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Q: jet pump basics

Could someone explain or point me toward a good published explanation of how the mathematics of a jet pump work. I understand how they work in concept and had one in my well for years, but have a problem with the following.

I understand (or think I do) how a fluid passing through a restriction or venturi results in a low pressure within the restriction. Consequently, I can see how the venturi in a carburator works for instance. In this case, there is an opening within the venturi (where the low pressure exists) that allows atmospheric pressure to "push" the gasoline into the venturi.

But in the case of a jet pump, fluid is pumped through the venturi and hence there is a low pressure within the venturi itself but I don't see how the fluid is lifted since that fluid is not being introduced into this low pressure zone. Therefore I assume that I am missing something about how to describe the control volume surrounding the discharge of the jet mathematically. I assume the jet reduces the pressure in the bottom of the well so that the fluid pressure is less than the weight of the column above.

Reference to a basic example of this concept in a text book or other source would be most helpful. I went back to my physics and fluids texts (pretty old now) and keep getting stuck on the control volume that includes the region just beyond the discharge of the jet. I'm sure it will turn out to be something simple.

I'm working on a concept similar to a jet pump that I'm intuitively sure will work. I would just like to be able to prove it to myself mathematically to aid in sizing components.

Reply to
Jon Juhlin
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Dear Jon Juhlin:

I think you have two different pumps in mind. There are jet pumps in wells, and they are essentially multi-stage centrifugal pumps. The ones you are referring to are also called eductors, venturis, injectors, and yes, some call them "jet pumps".

Actually, pressure and velocity are inversely related when no heat is added. Low pressure doesn't "exist", it is actively formed.

No. Eductors can be made to pull in excess of 27 inches of mercury vacuum, but this won't pull any significant volume of water. None at all if you need in excess of a 30 foot lift.

It has already been done, and you will be putting your effort into a field where competition is *very* cut throat. Beyond the major manufacturers (I'll assume you are already aware of Penberthy, who call them jet pumps), there are ozone generator manufacturers that also try their hand at making them.

A very inexpensive injector: URL:

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And there are cheap "Chinese" knockoffs to be had in PVC.

David A. Smith

Reply to
N:dlzc D:aol T:com (dlzc)

You are correct that the converging nozzle (increase in velocity) portion causes a decrease in pressure to draw addition fluid into the eductor. But an eductor also has a divering defuser that does the oposite: decreasing velocity for increasing pressure.

Write Bernouli's equation across the eductor. remember to include an increase in mass flow through the discharge.

also realize there will NOT be a single unique solution but a flow vs. prssure relationship like a centrifugal pump. the actual operating point will be at the intersection of the "pump curve" and the "system curve."

Eductor performance is very "geometry" dependent. I am most familiar with steam jet eductor moving gases. there are limits to the discharge pressures. Moving the "jet nozzle" closer to the body can increase discharge pressure on an otherwise "breaking" jet at the possible expense of capacity. Manufactures build scale models for testing rather than releying on the fluid physics alone for specialty application.

don

Reply to
doubl00

mathematically

Some basic applications of a jet pump that I have been involved in include: As a fuel boost pump for a jet engine inlet. Empty a fuel drain tank by returning the flow back to the boost inlet supply. Ecology considerations to collect all overboard fuel drains so they don't spill on the runway.

Reply to
MLD

I'll give it a brief shot:

for a suitable nozzle and augmentor geometry where the nozzle flows into the augmentor throat, a nozzle's cross section area times the jet efflux speed is lower than the augmentor cross-section times the augmentor efflux mean speed (of the jet efflux and augmentor entrained flow).

This constitutes a pump.

Any help?

Brian Whatcott Altus OK

Reply to
Brian Whatcott

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