I am looking for fundamental fluid mechanics equations + associated
sketches to help me understand and design a subsea venturi lift
eductor pump.

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Request for Question Clarification by redhoss-ga on 06 Mar 2006 05:25 PST

From what depth do you plan to pump.

Hello pierre16, I beleive that I know what you are looking for. A
venturi pump uses atmospheric pressure to lift fluids and is limited
to about 20 feet of lift. Here is some info to back up that statement:

http://www.nciweb.net/eductors.htm

What I think you need is called "air lift":

http://www.globalsecurity.org/military/library/policy/army/fm/5-484/Ch4.htm

Principle. Water can be readily pumped from a well (or the sea floor)
using an air-lift pump. There are no air-lift pumps in the Army supply
system; however, in the field, you can improvise and make a pump using
compressed air and the proper piping arrangement. The assembly
consists of a vertical discharge (eductor) pipe and a smaller air
pipe. Both pipes are submerged in the well (or sea water) below the
pumping level for about two-thirds of the pump's length. The
compressed air goes through the air pipe to within a few feet of the
bottom of the eductor pipe and is then released inside the eductor
pipe. A mixture of air bubbles and water forms inside the eductor
pipe. This mixture flows up and out the top of the eductor pipe. The
pumping action that causes water to rise as long as compressed air is
supplied is the difference in hydrostatic pressure inside and outside
the pipe resulting from the lowered specific gravity of the mixed
column of water and air bubbles. The energy operating the air lift is
contained in the compressed air and released in the form of bubbles in
the water. Figure 4-9 shows the operating air-lift principle.

All of the formulas and charts showing submergence, air
pressure/volume required, and gallons of water pumped per cubic feet
of air are shown. Scroll down to the bottom of the page to find the
info. This should be all that you need to size a compressor to move
the volume of water you want to pump. If you have any questions,
please ask for a clarification and I will help you further.

Redhoss