4 ms·

In theory, wouldn’t you be able to just keep pumping from the surface of the pipe (increasing x) until x provided a sufficient differential pass through the mem

In theory, wouldn’t you be able to just keep pumping from the surface of the pipe (increasing x) until x provided a sufficient differential pass through the membrane? It would then stay at x even while you continue pumping. The pump would merely need to lift the water from x below sea level.

p1mrx 3y ago
Pumping from the surface, like with a vacuum? The maximum height of a drinking straw is about 10 meters. It's generally easier to lift water by pushing from the bottom than pulling from the top.
- jychang 3y ago
  10 meters at sea level. A lot more when you have an ocean’s weight of water pushing on the other end.
  - p1mrx 3y ago
    That's irrelevant, because the pressure at the water surface is ~1 atm regardless of its depth below sea level. Air pressure increases slightly as you descend a well, but not enough to change the outcome.
    - jychang 3y ago
      The site pressure at a bottom of a well is irrelevant. You do realize air pressure is not what matters, but pressure as a whole? That includes water pressure. The bottom of the straw is not in a well; it’s more akin to a cassion, so you need to factor in the water pressure as well. What you’re saying would imply that the Titan submersible would be at the same pressure whether under an ocean of water, or in a well the same depth. No. The former is 375atm, the latter is a bit more than 1atm. You only need to lift the top layer of water a little bit. The rest of the water column would come up after it. Of course, you cannot lift the top of the siphon more than 10m above sea level.
      - p1mrx 3y ago
        In order for the reverse osmosis membrane to function, you need a rigid pipe at atmospheric pressure, without water in it. The pressure difference inside/outside the pipe is what powers the desalination process. While operating, it's basically a deep open well with a bit of water at the bottom. You need to pump that water out to keep the process going.
- amscanne 3y ago
  I mean the “pump” probably isn’t a vacuum pump. Maybe it’s a water screw. Maybe it’s a rope and bucket. The effect is the same, no? The water must be lifted X.
  - flaminHotSpeedo 3y ago
    Yes, the effect _is_ the same. Regardless of the mechanism, you can only lift water from above with a sufficiently short hose. It is incontrovertible that this system would have to push the water up from below.

p1mrx 3y ago

Pumping from the surface, like with a vacuum? The maximum height of a drinking straw is about 10 meters. It's generally easier to lift water by pushing from the bottom than pulling from the top.

jychang 3y ago
10 meters at sea level. A lot more when you have an ocean’s weight of water pushing on the other end.
- p1mrx 3y ago
  That's irrelevant, because the pressure at the water surface is ~1 atm regardless of its depth below sea level. Air pressure increases slightly as you descend a well, but not enough to change the outcome.
  - jychang 3y ago
    The site pressure at a bottom of a well is irrelevant. You do realize air pressure is not what matters, but pressure as a whole? That includes water pressure. The bottom of the straw is not in a well; it’s more akin to a cassion, so you need to factor in the water pressure as well. What you’re saying would imply that the Titan submersible would be at the same pressure whether under an ocean of water, or in a well the same depth. No. The former is 375atm, the latter is a bit more than 1atm. You only need to lift the top layer of water a little bit. The rest of the water column would come up after it. Of course, you cannot lift the top of the siphon more than 10m above sea level.
    - p1mrx 3y ago
      In order for the reverse osmosis membrane to function, you need a rigid pipe at atmospheric pressure, without water in it. The pressure difference inside/outside the pipe is what powers the desalination process. While operating, it's basically a deep open well with a bit of water at the bottom. You need to pump that water out to keep the process going.
amscanne 3y ago
I mean the “pump” probably isn’t a vacuum pump. Maybe it’s a water screw. Maybe it’s a rope and bucket. The effect is the same, no? The water must be lifted X.
- flaminHotSpeedo 3y ago
  Yes, the effect _is_ the same. Regardless of the mechanism, you can only lift water from above with a sufficiently short hose. It is incontrovertible that this system would have to push the water up from below.