What will be the best thermal insulation material for insulation of pipe lines having temperature of 500℃. Mineral wool and Calcium Silicate can be used but here we have a constraint of both weight and space.
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1$\begingroup$ Can you better define "best"? Performance-wise, "best" probably means paint it with an anti-emissive coating and vacuum seal it. Thats probably not cost effective or durable though. On a more practical level, aerogels are maybe the next best. But theres no way you can afford to insulate most industrial-scale equipment with that. Power plants typically use mineral wool I believe to balance effectiveness and cost. $\endgroup$– ericksonlaMar 3, 2017 at 13:31
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There is a well known but counter-intuitive result that for a given temperature, below a certain diameter, any insulation at all is worse than no insulation, because it conducts heat (poorly but better than air) to a larger external radiating surface.
Details should be in any good book on heat flow, but for common steam pipe temperatures, the critical diameter is of the order of 5mm.
So, below a certain pipe diameter, leave the pipe exposed to keep the radiating area small. We don't know from your question if your pipe dia can be small enough to allow this.
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$\begingroup$ The pipe dia is in the range of 16" to 24" and hence can't be left exposed. $\endgroup$ Mar 3, 2017 at 13:18
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$\begingroup$ This seems like it could easily be overcome. Is this part of the reason mineral wool is clad with aluminum, which is a very poor radiative emitter? $\endgroup$ Mar 3, 2017 at 13:33
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$\begingroup$ Thanks for the response. I think mineral wool will cost effective and use aerogels at place where we have space constraint. $\endgroup$ Mar 3, 2017 at 15:59
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1$\begingroup$ No need to accept my answer as it doesn't appear to apply to your case. $\endgroup$ Mar 3, 2017 at 16:00