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Date: Thu, 12 Jan 2012 08:46:51 -0500
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From: Gary Casey <casey.gary@yahoo.com>
Reply-To: Gary Casey <casey.gary@yahoo.com>
Subject: Re: Ceramic exhaust coatings
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I guess I'm just not convinced about the effectiveness of typical ceramic c=
oatings. =A0From what I can find out they are typically .001 to .002 thick,=
 about 5% of the thickness of the metal. =A0In order to significantly reduc=
e the heat transfer compared to the metal, they would have to have thermal =
conductivity in that order compared to steel. =A0I can't find out what mate=
rial is used, but some might use zirconia, a very good insulator, which has=
 about 10 to 20% of the conductivity of steel. =A0But that's not the whole =
story. =A0Inside the pipe is a gas at perhaps 1500F moving at a relatively =
high velocity. =A0The conductivity to the metal is therefore relatively goo=
d, resulting in a metal temperature of probably 1200F. =A0The air on the ou=
tside is at about 180F and it is moving slowly, so the heat transfer from t=
he pipe to the air is "poor." =A0My guess is that the surface temperature o=
f the ceramic is going to be very close to what the metal would be without
 the coating. =A0There just isn't enough thickness for it to be well insula=
ted. =A0Swain Technologies has a proprietary process that puts .015 thickne=
ss on metal and that would probably work. =A0A big factor in heat transfer =
is radiation and the best way to reduce that is with a shiny metal surface =
spaced away from the exhaust pipe, or from the device to be protected.=0A=
=0AMaybe ceramic coatings work well, but I'm afraid I'm not convinced.=0A=
=0AGary Casey=0AES 157
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<html><body><div style=3D"color:#000; background-color:#fff; font-family:bo=
okman old style, new york, times, serif;font-size:12pt"><div>I guess I'm ju=
st not convinced about the effectiveness of typical ceramic coatings. &nbsp=
;From what I can find out they are typically .001 to .002 thick, about 5% o=
f the thickness of the metal. &nbsp;In order to significantly reduce the he=
at transfer compared to the metal, they would have to have thermal conducti=
vity in that order compared to steel. &nbsp;I can't find out what material =
is used, but some might use zirconia, a very good insulator, which has abou=
t 10 to 20% of the conductivity of steel. &nbsp;But that's not the whole st=
ory. &nbsp;Inside the pipe is a gas at perhaps 1500F moving at a relatively=
 high velocity. &nbsp;The conductivity to the metal is therefore relatively=
 good, resulting in a metal temperature of probably 1200F. &nbsp;The air on=
 the outside is at about 180F and it is moving slowly, so the heat
 transfer from the pipe to the air is "poor." &nbsp;My guess is that the su=
rface temperature of the ceramic is going to be very close to what the meta=
l would be without the coating. &nbsp;There just isn't enough thickness for=
 it to be well insulated. &nbsp;Swain Technologies has a proprietary proces=
s that puts .015 thickness on metal and that would probably work. &nbsp;A b=
ig factor in heat transfer is radiation and the best way to reduce that is =
with a shiny metal surface spaced away from the exhaust pipe, or from the d=
evice to be protected.</div><div><br></div><div>Maybe ceramic coatings work=
 well, but I'm afraid I'm not convinced.</div><div><br></div><div>Gary Case=
y</div><div>ES 157</div>  </div></body></html>
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