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  1. #11
    Senior Member jeff-oh's Avatar
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    Wow Jdurth, what a great project and a great opportunity you have at your school to pursue this type of education. I am actually surprised at the initial responses you have received. But they too are a great part of this education process. Any new idea or pursuit will come with plenty of criticism and nay sayers the will try and discourage you. This is already been done, this is not needed, or your crazy and have not clue what your talking about. Let me encourage you to push through all that and persevere. Funny I was just watching a documentary on Frank Whittle just before seeing this post. He had his detractors in spades but still changed the world.

    Back to your project, It is intriguing and has merit. There may be some similar ideas out there but none are exactly like you are envisioning. I would engorge you to set out and identify the design space you want to attack. i.e. do not try to make a one-size fits all design. Refine you goals to say design a insulation free hammock to perform in the 65F to 50F or even down to 40F range.

    Items that may be a challenge include how to make you air chambers sealed, yet allow them to pack down. (flexibility in the fabric) will continued folding and flexing cause leaks.

    The post that dismissed this idea saying air insulation is not viable does not correct but is not 100% wrong. Air makes a great insulation, however, the practical experience expressed highlights another issue you will need to solve. That is how to control convection in the insulation layer.

    Let me conclude buy reiterating my encouragement in pursuing this idea. Go for it. make it happen and ignore those that say you can't.

    For my colleagues here on this forum, please remember, this is a high school project, where would you be if you had people around you that encouraged you instead of knocking you down. Where would the Tenashedron stand be if we gave leatherdome this kinda of initial feedback a year go.

  2. #12
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    I truly believe that the problems discussed are not convection at all. Convection within a closed space brings the warmer air to the top, just exactly where you would want it to be! Convection does NOT cause warm air to fall. I believe the physics that apply here is that, without some material in the space that is actually a poor conductor of heat, the bottom of the upper skin radiates heat that is absorbed by the bottom layer and is then, in turn, either radiated once again into the air or conducted on to the next material, that being floor, ground, etc.

    Where convection truly become a problem is where the warmest air accumulates at the top of a wall cavity or at the ceiling of a room and then the differential between conditioned and unconditioned space causes faster heat transfer.

    It's a complex combination of radiation, conduction, and (to a lesser extent) convection that leads to most heat loss.

    Sometimes windchill is equated with convection and they are definitely not the same thing. Wind moves warm air away from, in this discussion, the hammock at a much faster rate than any convection current ever could.

  3. #13

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    The idea of integrating insulation into the hammock has merit enough to have been done many times. But nobody's yet found the secret of a resoundingly superior way. The fact that light and effective underquilts tend to cost quite a bit more than hammocks themselves is natural given the cost of the known most desirable materials (down) and construction labor, but does lead to a lot of cognitive dissonance among buyers. I think there's definitely opportunity to find some sweet spot of price/performance to grow the market from the middle, rather than from the ends (cheap and heavy/bulky or just not very warm at low end, really expensive and really nice at high). If it was easy, maybe it would already have been done!

    As has been mentioned, air that's free to move around in an open chamber isn't that great an insulator. But fill the chamber with something fluffy and packed bulk/weight goes up. If your chambers are airtight, they are also non-breathable, which will lead to condensation problems inside or out as the dew point will turn all that moist breath into a mildew/stink hazard. Also as any air-mattress or pad user knows, one tiny pinprick can ruin your night. In a hammock where comfort doesn't depend on the padding an inflated pad can provide, I don't see much upside to inflation. Add the fact that any inflated non-flexible membrane with some internal pressure has a firm/stiff surface that isn't going to conform to what it's held against. Sort of why you've never heard of an inflatable topquilt: it's not going to seal and eliminate gaps or voids.

    Really hard to beat just immobilizing a certain amount of air underneath the hammock in a breathable manner, possibly incorporating a radiant layer as well to minimize the amount of trapped air necessary to perform at a given temp. Down is the gold standard here, but pricey and can't let it get wet. Synthetics can work as well, better in wet conditions, and cheaper but neither as light nor compressible.

    Here's a thin down UQ that claims to boost the rating with a breathable radiant layer: https://www.2gosystems.com/collectio...t=501404958729 . I don't know how well it works, but I'm intrigued: what if sewn into a hammock? How much bulk and weight in down or synthetic insulation can be replaced with that radiant layer?

    Here's a simple cheap poly-fill quilted hammock I use and like for indoor travel: https://www.lasiesta.com/us/en/colle...nsion-cqh15-49
    Last edited by Latherdome; 09-29-2018 at 16:59.
    --
    Tensa Outdoor, LLC, maker of the Tensa4 tensahedron hammock stand, and the Tensa Solo ultralight flavor too.
    http://tensaoutdoor.com/

  4. #14
    SilvrSurfr's Avatar
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    I don't think much of pads (I get tons of condensation), and I definitely don't think air is much of an insulator, but there are some who do:

    https://hammockforums.net/forum/show...ill-for-and-UQ

    Or the guy who wanted to use bellybutton lint as insulation:

    https://hammockforums.net/forum/show...ent-Insulation
    "A foolish consistency is the hobgoblin of little minds." Ralph Waldo Emerson

  5. #15
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    Quote Originally Posted by SilvrSurfr View Post
    ...
    Or the guy who wanted to use bellybutton lint as insulation:

    https://hammockforums.net/forum/show...ent-Insulation
    Maybe hummingbird down!

  6. #16
    Senior Member jeff-oh's Avatar
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    Quote Originally Posted by TominMN View Post
    Sometimes windchill is equated with convection and they are definitely not the same thing. Wind moves warm air away from, in this discussion, the hammock at a much faster rate than any convection current ever could.
    Ah, That is the definition of convection... Heat transfer due to the movement of a fluid. You are describing natural convection and forced convection. Also, it is incorrect to think that air in a closed system is static and there are no currents, as is pointed out on Earth hot air rises, thus as there is a heat source, the person, and a heat sink, the bottom of the pad, there will always be current and convection heat transfer. In this system it is the dominant mode a heat transfer. Wind chill is a human perception of air temperature vs. actual air temperature.
    Last edited by jeff-oh; 09-30-2018 at 09:09.

  7. #17
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    Quote Originally Posted by jeff-oh View Post
    Ah, That is the definition of convection... Heat transfer due to the movement of a fluid. You are describing natural convection and forced convection. Also, it is incorrect to think that air in a closed system is static and there are no currents, as is pointed out on Earth hot air rises, thus as there is a heat source, the person, and a heat sink, the bottom of the pad, there will always be current and convection heat transfer. In this system it is the dominant mode a heat transfer. Wind chill is a human perception of air temperature vs. actual air temperature.
    Yes, of course hot air rises, except under very peculiar circumstances. As does warm water. I suppose that it might be even more accurate to state that warm air is forced up as heavier, cooler air sinks. But the effect is the same. I'd hardly call Earth and the surrounding atmosphere a closed system though!

    You are correct. I was only considering natural convection. I've never considered "forced convection" as a truly accurate description of the physics (maybe even an oxymoron), even though the term seems to be in general usage. And convection is heat movement, not transfer, per se; The heat remains in the medium.

    I should have typed "wind effect" instead of "wind chill."

    And, I wouldn't ever claim that air in a closed system is static. As long as there are molecules present, particularly water vapor, it is going to move around. Still, the warmest air will generally be at the upper portion of the chamber. Convection isn't the vehicle that moves the heat to the next medium.

    And FWIW, VERY dry air actually has a relatively high "r" value; it does not conduct heat very well at all. It just doesn't commonly exist.

    Heat sinks rely on conduction. That would be heat transfer from the air to the bottom of the pad. Doubt the bottom of the pad has enough mass to hold much heat. Now, if that pad is in contact with the ground, then the two substances combined would constitute a heat sink. Otherwise the heat is radiating and/or conducting to air on the other side at roughly the same rate as it is absorbing from the air inside.
    Last edited by TominMN; 10-01-2018 at 10:55.

  8. #18
    New Member Vtmimib's Avatar
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    That sounds like a great product you are trying to innovate. I would suggest if you have the gear, to hang and nap, or hang and sleep in a variety of temps and tree set ups. This gear to me sounds like it would work well for car camping, or sleeping outside your house, camp, etc... Hammockers find themselves in a variety of trees, poles, and underbrush when hanging. How would it work if space to hang was close together, or far apart? Diagonal lay or banana lay?
    I hope you discover lots of information and have fun with this project. I find that highschool students can be quite innovative, even when the adults around them can be less than supportive, or think they know better so why try your idea. Sometimes the adults are right, but I have been surprised and amazed more often than not when teens are left alone to work out and discover their own methods and ideas.
    Good Luck!

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