Using low pressure water flow to generate low flow enhanced pressure. 2

[asimpson]

I have a project where a water supply of less than 0.1 bar and flow rate 5-10 L/min. I would like to use this water flow to produce a 2 bar stream of water at 0.2 L/min. Effectively intensify pressure using the kinetic energy of the flowing water. I have seen systems like hydraulic ram pumps that use river flow to pump small amount of water well above level or river.

http://en.wikipedia.org/wiki/Hydraulic_ram_pump

However these are large and pulse at low frequency (0.5 or less Hz).

Anybody come across a miniature version that pulses at 10 Hz or higher to produce a smoother flow?

I have the system working with a miniature electric pump the performs well but I would like to eliminate the need for external power source.

Application is domestic water.

Thanks

 

[micalbrch]

You need a pump and if you can not (or do not want to) work with electricity, what about compressed air? There are air driven diaphragm pumps available.

 

[1gibson]

Look at the water horsepower available vs required, see if you are trying to create energy or not.

GPM x 8.33 lbs/gallon x specific gravity = lbs/minute of fluid
x head (ft) = ft-lbs/min
33,000 ft-lbs/min = 1 hp

Sorry for the units, but check your available conditions vs what you want to generate. Make sure you factor in efficiency allowance your device(s.) If you have enough margin on efficiency, you might even be able to use a turbine as a generator for low pressure side, then connect to a motor for the high pressure pump. Battery as a buffer, add solar panel for additional energy?

Maybe some sort of direct drive device if you are cutting it close on efficiency.

 

[TheTick]

What about a diffuser? Increase cross section --> slower speed --> increased pressure (according to Bernoulli).

 

[hydtools]

The miniBooster has the pressure ratio you want, 20:1, but I do not know if it will work at your low pressures.

http://www.minibooster.com/products/boosters-oil/hc3.html

They are not cheap.

Ted

 

[btrueblood]

asimpson,

What velocity does the main stream have or can it be made to achieve?

 

[MintJulep]

These are intended for air, but the same concept should work for water.

http://www.haskel.com/corp/details/0,,CLI1_DIV139_ETI9791,00.html

 

[zdas04]

Have you ever seen a water-bed pump? How about a hose-end sprayer? They are called "eductors". They do exactly what you are trying to do.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

 

[btrueblood]

I was going to suggest the amplifier pumps like Mint suggests...but at 1 psi, you will struggle with seal friction using typical hydraulic cylinder seals. It might still work with a low-friction piston, perhaps using diaphragm seals, but you would have to build it "custom"....and the overhead work for the cylinder valves might reduce your efficiency to zero with such low working head.

The eductors like Dave suggests might also work, but that assumes you have a high flow velocity - not sure that's true here, it's the one piece of information asimpson hasn't given us. If the velocity is high enough for an eductor to generate the required pressure, then even a simple pitot tube would provide the required flow...

 

[zdas04]

He's got 5-10 L/min and wants 0.2 L/min of the combined stream. If you know volume flow rate, velocity is simply a function of pipe diameter. You can get the velocity you want/need by picking the right pipe.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

 

[asimpson]

Thanks everyone.

I am not sure how diffuser would work.

I'm afraid I don't want to use any other power source other than the motive power of the water.

The velocity through 1/2" pipe would be 129 f/min or 39 m/min. Given the low pressure supply. In this case about 2 m head of 6 ft. for the supply pressure. Using a nozzle to increase velocity may be ineffective and just result in lower flow rate.

I don't see how an eductor could produce a pressure greater than the supply pressure. I understand how they can pump large volumes of liquid using a small flow supply that has high velocity by jetting it through nozzle under pressure.

Mechanical pressure intensifiers seem to be on a much larger power scale than in my situation and friction losses would probably overcome the whole system. That is why the ram pump seemed like a possible solution. It has virtually no moving parts . But I have seen no examples on the scale I require.

 

[TheTick]

I am not sure how diffuser would work.

Respectfully, I'm guessing that your schooling was not in ME, or it all would have clicked when you heard "Bernoulli".

For a given stream of constant mass flow, velocity and pressure can be manipulated by changing cross-sectional area.

[URL unfurl="true"]http://www.learnthermo.com/T1-tutorial/ch05/lesson-C/pg07.php[/url]

 

[rb1957]

"But I have seen no examples on the scale I require." ... talk to a manufacturer about scaling

"I don't want to use any other power source other than the motive power of the water" ... i don't know this equipment but i'd've thought you were doing work on the fluid to increase its pressure (so i think you need external power.

 

[77JQX]

You're looking for a pertty high efficiency: 40 to 80% depending on the supply flow. I think a hydraulic ram is your only bet. Have you seen this manufacturer's data?

http://www.riferam.com/rams/ramspecs.html

It looks like you'd need a Davey #2

 

[zdas04]

You are right, an eductor must discharge into a lower pressure than the power fluid pressure. I read your original post too quickly.

This sounds like a water wheel driving a centrifugal pump kind of application.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

 

[asimpson]

I am familiar with the Bernoulli effect , I was just not sure what is meant by a diffuser. If this is an increase in CSA of pipe, how could this increase pressure with respect to pressure driving flow. As I understand the Bernoulli effect generates a pressure difference when velocity is increased by narrowing of CSA dropping pressure at this point with respect to larger CSA before and after narrowing.
Could this be used to pump a small portion of water say 10% to a tank higher than the header tank feeding the main flow? Just like a hydraulic ram pump.

 

[rb1957]

i think bernoulli = "red herring" in this case. 77's link looks to be exactly what you want !?

 

[TheTick]

I think you're right, RB. I've put more thought into this. To get a parcel of water to rise above it's original level, it's total specific energy must increase. Simply trading enthalpy for kinetic energy and incurring losses along the way won't do it.

One of two things must happen:
1.) outside energy input
2.) energy transfered from one portion of the flow to another (e.g. turbine pump).

I thought there might be a way to do this without a pump, but I'm not geting there.

 

[rmw]

Aw shucks, and just when I thought we were about to invent perpetual motion in this thread.....

rmw

 

[KENAT]

http://en.wikipedia.org/wiki/Hydraulic_ram

as mentioned previously.

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