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Hammock Camping Re: Oh Boy, Cold Wars II, winding up!

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  • Dave Womble
    David, Rick is right about the wind not penetrating closed cell foam. Heat transfer on a detailed basics can be difficult to understand. You are absolutely
    Message 1 of 57 , Sep 7 5:55 AM
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      David,

      Rick is right about the wind not penetrating closed cell foam. Heat
      transfer on a detailed basics can be difficult to understand. You
      are absolutely right about it being cooler when the wind blows across
      your insulation. Without the wind the convection heat transfer is by
      a process caused natural convection, which occurs because the warm
      air rises and is displaced by cooler air. When the wind blows, the
      process is called forced convection and is a much more efficient
      means of heat transfer than natural convection because it moves more
      air and moves it quicker, effectively removing your layer of
      insulating 'dead air'.

      Youngblood


      --- In hammockcamping@yahoogroups.com, "Risk" <geoflyfisher@y...>
      wrote:
      > David,
      >
      > Good morning. I think you are right and wrong about wind and foam.
      > There is no doubt that wind blowing across closed cell foam that is
      > something like .25-.5 in thick will quickly cool your skin.
      However,
      > the physics of the materials does not allow the air molecules in
      that
      > wind to penetrate the foam.
      >
      > I looked into closed cell and regular latex foam rubber when I was
      > building kayaks more. An engineer friend that runs one of the
      > mattress production companies helped me out on the science. Closed
      > cell foam is built of very many small gas filled spheres, tightly
      > melted against each other. The air molecules in the foam are
      basicly
      > stuck there and have been there since the foam was built. This is
      > very different from the air cells of the foam in a mattress, most of
      > which do have connection with the outside air. By the way, closed
      cell
      > foam is much more expensive to make than foam rubber.
      >
      > My experience with thin pads is that whenever wind is blowing the
      skin
      > on my back cools and it may even feel like the wind is coming
      through
      > the pad... But it is not. I have proved that by creating an air
      > tight chamber out of closed cell foam. Even under pressure, air
      does
      > not get through the closed cell.
      >
      > What really happens, as I understand it, is this: If I lay directly
      > on the foam, heat from my back warms the first layer bubbles in the
      > foam. THis is mostly due to conduction of heat directly, but there
      is
      > a little radiatiant heat loss as well. That layer of bubbles
      conducts
      > and radiates heat to the next 1/16 inch or so of foam bubbles.
      Inside
      > each bubble, there is a little convection current (an internal wind
      in
      > the bubble) in which the warm air rises and is replaced by the cool
      > air from the other side of the bubble. The structure of the rubber
      > concucts heat reasonably well, but the air does not conduct heat
      well,
      > almost all the heat that makes it across each air space is from
      > convection in the bubble. This process is carried out layer after
      > layer away from my body -- as long as the air outside the foam and
      my
      > hammock is cooler than my skin.
      >
      > What is happening from the outside is that heat is lost to the
      > environment. The rate at which heat is lost depends on a number of
      > factors... Mostly, the air on the outer surface of the hammock,
      which
      > has been warmed by my body, through all those layers of bubbles,
      > drifts away and is replaced by colder air, which is more efficient
      at
      > collecting more of my precious heat. If the air is blowing by the
      > hammock, more heat is absorbed from the surface. In effect, the
      > temperature down 1/16 in the foam and 2/16 and so on, is colder. It
      > ends up being colder against my skin, and more of my heat is lost to
      > that first layer of bubbles on the inside.
      >
      > If the goal is to keep body heat in, then anything which makes that
      > effective distance from the outside air to the skin bigger is good.
      > It is also good to make the distance full of lots of small chambers,
      > instead of large chambers. (Heat travels across large chambers by
      > convection almost as well as it travels across small chambers) This
      > is the reason that an old fashioned air mattress (no foam inside)
      is a
      > pretty poor insulator even if it is an inch or more thick. It is
      only
      > one chamber thick. This is the reason that the Garlington insulator
      > is improved a lot when the spaces are filled with some material
      which
      > breaks up the space into a lot of little spaces. (newspaper,
      > styrafoam peanuts, leaves, crinkled space blanket).
      >
      > Another small aside: It is important to keep that cold outside air
      > from getting inbetween any layers of the insulation. If wind is
      > blowing and inflates a Garlington Insulator by getting between the
      > hammock and the insulator, all the effect of the insulation is
      > temporarially lost. I learned this one windy snowy night when the GI
      > kept getting blown downwind like a sail.
      >
      > Your idea of a tent like chamber beneath the hammock has a lot of
      > merit in that it can keep cold air from blowing across the hammock.
      > However, it has the problem that it can be a large volume. To be
      > effective as insulation, my body will need to begin to warm the air
      > inside that large bubble and the ground beneath.
      >
      > I look forward to your experiments this winter. I enjoy the give
      and
      > take on this group. I look forward to continued discussion.
      >
      > Rick
      >
      > --- In hammockcamping@yahoogroups.com, "o123david" <o123david@y...>
      wrote:
      > > Some ideas and responses. I hope they help.
      > >
      > > 1. Cold wind DOES blow through closed cell foam. I have felt it.
      > > Closed cell foam is just one more form of insulation where, to
      the
      > > extent that cold air blows into it, it loses its ability to
      > > insulate. This is both my experience and what is predicted by
      > > Newton's Law of Cooling.
      > >
      > > In other words, closed cell foam does not protect you from more
      than
      > > a little bit of wind.
      > >
      > > 2. Thank you for pointing out a serious mistake that I made.
      > >
      > > While it is true that convection results in stagnant air being
      less
      > > that a perfect insulator, it is not true that that this prevents
      > > stagnant air from providing any insulation. If obviously does.
      It is
      > > definitely warmer in a two layer tent. Stagnant air definitely
      > > provides what can be a significant amount of insulation.
      > >
      > > In other words, if you have a windproof material surrounding the
      > > hammock and hold it away from the hammock you will be warmer
      than if
      > > you let the windproof material blow up against the hammock. And
      if
      > > you connect this to a tarp above and a floor below (or just
      bring it
      > > down to the ground) you will be warmer still. This can easily be
      > > done using a diamond-shaped tarp, the two stakes already used to
      > > hold the tarp down, and a cord at each end going around the
      bottom
      > > of each tree. Condensation could be controlled with a couple of
      > > vents at the bottom to let in dry cool air and a couple of vents
      > > at the top to let out warm moist air, as Stephenson has done
      with his
      > > Warmlite tents. Since this is very similar to his tents it is
      clear
      > > that it would work. Netting protecting each vent would eliminate
      the
      > > need for add netting over the hammock. The entrance could be
      through
      > > the floor held up by velcro since any other design would probably
      > > result in accidents and damage to the tent. It appears that this
      > > would work very well with a Peapod or a thicker bag filled with
      down.
      > >
      > > I don't like this idea because it is unnecessarily heavy and
      > > complicated.
      > > But it isn't that heavy and it might be a good idea.
      > > I spent a lot of time while thruhiking the AT last year ('02)
      > > thinking up this design. It would be nice if somebody would try
      it.
      > > Maybe it is a mistake to include the hammock as one layer of a
      two
      > > layer tent and it would be best to build the tent as a two layer
      > > tent.
      > > Whatever, if you try it, please post a message on this list so I
      can
      > > hear about how it works (or doesn't work).
      > >
      > > 3. One other idea. This would make it so you wouldn't need a
      separate
      > > barrier to block the wind.
      > >
      > > You could construct the hammock from three parallel pieces of
      > > material going lengthwise. The two outer pieces of material
      would be
      > > windproof, such as the 1.9 oz ripstop which is then silicon
      > > impregnated. The inner piece would be breathable, such as
      uncoated
      > > 1.9 oz ripstop. It would be interesting to see if this is both
      > > sufficiently windproof and provides sufficient fresh air to
      prevent
      > > condensation. --David
    • Thomas Peltier
      Looks very nice. _____ From: Chet Clocksin [mailto:cclocksin@buckeye-express.com] Sent: Friday, September 12, 2003 5:55 AM To: hammockcamping@yahoogroups.com I
      Message 57 of 57 , Sep 12 12:00 PM
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        Looks very nice.

         

         


        From: Chet Clocksin [mailto:cclocksin@...]
        Sent: Friday, September 12, 2003 5:55 AM
        To: hammockcamping@yahoogroups.com

         

        I just posted another photo in "chet's home made" folder (I also deleted a few) Take a look at the last photo in the folder. A dog could be very cozy in there, and provide some additional heat. This set-up should also be a true storm proof set-up simply by closing the "doors" at the bottom.

         

        Chet

        -----Original Message-----
        From: chcoa [mailto:jdeben@...]
        Sent: Friday, September 12, 2003 2:25 AM
        To: hammockcamping@yahoogroups.com
        Subject: Hammock Camping Oh Boy, Cold Wars II, Doggie heater

        The ground in more what I was thinking for several reasons, material
        strength, warmth, etc.. but you are right they could hang a little
        too.  My only concern with this idea is that in the night if for some
        weird reason the hammock malfunctioned and I fell on her.  I wouldn't
        want to do that of course!  ACK!

        jamie in az

        --- In hammockcamping@yahoogroups.com, "Ray Garlington"
        <rgarling@y...> wrote:

        > This is a really good idea.  An open-bottom cone could be staked to
        > the ground with a side entry hole for the dog.  He would have a
        nice
        > house separate from your sleeping quarters & he could contribute
        some
        > heat.  Much better than tenting with a wet dog!
        >
        > If the dog was 'hammock trained', you could have a closed-bottom
        cone
        > with a side entry for the dog.  He would then be suspended above
        the
        > ground.



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