oil diffusion pump.

What if an aspirator were run on recirculating liquid that had minimal vapour pressure? Water has a nominal vapour pressure of 2,333Pa, while ethylene glycol has a vapour pressure of 10.66Pa and 1,4-Butanediol has a vapour pressure of 1Pa. There are, of course, liquids with substantially better numbers than that, but ethylene glycol is not precisely hard to find and would prove or disprove the theory.

It would also open the door to high-vacuum in a space limited, low energy type application.

Fluid dynamics, like viscosity, will have to be accounted for with compounds like ethylene glycol, NOT just it's vapour pressure.

Vapour pressure is directly proportional to temperature.



Consider this at the Aspirator: Water at 20 oC, at water pressure X, WILL have less vacuum than Water at 2 oC, at the same water pressure X.

« Last Edit: December 18, 2011, 10:29:23 PM by Wizard X »
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no1uno

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Re: Aspirator ==> High Vacuum?
« Reply #3 on: December 18, 2011, 01:48:21 AM »
Yes, both are true - ANY water in the system will fuck the vacuum as will virtually any dissolved organics. And yes, the viscosity will also be a major factor, which will generally be more problematic with temperature to boot. That said, a drying train (something like sodium/calcium oxide that fixes water chemically) should remove the water from the atmosphere being pumped, while something like mol. sieves could probably dry the fluid to a certain point outside the vacuum in the recirculating area. Also, ethylene glycol is not as viscous as most glycols and should prove a decent test-bed.
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    There shallow draughts intoxicate the brain,
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fresh1

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Re: Aspirator ==> High Vacuum?
« Reply #4 on: December 18, 2011, 11:46:18 AM »
This is an area well worthy of investigation, but obviously, if one is using ehthylene glycol its in a closed system, however...

 I wonder though, about the possible "problems" with fluids other than water, especially in recirculating systems?  :-\

I personally have problems seeing water being wasted, and I get a weird guilt trip using aspirators than run freely down to the sea!

 So rubbish bins and 12v pumps work pretty well, but its bloody hard keeping a rubbish bin full of cold water on a 40c day! (and the water temp does effect pressure)  and this applies to most things outside a controlled enviroment :P
 A lesson well learned just recently, when the ambient temp changed from about 12c in the mid morning, to 35c by 2pm. Its surprising what a difference 20c makes :o,

and on more things than just the water! ???
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no1uno

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Re: Aspirator ==> High Vacuum?
« Reply #5 on: December 19, 2011, 03:55:35 AM »
Anyone got a link to where to find a proper, all metal aspirator in Oz please PM me a link
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    There shallow draughts intoxicate the brain,
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..."

lugh

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Re: Aspirator ==> High Vacuum?
« Reply #6 on: December 19, 2011, 04:13:01 AM »
A glass design from Journal of Chemical Society 123, 3414-15 (1923)   8)
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Wizard X

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Re: Aspirator ==> High Vacuum?
« Reply #7 on: December 19, 2011, 09:19:33 AM »
Or make your own metal Aspirator http://en.wikipedia.org/wiki/Aspirator_%28pump%29
« Last Edit: December 21, 2011, 01:14:22 AM by Wizard X »
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jon

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Re: Aspirator ==> High Vacuum?
« Reply #8 on: December 19, 2011, 01:07:30 PM »
no go buy one of those aspirators with a check valve trust me it will save you a lot of headaches

Wizard X

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Re: Aspirator ==> High Vacuum?
« Reply #9 on: December 20, 2011, 11:11:11 PM »
Quote from: reckless on December 19, 2011, 02:20:00 PM
Quote from: Wizard X on December 17, 2011, 11:49:51 PM
Vapour pressure is directly proportional to temperature.
Wrong. http://en.wikipedia.org/wiki/Antoine_equation That is whtat is shown on your picture.

reckless : Have a look at this Vapour pressure of water. http://en.wikipedia.org/wiki/Vapour_pressure_of_water and the table. And this http://en.wikipedia.org/wiki/Vapor_pressure#Relation_to_boiling_point_of_liquids

Adding ethylene glycol to water, will allow water to be cooled below it's freezing point and thus decease the vapour pressure even further. http://en.wikipedia.org/wiki/Ethylene_glycol#Antifreeze

Quote from: jon on December 19, 2011, 01:07:30 PM
no go buy one of those aspirators with a check valve trust me it will save you a lot of headaches

Agreed! If you can, buy an aspirator first. If you can't, then make one.
« Last Edit: December 20, 2011, 11:47:15 PM by Wizard X »
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Vesp

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Re: Aspirator ==> High Vacuum?
« Reply #10 on: December 21, 2011, 01:47:23 AM »
Yeah, decent aspirators can be had for $17 USD plus shipping.
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fresh1

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Re: Aspirator ==> High Vacuum?
« Reply #11 on: December 21, 2011, 03:03:39 AM »
I believe that providing sources is against the "rules" so please do what you think fit with this Vesp :-\

Its worth having a look at "The Laboratory.org" (not sure about the capital letters)
 but there are some good examples to be seen there, or linked,  Vesp maybe you could provide something more specific, or delete as you see fit. ???

Their aspies ( ;)) seem to be quality stainless steel, at the right price ;D although I guess shipping wouldnt be more than $5-10 max.

The site in general may be helpful to many members, so I suggest those who have the time, go have a look, its a 'cousin' so to speak 8)

And remember, "we GET WHAT WE GIVE, just NOT (neccesarily) where you Gave It!" 8) aka "karma" aka "as you sow, so shall you reap", or its more generalised term which is known as "causality"

http://en.wikipedia.org/wiki/Causality   Most of us in our dreams, deal with a highly tangible form of causality ;)

Cheers all f1
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Wizard X

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Re: Aspirator ==> High Vacuum?
« Reply #12 on: December 22, 2011, 10:42:52 PM »
Albert Einstein - "Great ideas often receive violent opposition from mediocre minds."
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