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gsd
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Since this thread was reopened by mossydie, throughout the posts nobody has talked about what vacuum is required? is it 100 torr, 30 torr or 1 torr?
If we are discussing anything below 30 torr then even a very properly designed water jet ejector (the so called "aspirator") will not do the job as at
that pressure, the tap water at normal temperature will start boiling.
The only practical alternative - however messy - remains is oil ring vacuum pump.
gsd
[Edited on 4-10-2009 by gsd]
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entropy51
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Quote: Originally posted by gsd  |
If we are discussing anything below 30 torr then even a very properly designed water jet ejector (the so called "aspirator") will not do the job as at
that pressure, the tap water at normal temperature will start boiling. |
Bullshit. The vapor pressure of H2O isn't 30 torr until 29 C, which is a lot warmer than my tap water ever gets.
My aspirator easily reaches 15 torr in the summer when the tap water is relatively warm. It reaches 10 torr in the winter when the water is quite
cold.
See vapor pressure table
http://intro.chem.okstate.edu/1515SP01/Database/VPWater.html
I knew you were blowing smoke out your arse about being a distillation expert.
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gsd
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| Quote: Originally posted by entropy51 |
Bullshit. The vapor pressure of H2O isn't 30 torr until 29 C, which is a lot warmer than my tap water ever gets. |
Thats what I said. In my part of the world tap water temperature almost round the year is between 30 to 35 Deg. C. So pulling vacuum below 30 torr
with that is not possible on sustainable basis.
I of course had no way to know where you live. In tundra or in tropics.
| Quote: Originally posted by entropy51 |
My aspirator easily reaches 15 torr in the summer when the tap water is relatively warm. It reaches 10 torr in the winter when the water is quite
cold. |
Yes sure. in Alaska you can get 5 torr most of the time. But everybody can't go there just to do distillation.
LOL. looks like still smarting over the loss of face in the last encounter' 
Well mover over smart "arse" It is you who is farting around by discussing topic in air without giving any specifics.
gsd
PS. Vapour pressure of water in mmHg can be calculated by using the Antoine's Equation:
Log Ps = 7.96681 - (1668.2/(228 +T))
Where Log is to the base 10
Ps is vapour pressure in mmHg (or torr)
and T is in Deg C.
gsd
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entropy51
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| Quote: | | Thats what I said. In my part of the world tap water temperature almost round the year is between 30 to 35 Deg. C |
Sounds like you're drinking urine to me. More BS.
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gsd
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| Quote: Originally posted by entropy51 | | Quote: | | Thats what I said. In my part of the world tap water temperature almost round the year is between 30 to 35 Deg. C |
Sounds like you're drinking urine to me. More BS. |
ROFLOL 
What a specimen!
Is prepared to go to any length to have a last word!
It takes all sorts to make this wonderful virtual world of sciencemadness 
gsd
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entropy51
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You may have the last word. Please don't take my jibes seriously.
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gsd
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Taking your jibes seriously?
In case you have not noticed, I was 'Rolling On Floor Laughing Out Loudly" after reading your childish rejoinder.
gsd
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1281371269
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Sorry to have caused an argument 
I can get something like this:
http://cgi.ebay.co.uk/Lotus-Diamond-600-Pond-Pump_W0QQitemZ1...
with perhaps a little more power if necessary, or a central heating pump, for much cheaper than a vacuum pump and grease. Of course I'd also need to
work out connectors, a reservoir (would a bucket do or should it be a bit more high tech?) and buy an aspirator, but it would still work out quite a
bit cheaper. Will the above link have enough power? If not, what sort of pumps should I look for or should I get the vacuum pump linked to before?
Sorry for all these questions, I haven't been able to find much information on this anywhere...
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UnintentionalChaos
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| Quote: Originally posted by Mossydie | Sorry to have caused an argument
I can get something like this:
http://cgi.ebay.co.uk/Lotus-Diamond-600-Pond-Pump_W0QQitemZ1...
with perhaps a little more power if necessary, or a central heating pump, for much cheaper than a vacuum pump and grease. Of course I'd also need to
work out connectors, a reservoir (would a bucket do or should it be a bit more high tech?) and buy an aspirator, but it would still work out quite a
bit cheaper. Will the above link have enough power? If not, what sort of pumps should I look for or should I get the vacuum pump linked to before?
Sorry for all these questions, I haven't been able to find much information on this anywhere... |
That's a very low powered pump, unfortunately. "Maximum head height" is as high as the pump can move a column of water with it's current output hose
(0 flow rate, simply fighting gravity).
Aspirators are meant to run at sink pressures, which are usually between 20 and 40psig, IIRC (1.4~2.7bar). Using the maximum head to represent the
most pressure the pump can put out, and simple barometer equations, we find that the maximum output pressue of that pump (assuming no friction losses
and without raising the tubing at all at the original output diameter) is 0.0784bar.
If I'm not mistaken, scaling down the output hose diameter will net you a significant boost in pressure, since P=Fa. There will be losses from
friction, however. You'll need to match the diameter of the threading on your aspirator.
I'm used to using the nalgene aspirators in lab, and they claim to be effective down to 8psig, though I can't imagine their performance is stunning at
those kinds of pressures.
There may be some faulty logic in there. Feel free to correct me. Maybe the output pressure will change relative to hose volume instead....I'm not too
sure.
[Edited on 10-5-09 by UnintentionalChaos]
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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grndpndr
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I have some interest in a vacum distillation setup using the inexpensive
water aspirator.Does water temp have an effect on vacum one could expect from the water aspirator.Our well water leaves the well head at over 130f and
depending on where you live in town the tap water can exceed115f.In fact most houses dont need thier water heaters even in summer thier used instead
for cool water reserviors.
[Edited on 6-10-2009 by grndpndr]
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gsd
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@grndpndr
Let us say your house receives water at 115 Deg F = 46.1 Deg. C. As per Antoine's Equation given upthread, this corresponds to vapour pressure of
water = 76 mmHg or 76 Torr.
This is the maximum THEORATICAL vacuum you can pull. Even with the best of hardware and very carefully made leak proof system, you can expect to go up
to about 80 to 85 torr. Make generous allowances for your Inexpensive setup.
gsd
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1281371269
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http://cgi.ebay.co.uk/Stuart-Turner-Monsoon-3-bar-twin-showe...
Something like that seems the way to go.
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1281371269
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Phillip Harris have just delightfully informed me that they have discontinued the vacuum adaptor (did they tell me this when I placed the order? Of
course not. I had to email them asking why it hadn't arrived to be informed  )
and I can't find any others.
There's only one thing I can forsee needing a vacuum for which is white fuming HNO3, and I don't need any of that, so I'm going to put this whole
thing on hold until I'm better armed with knowledge, necessity and finance to tackle it.
Thanks so much to those who have answered my questions on the topic, I'm sure the information will be of use in the future.
[Edited on 6-10-2009 by Mossydie]
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