Talk:Multi-layer insulation

Outside surfaces highly reflective?

From the article: The blanket can be further improved by making the side(s) that face the warmer surface(s) highly reflective to thermal radiation. -- High reflection means a low emissivity. A low emissivity affects both thermal absorption and thermal emission, so both outward surfaces of the blanket are better reflective, isn't it? I changed this in the article. I am not sure about the inside layers, though; I think the emissivity there doesn't matter so much; the metal coating there is mainly because 6 microns of mylar/kapton are not fully opaque for infrared radiation. I'm not sure about this; can anybody confirm? Han-Kwang (t) 16:58, 12 May 2010 (UTC)

I just did a quick calculation; for two parallel surfaces with emissivities $\epsilon _{1}$ and $\epsilon _{2}$ and a small temperature difference $\Delta T$, the net radiation flux from one layer to the next is

$j_{\mathrm {net} }={\frac {\epsilon _{1}\epsilon _{2}\Delta T}{\epsilon _{1}+\epsilon _{2}-\epsilon _{1}\epsilon _{2}}}4\sigma T^{3}$.

This implies that it certainly pays off to have one side of each layer coated ($\epsilon _{1}=0.01,\epsilon _{2}=1$), but the additional benefit of a coating on the other side is only an extra factor 2:

$\epsilon _{1}$	$\epsilon _{2}$	$j/4\sigma T^{3}\Delta T$
1	1	1
1	0.01	0.01
0.01	1	0.01
0.01	0.01	0.00503

Any thoughts on this? Han-Kwang (t) 17:22, 12 May 2010 (UTC)

one or two?

From the article:

> "coated on one side with a thin layer of metal on both sides, typically silver or aluminum"

So, "one side" or "both sides"? ---R. S. Shaw (talk) 18:47, 9 July 2011 (UTC)

does not seem encyclopaedic

the function and design section reads more like a textbook and less like an encyclopaedia. can someone with more wiki-knowledge put the appropriate flag on this article? — Preceding unsigned comment added by 184.68.145.90 (talk) 01:12, 3 March 2015 (UTC)