Recirculating Fluid Turbine: A Thermodynamic Challenge

[paul turbine]

I think it is possible to design a machine capable of generating useful electricity using recirculated fluid flow. But the laws of thermodynamics make it very difficult.

The three laws of thermodynamics can be summarized by saying: "You can break even but only at absolute zero".

So we know for sure we will never be able to get more energy out of a system than we put into it in the first place.

Secondly, the value of entropy in a system governs what is possible or impossible.

If entropy is zero or negative, then whatever we had hoped to achieve is impossible. It is simply not permitted by the laws of physics that govern the universe.

An example would be trying to reverse the smashing of an egg on the floor. A reversal of the process (where the egg lifts off the floor and recombines into a pristine egg)would require a negative value for entropy (S). Accordingly, we can be certain a reversal of the process is impossible.

Unfortunately, the laws of thermodynamics and the related law concerning entropy constitute reality. If we don't like it, we will have to go and live in another universe.

Bearing in mind the laws we are stuck with, the next step is to think about what types of system might be useful for generating electricity, bearing in mind these serious limitations.

There are three types of systems. Isolated, closed and open systems.

In isolated systems, neither mass nor energy can pass through the system boundaries (think of a perfectly insulated thermos flask).

We will never generate useful electricity from an isolated system. For a start we won't get any energy out of it in the first place. If we could, it would not be an isolated system.

So we can forget about isolated systems.

What about closed systems? They allow energy to pass through system boundaries, but prevent mass passing through them. Think of a badly (thermally) insulated thermos flask that is perfectly airtight and watertight.

The problem with closed systems is that you always get less energy out of them than you put into begin with.

Our only hope is an open system in which both mass and energy can pass through the system boundaries.

So this has to be our starting point.

We must invent a machine that allows mass to pass in and out of the system boundaries, and also allows energy to do so as well.

In practical terms this means we need help from the environment.

External work must be done on the system (eg solar energy or water from a flowing stream) to provide energy from outside the system boundary.

External mass (eg air or water) from outside the system boundary must be able to pass through the boundaries as well.

The best idea I can come up with as to how we can generate useful electricity using fluid flow began as a thought experiment:

There are two 25m high cylinders each of diameter 1m (only the most intrepid amongst you will want these things in your back garden, so they are intended for industrial use).

Cylinder A is full to the brim with water.

Cylinder B is 10% full of water.

An impulse turbine (for example a Pelton turbine) is placed 3m from the bottom of cylinder B (allowing a space beneath it for tailgate water to accumulate).

The cylinders are connected to one another such that water flows from A to B, allowing it to fall down a 20m+ drop in cylinder B before striking the impulse turbine.

At a mass flow rate of one cubic meter per second (which is an enormous flow rate) and allowing for system efficiency of 0.85 (this being a unit-less fraction where 0= total inefficiency and 1= perfect efficiency), the electrical power output in watts (using water of density 1000kg/m3 as the working fluid) is as follows:

Pw = 1000kg/m3 x 20m x 9.81 m/s/s x 0.85

Pw = 166770 watts = 166.77kW.

So this looks promising.

But there are serious practical problems.

Water that collects at the bottom of cylinder B (the tail-gate water) will rise until the point it prevents the impulse turbine turning. It will swamp the turbine and stop it moving.

So the water that builds up at the base of cylinder B has somehow got to be forced back into the base of cylinder A (which requires energy expenditure because of the higher water pressure at the base of cylinder A).

I think I have found a way of recirculating the water without having to use enormous amounts of external energy (to lift or pump fluid back into tank A).

I would much appreciate private (not to be published) dialogue hopefully with a co-inventor familiar with thermodynamics, Bernoulli, and Newtonian fluid flows.

Preferably a doctorate in applied physics/fluid dynamics.

My aim is to share an energy efficient recirculation novelty, test same using a comprehensive parametric equation, and apply for a patent relating to industrial electricity generation.

I can be contacted at:

<< personal e-mail deleted by berkeman >>
Thanks for reading the post. I hope you enjoy thinking of your own solutions to the problem as much as I have done.

 

[QuantumPion]

Your device sounds like a hydroelectric dam. And like a dam, the only way to get net power out of it is to let nature refill the reservoir for you. There is no way to pump the water back up using less power than you generated when the water fell down to begin with.

 

[AlephZero]

I think it is possible to design a machine capable of generating useful electricity using recirculated fluid flow. But the laws of thermodynamics make it very difficult.

Why is it difficult? People have been designing external combustion heat engines that work like this for at least 100 years already.

You probably have one in your house - it's called a refrigerator.

 

[paul turbine]

Thank you in the first response for pointing out it is impossible.
Thank you in the second response for pointing out it is not difficult.

 

[berkeman]

Thank you in the first response for pointing out it is impossible.
Thank you in the second response for pointing out it is not difficult.

Pion's response what not that it was impossible. He was saying that it takes solar energy to refill the reservoir in his example. As long as you put energy in somehow, you can make the turbines run.

 

[russ_watters]

...however you can't make it self-powering.

 

[paul turbine]

I agree no such system can be 'self powering'. That would be tantamount to perpetual motion.

On the contrary, it is an energy converter. It uses energy from outside the system boundary to circulate fluid striking a turbine.

Massive amounts of energy (up to 5 times the turbine output) would be needed to pump 1000kg of water 25m upwards.

So the turbine (connected to an alternator motor) cannot generate enough energy to move its own working fluid around.

This means brute force does not work, as you end up 'spending' more energy pumping water around than you get back from the turbine.

The problem requires a different and counter-intuitive approach.

 

[Drakkith]

I think I have found a way of recirculating the water without having to use enormous amounts of external energy (to lift or pump fluid back into tank A).

I hope your not thinking of something like Heat or Sunlight, because that IS external energy.

I agree no such system can be 'self powering'. That would be tantamount to perpetual motion.

Do you have a way of providing the energy required to move the fluid without it being external? Which would be perpetual motion effectively.

 

[paul turbine]

I have found a way to minimise the work needed to recirculate the fluid. That's all.

At best it is a more efficient energy conversion system. But you still have to spend more than you get out (when total energy is taken into account).

If perpetual motion had been an apparent consequence, I would have known with certainty I at that point that I had fallen into error. Fortunately it is not.

Though path dependent in terms of efficiency, the energy saving thought to arise from the path used simply reduces external energy expenditure, making the system more efficient or profitable than other methods such as the brute force approach of trying to raise 1000kg of water a second 25m into the air.

 

[Drakkith]

Ah, ok.

 

[russ_watters]

In one post you said it doesn't use outside energy, in another post you said it does. Then you said you are trying to minimize the work required to lift the water. The work is what it is: there is only one amount it could be and it is non negotiable. Sounds like you're trying to argue your way out of conservation of energy to me.

 

[Curl]

If entropy is zero or negative, then whatever we had hoped to achieve is impossible. It is simply not permitted by the laws of physics that govern the universe.

The 2nd "law" of thermodynamics is not a fundamental law the governs the universe. It is a statement about probabilities: not a fundamental law at all.

 

[paul turbine]

It is important to distinguish between conditions of state and path dependent conditions.

The work required to lift 1000kg of water per second upwards 25m will for these purposes be the same.

But the actual energy cost of carrying out that work is path dependant and therefore variable. The energy cost is not a condition of state.

For example, you could use a thousand hydraulic 1 litre buckets to lift 1000kg of water per second 25m up into the air.

Each bucket powered by its own electric motor.

The cost of doing that (in watts) would be greater than the energy consumed by a single efficient electric water pump doing the same work.

So I do not agree that 'it is what it is' because the system has conditions of state as well as having path dependent components.

As for entropy not being a law, I respectfully disagree. The best possible test of whether something is possible or impossible is to calculate the value of the entropy for that event.

If the value would be zero or negative, it is impossible. If the value is positive, it is possible. The probability it will happen increases as the positive value of entropy rises.

Quantum physicists may have expressed this mathematically (when expressing probability). I would be surprised if they have not. It seems fairly obvious.

 

[berkeman]

The work required to lift 1000kg of water per second upwards 25m will for these purposes be the same.

But the actual energy cost of carrying out that work is path dependant and therefore variable.

No. The force due to gravity (at least in a classical sense) is conservative, and therefore the work due to gravity is path independent. You do understand that, right?


EDIT -- Adding PF Library reference:

https://www.physicsforums.com/library.php?do=view_item&itemid=174

.

 

[paul turbine]

I don't think I am disagreeing with you. I did not assert gravity is path dependent.

What I am suggesting is that it is a path dependent 'system' in terms of energy expenditure when it comes to doing the work required to recirculate the water.

There are several ways of recirculating water in such systems. Some of these ways or paths consume more energy than others.

Which is to say it is the system that is path dependent. Not gravity.

 

[russ_watters]

The INPUT can be different but the OUTPUT is always the same for the energy to lift the water.

And since that value is also the same as the max you can get out of your turbine, the system can never produce excess energy.

 

[russ_watters]

The 2nd "law" of thermodynamics is not a fundamental law the governs the universe. It is a statement about probabilities: not a fundamental law at all.

No. Just because it is statistical doesn't mean it isn't still true.

There is little in science more fundamental than the laws of thermo.

 

[paul turbine]

Thanks Russ. I am sure are correct about that. in truth I find the second law counter-intuitive, but I accept it applies in all cases.

I have had recurring delusions of high efficiency. But at the same time I know nature will always find a way to maximise output in the way you have said.

Bluntly, what I have tried to do is to use gravity to slam a high flow rate of water into a turbine from a significant height (leading inevitably to high power output in watts), and then to think of innovative ways to recirculate the working fluid as energy efficiently as possible.

This has been done in the hope total energy output will exceed the energy needed to recirculate the water. And yes I know it seems a fools errand, but that is what I have tried to do.

In order to understand the proposed system fully, I am hoping someone will help me prepare a comprehensive parametric equation, because the mathematics of the system will tell the story of the system very clearly.

So I think you were right to say I have been flirting with a second law breach (who has'nt at some point) but for the avoidance of doubt I agree completely with you that this is not possible.

 

[berkeman]

So since the goal is over-unity energy production, we are done with the discussion.

 

[russ_watters]

Just a quick postscript:

1. It's the 1st law that is the problem here, not the second.
2. This is one of the original, ancient PMMs: the self-powered water wheel. It has been around for at least 500 years. Please put some trust into 500 years of technological advancement and confirmation of the 1st law of thermodynamics and stop looking for something that doesn't exist. You'll save yourself much time, money and heartache. For more info on this, the Museum of Unworkable Devices is a great technical and historical resource: http://www.lhup.edu/~dsimanek/museum/unwork.htm