Differential pressure equivalent, please?

[Externet]

An osmotic membrane takes 1000 psigauge on the inlet side, and atmospheric pressure at its outlet side to perform its work.

 

If the same osmotic membrane is left at atmospheric pressure at the inlet side; how many inches of mercury should be applied at the outlet to perform equally ?

[swansont]

http://www.onlineconversion.com/pressure.htm

[Externet]

Thanks. Am sorry, does not make sense

 

Differentials between pressure and partial vacuum are not this table thing.

Edited February 19, 2012 by Externet

[John Cuthber]

The answer is about 30, provided that you can find a planet where the ambient pressure is 1000 psi.

Otherwise it simply won't work.

[doG]

If 30 inches of mercury is approximately 1 atmosphere then how many atmospheres is 1000 PSIG? You will need the same ratio to do the same work. BTW, why don't you convert your reference to PSIG to PSIA since as John suggested, you will be hunting for another planet to get this to work.

[John Cuthber]

You don't need the same ratio.

You need the same difference; about 985 PSI.

With an upstream pressure of 15 that's not possible.

Edited February 19, 2012 by John Cuthber

[Externet]

Obviously my question had a very wrong wording. Or concept. Thanks for your patience.

 

Trying again...

 

Can only suction from a vacuum pump at the discharge side of an osmotic membrane and nothing at the inlet, achieve the same osmotic effect instead of the 'normal' case of applying pressure at the inlet and nothing at the outlet ?

 

Reverse osmosis "normal process" : 1000psig ----->inlet---->membrane----->outlet----->atmospheric discharge

 

If I only have a vacuum pump and no compressor, can the same reverse osmotic process be achieved ?

 

Atmospheric------>inlet----->membrane------>outlet------>?inchesHg vacuum pump

 

What amount of vacuum capability should the vacuum pump be ?

Edited February 19, 2012 by Externet

[John Cuthber]

Which part of "no" is giving you trouble?

The only thing you might manage is to bugger up the osmosis system and your vacuum pump.

[doG]

What amount of vacuum capability should the vacuum pump be ?

About 2000 inches of mercury...

[doG]

Can only suction from a vacuum pump at the discharge side of an osmotic membrane and nothing at the inlet, achieve the same osmotic effect instead of the 'normal' case of applying pressure at the inlet and nothing at the outlet ?

I would say yes, as long as you increase the surface area of the membrane proportionately to the decrease you will suffer from operating at a lower pressure differential.

[Externet]

Thanks, gentlemen for your patience. I think I got the misconception clearer with your help.

Perhaps the reason of my stubborness was the wrong perception of vacuum as being "omnipotent" when it is not.

[John Cuthber]

I would say yes, as long as you increase the surface area of the membrane proportionately to the decrease you will suffer from operating at a lower pressure differential.

And I would say no because most of the pressure is not to drive the liquid through in spite of viscous forces where increasing the area would help.

Most of the pressure is there to overcome osmotic pressure which is defined by the concentration of solutes in the incoming water.

 

Also if you put water in a vacuum, it boils, is carried into your pump and screws it up.

 

So, once more, which part of "no" is giving you trouble?

[doG]

Most of the pressure is there to overcome osmotic pressure which is defined by the concentration of solutes in the incoming water.

 

Also if you put water in a vacuum, it boils, is carried into your pump and screws it up.

Most but not all. With enough surface area you could get by on atmospheric pressure. The surface water exposed to the vacuum doesn't have to be the water feeding the pump. Even if it were the cavitation created on the pressure side would only be destructive at high pressure.