Temperature drop over hydraulic turbine
Temperature drop over hydraulic turbine
(OP)
Assuming an hydraulic turbine of an hydro electric plant. Is it correct to assume that the water temperature at the outlet of the turbine can be calculated from the balance:
enthalpy of water at outlet = (enthalpy of water at inlet) minus (shaft power hydraulic turbine)?
Thanks
enthalpy of water at outlet = (enthalpy of water at inlet) minus (shaft power hydraulic turbine)?
Thanks





RE: Temperature drop over hydraulic turbine
RE: Temperature drop over hydraulic turbine
I really mean a Hydraulic (water) turbine (Francis / Kaplan / Pelton turbine). If above mentioned heat balance is not applicable, what would be applicable?
RE: Temperature drop over hydraulic turbine
RE: Temperature drop over hydraulic turbine
RE: Temperature drop over hydraulic turbine
V1^2/2g+h1=V2^2/2g+h2+ Work done on turbine.
So, if you can get V1,V2 and the work done, you can get delta h, the change of enthalpy. In an incompressible fluid, h is not a function of temperature alone, so you will have to get delta pv of the water before you get delta u, the internal energy and then delta T.
RE: Temperature drop over hydraulic turbine
Is there any heat gain by the water from the turbines inefficiency, assuming most of the heat lost to friction is carried off by the water?
**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch
http://virtualpipeline.spaces.live.com/
RE: Temperature drop over hydraulic turbine
RE: Temperature drop over hydraulic turbine
**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch
http://virtualpipeline.spaces.live.com/
RE: Temperature drop over hydraulic turbine
RE: Temperature drop over hydraulic turbine
**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch
http://virtualpipeline.spaces.live.com/
RE: Temperature drop over hydraulic turbine
There will be a temperature change due to losses (friction>> turbulence >> heating, even for a theoretically incompressible fluid.
And, yeah, velocities matter. So does vertical (head) change.
RE: Temperature drop over hydraulic turbine
**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch
http://virtualpipeline.spaces.live.com/
RE: Temperature drop over hydraulic turbine
RE: Temperature drop over hydraulic turbine
I know this is a little hard to accept - but its the same with liquid through valves - the temperature increases!
This about it: Where will the potential energy go? It can only go into the fluid - thus increasing temperature.
Best regards
Morten
RE: Temperature drop over hydraulic turbine
While the SPL doesn't have ready-made hydro-power turbines, I suppose I could make a turbine curve, call it a pump and spin it backwards to see what happens. Not today though. I'm not sure I could handle all the "parameter out of bounds" warnings on a Friday.
**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch
http://virtualpipeline.spaces.live.com/
RE: Temperature drop over hydraulic turbine
1. Water still possesses kinetic energy when it leaves the bucket, related to its leaving velocity
2. Part of the energy is dissipated by friction in shaft bearing system.
How could anyway be the temperature of the water at the exit of nozzle, different from that which leaves the bucket after impact?
RE: Temperature drop over hydraulic turbine
**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch
http://virtualpipeline.spaces.live.com/
RE: Temperature drop over hydraulic turbine
Sincerely I think inefficiency is due to the fact the wheel rotates in the air which offers resitance to the movement and it is responsible of the energy loss.
RE: Temperature drop over hydraulic turbine
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Nope, because in a vacuum that would mean turbines could be 100% efficient. Friction is from atoms rubbing against atoms, whether they form a solid, a gas or a liquid. Impact and friction both make heat. Ever touch a penny just after it got hit by a bullet? That wasn't the heat from the gunpowder. And the bullet was hot too. If it was a water bullet, do you think the water and the penny would both get hot? I do.
**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch
http://virtualpipeline.spaces.live.com/
RE: Temperature drop over hydraulic turbine
Kudos, I didn't think about the enthalpy equation (my background is gas turbines, not water wheels), but you are right, a water flow turbine would be better modelled by the velocity (momentum) equations. The enthaply equation would work, but you'd have to calculate from near-static conditions upstream and d/s. Still get a temp. rise, though ;).
FWIW, have you ever seen an installed Pelton wheel being used? I'm wondering under what circumstances it is more practical than a Francis or screw turbine.
RE: Temperature drop over hydraulic turbine
I agree that gas/steam turbines are another beast (this is why in my first reply I have asked for a confirmation the OP was talking about hydraulic turbines).
In Italy we have some. Due to the particular morphology of my country it is possible to exploit this kind of installations. Pelton wheels are characterized by relatively small flow rates and big geodetic heads (up to 2000 m), whilst reaction turbines have got higher flow rates and smaller geodetic heads.
RE: Temperature drop over hydraulic turbine
**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch
http://virtualpipeline.spaces.live.com/