Hammock Camping Re: Oh Boy, Cold Wars II, winding up!
- --- In email@example.com, "Dave Womble" <dpwomble@y...>
> Rick is right about the wind not penetrating closed cell foam.
> transfer on a detailed basics can be difficult to understand. Youacross
> are absolutely right about it being cooler when the wind blows
> your insulation. Without the wind the convection heat transfer isby
> a process caused natural convection, which occurs because the warmmore
> 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
> air and moves it quicker, effectively removing your layer ofWhile I am talking about this let me add this. When the wind blows
> insulating 'dead air'.
and removes the layer of insulating 'dead air' on the outer surface
of your insulation, a quick cooling effect is sometimes noticed even
though you're insulated by a wind-proof insulation. This is because
the conductive heat transfer rate changes-- conductive heat transfer
is proportional to the temperature differential between the two
surfaces of the insulation and since the outer surface temperature
changes due to the wind and its associated force convection heat
transfer, the inner surface temperature will also change because of
conductive heat transfer. How fast & how much are determined by the
temperatue differential and how much insulation you have (i.e. R-
value, thickness, material type, etc.). In cases where you are using
marginal insulation, you will very much notice the effects of the
wind. In cases where you have more insulation, you will notice the
effects less and with enough insulation you won't notice it at all.
But even in the cases where you are using enough insulation to not
notice it all, the effect of the wind on convection heat transfer and
conductive heat transfer is still there... the wind is just not
blowing hard enough or it is not cold enough for it to bother you...
at least not yet!
I think this is pretty much what Rick described, just another
description of the same processes. For those that had forgotten,
convective heat transfer is with fluids (liquids & gases-- in this
case air) and conductive heat transfer is with solids (your
insulating pads). Like I have said before, the detail of heat
transfer can be very difficult to understand. One of the many
reasons for that is that it can change back and forth between the
three primary types that we deal with when we try to stay warm in our
hammocks-- radiant heat transfer, conductive heat transfer and
convective heat transfer. And then there is the complication that
our heat source, our bodies, doen't always perform uniformly.