## RE: [microhydro] Need clearification

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• Rupert, The units given were correct:, power (watts) = rho (kg/m3) x g (m/s2) x Q (m3/s) x H (m) x Eff (per unit) Your formula ignores rho (approx 1000 kg/m3)
Message 1 of 7 , Sep 23, 2001
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Rupert,

The units given were correct:,

power (watts) = rho (kg/m3) x g (m/s2) x Q (m3/s) x H (m) x Eff (per unit)

Your formula ignores rho (approx 1000 kg/m3) so that is why you think there
is a decimal point in the wrong place. Using flow in m3/sec and including
rho the result will be in watts.

Admittedly gravity and rho only vary by about half a percent each (unless
you are using sea water as some Japanese pump storage schemes do) so are
really only of importance when performing efficiency tests to ensure
manufacturers have meet guarantees.

Peter.

-----Original Message-----
From: evansengineering@... [mailto:evansengineering@...]
Sent: Friday, 21 September 2001 07:22
To: microhydro@yahoogroups.com
Subject: Re: [microhydro] Need clearification

I am not quite sure why you are worrying about the variation in g due to
altitude and latitude, when you appear to have the decimal point in the
wrong
place! ( If flow is in mt3/sec the power will be in kW not watts )

Head (metres) X flow (lt/sec) X (9.8 or 10 if you like !!!) = theoretical
power at 100% (Watts) Take 65% overall efficiency for a small plant and
you won't be far out.
Regards
Rupert (in a pedantic mood !)

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• Dear Peter, You my be concerned by what is correct in terms of scientific notation but my objective (and I appreciate that it may not be your way ) is to
Message 2 of 7 , Oct 15, 2001
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Dear Peter,
You my be concerned by what is 'correct' in terms of scientific notation but
my objective (and I appreciate that it may not be your way ) is to make
hydraulics easily understood and applicable by non-technical farmers and the
like. If you take the flow in litres per second, times the head in metres and
multiply it by 10 and an efficiency figure of about 65%, you will have the
power in watts at the output of the generator. Anyone capable of more
accurate calculation can do it for themselves. I thought this group was more
interested in practical engineering and application than arguing about
detailed maths and perpetual motion machines.

With this in mind I am restarting training courses (I first ran them 20 years
ago) at what will be 'The International Centre for Water Engineering.' They
last from 1 week to about 4 months and are aimed at training field workers in
hydro equipment, irrigation structures and flood control. It is very hands-on
and will involve the design and installation of at lease one real project
during each course.

If anyone is interested in taking part or being a recipient of suitably
trained field workers, please let me know.

Regards
Rupert Evans
www.microhydro.com

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