Naked Science Forum
Non Life Sciences => Technology => Topic started by: McQueen on 26/02/2011 15:48:18
-
This new micro hydel project of mine, has the potential of churning out a respectable 2 Kw to 3 Kw of power throughout the 24 hours of the day. How does it do it? Think of the Californian redwood, these trees suck up upwards of 4 tons of water a day to heights exceeding 300 feet. Absolutely incredible figures, right. So my idea is have one tank at ground level and one or two tanks at 40 feet above ground, either supported on its own tower or on some other structure (roof etc.,) A 4 inch pipe, it can be of any material, connects the upper tank to a generator at ground level, the water from the pipe spins a generator and then feeds the water back to the lower most tank. A 4 inch pipe using water falling from a head of 40 feet will generate a steady 2.2 KW of energy and use 850 gallons (3000 litres approx) of water a minute. Connecting the lower and upper tanks is a massive tree trunk sized one metre diameter pipe packed with 25 micron (or less) inner diameter capillary tubes. Call the tank at ground level holding tank A, Call the holding tank 40 feet up Holding Tank B, call the tank next to Tank B i.e., the precipitation tank, Tank C Holding tank B is fully, sealed it is joined to tank C by a 6 inch diameter pipe, attached to this pipe is an air pipe reaching above the height of both tanks to ensure water flow and prevent air lock. Then as the water level rapidly sinks in Tank B the sinking water level acts like a piston creating a vacuum (in Tank B), this facilitates the flow through the capillary pipes. So we have water going out of the tank from a 4 inch diameter pipe and water being fed back into the tank by a massive 1 metre pipe. Everything can be monitored by electronics to ensure its smooth working AND the same water (filtered) is used over and over again with timely top ups. Will the idea work ?
-
Think of the Californian redwood ...
It has leaves ... http://en.wikipedia.org/wiki/Transpirational_pull , and plently of (Californian) sunlight.
-
RD
OK, look at this problem in a detached and logical manner. First of all start by making concessions instead of 40 ft make the height of the water tower 25 ft. Instead of 25 microns and less make the inner dia of the capillary tubes 1mm – 0.5 mm. Next prep the whole system as follows. Let there be a stopcock at the outlet from the precipitation Tank C and let it be closed. Fill Holding Tank B on the tower with water so that the 1 metre inlet pipe packed with capillary tubes rises about 10 cm above the level of the water. Next use a pump to exhaust all the air in Tank B to create a vacuum. So far everything is in equilibrium, nothing is happening, no water is flowing. Next open the stopcock so that water starts to flow out of Tank C through the generator pipe to the ground turning the turbine. A 4.75 inch dia outlet pipe will discharge at the rate of almost 5000 litres per minute and in the process generate about 2.2 Kw of energy (possibly slightly more). In the presence of a vacuum, atmospheric pressure will support a column of water 32 feet high ( 1 atmosphere) when Tank B is evacuated of air, the water in the capillary tubes in the 1 metre inlet pipe should rise to the top or start to overflow because of the imbalance in pressure. When the stopcock to the generator pipe is opened in Tank C the water level in Tank B starts to sink, acting like a giant piston and maintaining the vacuum. As the diameter of the pipe is huge ( one meter) the outflow of 5000 litres/minute approx. should be compensated or more than compensated by the inflow. True the California redwood does have millions of leaves true there is sunlight. BUT this system has atmospheric pressure, the presence of a vaccum and hundreds of thousands of straight well designed capillary tubes on its side. . Why won’t it work, those little dipping birds do.
-
What purpose do the capillary tubes serve. They divide up the column of incoming water so that the weight of each column of water is reduced to an acceptable degree and they allow for the molecules of water to bind to the sides, further strengthening the column of water.
-
Why won’t it work, those little dipping birds do.
The "dipping birds", (like the tree (http://en.wikipedia.org/wiki/Transpirational_pull#Mechanisms)), require evaporation ... http://en.wikipedia.org/wiki/Drinking_bird#How_it_works
-
RD
I appreciate that the dipping bird is a type of heat engine and that evaporation sets everything going. Stick to specifics, like why atmospheric pressure won't support a column of water 25 ft high in this particular case, or why a vacuum can't be maintained in a fully sealed air tight tank that has water flowing out of it and the water level dropping creating a piston like effect. If you address these questions then the discussion might be going some where.
-
Stick to specifics
General principles are sufficient to tell you it won't work ... http://en.wikipedia.org/wiki/First_law_of_thermodynamics
The tree is using solar energy to raise the water, where is the energy coming from which you are attempting to harness ?
A common misconception is that water moves in xylem by capillary action—the movement of water along a small-diameter conduit (such as a capillary) as a result of surface tension in the meniscus at the leading surface of the moving water. Surface tension does play a critical role in water movement in xylem, as described above, but the relevant force acts at the surface site of evaporation within leaves, not within the xylem conduits. Water movement within the xylem conduits is driven by a pressure gradient created by such force, not by capillary action.
http://en.wikipedia.org/wiki/Transpirational_pull
-
As RD points out, you need a source of energy. It takes a certain amount of work to elevate water, so some sort of engine is required to drive a pump, even in the case of a tree.
Unfortunately, once you've elevated the water, it's impossible to get it to do as much work on the way back down as was spent on the way up, so it's going to consume more energy than it produces. Sadly, there can be no free lunch.
-
Geezer and RD,
I appreciate your replies but it might help if you read what I have written, the maximum height of the 1 metre diameter pipe packed with smaller pipes is below 30 ft. Atmospheric pressure will support a column of water 32 feet in height. So when a vacuum is created in Tank B water flows from Tank A into Tank B through a siphon action, as long as the vacuum is maintained the cycle should continue and electricity should be generated continuously.
-
McQ,
It's a bit difficult to understand what your system looks like from your description. A sketch might help.
If I get the general idea, you are relying on atmospheric pressure to elevate the water. It can support a 30 foot column of water, but only because of the pressure difference between air pressure and the absence of air pressure above the column.
In order to make air pressure continually lift water to, say, 25 feet, you'll have to continually create a vacuum above the column of water, and that requires a lot of work to be done. Lift pumps actually work that way and they are limited in the height they can lift water by atmospheric pressure.
I don't like to be a wet blanket, but if you can't identify the source of the energy that makes your system work, you are trying to get something for nothing. Disappointment is guaranteed to follow.
-
Geezer,
I will try to post a sketch later today. But the idea is that there are two tanks at 25ft above ground level Tank B and Tank C. One tank (Tank B) is airtight and it is into this tank that the 1m siphon consisting of thousands of little pipes enters. The other tank (Tank C) at 25ft to which Tank B is attached by a pipe, is well ventilated so that atmospheric pressure is present. Water flows from the well ventilated Tank C down a pipe and to the turbine and then to the tank at Ground level Tank A. As the water flows out of Tank C water flows into it from Tank B. And as the water level goes down in Tank B, because the tank is airtight it creates a vacuum activating the siphon, so as long as the flow of water is balanced the vacuum in Tank B will exist and the system should work continuously. So the flow of water itself creates the vacuum.
-
Geezer,
Here's the drawing that I said I would do. [diagram=623_0] I do not know how to put letters into the diagram which would certainly make things easier. But call the lower tank, Holding Tank A, call the tank immediately above it Holding Tank B, call the tank next to Tank B (i.e., the precipitation tank ), Tank C. Tank A and Tank B are connected by a 1m diameter pipe filled with smaller diameter pipes. There is a one way valve on the pipe between Tank B and Tank C and a stop cock on the pipe leading to the generator from Tank C. The stop cock is closed and a pump is used to create a vacuum in Tank B, the pump is then removed. Water starts to flow into Tank B, which is completely sealed and airtight, from the 1 meter pipe, due to atmospheric pressure. The stop cock at Tank C is opened and water starts to flow out of Tank C and to the generator, as water flows out of Tank C , water flows into it from Tank B, causing the level of the water In tank B to drop and reinforcing the vacuum with the consequence that more water flows into Tank B from Tank A creating a continuous cycle. This does work as has been demonstrated in numerous experiments. . A vacuum in Tank B would cause the water in Tank A to travel up the small diameter pipes in the big 1 metre diameter pipe and flow into Tank B. The only way in which the vacuum in Tank B can be broken is by air bubbles flowing into Tank B and disrupting the vacuum OR if the water in Tank B goes up past the level of the 1 metre pipe in Tank B. Will the one way valve prevent bubbles from flowing into Tank B ? Otherwise , theoretically, as long as everything is balanced, i.e., water flowing out of and into Tank C is maintained with respect to the water flowing into Tank B the system should continue indefinitely. Shouldn't it ?
-
Thanks! That helps.
I think the reason it won't work is because the vacuum above the water in B will prevent the water from leaving B to return to A. In fact, the vacuum in B will cause the water to flow backwards through the turbine to get from A to B rather than take the direct path through the stack of tubes. That's because the water does not have to be lifted so far to take the "shortcut" via C.
Unless you continually do work to make the water flow around the circuit, it will simply reach a state of static equilibrium.
-
Geezer,
Just fit a one way valve between Tank B and Tank C, then the difference in pressure will tell. As water flows out of Tank C it creates a pressure difference opening the one way valve. So your theory doesn't hold water (pardon the pun) remember Tank C is open to atmospheric pressure, so like it or not water will flow out of it at flow rate dictated by atmospheric pressure, when pressure in Tank C is lower than in Tank B, water will flow, strengthening the vacuum already existing in Tank B. Furthermore because the two tanks are connected , albiet with a one way valve in between, they can be visualised as one system.
-
If you are so sure about this, why don't you just build a small working model and post a video of it running on Youtube. You can even leave out the turbine for now. All you need to do is show the water circulating automatically. You should be able to knock something together with a few clear plastic bottles and some plastic tubing.
Or, you could simply check out http://en.wikipedia.org/wiki/Perpetual_motion and try to figure out where you are going wrong.
-
Geezer,
You are right, I have been doing the calculations, the combined weight of atmospheric pressure and water in Tank C would be about 112,000 lbs or more, so water will never flow out of Tank b. The solution is to make Tank C into several smaller interlinked tanks with a small surface area. So If Tank C consists of twenty 1ft x 1ft x 10 ft tanks all interconnected, the total weight of the whole system, atmospheric and water would be the weight of one tank or about 2600 lbs, the weight of the water in Tank B at 24,000 lbs is heavier than this. So when water begins to flow out of Tank C, water will flow into the system of interconnected tanks through the one way valve from Tank B. The system should be self sustaining.
-
McQ - as a mental challenge and a test of mathematical application the above is great, but when you try to get any system to "produce" energy you will run smack into the laws of thermodynamics. Without an external source of energy your system will just find a low energy point and stop - that's what stuff does. I have no doubt it will improve your maths and physics to find out where your miscalculation or false assumption is - but be aware that your system has a fatal flaw. If you can find a way to tweak your design to allow the sun's heat or winds power to provide an energy input it might work - but then we already have ways of converting sunlight and wind to electricity
-
Quote from wikipedia. “Machines which comply with both laws of thermodynamics by accessing energy from unconventional sources are sometimes referred to as perpetual motion machines, although they do not meet the standard criteria for the name. By way of example, clocks and other low-power machines, such as Cox's timepiece, have been designed to run on the differences in barometric pressure or temperature between night and day. These machines have a source of energy, albeit one which is not readily apparent so that they only seem to violate the laws of thermodynamics.” One of these clocks the Beverly clock : has been running since 1864. So what I have described is by no means a perpetual motion machine, since it uses atmospheric pressure as energy. Granted the vacuum in Tank B, might get degraded from time to time, but attaching a vacuum pump permanently to an outlet in Tank B and switching it on when sensors detect a drop in vacuum pressure, should ensure continuity. Further once the machine is working it should be possible to find ways to make the vacuum more enduring.
http://en.wikipedia.org/wiki/Beverly_Clock (http://en.wikipedia.org/wiki/Beverly_Clock)
-
the beverly clock uses the heat of the sun - in a beautifully-engineered and elegant way.
-
Granted...?
-
You need an input of energy - atmospheric pressure might push a system that is out of equilibrium to one that is in balance, but it will not drive a system continually. The beverly clock uses atmospheric pressure as part of the mechanism - but the energy comes from sunlight.
-
McQueen,
If you cannot accept that you are attempting to violate the basic laws of thermodynamics, the best thing you can do is get busy and build a working model. Matt and I are only trying to spare you the pain of disappointment, but it looks like that is unavoidable.
-
Geezer,
If you don’t want to approach the problem from a theoretical point of view, that’s fine with me. As a matter of fact I agree with you, it is always best to build a practical model and THEN see what happens. In this case, I don’t have the resources. Still, what with the energy crisis, global warming and melting ice caps etc., don’t you think that an idea that, at least in theory, will yield 2.2Kw of energy (51.6 Kwh/day) should at least be considered. Especially since it is ecologically friendly and green. Sure, it’s OK, to say it won’t work and it’s a waste of time, but under the circumstances, is it ? Remember that atmospheric pressure varies by only 0.28% even on top of the Himalayas, it is not a once off thing , it can be used over and over again practically indefinitely. Further I have demonstrated a method by which water can be pushed out of a tank containing a vacuum, using the weight of the water itself, and how this process, (i.e., suction caused when water level in the sealed tank drops) can re-inforce the vacuum. Don’t you think these facts have to be considered and if not why ?
[;)]
-
McQ - no you haven't demonstrated such a system. "Remember that atmospheric pressure varies by only 0.28% even on top of the Himalayas" - this is the whole point. It is only differences in pressure that can be used to drive a system. Your idea tries to use the stable atmospheric pressure to create a difference in pressure (or to maintain it whilst lifting water). this violates the laws of thermodynamics - I don't have the time to go through your idea and see where the flaw is - it might just be fluid friction / viscous drag, or it might be more fundamental; but what ever it is, the basic problem is that you are getting something for nothing
Extra question added
Could you explain why water should flow from your sealed tank to your open tank and thus to turbine. If valved tube is narrow then vacuum in sealed tank will hold the water upto valve, if valved tube is wide enough to break coherence then air will flow to valve and everything will again stop. Ie if your vacuum is strong enough to haul water from 25 feet away (even with the very marginal benefit of capillary action)- why is it not strong enough to stop water moving the small distance down to tank b?
-
Matt,
I will take the time to try and address your questions even though, your queries do seem to be a bit obtuse.
a) Atmospheric pressure is 14.7 lbs per sq. in. This amount of pressure will support a column of water 32 ft high, give or take a 0.28% variation. Are you with me so far?
So if you create a vacuum on top of a column of water, the column of water will rise to a height of 32 ft and if to a less height, spill over into whatever container the vacuum exists in. Of course there are variables such as the thickness of the tubes containing the water etc., Are you still with me, if not click on this link:
http://www.education.com/science-fair/article/air-pressure-fountain/
That addresses question (a) now onto (b)
A vacuum will hold a liquid in a tube as you rightly state BUT again this is just a question of logistics, and has nothing to with thermodynamics. For instance the reason why petrol stops flowing from the filler after the correct amount has been filled is because of just such a vacuum lock. Again as I had explained this has just to do with the weight of the atmospheric pressure pressing against the fluid in the pump filler and holding it in, nothing else. So in the end all it is, is logistics, even with a tank that is many square feet in area, water will be held in if the atmospheric pressure is greater than the weight of the water trying to get out : http://www.thenakedscientists.com/forum/index.php?topic=37537.msg346218#msg346218 . There is absolutely no reason for bubbles to flow in and replace the water that is flowing out. The old ‘nature abhors a vacuum theory’ has long been disproved, and bubbles flowing into Tank B can be prevented. What say.
-
McQ -no you haven't answer the thermodynamic question (because it cannot be dodged) - the fact that you quote another very simple experiment that relies on heating and cooling to provide a one off pressure differential is indicative that you still haven't grasped the problem.
and b - you still haven't given a reason why the water would flow and increase the vacuum (or maintain it under the presence of flow). What force is causing the water to move, and what force is your vacuum system supposedly counteracting? It's the same force and it won't work.
-
Matt,
Why do I get the impression that you are just stating and restating your preconceived thoughts on the subject without even bothering to read what I have written. If that is really the case. Then fine keep stating and restating what you have already said.
-
McQueen,
You could quite easily produce a small model to demonstrtate that your idea works. It will only require some old plastic bottles and some plastic tubing.
I eagerly await seeing your demonstration on Youtube.
-
Geezer,
The reason that I view this as pedantry and not scientific precision are statements like " you still haven't grasped the problem..."
OK, if Tank C is divided into 20 smaller and separate but interconnected tanks as I had suggested, WILL it result in a total pressure (atmospheric and weight of water ) of only 2600 pounds ( dimensions of 1ft x 1 ft x10ft.)at any point in the network of pipes connecting these tanks together. IF so, why should not water flow from Tank B where the weight is in excess of 24,000 lbs as against a combined weight of the 20 tanks in Tank C of 2600 lbs. IF the water does not flow from Tank B in spite of the preponderance of weight(if the water alone in Tank B weighs 24,000lbs, not counting atmospheric pressure),does it have anything to do with thermodynamics. Further, will both of you depend on the old wives tale that " nature abhors a vacuum" to press home your argument that as water flows from Tank B into Tank C air will flow in a counter direction to displace the vacuum in Tank B. COME ON !!!!!! These are the questions I need answers to, not snotty nosed statements that I don't have a grasp of things ..... !!!
-
McQeen,
I think you would be better to spend your time constructing a working model than trying to browbeat people into believeing in something that obviously violates the laws of thermodynamics.
-
Geezer,
I will give the building of a model serious thought. For the moment though, I would appreciate some answers to the questions in my last post.
-
McQueen,
I'm sorry, but your explanation is still far from clear, and I'm not inclined to spend a lot of time trying to work out why it won't work when all the theory from the last several hundred years says it can't.
It seems to me that you are assuming you can get more work done by a mass of water that is flowing downhill than the work that was put into elevating the water in the first place. Bottom line is, you can't. Even if there were no losses in the system, you could only get back what you put in, so it would be a waste of time. In practice, any real system has losses (due to friction) so you are doomed to get back less than you put it, so it's worse than a waste of time.
If you want people to take you seriously, I think you have two options;
The most effective method would be to build a working model. It does not need to be very fancy. It just needs to demonstrate that the water will circulate automatically.
The alternative would be prove mathematically that you can obtain energy from a system that has no energy input.
-
Geezer,
Still, in spite of all that you say and your quite right skepticism isn't it interesting that in the link given below, ALL of the water in the lower beaker goes into the upended flask containing a vacuum. http://www.education.com/science-fair/article/air-pressure-fountain/ (http://www.education.com/science-fair/article/air-pressure-fountain/)
-
It's not surprising at all. Air pressure is simply forcing water into the flask to eliminate the partial vacuum.
What is much more interesting is that once the pressure equalizes, the water stops flowing.
-
McQ - how's the working model going? Cos that's gonna be the only thing that will convince you that you cannot use atmospheric pressure in this way. You need to think about where energy for your system will come from - or alternatively you can try working out the forces involved, you have water going up: where is the force for this coming from? Bear in mind Geezer's last comment above - your school science experiment on video only work once; for it to continue you need energy input.