The Naked Scientists Forum

Author Topic: What do water turbines need in order to work?  (Read 2436 times)

enochmiller

• First timers
• Posts: 4
What do water turbines need in order to work?
« on: 13/05/2012 02:40:54 »
I know that Francis turbines need hydraulic head and that Kaplan turbines depend on the flow of water, but I mean, what turns them? Is it merely the impact of the water hitting them, or the act of water flowing through? I ask this because I was wondering if it would be possible to create a hydroelectrical system using a (hypothetical) really, really, dense fluid instead of water.

Wikipedia says:

"The power available from falling water can be calculated from the flow rate and density of water, the height of fall, and the local acceleration due to gravity. In SI units, the power is:

P = npQgh
where
P is power in watts
η is the dimensionless efficiency of the turbine
ρ is the density of water in kilograms per cubic metre
Q is the flow in cubic metres per second
g is the acceleration due to gravity
h is the height difference between inlet and outlet."

That makes me wonder, if there was a lot of density in a fluid and no flow at all, would a hydroelectric system work like it usually does? (Or, would it work at all?)
« Last Edit: 13/05/2012 02:43:42 by enochmiller »

Geezer

• Neilep Level Member
• Posts: 8328
• "Vive la résistance!"
Re: What do water turbines need in order to work?
« Reply #1 on: 13/05/2012 02:50:18 »

if there was a lot of density in a fluid and no flow at all, would a hydroelectric system work

Alas, no. There is no work without motion.

CliffordK

• Neilep Level Member
• Posts: 6321
• Thanked: 3 times
• Site Moderator
Re: What do water turbines need in order to work?
« Reply #2 on: 13/05/2012 03:09:54 »
You could, of course, use something like liquid Mercury.
Or for that matter, choose something more dense.  Perhaps liquid Osmium with a density of about 20 x the density of water.

With Mercury, you could achieve 1/13 the flow of water.  Liquid Osmium would require about 1/20 the flow of water.

Could you achieve higher density with plasma at high temperatures and pressures?

So, if you were pumping uphill, you could pump less volume of Mercury than water, for the same energy however, water is very cheap, and relatively easy to handle, not the same with Mercury, and definitely not true with metals requiring heat to liquefy.  Handling a plasma would be much more difficult.

Obviously you never truly get to zero flow.

enochmiller

• First timers
• Posts: 4
Re: What do water turbines need in order to work?
« Reply #3 on: 13/05/2012 03:20:03 »
Interesting...thanks!  :)

enochmiller

• First timers
• Posts: 4
Re: What do water turbines need in order to work?
« Reply #4 on: 13/05/2012 03:26:57 »
Thank you for the help! However, in regards to Geezer's comment:

What if the (hypothetically very dense, easy to produce, and easy to use) fluid and the turbine were at a 90 degree angle to each other, where the fluid would be vertical and falling quickly on the turbine and the turbine would be horizontal and spinning from the force of the fluid on its blades? Would that work?

Is there something I'm not understanding?
« Last Edit: 13/05/2012 03:31:58 by enochmiller »

wolfekeeper

• Neilep Level Member
• Posts: 1092
• Thanked: 11 times
Re: What do water turbines need in order to work?
« Reply #5 on: 14/05/2012 17:01:09 »
I know that Francis turbines need hydraulic head and that Kaplan turbines depend on the flow of water, but I mean, what turns them? Is it merely the impact of the water hitting them, or the act of water flowing through?
It's the flow. The Francis turbines turn the head into flow and then use the flow to turn a turbine.

You get energy by slowing water down. As the blade recedes from the water, pushed by the water, it slows the water that leaves.

Energy goes as 0.5 m v^2.

So a very slow flow would have awfully low power.

The Naked Scientists Forum

Re: What do water turbines need in order to work?
« Reply #5 on: 14/05/2012 17:01:09 »