[Externet]

Hi. On a reverse osmosis process,
If the seawater compartment on a desalination process is at 1000 psi; and the desalinated water compartment is at atmospheric pressure;

Seawater @1000 psi -----> membrane -----> desalinated water @0psi

What would be the equivalent pressure differential using atmospheric seawater compartment and partial vacuum to achieve same results ?

Seawater @0psi -----> membrane -----> desalinated water @??? inches of Hg

How is it calculated ?
Thanks

This post has been edited by Externet: 17 October 2011 - 01:40 AM

[Schrödinger's hat]

Externet, on 17 October 2011 - 01:38 AM, said:

Hi. On a reverse osmosis process,
If the seawater compartment on a desalination process is at 1000 psi; and the desalinated water compartment is at atmospheric pressure;

Seawater @1000 psi -----> membrane -----> desalinated water @0psi

What would be the equivalent pressure differential using atmospheric seawater compartment and partial vacuum to achieve same results ?

Seawater @0psi -----> membrane -----> desalinated water @??? inches of Hg

How is it calculated ?
Thanks

You're going to have to describe what you're asking a little bit more clearly.
Are the pressures gauge pressure or absolute?
If you meant absolute pressure, are you sure you meant for the seawater to be 0psi and not the desalinated water?
As you posted this in applied mathematics, some more description of the context or model you are using would be helpful.Then we can be more helpful.

[Externet]

Thanks.
Gauge pressures. Yes, seawater at atmospheric pressure.

The point is replacing presurizing the seawater compartment with suctioning the desalinated compartment;
or,
replacing a compressor at the inlet with a vacuum pump at the outlet to achieve same amount of differential pressure in the process.

[John Cuthber]

You need at least 27 bar pressure (g) across the membrane if you want to drive fresh water out of sea water.
Putting a vacuum on one side wouldn't help a lot ( you would still need to supply 27 bar (a)) and the water would evaporate into the vacuum so you really wouldn't help things.