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Brad
>Helium is lighter (less dense)than air, and therefore it conducts heat =
much more quickly.
To my understanding, density (quantity of matter in a volume) in gases =
is a function of pressure and temperature. Mass is an inherant property =
specific to each individual elements. Heat transfer are can only occur =
in three means: Conduction, convection and radiation.=20
Conduction can be use alone in explanining (alltrough not exact) heat =
transfers meaningfull to divers.
One equation of conduction is Q =3D k ( (T1-T2)/L) .
Q, the heat flux is in Joules (J)
k , the thermal conductibility constant, a property of the transfer =
medium (gases in this case), in Watt/Meters x Kelvin (W/m.K)
T1-T2 temperature difference (body vs. water), in deg. Kelvin (K)
L is the length of the transfert medium (betwenn the temp. difference), =
your suit and insulation layers filled by gases. in Meters
Marcelo Moorea,
>>(Q =3D mc delta t)=20
"m" or "c" is k, the other is a distance factor. "Delta t" is (T1-T2) =
Notation change from one source to another
From the above equation, the only possible way to have less heat =
transfert is to either change k (switch to other gases) or have more =
distance between the two medium wich are at different temp.(body vs. =
water).
Also, the densier the matter, the more conductibility (better channel to =
exchange heat). If your explanation is correct, Brad, then we would =
freeze at the surface and overheat at depth.:-)))))
For gas properties go to http://www.webelements.com/ . The ratio of =
different constant (k) will give you the net gain or loss in insulation. =
Argon is not the best choice, but only the best affordable choice.
=20
This is a simplistic explanation and it is not complete in any way. =
Readers are suggested to consult accurate sources. Mine is the third =
edition of "Fundamental of heat and mass transfer", by Frank P. =
Incropera & David P. De Witt. Since the fourth edition is out maybe =
things may have changed.:-)
Martin Baron
From: moorea(uol)=20
To: techdiver@aquanaut.com=20
Sent: Tuesday, February 20, 2001 8:05 AM
Subject: Helium thermal properties
=20
=20
Hello all !=20
I=B4ve been diving since 86, and nowadays i made my own mixes, but =
now, i decided to go certified.
My instructor, talking about thermal loss in a trimix class, explain =
me that the heat exchange is a direct relationship with gas density.
I=B4ve read and learn in the past (including in phisics class at =
regular school) that heat exchange depends of thermal conductivity of =
the media (Q =3D mc delta t) where "c" is the thermal conductivity.
Can you help me with that ?
Am i right ?
=20
thanks=20
=20
Marcelo Moorea
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<DIV><FONT face=3DArial size=3D2>Brad</FONT></DIV>
<DIV><FONT face=3DArial size=3D2><BR> </DIV></FONT>
<DIV>
<DIV><FONT face=3DArial size=3D2>>Helium is lighter (less dense)than =
air, and=20
therefore it conducts heat much more quickly.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT color=3D#000000 size=3D2>To my understanding, density =
(quantity of matter=20
in a volume) in gases is a function of pressure and temperature. Mass is =
an=20
inherant property specific to each individual elements. Heat transfer =
are can=20
only occur in three means: Conduction, convection and radiation. =
</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT> </DIV>
<DIV><FONT color=3D#000000 size=3D2>Conduction can be use alone in =
explanining=20
(alltrough not exact) heat transfers meaningfull to divers.</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>One equation of conduction is Q =3D k ( (T1-T2)/L)=20
..</FONT></DIV>
<DIV> </DIV>
<DIV><FONT color=3D#000000 size=3D2>Q, the heat flux is in Joules =
(J)</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT><FONT size=3D2>k , the =
thermal=20
conductibility constant, a property of the transfer medium (gases in =
this case),=20
in Watt/Meters x Kelvin (W/m.K)</FONT></DIV>
<DIV><FONT size=3D2></FONT><FONT size=3D2>T1-T2 temperature
difference =
(body vs.=20
water), in deg. Kelvin (K)</FONT></DIV>
<DIV><FONT size=3D2>L is the length of the transfert medium (betwenn the =
temp.=20
difference), your suit and insulation layers filled by gases. in=20
Meters</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV>
<DIV><FONT face=3DArial size=3D2>Marcelo Moorea<FONT=20
color=3D#000000>,</FONT></FONT></DIV></DIV>
<DIV> </DIV>
<DIV>>>(Q =3D mc delta t) </DIV>
<DIV> </DIV>
<DIV><FONT color=3D#000000 size=3D2>"m" or "c" is k, =
the other=20
is a distance factor. "Delta t" is (T1-T2) Notation change =
from one=20
source to another</FONT></DIV>
<DIV> </DIV>
<DIV><FONT color=3D#000000 size=3D2>From the above equation, the only =
possible way=20
to have less heat transfert is to either change k (switch to other =
gases) or=20
have more distance between the two medium wich are at different =
temp.(body vs.=20
water).</FONT></DIV>
<DIV> </DIV>
<DIV><FONT color=3D#000000 size=3D2>Also, the densier the matter, the =
more=20
conductibility (better channel to exchange heat). If your explanation is =
correct, Brad, then we would freeze at the surface and overheat at=20
depth.:-)))))</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=3D2>For gas properties go to <A=20
href=3D"http://www.webelements.com/">http://www.webelements.com/</A> . =
The ratio=20
of different constant (k) will give you the net gain or loss in =
insulation.=20
Argon is not the best choice, but only the best affordable =
choice.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT color=3D#000000 size=3D2>This is a simplistic explanation and =
it is not=20
complete in any way. Readers are suggested to consult accurate sources. =
Mine is=20
the third edition of "Fundamental of heat and mass transfer", =
by Frank=20
P. Incropera & David P. De Witt. Since the fourth edition is out =
maybe=20
things may have changed.:-)</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>Martin Baron</FONT></DIV>
<DIV> </DIV></DIV>
<BLOCKQUOTE=20
style=3D"BORDER-LEFT: #000000 solid 2px; MARGIN-LEFT: 5px; MARGIN-RIGHT: =
0px; PADDING-LEFT: 5px; PADDING-RIGHT: 0px"=20
dir =3D ltr>
<DIV=20
style=3D"BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: =
black"><B>From:</B>=20
<A href=3D"mailto:moorea@uo*.co*.br*" =
title=3Dmoorea@uo*.co*.br*>moorea(uol)</A>=20
</DIV>
<DIV style=3D"FONT: 10pt arial"><B>To:</B> <A=20
href=3D"mailto:techdiver@aquanaut.com"=20
title=3Dtechdiver@aquanaut.com>techdiver@aquanaut.com</A> </DIV>
<DIV style=3D"FONT: 10pt arial"><B>Sent:</B> Tuesday, February 20,
=
2001 8:05=20
AM</DIV>
<DIV style=3D"FONT: 10pt arial"><B>Subject:</B> Helium thermal=20
properties</DIV>
<DIV><BR></DIV>
<DIV><FONT face=3DArial size=3D2>Hello all ! </FONT></DIV>
<DIV><FONT face=3DArial size=3D2>I´ve been diving since 86, =
and nowadays i=20
made my own mixes, but now, i decided to go certified.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>My instructor, talking about =
thermal loss in a=20
trimix class, explain me that the heat exchange is a=20
direct relationship with gas density.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>I´ve read and learn in the =
past=20
(including in phisics class at regular school) that heat =
exchange=20
depends of thermal conductivity of the media (Q =3D mc delta =
t) where=20
"c" is the thermal conductivity.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>Can you help me with that =
?</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>Am i right ?</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=3DArial size=3D2>thanks </FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=3DArial size=3D2>Marcelo=20
Moorea</FONT></DIV></BLOCKQUOTE></BODY></HTML>
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