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Re: [Hammock Camping] Radiation/absorption question

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  • Randy Saylor
    This is tricky stuff. Consider light energy absorption. A black surface is black because it absorbs the light and does not reflect it. A pure white surface
    Message 1 of 12 , Oct 30, 2004
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      This is tricky stuff. Consider light energy absorption. A black surface is black because it absorbs the light and does not reflect it. A pure white surface reflects all the light and absorbs very little. Therefore the black surface will get warmer. Thus dark clothing will make us hot in bright sunshine more so than light clothing.
       
      Now emission or radiation is different. A warm body will emit heat energy in the form of infra red radiation. Also it will lose heat by conduction to material it is in contact with. Conduction is affected more by the nature of the material (metal vs cloth, for example) than it is by the color of the material. If a gas (air) or liquid is in contact with the warm body then the heat will conduct away and then be removed by convection. The color makes a difference with radiation where the black body will radiate infra red more efficiently. In a hammock, limiting conduction is the most critical factor and thus all the effort to provide an insulating barrier.
       
      This is how I understand this topic and I would welcome any clarification.
       
      Randy 
      ----- Original Message -----
      Sent: Saturday, October 30, 2004 7:38 AM
      Subject: Re: [Hammock Camping] Radiation/absorption question


      Opps, maybe not.  I think we are saying the same thing... I didn't
      read it carefully enough.

      Sorry,
      Youngblood

      --- In hammockcamping@yahoogroups.com, "Dave Womble" <dpwomble@y...>
      wrote:
      >
      > Ralph,
      >
      > I have this figured differently than you.  I believe that darker
      > materials are better at both absorbing and emmitting radiant heat. 
      >
      > Youngblood
      >
      > --- In hammockcamping@yahoogroups.com, Ralph Oborn
      <Ralph.oborn@g...>
      > wrote:
      > > You would also want it darker (better absorbing) in the infrared.
      If
      > > it is bright (emmittive) in the IR then even at night you are
      losing
      > > energy (warmth). IR reflectors (foils) will slow it down, unless
      you
      > > are touching it then it is conductive heat transfer.
      > >
      > > Ralph Oborn
      > >
      > >




    • zippydooda
      Youngblood, you are correct. So, you paint your radiators black, since you want for the heat to get out of them. But, you use a brightly polished teakettle
      Message 2 of 12 , Oct 31, 2004
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        Youngblood, you are correct. So, you paint your radiators black,
        since you want for the heat to get out of them. But, you use a
        brightly polished teakettle (or light colored, I guess), because it
        keeps the heat in.

        At night, the outside surface of your peapod (or underquilt) is
        warmer than the surroundings, so you want to try to keep that heat
        in. So, you use a light color or even a reflective cover. If you
        make it dark, you will radiate more heat. You can't soak up heat at
        night with a dark peapod, because heat has to move from hotter to
        colder items (it's a law).

        Like others said, the color of the inside of the bag doesn't matter
        too much, since it's more of a conductive thing going on there. So
        black would be nice since it hides dirt and makes it easier to dry
        your bag in the sun.

        All this radiation stuff works the same with heat flowing the other
        way, too, right? Dark stuff gets hotter in the sun than light
        stuff. The color of a surface (or whether it is rough or polished,
        in the case of metal) influences heat going both in and out.

        Hopefully this makes sense.

        Bill in Houston


        --- In hammockcamping@yahoogroups.com, "Dave Womble" <dpwomble@y...>
        wrote:
        >
        > Ralph,
        >
        > I have this figured differently than you. I believe that darker
        > materials are better at both absorbing and emmitting radiant heat.
        >
        > Youngblood
        >
        > --- In hammockcamping@yahoogroups.com, Ralph Oborn
        <Ralph.oborn@g...>
        > wrote:
        > > You would also want it darker (better absorbing) in the infrared.
        If
        > > it is bright (emmittive) in the IR then even at night you are
        losing
        > > energy (warmth). IR reflectors (foils) will slow it down, unless
        you
        > > are touching it then it is conductive heat transfer.
        > >
        > > Ralph Oborn
        > >
        > >
      • dlfrost_1
        ... camouflage? Probably for both reasons. The hairs of a Polar Bear are almost clear and are hollow. The white appearance comes from the even scattering of
        Message 3 of 12 , Oct 31, 2004
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          --- In hammockcamping@yahoogroups.com, "Randy Saylor" <r.saylor@s...>
          wrote:
          > Why are polar bears white? Is it to reduce radiation or give good
          camouflage? Probably for both reasons.

          The hairs of a Polar Bear are almost clear and are hollow. The white
          appearance comes from the even scattering of light and is vital for
          camouflage, as these animals are mainly ambush hunters. Because of
          the internal scattering, the fur is also efficient at absorbing
          infrared warmth from the sun. Their skin is dark back to protect
          against UV light. (This why you see black around the eyes and nose--
          the fur is thinnest there.)

          Doug Frost
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