Gravity Mill - any comments to this idea?

[hartiberlin]

Hi Pranja, looks good your new Graphics. Maybe you can draw the Weight of the shuttle onto it additionally, so it gets more clear, why it sinks at all. Also maybe you can draw it this way, that you show 4 single pics which show the shuttle in each deepth position. Did you calculate yet, with how much air you have to refill your shuttle at the top and how much energy this costs ?
Thanks.

[prajna]

Stefan, I suggest you forget the nozzle idea or you will get caught up in static head, nozzle head, viscosity, flow rate etc.  Let's keep this simple and consider a tube extending above water level.  I seriously doubt that a nozzle is more efficient at raising water than a simple tube is (except that we don't need to worry about viscosity which is a very small component of the force required.)

As tbird suggested, for any given diameter of tube the pressure doubles as the diameter halves (roughly).  If the pressure required to lift 1 litre of water to 1m above water level is, say, 1 pascal* in a tube of 10cm² cross sectional area then that same pressure will lift that same litre of water 2m above water level in a tube with a 5cm² cross sesction.

* this figure is simply for illustrative purposes.  Don't use it in calculations; I haven't calculated what pressure it would actually take in this example.

[tbird]

hi stefan,

can't resist answering this now.  i thought when you said you agreed with me about the size of the exit pipe, you had a handle on it.  obviously you don't.  maybe you've been looking in the wrong place for the answer.  it's a hydraulic thing.  for your formula, look for the relationship between vol and pressure and flow.  to have the same flow if you change pipe diameter (area) you have to increase flow (at same pressure) to produce same volume delivered in same time.  remember we are now talking about liquid, not gas.

don't know if that helped, but should get you down the right path.

tbird

[prajna]

@tbird

The reason I use absolute pressure in my calculations is that it keeps eveything simple and intuitive.  At sea level there is a pressure of 14.7psi - equivalent of 1 bar - at 10m there is twice that.

That is not where your confusion arrises though.  The 6 bar, or 6 times atmospherical pressure, is required to squeeze 3 litres of air into the reservoir tank that only has a capacity of 0.5 litres.  To do that we must compress it to one sixth of it's volume or, to say it another way, six times its normal pressure.  Does that clear that up?

[hartiberlin]

Pranja and Tbird you are right, that an exit smaller pipe would be better, but I still have problems with the hydrostatic paradoxon, as this water colums above seawaterlevel is negatively influencing the buoyant force and for this reason the shuttle must be much bigger under water. So the best thing would be to have a nozzle sprinkling out the water into the upper basin.