Siphon Turbine Priming and Air Regulation

[gh4063]

Hello All,

I'm doing testing on a siphon turbine model and I'm trying to work out how to achieve automated priming and air flow regulation through a valve at the apex (highest point) of the siphon ductwork - specifically I'm after some advice on valve and pump arrangements (I'm afraid I'm ignorant about most of the terminology).

I need to suck air out of the apex bend to start the siphon, but to autmatically stop when the water level reaches the air line valve. I also want to be able to introduce air to regulate flow through the system and periodcally I want to supply enough air to break the siphon completely.

Both the inlet and outlet of the siphon are always submerged, with an average ductwork diameter of around 140mm and the minimum pressure observed at the apex is less than 400mmH20 below atmosphere (29mmHg or 0.04bar below atmosphere), so I assume a small vacuum pump would be adequate?

Many thanks, in advance, for any advice.
George

 

[bimr]

You probably would want to use a vacuum ejector for this application.

 

[BigInch]

I'd like to know if controlling a flowrate to a turbine by varying the amount of air in the gooseneck is recommended practice?

It seems like, siphons being what they are, you could easily slug the turbine with too much air, then too much water and do quite a lot of damage.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[gh4063]

Thanks Bimr. BigInch, although breaking the siphon too quickly does cause severe vibration, at high flow rates a significant amount of air is entrained and so with a controlled air feed at the apex slugging can be avoided. Having said that, the air water mixture could cause uneven loading on the turbine runner - this will be explored.

I'm starting to think that an eductor (jet pump) would be suitable. Since the gauge pressures are small, do you think I could get away with a small air-compressor and eductor arrangement? And can someone suggest a valve to join the eductor to the siphon ductwork that could prevent water being sucked out of the system?

Cheers,
George

 

[BigInch]

OK. It was just personal interest, as I have no experience with water turbines, but I have noticed in other applications, siphons sometimes run away then recover. If you're confident it can be controlled, go for it.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/