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re: solar paint - who can ?
21 aug 1997
david wells wrote:
>some other folks have kicked around the idea of making their own
>selective surface...
>i always wondered: is there an aluminum anodize that will work?
haven't heard of that...
iron is 3x cheaper than al. bruce anderson's solar home book lists "nickel
black on galvanized iron" as a commercial process with a solar absorptance of
0.89 and long-wave emittance of 0.12. duffie and beckman's book has references
to recipes for nickel black over galvanized iron by tabor. appendix iii of
anderson's master's thesis lists "galvanized iron, clean, new," as having a
solar absorptance of 0.65 and long-wave emittance of 0.13 and "galvanized
sheet iron, gray, oxidized," with 0.8 and 0.28.
deepish cavities can improve absorption. so can a dark semi-transparent mesh
in front of an absorber plate, in an air heater. the mesh can block some
reradiation from the absorber, as well as increasing the effective plate-air
heat exchange area, which lowers the average plate temperature and reradiation
loss. if air flows through the mesh towards the plate, the mesh can also help
confine sun-warmed air between the mesh and the plate, so the air near the
glazing is cooler, which lowers the heat loss through the glazing. black
window screen seems to work well. what is the optimum mesh transmittance?
nick
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