On Wednesday, January 22, 2014 7:00:08 AM UTC-5, micky wrote:
Yeah, good idea. Focus on that instead of the fact that you
have the science wrong.
Good grief is an insult? What you don't like is being told
that you're wrong and having it explained to you.
Otherwise, you'd be discussing and replying
to the two examples I just gave you. Wind removes heat from
exposed skin via convection, just like it does from any object
that is above ambient temperature. Evaporation is not necessary.
The cooling of exposed skin
is *not* driven primarily by evaporation, unless you're sweating
when it's 15F out. Seems hundreds of millions of years of
evolution has figured that out. It's driven by convection,
just like using *moving* air through a car radiator works.
And BTW, I figured the good grief was appropriate because
I've clearly explained this to you ten times now, here and
in the other thread. CL told you the same thing.
On Wednesday, January 22, 2014 11:57:51 AM UTC-5, email@example.com wrote:
Thanks for the support. And I'd also point out that I'm not impressed
by the number of voices. It's not the number, it's if what they
are saying follows physics or is just nonsense. If a growing number
of people say that V=IR^2, does that make it right? good grief.
It pains me to do this, but Trader's right about this. The concept of
higher air flow resulting in greater heat transfer is the guiding principle
behind the calculation of the wind chill index. Any restrictions placed on
what wind chill means are irrespective of the science behind its
The clearest example I can think of heat transfer via moving air is like
Trader's car fan example. Faster computer CPU speeds (and power
consumption) forced the industry to mount fans atop their CPUs. They did
that because passive cooling, even from massive heat sinks, caused the
faster CPUs to burn up. Moving air removes heat more quickly than still
air, whether it's a CPU, a pipe or a human being. Hair dryers would
incinerate themselves without a fan to transfer heat from the heating coils.
from any object
Correct, but evaporation does play a small role, as do many other things.
Ask yourself whether you'd rather be stranded outside at 0F with a wet
jacket or a dry one. (-: (And yes, I know that wet clothes transfer heat
more rapidly than dry ones and insulation loses R-value when wet.)
Evaporative cooling is more important to windchill's fraternal twin, the
heat index. That's when sweating in a humid environment does not cool the
skin well and so 100F degrees in Atlanta or DC can feel like 110F in the
desert. It seems that the two concepts got slightly mashed up in this
thread. There's fascinating reading at:
that describes a number of controversies associated with calculating
wind-chill, windchill, wind chill, wind chill index or the wind chill factor
(the fact that no one can agree what to call it speaks volumes about its
<<The method for calculating wind chill has been controversial because
experts disagree on whether it should be based on whole body cooling either
while naked or while wearing appropriate clothing, or if it should be based
instead on local cooling of the most exposed skin, such as the face. The
internal thermal resistance is also a point of contention. It varies widely
from person to person. Had the average value for the subjects been used,
calculated WCET's would be a few degrees more severe.
The 2001 WCET is a steady state calculation (except for the time to
frostbite estimates). There are significant time-dependent aspects to
wind chill because cooling is most rapid at the start of any exposure, when
the skin is still warm.>>
While there can be some defintional arguments about whether wind chill can
be used when discussing non-human objects, there's no argument that air
moving over something will transfer heat faster than no air movement.
Generally, wind chill cannot lower the temperature of something lower than
the ambient temperature *unless* there's enough liquid evaporating (think
Great Lakes) to account for a substantial temperature drop. If my wife
hadn't declared a moratorium on freezer-related experiments, I would even
try hooking up some thermocouples to both wet and dry pipe sections in the
freezer to see whether a wet pipe had a noticeable temperature difference
due to evaporation. Maybe some bachelor will do "the science" for us. (-:
Definitional purists would be correct in saying that wind chill does not
apply to inanimate objects but the scientific formula for computing it still
remains in place and that says the faster the wind, the greater the heat
transfer. For humans, pipes, dogs and CPU's alike.
The Aussies have created an AAT (Aussie Apparent Temperature) just to
confuse things further.
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