high emissivity fibers and coatings

[simisastry]

Are there natural high emissivity fibers that can be spun?
vispel polyimide seems to be the only polymer with emissivity of 0.9 but it cannot be spun.Can polyimide P84 used for fire retardant textile have such a high emissivity too?Can we Apply high emissivity coatings on textile surfaces,that are not dark in colour and if we find lighter coloured coatings,do they allow reprinting(colours) on them.and if they do how does the colour of print now change the emissivity of the high emissivity coating?Are there coatings that behave as high emissivity surfaces at day time (absorbing solar energy) and behave as low emissivity surfaces at night(high relectance).?how does a high emissivity coating in general behave at night?

 

[simisastry]

and i know that carbon fibers can be used to manufacture nets and fabrics but are there fibers that are not dark in colour.Does a carbon fiber textile reduce its emissivity if its printed on?

 

[Glave]

In most cases color has little to no effect on emissivity of a traget as it is applied to Thermograpghic cameras when measuring temperatures. This link

http://snellinfrared.com/library/_next_view.asp?id=83&refid=20

is a great visual example of this

 

[simisastry]

I hear crystal paints change the emissivity of surfaces,where do i find such paints fpr textile surfaces.

 

[IRstuff]

Glave,

It would seem to be dependent on the paint and possibly some interaction with the hot fabric as well as possibly wavelength.

I've seen cold targets with camouflage paint that was extremely evident in the MWIR.

TTFN

 

[Glave]

Emissivity is affected by the molecular make-up of the target, this is true. If all material is equal within the target itself then color will not affect your temperature reading. The emissivity of a material is a property of its molecular structure, transmissivty and absorbtion, all of which contribute to the targets "ability" to radiate energy. In the case used for crystal paints, yes they may change the E value of the material they are applied to, but not because of it's color, because of the differing crystals in the paints used to make up that color.

A simple experiment can be performed with various colors of electrical tape applied to a low E canister (Stainless Steel). Put 3 to 4 different color tapes on the canister, fill canister with warm/hot water. Image tape with a thermal imager. Provided the tape was all from the same manufacture they will all appear the same temp. And in fact if you use a Radiometric camera will measure the same temps.

My only point behind the whole discussion is that color alone does not change the E value of a target. As to materials and fibers, the military has done extensive studies on this same subject in regards to a soldiers clothing, none of which are available to JQP.

Hope this helps

 

[JKEngineer]

I think the OP (simisastry) is trying to deal with an issue other than thermal imaging. It appears from his (?) posts that he wants a solar absorptive coating for daytime heat gain and a night time reflective coating for reduced thermal loss. This will be a function of, among other things, the wavelength dependency of the emissivity of the surface. For solar gain, color IS a factor.

It appears that he wants a spinnable fiber or a coating for cloth that gains in the visible and near visible regions, i.e. has high emissivity/absorptivity for solar radiative temperatures, and has low emissivity/absorptivity for wavelengths in the mid to long IR corresponding to surface temperatures of the order of 50 to 150F (10 TO 65C).

OP needs to be careful using "handbook" values for emissivity. Depending on the purpose of the handbook the listed values may be broad spectrum or only relating to a narrow wavelength band, be it visible, near IR, mid IR, or long IR.

If I have hit this correctly, then much of the discussion above, while correct, is off-target.

Jack M. Kleinfeld, P.E. Kleinfeld Technical Services, Inc.
Infrared Thermography, Finite Element Analysis, Process Engineering

http://www.KleinfeldTechnical.com