Re: [AWES] Liquid air in AWES?
- Gabor,Thank you very much for the response. It was helpful.I would bring attention to two interesting quantifications of this engineering challenge of employing Liquid Air (LA) for energy storage.1. The rate at which energy can be "retrieved" from LA (power retrieval capability), and2. The Ratio of "energy that can be retrieved" from LA vs "energy expended to produce the LA" (ie. end-to-end efficiency ETEE).Elaboration…item 1: We know that if LA energy RETRIEVAL RATE demands are LOW, then we could rely on a gasification heat source as simple as just letting the LA gasify under the influence of un-augmented ambient heat sources (which would likely represent a low power-retrieval potential, producing a rate of energy-retrieval of little value for industrial-scale storage. However, far more complex heat-exchangers and capable heat sources would be needed to augment the energy-release mechanism to produce significant power retrieval. Are such achievable for practical, cost effective power retrieval?item 2: It seems one could easily test the ETEE by measuring the simple energy-use of the electric-powered compression system proposed for such as an energy-glider, then taking the resulting LA and submitting it to the energy retrieval process machine (that, presumably results once again in electrical energy) to see what energy would be yielded back.I bring up these subjects since it seems that for energy gliders to be practical using the LA scheme as the energy-harvest repository, then said LA storage system must prove worthy (in both design weight and efficiency), else the energy glider will be forced to rely on some other airborne energy transmission scheme (that must pass similar scrutiny), or stand in danger of being impractical. These LA energy-storage assessments can be made even without the full knowledge of the extent of raw energy harvest a glider might be expected to produce (ie. predicted via time-domain simulation of a typical glider/system and maneuver design).RegardsDaveLOn Aug 24, 2013, at 2:49 PM, Gabor Dobos <dobosg001@...> wrote:
Let's begin with the answer:
The heat of evaporation (that is needed to convert liquid air into gaseous form to perform useful work) may come from everywhere. You may apply e.g. heating with a fire or the like. But our preferred solution is of course using the heat content of our surroundings to evaporate liquid air in a restricted volume and in this way pressurize it.
The concrete solution depends on the properties of the concrete device as well as on our own decision. The concrete source of heat may be the ambient air, the water of a river, a lake, or the sea, waste heat of a traditional heat power plant, the underground heat-collecting pipes of a heat-pump, etc.
I can say that you see the essence of the process correctly, and the analogy with water is also correct. Your rationale is not breaking down. You just forgot to mention the last step, namely that water vapor must condensate to supply energy by freeing up the condensation heat. Without condensation no heat develops. This process occurs if the water vapor contacts a solid or liquid surface or a gas that is cooler than the temperature of the water vapor. In this case some water vapor will condensate to liquid water and at the same time the condensation heat is released and warms up the above mentioned solid or liquid surface or gas. This heating up process ends if the temperature of the cooler matter reaches the temperature of the water vapor.
As you know, liquid air can be stored at atmospheric pressure while its temperature is equal to its boiling point at the same (ambient) pressure. Just to come closer to a real process, imagine a Dewar flask that has a heat isolating wall. Let this flask contain some liquid air. This is a usual arrangement for storing liquid air and at the same time it is a ready to use experimental setup to answer your question.
In short: due to the insufficient heat isolation, some heat flows continuously trough the wall of the Dewar flask and evaporates some liquid air. That is the explanation of the continuous loss of liquid air, and yes, it is the energy that you are seeking.
Since the temperature of the liquid air is exactly equal to the boiling point of it at the ambient pressure, some liquid air begins to boil and will be evaporated immediately. The quantity of the evaporated liquid air is in close relation to the heat reaching the liquid air through the wall of the flask. The following equation is valid:
q = m·ΔHv
q = heat energy
m = mass
ΔHv = heat of vaporization
Putting the liquid air into a ballon, we can blow up the ballon by heating it from te outside with the ambient air.. This simple experiment shows that mechanical work can be made by the liquid air ddue to thee
This simple qualitative picture is very useful.
Are you satisfied with the answer? Any other question?
On 2013-08-23 20:24, David Lang wrote:
Gabor,Maybe you or someone else could help educate me about where the heat-of-condensation (that is removed from the air during liquefaction) comes from in order to convert liquid air into gaseous form under pressure to perform useful work. It seems to me that crossing the phase-boundary to liquify air presents an energy retrieval issue when going the other direction since the energy removed from the air (to liquify it) is removed from the resulting product (the liquid air); I am not qualified in physical chemistry (as I think you might be Gabor), so I would appreciate any information you could provide here….I would learn a lot in such an explanation.An an aside, I trace my confusion here to a view point of relating "gaseous air" to "liquid air" much as I relate "steam" to "water" (and we all know that ENERGY must to supplied to "liquid water" to convert it into a gaseous water (steam) so as to provide useful work. Where is my rationale breaking down here?Thanks for any help.DaveLOn Aug 23, 2013, at 3:36 AM, Gabor Dobos <dobosg001@...>wrote:On 2013-08-22 16:10, Doug wrote:
"Why not just use compressed air?"
The reason is very simple. In the first approximation if you have a gas bottle full with p= 200 bar compressed air, upon expanding it isothermally to p= 1 bar, then the end-volume of the gas will be about 200 times the volume of the bottle. In the case of liquid air the end-volume will be about 700 times the volume of the bottle. That is, the volumetric energy density of liquid air is several times that of the compressed air. Therefore, compressed air as fuel is acceptable for short distances, and only a compressor is needed to produce the fuel. Therefore, in a depo it maybe an acceptable or even advantageous solution (no exhaust gases, quickly rechargeable compared to batteries, e.t.c.) But for a car the energy quantity that can be put in a „tank” is far not enough .
Continued and discussion of the topic in detail see in the DSUTWP forum soon.
As a witness to the seldom-seen phenomenon of "Angel Hair" falling from the sky I am onboard with balloon spiders migrating by floating silk strands. Was this ever in question by anyone, anywhere? One more time you try and change the subject. I'm beginning to lose faith in all you guys. I thought you were a genius but you are sounding more and more just "out to lunch" with every new post. It is interesting to read your statement that "Kiteboarding is sailing with kite power". OMG I bother to stop and read that?
Is that some new revelation? Could anyone argue with that statement? I mean why state the obvious over and over? There's no new information in your post. I'm trying to figure out what you're really saying. Sounds like the same old clap-trap: Kites can pull things through water, you COULD add a propeller and generator, power whatever, blah blah blah. (if you weren;t busy all day on the internet)
I'd reply with this:
If you guys think windsurfing is Airborne Wind Energy in the sense intended here, why not follow through and start covering windsurfing as a serious topic here? There must be windsurfing news every day, right?
It seems like you guys just pull this stuff out of your butts when confronted with the fact that nobody is generating a single useful Watt using airborne wind energy and the fact that there is no reason this should be so, except none of us are actually doing anything about it, but instead we sit here on the internet arguing about word definitions. Oh and all the well-funded teams insist on pursuing misguided efforts that lead nowhere but pulling kite strings. Wow a kite can pull. yeah I think I might have noticed that at 5 years old. We're supposed to get smarter as we get older not stuck at a 5-year-old's mentality for life.
"Well Doug you are so wrong because technically-speaking, this-or-that mundane and long-known activity COULD be SAID to be a FORM of airborne wind energy."
Hay you're not grasping a straws or anything are you?
Wow we have ANOTHER Einstein - an Einstein a day keeps any progress away!
My response is "Great, according to you, airborne wind energy is a mature art, practiced for thousands of years, so why keep talking about it as though it's new or even interesting?" Is not a spinnaker a flying sail? Why don't you guys devote a lot of time discussing spinnakers? I mean, technically-speaking, they COULD be SAID to be AWE, right? And isn't that all that seems to matter according to your posts? Words? Isn;t that all we're talking about here, empty words masquerading as progress?
I've got a couple more GREAT EXCUSES for you guys:
1) Existing sailplanes already practice airborne wind energy - they use the energy of the wind in the sky to glide around.
2) Flying kites IS airborne wind energy since it takes energy to keep a kite aloft and that energy is provided by the wind and it takes place supported by the air.
So there you go - all we have to do is keep redefining words and we can find more and more instances of AWE being thousands of years old. I guess we don;t need to build anything since AWE is such an old ann established art by our ever-evolving suite of new word definitions. Are you guys sure you don;t work for the government? I mean this is getting pretty illogical. Word definitions - maybe you should work on writing dictionaries instead of pursuing scientific progress and new engineering.
My further response is if someone is going to do wind energy in the sky it will need to go beyond arguing about word definitions to try and qualify simple boring 1000-year-old activities as the sought-after breakthrough.
--- In AirborneWindEnergy@yahoogroups.com, <firstname.lastname@example.org> wrote:Kiteboarding is sailing with kite power. Body-dragging with body as the paravane (water kite) is kite sailing Tens of thousands of trips using kite sailing in tiny-to-nil-sized "hull" are made each day on earth ... and the count is rising. Even these systems have the option of adding hydro turbines in the system to charge electrical batteries. The option of adding flygen or also solar-energy-conversion surfaces to the wing set is present. And for specified long-distance travel all such system parts may be tweaked to provide energy to feed warming, electrically dependent instruments and tools, visibility signalling, potable-water machines, and more. Such tiny world is not the most tiny available for kite systems that convert the upper winds gifts to task achievements. Ask the spiders that kite-sail across oceans. .