Is My Reasoning In Error?

[ZPDM]

Perhaps I should sleep on this as it just occured to me and I may be missing something obvious, however I would greatly appreciate feedback on this. I will give the background on what led me to this which I hope won't be overly boring, would just say if I am right I beleive this to be rather important.

So I was reading up on using abandoned oil wells for geothermal power. Tesla I beleive also mentioned this approach and noted you could use water or "ether" as the circulating fluid. Tesla also mentioned using more shallow wells for more localized energy production an approach not conventionally portrayed as feasible. From there I stumbled into Bob Hunt of Renewable Energy LLC, his attempts to commercialize exactly this abandoned oil well approach and a video talking about some of his work and research. TEDxAustin - Bob Hunt - 02/20/10 - YouTube!

From the little bit of reading I have been able to do, I am beginning to be able to hazard a very rough guess at how some one approaches issues and/or the possible influences on his approach. So when Bob Hunt mentioned things like working how nature does and living water, I paid close attention to his thinking. He noted for instance that turning water into steam and gathering the energy from a well is analogous to what is going on with the oceans to the rivers to hydroelectric plants already. He also had a strange proposal for a plane which flew by having a phase change between liquid and gas based on the termperature differential of the atmosphere and the resulting change in buoyancy of the craft.

So yes I think there is tremendous potential for helping solve the energy crisis through hydroelectric remediation of abandoned oil wells, and without anyone yelling that it can't be possible, however that is not why I am writing. I next was wondering if there are even easier ways to find that "neccessary" temperature differential for geothermal power eventually concluding that I couldn't easily think of any. There is where a very odd bit of reasoning occured. Let's revisit Bob's idea for his plane, and even simplify it to a balloon where there is a change between liquid and gas in the bouyancy compartment. Would such an approach work? Would a balloon bobbing up and down in the atmosphere be considered as potentially doing work? What is the temperature differential involved?

To boil all this down (oops sorry), the energy in geothermal or for that matter a steam engine doen't come primarily from the degree of temperature difference it comes from the phase change of the working fluid, i.e. liquid to gas. On the one hand this seems vaguely scientifically heretical to me, on the other commonsenically if there is no water in the boiler of a steam engine it is immaterial how hot the fire is. We also know that the energy released in this phase change is enormous, the volume occupied by the material going up by orders of magnitude. The force with which this gas wishes to expand can be seen when considering the neccessity for steam locomotive engineers to pay attention to boiler pressure lest they blow the thick cast iron reaction chamber up, or more recently the infrequent explosions of large building's hot water boilers.

However at 210 F(99 C) there is no work being done, at 214F (101 C) you have to release steam or have problems. The fire chamber might almost be viewed as a catalyst to bring about the phase change. So bear with me now, if the work is being done primarily by the phase change and not the termperature differential, well there are substances with different boiling points. Propane boils at -44F, Oxygen at -297F, octane at 258F, lead at 3,180F. Isopentane boils at 82-83F, Trichlorofluoromethane at 73.4F. Once again, it appears to me that the work is done by the massive volume expansion in going from liquid to gas, not an arbitrary temperature obtained or a large differential between the working fluid's initial and final temperatures. In conventional geothermal systems the gas is reliquified through a heat sink and, I believe, often used as a closed loop system. What would happen if you heated trichlorofluoromethane to 120 F, captured the steam (volume expansion) energy and cooled the gas in some pipes in the ground? If one filled a locomtive's boiler with trichlorofluoromethane and heated the chamber to 120F would the locomotive run?? What am I missing? Is my reaoning in error? Thx
Paul

[ZPDM]

I want to say a little more on this. First by way of preface as there have been no replies and I am certain this is a very intelligent board I would guess three possible things, 1) I am missing something so obvious people are embarrassed for me or disgusted 2) there are no immediately obvious holes in this approach and/or 3) it seems irrelevant or extraneous. As regards 3) would just point out that much if not the large majority of electricity is currently produced by steam turning a turbine.

So after a couple days I want to go back and look a little more concretely at the theory, consider a few examples of people doing similar things and finally consider practical ways to evaluate and possibly make use of this.

Theory: From the research of Robert Boyle and others we have the ideal gas law PV=nRT
P=Pressure
V=Volume
n=moles
R=Universal Gas Constant
T=Temperature in Kelvins
to approximate the behavior of gases. In situations where the pressure is constant (atmospheric), we can see that the volume of a given amount of gas will be directly proportional to temperature. We know that a Stirling engine (a closed cycle hot air engine) will run off a temperature differential of say 40 C (i.e. Kelvin). From the ideal gas equation, at room temperature 22C (295K), this difference would be 335K/295K =1.136. Therefore there is about a 14 percent volume expansion that is responsible for the movement of the piston in a Stirling engine running off a 40C temperature difference. Am I wrong here? I mean in all honesty this isn't my field. (As a really quick aside, I have seen videos of Stirling engines running at maybe a few hundred RPMS, I find it amazing that the gas is able to dissipate all of the heat needed to keep this temperature differential in the fraction of a second it is on the cool side). Stirling engines are considered one of the most efficient engines available.

Alright let's now look at a change of water from liquid to gas. While I don't have an authoritative reference yet, the figure I keep coming across is that there is an approximate 1600-1700 fold, (160,000 - 170,000 percent) volume expansion for water going to steam. The expansion ratio for other liquids seems to be I think generally a bit smaller, so let's say for the trichlorofluoromethane (freon R-11), mentioned in the first post and which boils at room temperature, it is 500 fold or 50,000 percent. That is still a bit more than 14 percent. And the specific heat of water is higher than many liquids (i.e. it takes more energy to raise a given amount of water 1 degree in temp than many other liquids). The best argument I have come up on my own against this would be, "you nincampoop!, you absolute moran, you come in here to a field you know nothing about with your high falutin ... sorry, yes the volume expansion is greatest at the phase change, however, the percent of liquid that changes to gas is a function of the temperature differential and only a tiny, tiny proportion will boil at 101C whereas more will boil off more rapidly at 110 and more at 200C, so the recoverable amount of energy is not greater around the phase change, that is why you need the large temperature differnential, idiyt!" Alright leaving aside my Gollum imitation, even if this were true, which I tend to guess is not the case for reasons I'll go into in a moment, it still would not negate the energy savings from having a substance that boils closer to ambient temperature than water. And I do suspect you can just try to cycle as closely as possible around the phase change temperature and extract usable energy.

Anecdotal:
This is a video of a toy called a hand boiler. Hand Boilers - From Gyroscope.com - YouTube A substance boils from the heat of the hand and travels up half a foot to a bowl at the top of the toy. That's a fair amount of work from the heat of a hand. It also looks to boil off extremely rapidly despite a small temperature differential. So one way you could use this approach would be simply to use the gaseous state to shuffle around mass. This appears to have already been done with what has been called the Wallace Minto Freon Power Wheel Wallace Minto: Freon Power Wheel, However as I noted above one might also use this approach to look to capture the energy in the volume expansion itself, exactly as we do with water to drive the majority of electricity turbines from steam.

Practical: How to evaluate and warnings!

First off this approach is by definition potentially dangerous. Despite my mention of isoheptane, never, ever use a flammable substance, vaporizing a flammable substance creates the conditions for what the military might call an air-fuel bomb. Second, apart from flammability, if one is ever vaporizing a liquid in a confined environment there exists the potential for what is termed a BLEVE - Boiling Liquid Expanding Vapor Explosion. Here is a training video for a BLEVE, air fuel explosion, along with underscoring danger it also serves to give an idea of the potential energy from a phase change. Bleve Demo - YouTube. Nonetheless despite the obvious danger it is not like we haven't been using the phase change of water to provide most of our electricity for quite some time now.

Next is what low boiling substance to use. My first thought was a variable mixture of water and ammonia hydroxide which could provide different boiling points. The drawback here I came to realize is that the difference in boiling points between water and ammonia hydroxide is great enough that you would perform a one pass simple distillation, i.e. boil off all the ammonium hydroxide. Still might have some value for one shot deals. The best I've come up with so far is Freon r11.

What I've come up with as an initial test bed, is an aeolipile, aka Hero turbine or impulse turbine. gyroscope.com sells one for about 100 bucks or I could build one. Hero Steam Turbine - From Gyroscope.com It is basically a teapot on a rotor with two steam nozzles 180 degrees apart around the equator, when the water boils the steam shoots out and spins the turbine. You could measure the rotational speed with water and again with other substances at different temperatures. Of course the drawback here is that the thing spinning around shooting off whatever is in it is going to make a sheet storm from whatever you are boiling. You would want to enclose it to avoid a trip to the ER. If these steps validated the approach the next thing I think of, which may not be the way to go would be a Stirling engine. The Stirling engine is a closed system so this would be dangerous, one would essentially be trying to create a controlled BLEVE, however, I do wonder what half an eye dropper of freon r11 introduced into a Stirling engine might do.

As I was driving home I thought of one other approach which if this phase change idea is meritorious would likely be the way to go long term. The boiling point of a liquid is also dependent on pressure. PV=nRT one wants to lower the boiling point of water from 100C (373K) to 22C (295K). 295/373 =.791. Unless I have the math wrong a 21 percent vacuum should lower the boiling point of water to ambient temperature, that seems small to me but that's what I get from the equation. So to sum it all up, make a partially evacuated Stirling engine and use the phase change from water to steam to drive it. Might not work, but if it does it looks to me to be theoretically orders of magnitude better than the hot air Stirling engine.

If one were able to use the output energy from such a device to maintain the necessary heat input for the machine, you would then have, often confused with perpetual motion or free energy, what I call (in my best Mike Meyer's Dr. Evil voice) a "chain reaction", where the output energy is sufficient to perpetuate and/or expand the initial reaction with energy left over for work. This "chain reaction" will continue until the conditions which brought it about no longer exist. It might be from a burning piece of wood, a fission nuclear reactor, a difference in voltage potential or magnetic or gravitational fields, or, in this case, using the ambient environment as a heat sink to facilitate a phase change between gas and liquid.

Any thoughts?

[ZPDM]

A few last thoughts on this as I think I am starting to get a handle on this then I'll shut up.

Yes you need a temperature differential. In the reaction chamber you generate steam in a semi-confined space which raises the pressure there, hence the liquid would stop boiling if the temperature is not increased further, so a temperature difference is needed to maintain a pressure difference or "work up a head of steam".

People have used and are using lower boiling point liquids in "steam engines". A historical example is the "Naptha engine" or "Naptha launch" from the 1890s. More recently in general terms such an approach is termed an organic Rankine cycle (ORC) engine. Power can be generated at lower temperatures though there are also some potential drawbacks depending on the pressure volume characteristics of the working fluid. This approach is being used by large companies (Ormat technolgies, Turboden/Pratt and Whitney) for industrial scale waste heat electricity generation. Often some type of freon is used as the working fluid. Two interesting examples of groups looking at smaller scale applications are 1) Infinity Turbine which is building ORC engines as small as 1-12 kW. They have an interesting website which I haven't gone though entirely yet but would just give an excerpt from their write up on "magnetic coupling"

"Another interesting effect of the spinning magnet is that you can put a solid piece of copper on the outside, and it will heat up via inductive heating. So much so, that the copper will get red hot, and can melt solder.

The uses of a waste heat to energy turbine, such as the ITmini are vast.

In recent tests, we were able to run the ITmini in a ORC cycle, with only 115 F (40 C) of input hot water. ..."

I won't add anything to that except it does make me wonder.

Matteran Technology Matteran: Technology has also made what I suspect is a very significant advance in this area. By way of background, ORC engines and indeed steam electricity engines are closed cycle, the same working fluid is shuttled back and forth from vapor to liquid. An inefficiency in the Rankine cycle approach is that you need to return the liquid back to the reaction chamber which is by neccessity at high pressure. So the "boiler pump" has to fight against this high pressure when returning the liquid. Jeffery Sterling of Matteran Technology has recently patented a new system which replaces the boiler pump. You would need to look at the website but basically he uses a timed airlock approach to do away with the boiler pump. This approach should both make conventional steam generators somewhat more effecient and also allows for electricity production from temperatures as low as 150F. He also uses the Venturi effect to provide refrigeration at no additional input cost. Pretty cool!

To my mind another closed cycle engine that doesn't have a boiler pump is again the Stirling engine, though this has always been used as a hot air engine. So I still have the question of could you run a Stirling engine as something akin to an ORC or steam engine and would this be an improvement? It also seems to me that the work done in a steam engine or ORC engine is from the differences in pressure throughout the system. If you lowered the pressure of the whole system either closed loop steam engine or Stirling engine you should still (I am guessing) have the same relative pressure differences throughout the system and hence same work capacity, while introducing a partial vacuum would allow you to have water boiling at near room temperature, decreasing the input energy needed and preserving the advantageous environmental, safety and thermodynamic properties of using water as the working fluid. There have also been improvements to the standard steam engine approach recently especially in how to distribute heat to the working fluid in the reaction chamber. I guess I should shut up now and try and see if I can't build a Striling engine and/or closed loop steam engine. Thx Paul