I’m not trying to save the world - just learning physics. Buoyancy and gravity: Build a huge submarine whose only reason for existence is to dive to The Mariana Trench and come back. The main parts of this vessel are a ballast and a generator. After some calculation someone (not me) comes up with a formula:
The generator uses electrolysis to displace some water in the ballast. A hole in the bottom should do it. Now at some depth the sub becomes buoyant and up she goes. At sealevel you happily burn the gases and start a new round.
The submarine is huge, but built so that the difference between diving and buoyance can be changed before the bottom of the Pacific. What’s wrong here?
Not sure what you are asking.
Do you think that you can repeat this cycle forever? If so, the answer is no, you can’t, because of losses in the system - no machine works with 100% efficiency.
So the water flow as the sub descends is powering the system? That means the energy is coming from outside the system and therefore it’s not perpetual motion.
Perpetual motion would be the generated gas drives a motor which would drive the generator to make electricity to power the electrolysis. Closed system.
Friction losses at every step and energy inefficiency would bring it to a stop in no time.
Example: the electricity from burning the gas would not make enough gas to keep the cycle going.
Let’s say that we have a submarine that is attached to a rubber band. The whole machine is placed above a vortex. When you drop the submarine, the vortex sucks it down and stretches the rubber band. The current is so strong and the shape of the submarine just so that it goes all the way to the bottom of the ocean, where the submarine is jostled by the rock beneath, which undoes a latch, that causes the submarine to change its shape to something more aerodynamic so that the rubber band can pull it back up. As soon as it launches out of the water the shock of being pulled causes the submarine to change back into its former shape before it plonks back down into the vortex.
Perpetual motion machine?
No. The current of the ocean is made by the world being slung about through space. You’re siphoning energy off of that system and in fact slowing the world down. That force might be so great that you can get massive quantities of energy from it and never notice the slowdown, but even so that is exactly what is happening.
In your example you seem to be burning water. This is depleting the amount of water in the ocean. Eventually you will have burnt it all, even if 99.99% of all water burnt is replaced after each pass. It may be a very efficient fuel, but nothing is 100%. Eventually the fuel will be depleted.
I think the catch is that the enormous pressure at the bottom of the trench makes the electrolysis expensive, in terms of energy - so it takes more energy to generate the gases to blow the tanks than you could ever hope to reclaim from the motion of the sub as it ascends and descends.
I just read a study saing that electrolysis if 5% more efficent in high pressure. You would also need a battery, because you don’t need more gases on the way up. So the sub would basically be a great battery ready to be used for elecro-powered ships passing by.
5% more efficient doesn’t mean 5% easier. And that might still mean 45% efficient instead of 40%.
As we discussed in the other thread, part of the energy of electrolysis at sea level is displacement of the atmosphere at normal pressure - so part of the energy cost of electrolysis at the ambient pressure at the bottom of the ocean is going to be displacement of water, at a phenomenal pressure.
We aren’t using water as fuel in the motion - gravity and buoyancy is the fuel. Hydrogen is the free energy part.
But I really would like to know what happens in this chemical process of “burning water”. Can we loose some of the water in time? How are the electrodes reacting? On the first lap down we have a lot of energy, but will the efficiency get rusted in time?
Buoyancy is an effect of gravity on fluids, which is why the idea won’t work - you can’t get out more than you put in.
Ignore the electrolysis bit for a moment and consider the buoyancy of a sealed air-filled container in a fishtank:
1 - When you push it down to the bottom, you expend energy. Some of the energy you expend is wasted on losses such as overcoming friction, etc - but when you push it down to the bottom, you’re essentially lifting up the water it displaces (against gravity).
2 - Now that the container is at the bottom, it wants to float back up - and we can harvest the energy from this action - as the object rises, it’s allowing the water it displaced to fall - that’s where the energy really comes from, and that can’t be more than it cost to push it down there. (and again, there are losses, so it you don’t even get back all you put in)
Now going back to the scenario whereby the buoyancy is created by filling the object with gases while its at the bottom - the energy cost of filling it with gases cannot be less than the cost of displacing the water (because that’s what you’re doing - displacing the water - i.e. lifting some water). And you won’t be able to harvest all of this on the way back up.
Regardless of whether you’re using it for motion or not, you are using it and you can’t complete the cycle without that input. Some of the water is turned into heat as you split the molecules, some into gas that’s burnt off. Eventually you will have burnt away the whole ocean. A perpetual motion machine with a fuel input that can be depleted is not a perpetual motion machine.
I sort of understand your meaning. How about the free energy efficiency - should I invest my money in electro-powered ships and hydro-powered submarine power plants?
Deep diving subs can’t/don’t use air or any gas for buoyancy. It would require obscene pressure(many gasses would liquefy) or buoyancy tanks with such thick walls that no buoyancy would be produced. Instead the tanks are filled with lighter-than-water liquid. Gasoline was used in the first ones…not sure of current practice. Since the liquid is largely incompressible, the tank walls act as a bladder rather than a pressure vessel.
But to get back to the spirit of the OP:
Now since you can’t blow the ballast tanks, the only option to get back up is to drop heavier-than-water ballast. All those weights falling from the surface to the floor of the sea are what powers the system.
