Re: Why isn't water used as a thermal-insulation?


Greg Neill wrote:
> "Brablo" <gestureofrespect@xxxxxxxxx> wrote in message
> news:1133977863.886928.256480@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> > It's specific heat (amount of energy to raise its temperature 1 degree)
> > is very high (4.184 J/K). Why isn't water, treated with something to
> > prevent it from freezing used as a housing insulation as opposed to
> > fiberglass? Water can even deter fires a little better.
>
> For insulation, thermal conductivity is the important
> factor, not specific heat. Lower is better.
>
> Thermal conductivity of water is about 0.58 , as compared
> to say, Styrofoam, which is about 0.033 . Even air is
> better at 0.026 . Fiberglass is around 0.04 . You might
> note that the number for fiberglass indicates that it
> is a worse insulator than air. Air would indeed be the
> superior insulator if it only transported heat by
> conduction. Unfortunately, air moves around and tends to
> transport heat by convection too. Fiberglass stays in
> place.

Actually most insulators (fibreglass, plastic foam, down, etc), are
really not the insulators after all. The real insulator is the air
trapped by the stuff. The purpose of the material is to stop
<convection> in the air by trapping it in place. The conductivity of
<solid> fibreglass, or solid unfoamed plastic, or (yuck) compressed
down is much greater...

Used to read of people who wanted extra insulation stuffing two layers
of fibreglass batts into a wall cavity deep enough for one... : (

.

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