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  • Mike90250
    replied
    Compressed air cars:
    https://www.popularmechanics.com/car...-air-car-myth/

    Leave a comment:


  • J.P.M.
    replied
    Originally posted by happy_hipster View Post
    It is also interesting to think about how an idea such as this could change how we think about space. Being that different gasses liquify at different pressures, it would be a good way to transport breathable air, store energy, and remove unwanted gasses from the enclosed environment. Not only could liquified gasses be used to recapture energy in the form of electrical generation, but also be used to vent unwanted gasses as thrust for the craft.
    I can happily deal with ignorance, and persistence in opinion is a virtue I appreciate, but ignorance with no inclination to learn or investigate reality is hard to overcome, especially when combined with argumentation with no purpose other than that of argument.

    Enjoy your ego and intransigence in the face of experience and training.

    Something I was made to memorize in high school comes to mind:

    "During my 87 years I have witnessed a whole succession of technological revolutions. But none of them has done away with the need for character in the individual or the ability to think."
    Bernard Baruch, American Businessman.

    I'm outa' this thread.
    Last edited by J.P.M.; 07-25-2021, 11:36 PM.

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  • happy_hipster
    replied
    It is also interesting to think about how an idea such as this could change how we think about space. Being that different gasses liquify at different pressures, it would be a good way to transport breathable air, store energy, and remove unwanted gasses from the enclosed environment. Not only could liquified gasses be used to recapture energy in the form of electrical generation, but also be used to vent unwanted gasses as thrust for the craft.

    Leave a comment:


  • happy_hipster
    replied
    Thank you for exploring this a little further. I really do appreciate it. It really makes no sense just in saying it wont work and going on. It also makes no sense in just calling me names and trying to bully me into discounting everything. Claiming that the model of the raised weights is more efficient helps, but what it does not do is concentrate the energy. The reason chemical batteries are so popular(besides temporary efficiency) is that they are portable and upgradable. Chemistry is cool like that. Compact. Somewhat lightweight. No moving parts.

    But the R&D has gone into it, and is going into it. I have heard of cars that run on compressed air. To me, the next step would be homes, and then cities.

    We did not see the first airplane work and then abandon it because trains were more efficient. Same thing here. We just need to refine the compressors and motors and heat exchangers and cooling systems to make it more efficient. Thank you all for taking a moment of your valuable time to consider and debate my seemingly pointless observations.

    However more efficient, chemical batteries are toxic, explosive and temporary and I do not like or condone them in any way. We need to explore all and any alternatives.

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  • J.P.M.
    replied
    Originally posted by Bala View Post
    I just looked for air motors and found one that will provide 1kw. It requires 1750 lpm ( Litres Per minute) of air to do so.

    Looking at a small handyman compressor with a 1kw motor it will make approx 160 lpm, so not even close to driving the 1kw air motor

    The bauer small dive compressor will pump to 3000psi, I have a petrol one but the electric one is listed with a 2kw motor and listed at 3.5 lpm. It takes an hr to fill a scuba tank to 3000psi from empty and that scuba tank full of air would not drive that 1kw air motor for long enough to anything meaningful, if at all.

    You also have a big maintenance factor in making, storing and using compressed air.

    I just dont have the time or need to work out the specifics of what would be needed to make enough air and store it to make electricity when I know its pointless.


    All that is a practical Q.E.D. to what I've been saying throughout this thread.

    With knowledge of Thermodynamics you can prove it to yourself. I prefer the independence to peddler's hype.

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  • Bala
    replied
    I just looked for air motors and found one that will provide 1kw. It requires 1750 lpm ( Litres Per minute) of air to do so.

    Looking at a small handyman compressor with a 1kw motor it will make approx 160 lpm, so not even close to driving the 1kw air motor

    The bauer small dive compressor will pump to 3000psi, I have a petrol one but the electric one is listed with a 2kw motor and listed at 3.5 lpm. It takes an hr to fill a scuba tank to 3000psi from empty and that scuba tank full of air would not drive that 1kw air motor for long enough to anything meaningful, if at all.

    You also have a big maintenance factor in making, storing and using compressed air.

    I just dont have the time or need to work out the specifics of what would be needed to make enough air and store it to make electricity when I know its pointless.



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  • J.P.M.
    replied
    Originally posted by Bala View Post
    I started on a response with an example of how much energy it would take to compress a qty of air to 3000psi and then how much electricity that would generate using an air motor but decided that Happy Hipster would ignore it anyway.
    How efficient the process you describe would be will depend on, among other things when and how much heat was removed from the air in the tank after compression but before expansion, and the (in)efficiencies of the equipment. That's a Thermodynamics 101 homework problem.

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  • chrisski
    replied
    Originally posted by Bala View Post
    I started on a response with an example of how much energy it would take to compress a qty of air to 3000psi and then how much electricity that would generate using an air motor but decided that Happy Hipster would ignore it anyway.
    Well if you’ve done the work already, I’d like to know.

    We used to have a portable compressor to charge Scuba Tanks at work. Certainly was not electric and used a gas motor. Another place I’d charge tanks used a gas motor also. I’ve found that when items are run off gas and not electricity, its because they use a lot of power, more than electricity can easily provide (This translates to no longer 120 volt powered, and need to go to 240 at least). I doubt the energy put into charging a 80 cu ft tank to 3000 PSI is anything close to the energy that comes out of it, even if you were to take a hammer and knock the valve off creating a missile.

    I never thought about the energy lost to heating and cooling.

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  • Bala
    replied
    I started on a response with an example of how much energy it would take to compress a qty of air to 3000psi and then how much electricity that would generate using an air motor but decided that Happy Hipster would ignore it anyway.

    Leave a comment:


  • J.P.M.
    replied
    Originally posted by happy_hipster View Post

    All of your thermodynamics excuses are just saying you cant take power and put in in a batter for later use. I've seen models of using concrete blocks lifted 1000ft in the air to store power. Just because the research is putting power into chemicals does not mean that is the most cost effective over time way to do it. It means that is the direction people are being pointed in.

    It still falls into the category of "If people could fly we'd a dun it already"
    Suit yourself. Opinions vary, but to call Thermodynamic principles an excuse does little more than put your ignorance on display. But I've called out your ignorance in that area enough.

    As for storing anything, an electrical "battery" (a battery of electrical "cells" that is) stores work, which is defined as moving a force through a distance. These days work is pretty much synonymous with the word energy. You'll be less ignorant if/when you take the time and make the effort you learn the difference between work and power, which is the time rate of doing work (or expending energy).

    If I was to say an electrical battery can't store energy, I'd be denying reality.

    While not necessarily speaking for Peakbagger, what we're saying is that the (potential) energy released by the partial expansion of a gas - while having some advantages - is thermodynamically inefficient compared to other methods of using stored (that is, potential) energy.

    The elevated block example you cite - and similar to a water reservoir BTW - is no more than an example of potential energy storage by virtue of elevation difference in a gravity field. That's what powers my tall case clock.

    Work stored by virtue of such elevation can be quite a bit more efficient than expansion work done by a gas, the expansion of which is a good textbook example - along with friction - of a process which produces a large increase in entropy - an efficiency killer.

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  • peakbagger
    replied
    BTW my bet it on the concrete block approach over pneumatic The wire to wire on the block approach seems to be pretty attractive.

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  • happy_hipster
    replied
    Im not talking about a perpetual motion machine, here folks. And I agree, in part, that I am not the first one to think of this. In fact, the paper I posted by someone who knows much more then me shows not that Im deluding myself, but that I'm onto something. Sure, I will give you that the efficiency is not up to your standards(yet) but if you are talking about a week a year retreat or a day a month offgrid Bnb, efficiency IS NOT AN ISSUE. What is an issue is if It can provide the power necessary for the time necessary.

    All of your thermodynamics excuses are just saying you cant take power and put in in a batter for later use. I've seen models of using concrete blocks lifted 1000ft in the air to store power. Just because the research is putting power into chemicals does not mean that is the most cost effective over time way to do it. It means that is the direction people are being pointed in.

    It still falls into the category of "If people could fly we'd a dun it already"

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  • J.P.M.
    replied
    Originally posted by happy_hipster View Post
    I generally regard views like this to be put in the category of "If people could fly, we woulda dun it already" Efficiency is something that comes with R&D, and so do breakthroughs. I think ideas like this dont get off the ground because they would be a solution to an expensive problem. The problem is not the efficiency of the capture of power, in this case, it is in using expensive, explosive, toxic DISPOSABLE batteries.

    Replacing thousands of dollars worth of batteries every 5 to 15 years does not sound very efficient. The reality is that very practical and efficient cars were mothballed for decades in order to continue profiting off of gas guzzlers, and it is only now they are being re-introduced because, well, they have to.

    It really seems that there is more feedback about why it is absolutely infeasible to make an alternative to chemical batteries, and little to nothing about how we could be smart enough to make it work. Maybe you are right, maybe we are all too stupid to make an efficient pneumatic battery. Maybe no one has the knowledge or training to even imagine it. I dunno.

    I hear Einstein created the concept of a three gas system for a refrigerator that worked without pumps, we just have not figured out how to do it yet, or dont WANT to because a permanent sealed refrigeration unit without moving parts is not disposable, and therefore not profitable.
    It isn't that your ideas won't work. It's just that they have poor efficiency and (meant as a reality statement) are in many ways unworkable for reasons you don't understand. The laws of Thermodynamics are against you on this one and so far, no amount of R & D has conquered them.

    You will serve yourself well to brush up on Thermodynamics if you want to continue this dialog. Until you do, it'll be difficult to have a meaningful exchange of information with you. If you do, you'll see where many others have covered this ground and have made their peace with it. Right now, it appears to me and maybe some others that you don't know what you don't know, including the idea that you're embarrassing yourself with your ignorance.

    Welcome to the forum of few(er) illusions.

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  • peakbagger
    replied
    You probably missed out on thermodynamics unless you have an engineering background and generally only mechanical engineers get into slightly more advanced thermodynamics. The first law is handy for basic calculations but it assumes reversibility. These are physical laws not political ones, no loopholes. First law math says you may pull it off, but sadly there is no such thing as a free lunch as the second law rears its ugly head in advanced thermodynamics. Second law says there is no such thing as a free lunch, systems always go from more ordered to less ordered so there no such thing as reversible system which is what you are proposing to store power. The way this disorder is tracked is by entropy. So given the entropy always happens, the trick is to minimize it and compressed air is not a great medium to do it with.

    The short hand for energy storage is wire to wire efficiency and CAES has pretty crappy wire to wire efficiency. Its been done on a large scale but the big reason is that with natural or unnatural underground caverns a lot of energy can be stored for relatively low capital cost. Pumped hydro storage is similar, a lot of power can be stored but unless there is natural feature it can be far more expensive to build. Its more efficient wire to wire. In both cases if you skip converting the air or water back to electricity the wire to work efficiency increases. So in the case of water, if you want to water the garden fill up an elevated tank with spare power and then run the hose to the garden rather than turning it back to electricity to run a pump. With air, compress the air in a big tank and run air tools off it. Batteries are fairly efficient wire to wire and their power density is high and getting higher and that is why the world is going to be using a lot more of them. .

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  • Bala
    replied
    Originally posted by happy_hipster View Post
    In the diagram, the 12v, 120v and 240v connections would come from the Generator, labeled 8. I was hoping to use a 6000W gasoline generator with the gas .motor part removed and replaced with a high RPM high torque pneumatic motor. I do not know how to estimate efficiency of the energy source without the specs on the imagined solar panels, pneumatic motor, generator, or compressor.
    On what I know your idea is not an option. If you think something will work then do some research.

    Look up Bauer dive compressors, they are used to fill scuba tanks to 3000psi. Look up the capacity of scuba tanks and you will have the data to calculate how much energy is required to capture x amount of air compressed to 3000psi.


    Look up air motors and you will get cfm required to run them. If you want to generate 6000w then you will need an air motor that can produce more than 6000w of power.


    So you will have the cfm of air at a given psi required for your air motor to run. Then you can calculate the energy required to make that air and the size tank required to store enough to run your motor for the time required.

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