Emmisivity as insulation thickness determinant ?

[sharshal]

Hi Sharshal,
are we talking of same emmisivity as defined in Photometry & Illumination?
"factors that give the relative intensity of radiation of the nonblack body and of the black body at the same temperature"

If we consider for example a Polyurethane insulation: what is its emmisivity? also pls include its source.

I thought i already have figure out most insulation and its usage, but with the above question, i again have doubts.

I hope some physicist can make a layman explanation of the emmisivity of insulation.

Hi Winfred.dela ..!

I am sorry its been long since you wrote, but as I hadn't seen a reply in a couple of days of my post, I thought my post was a little too deep for anybody to answer, so I had not checked the site further !

Anyways, I am talking of a specific case where I have to make a comparison between closed cell cross linked polyethylene and in-situ PUF insulation. The thickness of cross cell insulation, it seems, is linked to (along with the usual 'k' value) emmisivity. So to avoid condensation a manufacturer of XLPE (for cross linked poly ethylene) can indicate a lower thickness as its colour being a shade of grey close to black is high, so condensation is avoided !

But at the same time, if this 'black' coloured insulation is cladded with, say, aluminium, then it loses its emmisivity property and as such the thickness will have to be higher .. !

I was just as surprised as you are when I heard this, so I thought I should post this to know if we have anybody giving any further inputs !

[winfred.dela]

Hi Winfred.dela ..!
. . . .
I have to make a comparison between closed cell cross linked polyethylene and in-situ PUF insulation. The thickness of cross cell insulation, it seems, is linked to (along with the usual 'k' value) emmisivity. So to avoid condensation a manufacturer of XLPE (for cross linked poly ethylene) can indicate a lower thickness as its colour being a shade of grey close to black is high, so condensation is avoided !

But at the same time, if this 'black' coloured insulation is cladded with, say, aluminium, then it loses its emmisivity property and as such the thickness will have to be higher .. !

Have you seen airconditioning ductworks without insulation inside an airconditioned space?
Some have moisture and some does not have.
Have you checked what color have moisture?
Maybe, you can experiment the performance of ducts colored black vs. white colored one.

I just do not know if this is immisivity but you can have a better grasps of colors you may want to use.

To be able to explain more, i would like to add this tidbit of info from HPAC magazine (late 70s) about Pure Science vs. Applied Science where it was mentioned:

Engineering is not a fundamental science, it is by definition an applied science.
Engineering utilizes laws, physical relationships and other exacting knowledge developed within the pure sciences as its cornerstone.

Applied: used in actual practice or to work out practical problems.
Pure: restricted to the abstract or theoretical aspects

To help me in my consultancy works as an Engineer,
I always try to learn as much Pure Science as possible and try to link it with the Applied aspect.
This helps me a lot in converting technical concepts to customer's layman words.

Hope to have helped. . .