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Submerged Axial Flow Hydroturbine
5

Submerged Axial Flow Hydroturbine

Submerged Axial Flow Hydroturbine

(OP)
I am trying to build a submerged axial flow hydroturbine, but has only little experience with mechanical equipment building, and completely new to submerged equipment.

Will be grateful for your review/comments of the below concept and any answers for my questions.


Casing structure : The plan is to build two half-cylinders(steel/aluminium) with flanged ends, that can be bolted together with a neoprene gasket between the flanges. The aim of this design is to be watertight.

Casing openings : Two openings are expected on the casing - one for the turbine drive shaft and other for the electrical wire outlet. A shaft seal (eg: https://dir.indiamart.com/search.mp?ss=shaft+seal) will be provided at the drive shaft entry into the casing to prevent water ingress there. At the electrical wire outlet, a typical aquarium sealant will be used to waterproof.

Electrical/Mechanical components : Expected equipment are the same as a typical horizontal axis wind turbine- Bearings, Gearbox, Generator etc.


My questions
1) What problems do you see with the above design? Will it stay waterproof and work for long period?
2) How is water-tightness ensured typically for such equipment? Any resources/books where I could study about them?
3) Will there be an over-heating issue? Temperate water (20-26 deg.) is expected to constantly flow around the casing.


Thank you for the time.

RE: Submerged Axial Flow Hydroturbine

1) No reason why not, although your casing design is odd. A tube with O ringed threaded ends would be more conventional.
2) I know of no resources, buy a similar product and pull it apart. Obviously seal design is crucial. You might consider pressurising the thing with whatever compressed gas is easily available.
3) Do the math.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: Submerged Axial Flow Hydroturbine

When I left New Orleans about 8 years ago, the first crop of hydroturbines were then due to be submerged.
In the Mississippi.
Which is usually opaque with silt.
And regularly carries whole trees, and houses, and boats, and anything that falls in the rivers of half a continent.
I haven't heard much about the enormous amount of energy being harvested from the river there, but hey, it could happen.



Mike Halloran
Pembroke Pines, FL, USA

RE: Submerged Axial Flow Hydroturbine

Needs a drawing.

Why does this need to be watertight?

Axial flow hydro turbine could be anywhere. What are we talking about here? Bottom of a river? Connected to a dam?

There are many such designs, but you need to narrow it down a bit.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Submerged Axial Flow Hydroturbine

(OP)
Hi all,

Thanks for the replies.
I am new here, so just getting used to the policies.


GregLocock,
You are right about the casing. Was thinking it will be easier to fabricate flanged ones. But yes, have to try the threaded coupling option as well.


MikeHalloran,

The plan is to install in a river itself (in India). The turbine will be placed inside a structural frame with some protection members/chains in the front, to protect impact from trees, coconuts etc etc. Atleast that is the idea as of now, will see how it goes.


LittleInch,

This is a free stream turbine (i.e. no dams, diversions etc) . Please see the below pics/website for examples
https://www.smart-hydro.de/wp-content/uploads/2015...
http://www.builditsolar.com/Projects/Hydro/FlowOfR...
http://www.builditsolar.com/Projects/Hydro/FlowOfR...



Thank you again

RE: Submerged Axial Flow Hydroturbine

suggest you hire a turbine / pump designer experienced in this area. would also be a good idea to give a clue as to what size you are discussing, 1 kw or 1000kw and of course along with all other relevant data necessary.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

RE: Submerged Axial Flow Hydroturbine

It appears you're thinking of the mechanical reverse of a ship's propeller: Instead of using a big engine inside the ship moving the ship through (essentially) still water, you want to mount a fixed generator underwater with the moving water turning the propeller to turn the generator shaft. The generator then needs to be sealed and inside a watertight enclosure suitable for the depth required. The generator shaft would need a seal, and its bearings inside the WT enclosure need to be oiled and continuously lubricated, but the propeller bearings do not. One old bearing material in water is lignea vertim I think. (-1, spelling)

If so: Logs and debris large enough to bend and break the shaft or propeller blades would be even more likely to jam if there were a tube around the propeller/turbine.

Expect low speed revolutions: How will you gear your generator? DC instead? Ship's propellers at twenty foot diameter blades are designed for 15 knots forward motion. No river will ever be that fast = 2-3 knots is about the highest a river will run. If you "trap" massive amounts of water with a "dam" or large inlet, then focus the water through the tube and the turbine blades, you're going to get jams and debris problems.

RE: Submerged Axial Flow Hydroturbine

how deep is this installation ? how much pressure expected ??

another day in paradise, or is paradise one day closer ?

RE: Submerged Axial Flow Hydroturbine



My questions
1) What problems do you see with the above design? Will it stay waterproof and work for long period?
I don't think so. Any rotating shaft seal has a high potential to leak at least the odd drop every hour / day. The only way to ensure long term submerged sealing is to either pressurise the inside and maintain that pressure with e.g. an airline to the surface. Note this should be just above the hydrostatic pressure, but even then you might get some liquid inside the casing over time. Unless you use something like a magnetic coupling / mag drive between the shaft and the generator drive it will be difficult.

Or just include a drain line and pressure line and blow the water out every now and then.

2) How is water-tightness ensured typically for such equipment? Any resources/books where I could study about them?
See above. either seal it all off, make it work liquid filled or pressurize it.


3) Will there be an over-heating issue? Temperate water (20-26 deg.) is expected to constantly flow around the casing.
Maybe - Depends on the amount of heat your generator is developing and the surface area / heat sink / max temp. However the liquid flow will take a lot of heat away - you just need to work it out. The bigger it gets the worse it will become.

This must be a fairly mature technology by now - a simple google search throws up lots of systems.

however river flow velocity on its own is really quite low and very difficult to harness power effectively. you really need some sort of dam or weir to get the water to be collected better.

a water wheel must be more effective than this.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Submerged Axial Flow Hydroturbine

Consider using some form of strain relief/bend stiffener at the cable entry point.

"I love deadlines. I love the whooshing noise they make as they go past." Douglas Adams

RE: Submerged Axial Flow Hydroturbine

(OP)

Hi all,
Thanks again for the input.
Here is some general info.
Rotor diameter = ~ 1m to 1.5m
Water velocity = ~ 1.5m/sec to 2.5m/sec
Expected energy output = ~ 1 to 5kw
Depth of installation = ~1-2m below waterlevel

Artisi,
Couldn't find a suitable manufacturer yet. Most of them are experienced with Wind turbines (no issue of water tightness there), or high head/vortex based designs (eg: kaplan etc). Besides the scale is not big to attract typical manufacturers. This concept is almost like an R&D work at the moment.


racookpe1978,
Yes you are right, this is almost a modified propeller design. As you know already, difference here is that the blades are designed to generate maximum torque and an optimum axial thrust, whereas for the propeller the aim is maximum thrust at minimum torque.Do you know of any resource for information about propeller housing structure design?
And this will be a free stream turbine. So no dam/diversion is planned to be built.

Lubrication - expected operation time is maximum 2 months. Initial lubrication must be sufficient right?

Logs and debris - Yes, its expected to be there. But some protection structure will be provided 1-2 meters in front of the turbine.

Generator - Plan is to use a Permanent magnet generator and a converter to produce AC. May add a controller in future to optimise output. Anyway the project is in R&D stage at the moment. There is a chance to test out the system in a tow tank. About RPM, studies (done with Qblade) are showing that expected RPM is in the range of 100-200. So, would use a gearbox to connect to generator.


rb1957,
Expecting about 1-2m below water level, not much pressure really.


LittleInch
Noted. For my information, is seal leaking a usual occurrence for similar structures (eg: propeller housing)?, even with good quality shaft seals?

I dismantled a submerged pump btw. It had a permanent magnet rotor, located in a chamber where water can enter freely. The stator wiring and the electrical components were housed inside another chamber which was filled up fully with graphite or some compound.

Had looked at the water wheel concept as well. That type of device seems to have an efficiency of about 15%, whereas this type of horizontal axis turbines could give efficiencies in 40-50% range. Thatsy was trying to build expertise on this concept. If it can be done cheap, then its good option.


Thank you again


RE: Submerged Axial Flow Hydroturbine

Racookpe1978, Lignum Vitae? It's awesome stuff. I've made components for several restoration projects of old machinery using wood bearings.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

RE: Submerged Axial Flow Hydroturbine

how much will the upstream debris deflector, which will need to be a substantial (massive?) structure, affect the flow into the turbine ?

why not a traditional waterwheel ? one built from traditional materials (to make it easy to repair). particularly one with a holding pond upstream (to create a useful pressure drop across teh wheel) ??

another day in paradise, or is paradise one day closer ?

RE: Submerged Axial Flow Hydroturbine

What is your problem and what are you trying to achieve, especially after answering your own question with the following links you supplied.

his is a free stream turbine (i.e. no dams, diversions etc) . Please see the below pics/website for examples
https://www.smart-hydro.de/wp-content/uploads/2015...
http://www.builditsolar.com/Projects/Hydro/FlowOfR...
http://www.builditsolar.com/Projects/Hydro/FlowOfR...

Further: I suggested finding someone qualified to address your ideas, not find a supplier.
"Artisi,
Couldn't find a suitable manufacturer yet. Most of them are experienced with Wind turbines (no issue of water tightness there), or high head/vortex based designs (eg: kaplan etc). Besides the scale is not big to attract typical manufacturers. This concept is almost like an R&D work at the moment."

RE: Submerged Axial Flow Hydroturbine

Note: I have NOT designed any such structures nor the mechanical generator & seals internals.

At 1-2 meters deep lasting 2-3 months service, you could just haul it (the whole watertight casing and seals) up out of the water for maintenance. Use extra-long cables for the DC output to shore, as long as local theft is not a high probability.

But. The optimum would be a very large propeller at very low RPM in nearly clear (debris-free) water flowing at "high speed" through an unobstructed channel for almost all of the year, not threatened by shipping or the enviro's favored-creature-of-the-week. The best location I can think of is the very deep channel under the Golden Gate Bridge: At 377 feet deep, and over 4000 feet wide, the channel bottom is far below even the deepest ocean-going vessel. (Unlike the Hudson River or Thames or Mississippi or others worldwide.) Deep enough to allow a 50 or 80 foot propeller = you can get some real energy even at low RPM. Get that deep, and less debris will be flowing: It gets dropped out further up the San Francisco Bay in the shallow, low-speed areas.

The tides sweep in and out, reducing the net outflow part of the time. Either live with the predictable loss of power generation at predictable (but varying!) times every day, or build two generators with one facing each way. Then the fixed pitch propeller on each generator would be optimized for the direction of flow and speed of flow. Vastly more complicated, but with better efficiency, is a variable pitch propeller = Vastly more expensive and vastly more likely to breakdown.

RE: Submerged Axial Flow Hydroturbine

"This concept is almost like an R&D work at the moment."

then treat it as such ...
1) learn what you can about what is known (not much here by the sound of it, but there is knowledge out there),
2) learn what you can about similar things,
3) assess if you have a reasonable chance of success,
4) understand why traditional solutions won't work (why do you need to build a better mouse-trap ?),
or adopt/adapt a traditional solution,
5) build something you think might work, instrument to cr@p out of it (to collect data for re-designs),
6) go learn things.

I think what you're trying to do is "daunting" ...
1) very low energy source
2) very challenging operating environment (debris, silt, theft, maintenance support)
3) very little pay-back ?

another day in paradise, or is paradise one day closer ?

RE: Submerged Axial Flow Hydroturbine

(OP)
Thanks for all the advises and opinions till now.

After initial round of info gathering and learning, I have come up with a rough plan for the concept.
Please find the attached PDF for some 3D illustrations of the concept.

Would be grateful for your review and comments.

As mentioned earlier, I am pretty amateur at this, so feel free to comment/suggest anything.


Thanks

http://files.engineering.com/getfile.aspx?folder=9...

RE: Submerged Axial Flow Hydroturbine

Quote (Sreekanth Sivaraman)

Stiffness of this base plate and its tight connection to the housing ensures minimal vibrations of the equipment.

This base plate to be bolted to the Casing structure at 4 corners.
So what's going to ensure minimal vibration of the housing this is all placed in? A bolt at each corner is nor exactly a solid mount, particularly at the size you're talking about here, and that plate would have to be massively thick to prevent flexure with only four mounts.

Dan - Owner
http://www.Hi-TecDesigns.com

RE: Submerged Axial Flow Hydroturbine

Your pdf specifies "Deep Groove Ball Bearing" in several places; however, the image shows a tapered roller bearing in each instance. If you are that confused about ball bearings, you have much reading to do.

Mike Halloran
Pembroke Pines, FL, USA

RE: Submerged Axial Flow Hydroturbine

Looks like the horizontal axis turbine in the link on the tidal devices I had above.

Far too much effort for 1-2kW and does nothing for the river debris issue or the shaft sealing issue.

I would go for a more simple system, but look up these guys. http://www.builditsolar.com/Projects/Hydro/FlowOfR...

Note the size of what you would have to build to get anything like 1 kW and note the velocity issue. 1.5 m/sec = 3.4 MPH

And the smaller you go the worse the real life efficiency - you will struggle to get much more than 10-15%.


Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Submerged Axial Flow Hydroturbine

Sreekanth,

Please edit your post to remove your email (or at very least to disguise it (like ATgmailDOTcom) ... better not to post it at all (house rules).

another day in paradise, or is paradise one day closer ?

RE: Submerged Axial Flow Hydroturbine

It'll leak. That design of seal is not robustly proof against pressurised water migrating through the rotating joint as it wears. I'd use two in series and some sort of sump between them with a scavenge pump, or else a grease or oil filled chamber. That doesn't stop the water getting in, just that once it gets in it can't go anywhere you don't want it. Or reverse the seal and gas pressurise the interior.

Here's how it can be done
https://ca.binnacle.com/product_info.php?products_...

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: Submerged Axial Flow Hydroturbine

(OP)

Again thanks everyone for your valuable time and input.

I have updated the shaft sealing concept. Added one more Radial seal on the other side of the bearing and provided provision to pressurize the space between the seals. 2 options -
1) Pressurize the chamber with lubricating fluid. Pressure to be more than external pressure (~3psi)
2) Use pressure line + vent line and blow air into the chamber once in a while.
http://files.engineering.com/getfile.aspx?folder=4...
Two different scenarios are being considered
a) Maintenance free for a few days (1 week max)
b) Maintenance free for 2 years.

Option 1 or 2, which will be better suited for Scenario a and b ?


MacGyverS2000,
Was planning to use base plate of 15mm thick. No real calculations done yet, based on generator weight (~50kg) and Loads on bearings (1-3kN), it seemed that stiffness requirements will be met. But you have a point, I will run some checks. Will help in better judgment for a future bigger equipment as well.

MikeHalloran
The figures are misleading. At the time of making illustrations, a tapered roller bearing was modeled as axial loads were expected. But later based on design checks, it was found that Deep groove ball bearings are enough.

LittleInch

True, its just like one of those Horizontal axis turbines shown in the link you shared.
Basically this,
http://www.builditsolar.com/Projects/Hydro/FlowOfR...
This type of a device is the ultimate aim.

Actually water speed is a bit higher than 1.5m/sec as per latest info. 1.8-2m/sec is expected and there are times when the flow could go over 3m/sec.
Comparing fabrication/installation cost to Energy output, it looks like the costs can be covered in 2-3 years.

Based on the current blade design, on paper, efficiency is over 40%. I hope close to 40% is achieved eventually. Lets see.
There are some research articles about similar devices achieving over 40% efficiency.

For large debris, plan is to house this turbine a larger structural frame with a wire net (or similar) to protect - from drift wood, coconuts etc. Smaller debris hopefully wont cause a problem. The blades are reasonably strong actually.

Shaft sealing is where I couldnt reach a conclusion based on the info I gathered from internet searches. Seal catalogues of some companies seem to be saying that a simple lip seal of suitable material will serve the purpose, provided pressure rating is met. However, experienced people and some submersible pump designs seem to say otherwise. I am trying to be economical, thats why I had started off with a simple lip seal.
I have modified the design now. Please find the attachment, and description above. Any comments?



rb1957
Thanks for notifying. I cant edit the post anymore. I have notified the admin.

GregLocock
I have updated the concept, while trying to stay cheap and avoid mechanical seals. Please find the illustration attached and the description above. Any comments?


RE: Submerged Axial Flow Hydroturbine

Can you get the motor/generator in a dry area? Right angle gear drive, u-joints, long straight shaft at an angle if you can tolerate a bigger frame and an angled propeller? Much more DIY friendly than trying to design a submersible motor/generator from scratch, at low cost.

RE: Submerged Axial Flow Hydroturbine

Any dynamic seal will leak a little until it wears, and then it will leak a lot. Boat propeller shafts use packing glands and there will be a bilge pump. If the seal is unattended for a long period use a tiny pump to pump-out any leakage that is captured by a drip pan under the seal.

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