Re: [microhydro] Re: Relation of Qmax and runner length
- View Source
> Your question is very interesting because I am myself studyING aboutThis is correct - the formula for calculating discharge, needs an additional
> that wheel
> Do you know the works of Clemson university about that wheel ?
> (papers of NADIM M.AZIZ)
> I have disvovered tAat there is a real question about Qmax and that
> question is also in relation with the true Qmax which is lower that
> the product of nozzle section (Width * throat) * Speed of water
> A MENDRET
term, called the coefficient of discharge and denoted by C. Thus Qmax = C x
nozzle crossectional area x speed of water. This coefficient allows for losses
due to friction and losses due to contraction of the water stream as it passes
through the nozzle.
I do not know the value of this coefficient for crossflows, but have seen values
of 0.95 to 0.97 quoted for Pelton turbines.
- View Source--- In email@example.com, Max Enfield <max@p...> wrote:
> brijesh mainali wrote:mathematical
> > Hi friends,
> > I will be grateful to you, if any of you could suggest me the
> > expression [formula] for the maximum flow [Qmax] and runnerlength[L] in a
> > cross flow turbine.can be as
> > Regards
> > Brijesh Mainali
> One of the nice things about a crossflow is that the runner length
> chosen to suit the application and is independent of the runnerdiameter.
> However, usually the runner length does not exceed 3 x runnerdiameter.
>runner and has a
> At maximum flow the inlet stream occupies the full width of the
> thickness [T] designed to be 9% of the runner diameter.sqrt [2 x g x
> First calculate the velocity in m/sec using the usual formula V =
> H] where g [gravitational constant] = 9.8 m/sec^2 and H is the nethead in
> metres. Then Qmax = V x L x T. Using metric values throughout,Qmax is given
> in m^3/sec.Excuse me for the previuos mail incorrect
> Max Enfield
> Planetary Power
I am searching about crossflow and the works of Nadim m Aziz in
I cannot undestand the large lamda admission ( 90 degrees) and the
fact of the Q that couls pass in the nozzle is >> than the real Qmmax
(about twice and more)
So it seems that water fall in hard rain and not in compact jet in
I have no good onformation on the eventual position of a vane
Thanks for a reply
- View Sourceamader2003 wrote:
>If what you say is correct, then the coefficient of discharge is about 0.5. I
> Excuse me for the previuos mail incorrect
> I am searching about crossflow and the works of Nadim m Aziz in
> Clemson university
> I cannot undestand the large lamda admission ( 90 degrees) and the
> fact of the Q that couls pass in the nozzle is >> than the real Qmmax
> (about twice and more)
> So it seems that water fall in hard rain and not in compact jet in
> the wheel
> I have no good onformation on the eventual position of a vane
> Thanks for a reply
> A MENDRET
cannot accept that it is ever this low for a well designed turbine (or more
specifically a well designed nozzle).
In an earlier posting, I noted seeing values of 0.95 to 0.97 quoted for Pelton
turbines. It is probably a bit less than this for a crossflow, because the
rectangular nozzle has a larger wetted perimeter compared to a circular nozzle
with the same cross sectional area.
In our designs we have simplistically taken the discharge coefficient as 1.0.
If it were actually closer to 0.5 then our performance claims will have been
greatly overstated and we would by now have a lot of unhappy customers. This is
certainly not the case.