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Thread: Energy Density

  1. #1
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    Default Energy Density

    Better power storage is all the rage, for electric cars, phones, spacecraft, you name it. I understand that no current power storage technology can come close to the energy density of liquid fuels.

    And yet I see tiny ants foraging all day long, taking huge morsels of food back to the nest. I see songbirds migrating across oceans without food or rest.

    Evolution seems to have come up with solutions to the energy storage problem that far exceed even our liquid fuel technology. We couldn't come up with a machine as small as a bird that runs for as long and as far as a bird, even if 100% of its mass were liquid hydrogen and it used oxygen from the air - forget aviation fuel. But physically and chemically, how can that be? Is the Krebs cycle so much more efficient than anything we can do? Are sugar and fat better ways to store energy than hydrocarbons or our current battery technology?

    Any engineers or chemists out there care to shed some light on this?

  2. #2
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    Default Re: Energy Density

    You appear to be confusing an organisms basic need to fuel it's body, with the organisms need to drive a V-8.

    For what it is worth, if we organised ourselves and were so inclined, we could power all of our locomotive needs with bio-fuels.

    Hydrocarbon = carbohydrate.

  3. #3
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    Default Re: Energy Density

    There are some genius notions in the works.

    Scientists Create a Prototype 'Air Plasma' Engine That Works Without Fossil Fuels

    A prototype jet engine can propel itself without using any fossil fuels, potentially paving the way for carbon-neutral air travel.

    The device compresses air and ionizes it with microwaves, generating plasma that thrusts it forward, according to research published Tuesday in the journal AIP Advances. That means planes may someday fly using just electricity and the air around them as fuel.
    http://sciencealert.com/scientists-h...gine-prototype
    Speak softly and carry a mouthful of marbles.

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    Default Re: Energy Density

    i think the o.p. conflates advantages such as leverage and lift with energy.

  5. #5
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    Default Re: Energy Density

    You want energy density, nuclear power is a very good bet. (I'm serious. We've learned a great deal since the 1970s.)
    "For a successful technology, reality must take precedence over public relations,
    for nature cannot be fooled."

    Richard Feynman

  6. #6
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    Default Re: Energy Density

    Quote Originally Posted by L.W. Baxter View Post
    i think the o.p. conflates advantages such as leverage and lift with energy.
    Are you saying that where birds are more efficient is not in energy storage, but in aerodynamics and propulsion system?

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    Default Re: Energy Density

    Excellent question Georges.
    I've often had the same interrogation about the insects we can observe flying when sailing at more than 100 nm of any land.
    By the way I don't think insects are particularely efficient in the matter of flight
    Gerard.
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  8. #8
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    Default Re: Energy Density

    Quote Originally Posted by George. View Post
    Are you saying that where birds are more efficient is not in energy storage, but in aerodynamics and propulsion system?
    maybe. maybe you just aren't correctly estimating the amount of work done. It's not a job for intuition.

    the ant problem is simpler, to my mind.

    calculate how much work an ant can accomplish before depletion, relative to it's body weight.

    run an electric motor and battery on a chain hoist until the battery depletes. how many tons moved? divide by weight of motor and battery. compare to ant.

  9. #9
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    Default Re: Energy Density

    Quote Originally Posted by L.W. Baxter View Post
    maybe. maybe you just aren't correctly estimating the amount of work done. It's not a job for intuition.
    In the case of birds I don't need the absolute amount - just the relative amount. Consider a model airplane that weighs the same as a bird. Whatever the power source, it will fly a few dozen km at most. A bird of similar mass and wingspan can go thousands of km.

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    Default Re: Energy Density

    The bird does not have a schedule or a route ( except in general: " head south or north seasonally.") Therefore, birds can take advantage of favorable winds, and being so small, a light wind has a huge effect. And, they only need to get to their destination before it's too cold to live, or while the opposite sex is in mating mood, not by, " Tuesday the 25th, before 3pm."

    The bird is also not carrying a payload. It is equivalent to an empty plane.

    Kevin
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  11. #11
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    Default Re: Energy Density

    there are model aircraft that do everything the birds do with regards to endurance and distance; google the 'spirit of butt's farm'
    Simpler is better, except when complicated looks really cool.

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    Default Re: Energy Density

    Jfgi
    I'd much rather lay in my bunk all freakin day lookin at Youtube videos .

  13. #13
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    Default Re: Energy Density

    jewish federation of greater indianapolis???
    Simpler is better, except when complicated looks really cool.

  14. #14
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    Default Re: Energy Density

    Quote Originally Posted by Paul Pless View Post
    there are model aircraft that do everything the birds do with regards to endurance and distance; google the 'spirit of butt's farm'
    Cool!


    440px-Tam5.jpg

    It does come close to bird performance. However, at 5 kg and a 1.8 meter wingspan, it's competition might be something like an albatross, which can outperform it.

    BTW, the model plane carries no payload. The bird most certainly does. It carries a system able to feed, grow, and reproduce in addition to the bits involved in flying.

  15. #15
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    Default Re: Energy Density

    A bird has an extremely complex system for making in flight adjustments to the air frame.

    I am certain that you are approaching the energy storage density problem from the wrong end.

    Interesting notions to ponder though.

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    Default Re: Energy Density

    A bird only carries itself. When we humans want to go somewhere, we typically do it in a machine that weighs TWENTY TIMES AS MUCH as we do. A human on a bicycle, however, is incredibly efficient. A bowl of oatmeal with milk can power a human on a bike 80 miles.

  17. #17
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    Default Re: Energy Density

    Quote Originally Posted by phiil View Post
    A bird only carries itself. When we humans want to go somewhere, we typically do it in a machine that weighs TWENTY TIMES AS MUCH as we do. A human on a bicycle, however, is incredibly efficient. A bowl of oatmeal with milk can power a human on a bike 80 miles.
    just think how far the human could go if he could turn off his brain
    Simpler is better, except when complicated looks really cool.

  18. #18
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    Default Re: Energy Density

    I’d need more than a bowl of oatmeal for five to six hrs of riding.

  19. #19
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    Default Re: Energy Density

    Quote Originally Posted by Paul Pless View Post
    just think how far the human could go if he could turn off his brain
    Look no further than the Oval Office.
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  20. #20
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    Default Re: Energy Density

    A bicycle's efficiency declines substantially on unpaved surfaces, even more on ungraded ones.

  21. #21
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    Default Re: Energy Density

    A human on a bicycle, however, is incredibly efficient. A bowl of oatmeal with milk can power a human on a bike 80 miles.
    I would hazard that, while oatmeal may have been what the cyclist ate for breakfast, she will be well into burning fat stores before hitting 80 miles.

    A cup of oatmeal contains 300 calories, according to published sources. A cup of whole milk contains 103 calories.

    According to Harvard University, biking at a moderate speed of 12 to 13.9 miles per hour will cause a 155-pound person to burn 298 calories in 30 minutes. At a faster rate of 14 to 15.9 miles per hour, a person of the same weight will burn 372 calories.

    Kevin
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  22. #22
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    Default Re: Energy Density

    10 years ago, my work and family schedule allowed me to ride between 100 and 200 miles a week. I did not change my eating habits, but I was a lot thinner and had monster thighs.

    Mind you, I also own a mountain bike, not a lightweight and extremely efficient road bike
    "If you think you are too small to make a difference, try sleeping with a mosquito"

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  23. #23
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    Default Re: Energy Density

    Body fat is listed here.

    https://en.wikipedia.org/wiki/Energy...cific%20energy.

    I think birds are carefully optimized by evolution to make the best possible use of their energy. And they go to a different sort of schedule or tune than we humans do.

    But yes a human on a bicycle can do amazing things. To wit - the Solar Camper Cycle.

    Will

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