Thermodynamic cycle that can reuse latent heat of condensation 8

[haruosan]

I'm developing a thermodynamic cycle that transfers existing heat to generate steam. The heat transfer includes reusing the latent heat of condensation harvested at the condenser to heat the working fluid. Normally, this is not possible because the condenser is not the hottest point in the cycle and therefore any heat harvested cannot be transferred back into the working fluid which is hotter at any point in the cycle before the condenser. This limitation does not exist in the cycle I'm developing. Unlike a Rankine Cycle which generates high temperature heat for the generation of superheated steam, this cycle uses and re uses low temperature heat for the production of steam.

I'm looking for a mechanical engineer who'd like to be a cofounder for a green tech company based on this cycle. Preferably you live in CA or would be willing to move to CA at some point after funding is achieved and you are receiving a salary. The skills needed to prove the viability of the cycle and develop it are:

CFD
Heat Balance
MATLAB
Simulink
CAD
Turbomachinery
Electrical Engineering knowledge is a plus

I am familiar with OpenFOAM, Fusion360, MATLAB and other tools.

Please respond only if you are interested, have the skills, and are willing to become a cofounder.

 

[haruosan]

2) As drawn, there is no waste heat lost from your system, anywhere. You show three power inputs ('heater', 'pump', 'turbine') and no losses. Your cycle as drawn just heats the working fluid to higher and higher enthalpy, forever, with no losses and no extracted useful work.

This is all very droll, but you can prove that you aren't running afoul of Sergeant Carnot and Officer Planck very easily with a simple control volume analysis - just draw a box around your heat engine separating internal and external components and label (and quantify) all the flows of heat and work crossing the box.

Both of you are much more knowledgeable of steam power plant cycles than I. I appreciate and respect your comments and guidance. But, I will point out a flaw in your belief that the cold reservoir of a heat engine cannot be the heat engine itself. That notion does not make thermodynamic sense. I'll explain why and pose a thought experiment for you.

As an aside, this is a thought experiment and has nothing to do with the cycle I described above. I mention this because I used a couple of examples that were not the system in question to illustrate why your thinking that re-using latent heat back into the same cycle was impossible and violates the laws of thermodynamics. Interestingly, this sentiment of yours has now changed and you now do believe that heat can be reused in the same cycle, but with caveats: "in Rankine cycle terms, hot turbine exhaust absolutely cannot entirely transfer its heat back into the boiler feed water because it isn't possible for a process stream to cool itself." Okay, at one time you were adamantly opposed to this. Whatever was your intention by stating it was a thermodynamic impossibility, I'm certain at this point, both of you agree that the cold reservoir must be separate from the heat cycle itself. "draw a box around your heat engine separating internal and external components and label (and quantify) all the flows of heat and work crossing the box."

Why does waste heat have to cross the box?

I do believe it is a must for a heat cycle to shed heat. An ideal cycle is reversible and must shed heat to return to its starting state. But where it must shed heat can be anywhere as long as the heat is shed.

The thermodynamic cycle I'm proposing sheds a lot of heat in the condensation process. Although SwinnyGG, you keep saying the process doesn't shed heat.

The heat is shed in the turbine and transferred to the steam within the turbine.

Thought Experiment
Let's assume that cold vapor can be created and the intention is to use the latent heat of condensation to heat this cold vapor. But instead of doing this we shed the heat to cold water in a shell and tube condenser / heat exchange. Lets say the amount of heat transferred to the cooling fluid is 2,256 kJ/kg of steam. Now let's add an electric heater to the turbine to heat the cold vapor and we transfer 2,256 kJ/kg - the same amount of heat that was shed at the condenser.

The suggestion that latent heat reuse could never heat the vapor would mean the above scenario is impossible. Unless of course, the heat shed at the condenser is a different kind of heat than the electric heater generated. We both know this is not true. Heat is heat and it flows from hotter to colder.
If you shed heat during a condensation process, you will be able to transfer that heat to any colder temperature mass even if it is somewhere else in the same cycle.

The answer is in the second law: Heat transfers from hot to cold.
It is assumed that heat cannot flow back into a cycle because where heat is shed is usually the coolest part of the cycle and it would be impossible to reuse latent heat into the same cycle because everything else in the cycle is hotter. If the condensation process is the hottest part of the cycle, heat will transfer back into the cycle.

No, you are not correct when you say my proposed cycle does not shed heat. It does. It sheds it to the cold vapor.

1) As drawn, your cycle utilizes a 'turbine' which increases the enthalpy of the working fluid between inlet and outlet. This means your 'turbine' is applying work to the system, not extracting work from the system. When challenged on this thus far, you hand wave it away by saying 'the working fluid is heated in the turbine'. Physical realities of connecting a giant heat pipe to a moving turbine surface aside, in schematic terms you can't do that. Turbines extract energy from the system, they don't add energy in.

I understand why you made this statement, but you can extract work from a turbine as you're adding heat. The real question is does the work produced equal the work output? It's been studied. I don't know these guys, but they know this to be true.

https://www.youtube.com/watch?v=SJ4hCCaW_Y4

 

[GBTorpenhow]

But, I will point out a flaw in your belief that the cold reservoir of a heat engine cannot be the heat engine itself. That notion does not make thermodynamic sense.

The answer is in the second law: Heat transfers from hot to cold.

"Heat transfers from hot to cold" is not a complete understanding of the second law of thermodynamics. "The cold reservoir of a heat engine cannot be the heat engine itself" however, is actually a pretty decent way to state the second law - we'll call it the haruosan formulation of the second law, perhaps. I like Kelvin's formulation too - "It is impossible to construct a perfect heat engine that converts heat directly into work". <

https://farside.ph.utexas.edu/teaching/sm1/Thermalhtml/node69.html>

 

[SwinnyGG]

No, you are not correct when you say my proposed cycle does not shed heat. It does. It sheds it to the cold vapor.

Ok. What happens when you turn off the heater?

I understand why you made this statement, but you can extract work from a turbine as you're adding heat.

I’m not sure you do. I never said you can’t heat up air that’s also expanding in a turbine- I said that a turbine with a net positive enthalpy change across it is not extracting work from the system. Those are very different things.

If you truly want to figure out if this process you are imagining is viable, you have to stop thinking of building a physical system- you have to build a model first. If you do so, and your model uses schematic elements that do two things at once, you’re gonna have a very bad time getting people to understand what you’re trying to say.

So… again. Your diagram shows a ‘turbine’ (which is universally understood to be a work extraction device) with a net positive enthalpy change between input and output. This is nonsensical.

Calculate the state points, put them on a PV diagram, and post that PV diagram.

A lot of the difficulty in this conversation is rooted in the fact that you are asking questions based on a bunch of incorrect assumptions. In turn, you aren’t getting what you want from us because we are focused on correcting those assumptions in order to guide you toward asking the right questions. A few of these assumptions are:

1) you assume that current generation cycles don’t make use of latent heats. This is incorrect.

2) you assume unit entropy can be increased without input work (this is the core of what you’re arguing with GBT about)

3) you assume you can extract more work from a system than the value of the net entropy change of the system (this is a major component of 2nd law analysis point of view that you’re lacking)


I’d very strongly suggest you spend some time reviewing the basics of thermodynamic laws and the various ideal cycles (Carnot, etc). Until you have a moderate understanding of these concepts your not going to understand what we are trying to explain to you.

 

[MintJulep]

Guys,

Haruosan has a 100% confident, faith-based belief that his cycle will work.

Belief >> physics.

Please stop trying to convince them out of their belief. Just let then go away and build it.

It's ok to let people be wrong on the internet.

 

[haruosan]

If I was someone who didn't understand the laws of thermodynamics, it would be laughable. I understand there is a finite amount of energy in the universe and it moves from high quality / ordered energy to lower quality, dissipated energy-entropy. I do understand that you cannot get more energy out of a smaller quantity of energy. It's impossible.

Here's why I think this is worthy of investigation. In an "Ideal Case," you can produce more heat from the potential energy in hydrogen bonds than is required to generate the heat. Remember this is an ideal case and is only used to see what may be possible.

If you use a flash vaporization process to vaporize water, you can potentially extract more heat from potential energy than is required to vaporize the water in the first place.

Sensible Heat in 1 kg of Water
418,600 - Sensible Heat of Liquid Water - 4186 x 100 = 418,600
334,000 - Latent Heat of Fusion - 334,000
570,570 - Sensible Heat of Ice - 2090 x 273 = 570,570
1,321,170 - Total Sensible Heat - 1,321,170
Heat Added
934,830 - For Remaining Latent Heat of Vaporization
744,508 - Raising temperature to 100C
1,679,338 - Total Heat Added

2,256,000 - Latent Heat of Condensation - Max Potential

Basically, in this Ideal Case exercise, you could vaporize water and create 100C steam by adding 1,679 kJ/kg and you have potentially 2,256 kJ/kg to accomplish it if you reuse latent heat from the condensation process. This doesn't mean that it takes less heat to vaporize the water. If you add up all the heat, it still requires 2,256 kJ/kg to vaporize the water, but since your condensate returns at 100C (ideal case), it will always contain 60% of the latent heat of vaporization. The reason there is potentially more heat from condensation is because there is an advantage to heating water when it is a gas and extracting heat when it is liquid.

You have an additional 576,662 J/kg more from latent heat of condensation. This amount of heat is 25% of the total heat of condensation, so if you reused only 75% of the latent heat of condensation, there is enough thermal energy to maintain the cycle. This does not mean the cycle will continue indefinitely like a perpetual motion machine. There will be temperature degradation and the cycle will cease to work when the temperature of the steam reduces below 100C. But, it does mean that a small amount of heat to increase the temperature, will enable the cycle to continue. What does it mean to create a cycle that vaporizes enough water to generate 1MW, but does it with a lot less heat? Will there be enough power in the cycle to actually generate that much? Or will it cease to cycle when a load is put on the generator? I don't know the answer to these questions, but I do believe it is worthy of investigation.

I get that what I propose is counter-intuitive to everything you know about steam power cycles. The goal may not be a high temperature / high pressure steam cycle that contains enough pressure so steam can be accelerated through various stages of a traditional steam turbine. But maybe, a lesser kind of cycle can be maintained on a lower amount of energy. Maybe a 100kW input could generate a 50kW output. 50% efficiency in a cycle that is much less expensive to build and maintain, might be beneficial..

The National Science Foundation also believes it's worthy of investigation. A Phase I grant is enough to prove the premise. If Phase I sees positive results, Phase II is enough to build a prototype.

 

[SwinnyGG]

I get that what I propose is counter-intuitive to everything you know about steam power cycles

Quite the opposite. What you’re trying to say is relatively intuitive, but it violates the principles of a known thermodynamic law which is itself highly unintuitive. When we point that out, you ignore the commentary and just assume we don’t understand.

I do understand that you cannot get more energy out of a smaller quantity of energy.

If you use a flash vaporization process to vaporize water, you can potentially extract more heat from potential energy than is required to vaporize the water in the first place.

Not much left to say to this. It’s clear you came here to get some validation, and not for real feedback. That means we can’t help you. Good luck.

 

[haruosan]

SwinnyGG (Mechanical), et al,

I found the discourse very helpful and I did get real feedback that is very useful. I actually appreciated every bit of it.

Thank you, everyone.

 

[IRstuff]

If I was someone who didn't understand the laws of thermodynamics, it would be laughable.

Seems to me, you don't. You have a "Miracle happens here" buried in your heat exchanger/heat pipe/heat exchanger in your last drawing. No heat exchanger can transfer 100% of the inlet temperature, so there's a loss there, ditto at the turbine end. A phase change heat pipe sucks a huge amount of heat into the heat of fusion of the media, so that's another unrecoverable loss w.r.t. to temperature you want to achieve.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[haruosan]

Seems to me, you don't. You have a "Miracle happens here" buried in your heat exchanger/heat pipe/heat exchanger in your last drawing. No heat exchanger can transfer 100% of the inlet temperature, so there's a loss there, ditto at the turbine end. A phase change heat pipe sucks a huge amount of heat into the heat of fusion of the media, so that's another unrecoverable loss w.r.t. to temperature you want to achieve.

Yes, no heat exchanger can transfer 100% which is why heat is added just before the condenser. Otherwise the cycle would stop due to temperature degradation.

In a traditional process most, if not all, the latent heat would be lost to the atmosphere / cooling fluid. This process attempts to reuse that heat - why would it be any less efficient than dumping all of it to the atmosphere?

As for heat pipe technology, it's one of the most effective heat transfer technologies in use, but as a heat exchanger in steam power plants, it's still in its infancy. The tech is promising as it has been shown to be more effective. A company who develops heat pipe technology for NASA has verified they can create an OHP to transfer the required amount of heat. This was based on a 10 l/s flow of water.

Comparative study between heat pipe and shell-and-tube thermal energy storage

https://www.sciencedirect.com/science/article/pii/S135943112100421X

Steam condensation by heat pipes

https://iopscience.iop.org/article/10.1088/1742-6596/1473/1/012028/pdf

Application of Heat Pipe Technology in Thermal Power Plant

https://iopscience.iop.org/article/10.1088/1755-1315/170/4/042057/pdf

Comparison between Heat Pipes based condenser and Conventional condenser of Power Plant

https://assets.researchsquare.com/files/rs-172887/v1_covered.pdf?c=1631855215

Utilization of heat transfer through phase change in devices to increase thermal efficiency

https://www.sciencedirect.com/science/article/pii/S2352146521004221

FUNDAMENTAL STUDY OF HEAT PIPE DESIGN FOR HIGH HEAT FLUX SOURCE

https://tfaws.nasa.gov/TFAWS02/Data/Thermal/Oinuma.pdf

 

[3DDave]

"traditional process most, if not all, the latent heat would be lost to the atmosphere" is only true to the extent that entropy requires, which is by the temperature delta, not the absolute temperature. By recycling the heat, you are decreasing the temperature delta, lowering the efficiency. The heat has to go to a heatsink in order to extract useful work on the way.

 

[SwinnyGG]

In a traditional process most, if not all, the latent heat would be lost to the atmosphere / cooling fluid

This is fundamentally incorrect, from both a theoretical thermodynamic point of view as pointed out by 3DDave, and from a practical point of view in real world implementation of advanced power cycles.

There are many variations - literally dozens - that re-use SOME latent heat from working fluid flows to do various things, including returning some heat to the feedwater/steam loop. While there is still development work being done, many of these technologies are decades old and are relatively mature. The fact that existing processes don't recapture 100% of latent heat in working flows is because of the limiting factors imposed by the laws of physics, not because development of power generation technology stopped at some point in the past.

Look you're never going to understand what we're telling you unless you actually do the work of sitting down and calculating the enthalpy change across every system boundary in your proposed cycle. Just calculating temperatures is effectively meaningless. You have to do the work. That's it. When you actually do, what we're telling you is going to become obvious very quickly.

Food for thought: the field you are trying to enter is one which has been a focus of human effort for centuries, literally. Steam was being used to power mechanical devices in the 1500s. The system you're aiming to improve is the result of centuries of development by thousands upon thousands of people, and for that entire time there has been a gargantuan financial incentive to make these systems as efficient as possible. You're not turning over a new stone here.

I applaud your enthusiasm, but the reality is that what you're saying violates the laws of physics. If you understand those laws, it's very clear and it's not really a point that can be debated.

 

[IRstuff]

You're not turning over a new stone here.

Sure, he is; he's obviously smarter than all of us here and all the smart people that have broken their picks on this type of problem.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[GBTorpenhow]

We miss you, OP, any updates?

Does the NSF take the same laissez-faire attitude towards thermodynamic impossibilities as the US Patent Office?

Why does waste heat have to cross the box?

Have you answered this key question for yourself yet?