wrote:
wrote:

mm wrote:

I am told by experts in the field that one of several ways that
high-efficiency furnaces squeeze more BTU's from their fuels is by
using thinner and thinner heat exchangers

This seems like one of the false efficiencies...

That simply isn't true. The heat is going to transfer more effectively
across the thinner material. The thickness of the metal provides
a resistance to heat flow, just as thicker insulation, wood, or
anything else would.

But metals are such good conductors that making the metal thinner won't
help much, given high resistance air layers on both sides, and thicker
metal will spread out hot spots and increase efficiency.

Nick




Wrong. Making the metal thinner does have a direct and significant
impact on the heat transfer. Here's two references for you:

Theoretical, which from experience is the only type of source you
recognize:

http://hyperphysics.phy-astr.gsu.edu...mo/heatra.html
Conduction is heat transfer by means of molecular agitation within a
material without any motion of the material as a whole. If one end of a
metal rod is at a higher temperature, then energy will be transferred
down the rod toward the colder end because the higher speed particles
will collide with the slower ones with a net transfer of energy to the
slower ones. For heat transfer between two plane surfaces, such as heat
loss through the wall of a house, the rate of conduction heat transfer
is:

Calculation

Q/t = kA(Thot-Tcold)/d

Q = heat transferred in time = t
k = thermal conductivity of the barrier
A = area
T = temperature
d = thickness of barrier

Clearly from the above, the conducted heat transfer is proportional to
the thickness of the heat exchanger.


And second, from an industrial company that acutally makes air to air
heat exchangers:

http://www.anguil.com/downloads/Heat...ate-Anguil.pdf
In the spec sheet for their product it says:

"Plate thickness ranges from .024" for high efficiency to a heavy-duty
and durable .050" thick plate"

Cearly they agree cutting the thickness in half makes a significant
difference in efficiency.