Submerged Axial Flow Hydroturbine 5

[SreeSiv]

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.

 

[LittleInch]

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/FlowOfRiver/FlowOfRiver.htm

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.

 

[rb1957]

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 ?

 

[GregLocock]

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_id=9966

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[SreeSiv]

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/getfil...48cb-975c-fa7d345b1b20&file=Shaft_Sealing.pdf

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/FlowOfRiver/img2D.jpg

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?

 

[1gibson]

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.

 

[Compositepro]

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.