Hi Dominique,
Assuming you have info about the net pressure on the nozzle and the flow, rate:
Let: Q = flow rate, liters/second
h = net head, m
v = jet velocity, m/s
A = nozzle cross-sectional area, m^2
d = nozzle diameter, m
v = sqrt(2gh)
A = Q / (1000v )
d = sqrt(4A / pi)
Based on your site info, the nozzle diameter is 0.19 inch (4.8mm). Your best
bet for an alternator should be a permanent magnet type. If not available, just
use the smallest car alternator you can find. Most DC alternators consume power
for its excitation, typically around 40W (larger units consume more) at
1400RPM. If a permanent magnet motor is not available, you can improve the
efficiency of an ordinary car alternator by doing the following:
1. Remove the built-in fan. At 50W output, no significant winding heating will
occur, so the fan is just additional load and loss.
2. Increase the operating RPM of the alternator. Typical alternator field
windings have a resistance of about 5ohm. If a 5ohm/20W resistor is inserted in
series with the field winding, the alternator will have to operate at twice its
rated RPM to generate the same voltage. Excitation losses will be cut in half
(20W), but additional frictional losses is incurred by the bearings.
Best regards,
Eilrem
dominique both <[EMAIL PROTECTED]> wrote:
Hi Thor,
Very good advice on the dimensioning of the system, as
well as very good links. You gave the formula
regarding the diameter of the wheel vs the RPM. But I
wonder what is the best RPM for the system. Obviously
it should be given by the alternator we are using, but
I am planning to make a homemade alternator (like they
are doing it from scratch on several wind turbine
projects). Therefore what would be the best RPM for
such a system ?
Concerning the alternator, do u have any advice for me
? I wanted first to use a simple induction motor, but
many of them needs to have a gigantesque RPM (up to
10'000 for the little model I have !). For ur info, I
have a head of 22m (~67 feet), with 22l/min (~5.8gpm).
Hope to get ~50W at most, so nothing wilde, but I can
have it 24h a day, 365days a year. Think worth the
game !
Thanks for your help,
Dominique
--- Þórhallur Ragnarsson <[EMAIL PROTECTED]> wrote:
> Hi Sergio.
>
> Some useful links:
>
> http://www.tev.ntnu.no/vk/publikasjoner/
> A textbook for students on hydro power machinery.
>
http://www.tev.ntnu.no/vk/publikasjoner/pdf/ArneKjolle/chapter2.pdf
>
http://www.tev.ntnu.no/vk/publikasjoner/pdf/ArneKjolle/chapter3.pdf
> Detailed theory with formulas for many types of
> turbines.
>
> http://www.microhydropower.net/
> Good general explanation of the Pelton turbine with
> pictures.
> http://www.microhydropower.net/turbines.html#Pelton
>
> http://en.wikipedia.org/
> Wikipedia, the free encyclopedia that anyone can
> edit.
> http://en.wikipedia.org/wiki/Pelton_wheel
>
> http://www.ecoinn.co.nz/
> Very well made runners with plastic spoons,
> excellent pictures.
> http://www.ecoinn.co.nz/product_detail.php?id=58
>
> http://www.pressure-drop.com
> Software to calculate pressuredrop for all kinds of
> fluids, pipes,
> fittings, nozzles, etc.
> You can test it 4 weeks free. If you want use the
> program after this time
> you have to register by the author.
>
> Pressure-Drop can be used to find nozzle diameter
> (by trial and error).
> (I have not searched for a jet diameter formula
> based on pressure and flow).
>
>
http://www.du.edu/~jcalvert/tech/fluids/turbine.htm#Impu
> Good explanation of Pelton turbine with formulas.
>
> Summing this up:
> Bucket size approximately 2,5 - 4 times jet
> diameter.
> (Too small buckets do not use all the water
> efficiently,
> but too big buckets create more aerodynamic drag)
> Water exit angle approx. 165deg (so the water does
> not hit the back of next
> bucket).
> The edges where the jet hits the buckets should be
> sharp to minimize losses.
> The spacing between the buckets is made as big as
> possible,
> but not larger than to secure that all water
> particles will hit a bucket.
>
> Theoretical velocity of jet: V = sqrt(2gh). (In
> practice a bit less)
> Peripheral velocity of the runner: u (u can take any
> value from 0 to V)
> Maximum power is obtained when u = V/2 (again in
> practice a bit less)
> Theoretical optimum RPM = 60*sqrt(2gh)/(2*pi*D) so
> in theory D =
> 42.3*sqrt(h)/RPM
> A "practical" formula I found somewhere is: D =
> 38.6*sqrt(h)/RPM
> considering losses.
> Rotor diameter (D) and jet diameter (d) are not
> related in theory,
> but there is a practical limit around D/d = 10, (a
> large jet will partially
> miss a small rotor).
>
> (A simple solution to find suitable jet diameter for
> the pressure and flow
> you are dealing with, could be to take a conical
> nozzle from a sealant tube
> and experiment with a knife........)
>
> Best Regards.
>
> Thor.
>
--------------------------------------------------------------------
> Thorhallur Ragnarsson Electronics
> Technician/Instructor
> Holtakoti
> Verkmenntaskolinn Akureyri
> IS-641 HUSAVIK
> Eyrarlandsholti
> Iceland IS-600
> AKUREYRI
> [EMAIL PROTECTED] Iceland
> [EMAIL PROTECTED] [EMAIL PROTECTED]
> http://www.simnet.is/holtakot
> http://thor.vma.is/not/thor
>
--------------------------------------------------------------------
>
>
> At 17:10 17.9.2005 +0000, kunoserg1703 wrote:
> >Hi, it´s the Guatemalan student. I was wondering if
> any of you can
> >help me finding the formulas on pelton design.
> >
> >I specifically need to know the bucket dimensions,
> and what is their
> >relation with other pelton dimensions. I also need
> to know the
> >relationship between rotor and nozzle dimensions. I
> have tried to find
> >them over the internet, but I could only find the
> velocity relations,
> >and power formula. If anyone can point me to a web
> page that contains
> >the dimensions formulas, or email me them, I would
> appreciate it.
> >Thanx.
> >
> >Sergio Linares
> >
> >
> >
> >
> >
> >
> >
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>
>
>
>
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