Dear Tony,
Thank you for the great account of the temperature testing!
This is, of course, the way to proceed, to carry out precise
measurements. I have in fact reconsidered the issue after I read
your results and associated the obvious benefit of insulating with
ceramic sheet with another idea of a sandwich-like insulator structure
(I lost the reference to whoever suggested it, sorry).
The sandwich idea really appeals to me! Sandwich-like structures
have been successfully applied in many areas and also in heat
insulation. In fact, it seems possible to kill a couple of birds with
it. A sandwich-like composition of ceramic sheet and aluminium foil
should provide almost space-age insulating properties and can be made
to be waterproof on the side of the boiler.
I would probably opt for two layers of 0.5-1.0 mm ceramic sheet between
three layers of aluminium foil. However, I would put a thin
layer of isolation between the boiler and the aluminium - I think
copper and aluminium have very different electrochemical potentials
which may lead to corrosion of the boiler even without any water!
Perhaps painting the boiler with heat resistant silver paint (like
that used for home radiators) would be sufficient to protect the
boiler from corrosion. Alternatively, isolating aluminium with a
layer of thin glass fibre fabric like that used in small blankets for
home (kitchen) fire extinguishing may be another option. They are
extremely smooth and would not accumulate any water (the reason for
not using ceramic sheet or wool like stuff in direct contact with the
boiler), but I am not certain if they are just plain woven fibre or
coated with some stuff.
Fixing the lot in place and around sensitive places with some heat
resistant silicone kit (some work up to 400 C) should provide enough
protection from air, steam and water from above and any other side,
like the smoke box.
However, I would perhaps leave the sandwich open from the bottom
(small narrow gap or a few holes) to let possible air/steam/water escape.
Now, this seems to be a lot of consideration for the little engine
that I am putting together. It is a stock Aster C&S Mogul, and I am
sure there are many of them running without any insulation just like
Aster intended. I gather from various comments that an absolute
majority of Asters don't have any insulation around the boiler, but
the only other Aster in my possession - Frank S is insulated, perhaps
to prove its exceptional status;^)!
Concluding, the measurement arguments are most convincing. So far, after
having eliminated the corrosion argument, other than cost, mess and work,
I see no reason for not applying insulation. 30+ deg. C temperature
difference measured means a lot of heat, probably more than my out-of-the
blue 5%. The difference in engine size and boiler type etc. may
however matter a lot. Still, I would expect larger relative loss of
heat for smaller rather than larger engines (of the same design) due to
larger surface/volume ratio of smaller engines.
Best regards and happy steaming!
Zbigniew
PS While extensive dwelling on the subject of heat escape should make
me a perfect Dutchmen;^), I'm not - I just happen to live under the sea...!
