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Fish-way using low head hydro turbine

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Natreely:
The MS Excel spreadsheet _FishwayGWVPP.xlsx
Work through inputting some different numbers into Tank diameter at top left, then you'll quickly get the ballpark figures for the head height and flow range you have available.
Please could we have suggestions for improvement of this attachment. When in a technical aspect please include your source of the research and/or calculations by which you arrived at that point.
You may also find this 4.9Mb transcript to be an interesting read, particularly chapter 2 by Andreas Steinmann:
http://assets.hansgrohe.com/assets/global/Wassersymposium_2012_What_water_needs.pdf
Rgds, Nat

Natreely:
Maybe, I've glossed over some things, taking it for granted that you can read my mind and arrive at my reasoning!!! Like...
Turbine Diameter due to Orifice diameter
Reasoning that people will hardly bother with a mechanically adjustable orifice, to increase or decrease the orifice diameter according to the flow rate. Therefore the designer will chart the mean flow rates from history, fixing on an orifice diameter that is going to be optimum or close to optimum for the most time. The area of faster rotational flow does not extend anywhere near one third the radius of the tank. Seeming more relevant to tie the turbine diameter to the orifice size, it is just inside and just outside the orifice circumference that the rotational flow is best to be in contact with the blades. Remembering of course that we must have room between the blades and through the orifice for the species of fish involved.
Please note that as mentioned below the spreadsheet, having decided on a fixed orifice diameter then to multiply by 1.3 to get the turbine diameter may not be optimal as we haven't yet found adequate research to connect the two together. Therefore if the optimal factor is less than 1.3 then the RPM figure will be slightly more. Otherwise if the same length of blade was curved tighter to the shape of the vortex, there would still be the same surface area in contact with less diameter of turbine, consequently slightly higher RPM. This effect on the RPM can be seen as the Turbine Diameter is adjusted at top middle of the spreadsheet.
Due to the shape of the vortex, the height of the blades doesn't need to be higher than 75% of the maximum head height or 80% if curved up, therefore saving turbine weight.
Even though this spreadsheet was done with slow fish in mind, the parameters of the conditional formatting are easily adjusted, to give the green light for the design specifications suited to your local species.
When significant adjustments are made to the spreadsheet we can reattach it here.
Rgds, Nat

Natreely:
While rereading some of the research on blade experiments, it was noticeable that,
(a) Efficiency increases in extracting power from the water with increased blade area in contact with the water, in simple terms, more blades,
(b) Yet reaches a point very quickly that the extra blade weight putting pressure on the bearing counteracts the efficiency.
Then a Eureka moment, well, something clicked anyway... Why don't we increase the buoyancy of the individual blades so the turbine becomes weight neutral?
Having welded a few polymer things together before, we do find working with ABS relatively simple. A double skin in the submerged area with an air space enclosed and horizontal ribs to strengthen the blade, so how much air space is needed?
Firstly how much weight is involved in the turbine plus the shaft?
Working with a hypothetical 1.2m head height, 0.9m x 0.3m of blade submerged (allowing for some air core as it is a "critical" vortex), and using the online ASM Weight Calculator with 3mm ABS for the blade and 3mm wall 56mm OD ss pipe for the shaft... Gives us up to 7Kg for the shaft/brackets/bolts and 2.8 Kg per blade.
Then, for all the submerged square area an average of (AG = air gap B = buoyancy) 12mm AG = 3.2Kg B, 15mm AG = 4Kg B, 18mm AG = 4.86Kg B.
Now to follow through,
Where 4 blades is designed, 4.86 * 4 = 19.44Kg B minus the weight of  2.8 * 4 + 7 = 1.24Kg upthrust so reduce the AG slightly.
For 6 blades including a 15mm AG 4 * 6 = 24Kg B minus the weight of 2.8 * 6 + 7 = 0.2Kg upthrust.
Are we on the right track to increase mechanical power? Opinions???
Rgds, Nat

Natreely:
In the above post regarding "Turbine Diameter due to Orifice Diameter" we mentioned mean flow rates.
Mean flow data should not involve extreme flow rates, either of drought or flood. So we need to make clear that this is not about an overall average. An "average" is when lines of data are added together then divided by the number of lines, but if this data includes the worst drought period in 50 years or a 1 in 50 year flood, then this is going to be terrible on which to base a hydro turbine's operating range. You may not want to even include the dip / peak of of a 1 in 10 drought / flood, but you decide where to draw the line.
Why do we need to draw a line through it, flattening the data?
In the 30yr+ design life of a good hydro turbine, extreme events happen less than 5% of the time, not so extreme events (but still not normal) happen less than 15% of the time. So while it is helpful to know major flood heights, so that the expensive equipment can be winched out of the way, we want to base the normal operation on what happens at least 75% of the time. On that long term chart cut off the peaks and valleys (draw the line), for flooded "drown-out" or below marginal generation level drought are not operational time anyway.
Having a roughly accurate operating flow range to design from is crucial for giving vortex heights, orifice diameter and therefore tank diameter, in fact for the GWVPP the design mostly depends on what flow is available. As a fish race 0.5m to 1.5m is a good head height. According to the research mentioned above, 255 litres per second only gives 0.4m vortex height so we couldn't expect much more than 300 W at that flow rate. For a vortex, the flow rate dictates the head, so even if you held back 1.5m head of water then opened the orifice, it would briefly have a faster flow rate then drain down to whatever vortex height the flow could support.
Some good advice on finding data for assessing your flow rate history can be found at the following thread:
http://www.fieldlines.com/index.php/topic,148642.0.html
Hopefully the flow of information will help both the swimming of fish and the flow of electricity.
Rgds, Nat.

Natreely:
Yes we are serious in saying that 255 litres / second is very low flow for any low head hydro but...
Hypothetically saying that's what you have, with 1.5m of head height available. You just happen to own a concrete batching plant so the infrastructure cost is not going to be as huge as for most farmer Joe Citizens. So you put three 0.5m deep tanks one after the other, providing 3 x 300 Watts. Most high living people off-grid would say that a reliable 21.6Kw/day is not to be sneezed at. Well you do have the cost of three turbines, generators, wiring etc so ROI will be a tad longer. :( Still somewhat less work than a lot of systems with complex intakes, long penstocks and very regular maintenance programs. :D Generally the patent holder and others who are building this design are saying, "minimum 0.7m head with 450 litres/sec flow", which would give a quicker ROI.
Presently adjusting, extending details and cleaning up the spreadsheet before posting the improved version.
Rgds, Nat.

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