Gravity Mill - any comments to this idea?

[prajna]

Oops, forgot to attach the drawing...

[hartiberlin]

as far as having different pressures, that's ok.  did you realize the shuttle in the drawing is pre-pressurised at the surface, before it ever makes it's 1st run?  this pressure, when the shuttle is compressed so it will desend, will be 2 atmospheres (if we are taking it to 1 atmosphere, 10meters +or-).  30psi is a little more than that, but will make the shuttle expand to size, for sure.  to compress a shuttle that is based on a one cubic foot displacement, we'll say the top area is 12 inches square (144sq.in.total), would take 30psi times the 144 square inches which equals 4,320 pounds.  even if the shuttle is expanded with 15(+or-)psi at the surface, 4,320 pounds will compress it to the point where the air being compressed inside will be 30psi.  since we started with 15psi, the volume will be reduced by half.  back to the weight.  if you use a lever to hold the container that the compression water (weight) will be put in, for every foot out, less water will be needed.  if the lever was 5 feet long, the weight would only need to be 1/5th (864lbs) as much.  if you took it out 10 feet, 1/10th (432lbs.).  now at 10ft leverage we've reduced the amount of water needed to recompress from 7.67 cubic feet (4,320lbs.) to 0.767 cubic feet (432lbs.).  since we are goin down to 10 meters (+or-) and delivering water in both directions, we should have an excess of about 65 cubic feet (over 4200 lbs).  not bad for a 1 cubic foot unit, eah?  using the example from this drawing  http://www.icestuff.com/energy/elsa/, the height of the stored energy (water), (if you store it) could be as high as 72 inches using a 1 square inch exit pipe.

do you still want to only use the up stroke?

i have more about the shuttle, if you are not burnt out.

tbird

Hi TBird,
I try to read your posting, but it sounds to me all pretty confusing.
First you said, you start with 2 Amtmospheres, which is about 2 bar and about 30 psi,
then later you say " since we started with 15psi", so I completely don?t understand your
setup.
Maybe it is already too late over here.
Maybe you can just post your setup in a table-form
so you include all parameters at start and at end points,
so we can exactly see, what you mean.

Many thanks.

[hartiberlin]

Hi guys,

I'm hoping to simplify things a little with the attached drawing of a shuttle.  The displacement area can be full of water or air (depending on whether the shuttle is going up or going down.

Let's work with just one kilo of water and a shuttle weight of 0.5 kilos to keep things simple. We must also consider the volume of our shuttle because it will also displace that same volume of water, let's make things easy and assume it is 0.5 litres. The displacement volume, then, must be 1 litre  - 1 litre to displace 1 kilo of water plus 0.5 to displace the weight of our shuttle minus 0.5 because our shuttle already displaces that much water when the displacement area is full of water. The weight and volume of our shuttle cancel each other out if they are the same.  If the weight is less than the volume then it floats and if the weight is more than the volume it sinks.  Ok so far?

Hmm, I don?t get it yet. Maybe I am too tired ?
Maybe you can explain it again in other words and make
a table, what should be what in your shuttle ?
Also is the blue color for water or for air ?
Is the shuttle open at the bottom ?
Should there water be able to get where into your shuttle and
where should the be air in it ?

At 10m we will require 3 litres of air in our 0.5 litre reservoir so it must be at 6 times atmospheric pressure - if my logic is correct. That should be 14.7 * 6 = 88.2psi = approx 6.2 kilos/cm².

Hmm, if you have 0,5 Liter air at the top at sea level ( 1 bar)  and
at 10 Meter you have 2 bar and 0,25 Liter volume, if you let it shrink.
But if you don?t let it shrink it still has internally 1 bar pressure and
0,5 Liter, then only the walls get the more pressure.

Hmm, maybe you can put all your parameters also in table form
and also state the start and end conditions, so we can look at the complete
cycle. And please sign your picture with titles where the water and the air should
be and if it will really be open at the bottom.

Also it would be good, if we would choose and agree on one example of dimensions
we can all work on the same and that not everbody jumps on different
dimensions and sizes so it gets not too confusing.
Many thanks.

[prajna]

Sorry the drawing was not clear, Steve.  The blue is the air reservoir and is where the air is pressurised.  Blue was probably not a good choice of color. The shuttle is hollow at the bottom - water goes in there (because the air escapes via valve V3) when the shuttle reaches the top and gets pumped out by opening valve V2 when the shuttle reaches the bottom.

I found it much easier to calculate things based on lifting 1 litre of water than working with the figures you have been using and hoped that you might find my examples easier to understand than being confused about the air expanding as the shuttle rises.

I don't know that a table will help.  I hoped that by explaining the weight required to compress the air you might find it simpler to understand than getting your head around the formular you dug up.

I can certainly understand if you are tired: you guys have been hammering away at this thing like crazy.  It took me ages to read all the posts and to figure out the physics of it!

[tbird]

hi  prajna,

i've been out this evening for special event, so a bit late with this reply.  i first have to say it was very refreshing to read your post.  i like to keep things simple too (as you may have noticed in some of my posts).  i think you have a good point about keeping things smaller and easier to understand.  i don't have a problem reducing my stuff, but i may not be as effective with the metric stuff.  hard to teach an old dog new tricks.  i actual did follow you very well until you got to the 6 times stuff at the bottom of the run. you shouldn't need more than 2 bar at that depth.  i think this is wrong and as a result, all things based on it there after would be wrong too.  so far (maybe i shouldn't say this out loud) i think you have the best handle on the project.  not to say others don't have good ideas, just that you are closest to the spirit of Mr. Herring.

having said that, at this point i should say something straight out.  lets get away from suppling air at the bottom of the run!  as far as that goes, forget using an external air compressor all together.  my reason to say this is to deliver air to depth can never be as efficient  as at the surface, if for no other reason than you need more air just to fill the pipe.  i have worked with air compressors before and can say from  experience, i'm glad i don't have to now.  let's keep it simple, air compressors are not. 

i probably should have said something sooner, but thought we all would have proved it a bad idea long ago.  sorry for my bad judgement.

i think i should stop for now and do a quick reply for stefan before i hit the bed.

tbird