Homebrewed Electricity > Hydro
My Jungle hydro project- 5kw pelton to power future eco-hostel
SparWeb:
That's a poncelet wheel. It's for trapping flow without having pressure, or a conduit. More like a water wheel in a river.
clockmanFRA:
This is a low cost manufacturer in New Zealand.
https://www.powerspout.com/
They have been making them for many many years, and have perfected small hydro systems and have a good track record.
junglehydro:
--- Quote from: SparWeb on March 26, 2021, 09:01:24 PM ---You need the exit velocity of the water from the nozzle. That depends on nozzle geometry and the head.
Do I recall correctly that the charts I gave you on the previous thread give you some idea of that?
--- End quote ---
Alright so from what I can figure out I would get a velocity of discharge at around 102 feet per second at my site(50m/165 feet of head), giving me a discharge of 250 GPM (per nozzle, so total would be double that) However from the powerspout advanced calculator I get a total possible water flow of about 370 GPM for my give penstock size (4"/ 10cm)
The size calculations for my nozzles (a total of around 850mm²) do match up between the powerspout calculator and the table that you posted in the other thread. But looking at the info in the goulds sheet it looks like 2 25mm nozzles would drain my penstock...
So how would I convert those 102feet per second into RPM's for my wheel?
I am planning to put ball valves on both pipes that lead to the nozzles, should I regulate my flow with them to prevent my penstock from draining? Or will that give me an efficiency loss that is too great and should I opt for slightly smaller nozzles?
Right now I am leaning to make the nozzles tapered cones with an opening of about 22mm, and that I can just shave of a bit of the tip to make the opening wider to experiment with the outcome.
--- Quote from: SparWeb on March 26, 2021, 09:01:24 PM ---I don't have Thake's book, so I need to ask: Does Thake get into the definition of power? You need both flow and pressure. The nozzle you have diagrammed may have a 1/2" port. Is that enough flow to make the power you want to get? Do you only have 1 nozzle?
--- End quote ---
From the table i concluded that with my head and flow, and the fact that I am using 2 nozzles the nozzles are going to be 25 mm in diameter. They re going to be removable however, so I will be able to experiment with different sized nozzles and see what works best. But your chart definitely helps taking most of the guessing out of it.
The book goes into power as in it gives the formula :
So let me see if I can work with that and figure it out :-)
--- Quote from: clockmanFRA on March 28, 2021, 06:02:37 AM ---This is a low cost manufacturer in New Zealand.
Powerspout
--- End quote ---
Hi Clockman, yes as you can read in my start post I know of powerspout. I have chosen to build something with local parts so that I figured it would fit our usecase better and the maintenance in the future might be easier if it is made with local parts. Plus this process allows me to learn more about these systems than just installing something off the shelf, so I am better equipped to do any future work on the system.
--- Quote from: SparWeb on March 26, 2021, 09:04:33 PM ---Here's a photo of a pelton with 2 nozzles pointed at it.
I have seen an arrangement with 4 before, perhaps in Home Power magazine.
--- End quote ---
Isn't that losing a lot of efficiency by the nozzles being so far away from the wheel? I am trying to get them as close to the wheel as I can get them without them actually touching, but from looking at this design I'd think that having 10cm between my wheel and Nozzle doesn't present such a problem.
SparWeb:
Hi JH,
One thing to check is the volume of the flow in the penstock (Area * velocity) and compare with the nozzle flow volume (Area * velocity). Put that way, kinda obvious that they'd be equal, but the reason to point it out is to make sure it's considered in your math. It can give you a solved variable that otherwise wasn't certain. A few calculations to size up the nozzles, penstocks, and wheel in general, followed by experimenting with nozzle sizes, should allow you to tune in the generator to the point you're happy with it.
I haven't experimented with these personally, so I can't say anything useful about the distance of the nozzles from the wheel. I guess it would depend on how well... "collimated" the "beam" is... I don't think I'm using the right terms; I hope you get what I mean. There's another factor that getting the water OUT of the compartment may also be an issue.
bigrockcandymountain:
So to calculate rpm from velocity, you can just use your basic geometry. Circumference is diameter x 3.14
Say a wheel with diameter 2 feet x 3.14 is 6.28' circumference.
102fps discharge divided by 6.28 is 16.24 rps or 975 rpm. That is unloaded rpm. Under load, your wheel will run slower than that. How much slower is optimum? I'm not sure but i bet the knowledge is out there. I would estimate 25% to 50% slower might be close.
Another question would be is it better to have a large low rpm pelton wheel or a small high rpm. I would think you are close thinking a 3:1 ratio with your pelton running 600rpm and your generator running 1800 rpm but that would be a good question to ask.
I really know nothing about hydro, so I'm mostly just thinking about questions that need to be asked.
I would suggest the inside of the nozzle is pretty important to make the right smooth shape. You want laminar flow exiting the nozzle, so any valve pinching should be done a distance back from the nozzle and in the larger diameter pipe. That is just a guess, but I could see messy turbulent flow near the nozzle really hurting efficiency. As spar would say, you want a nice "collimated beam" of water. ;) I don't know any better term, so i better not laugh.
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