Emissivity

every material has an emissivity factor. The higher the emissivity, the slower the radiant heat transfer from one thing to another. The lower the emissivity, the faster the radiant heat transfer from one thing to another. Three things can happen to the energy radiated from one surface to another: the transferred heat is either absorbed, reflected, or transmitted through the surface or a combination thereof. Emissivity factor= ratio of absorbed vs. reflected or transmited energy. Ex. Jeans have an emissivity factor of .83, which means 83% of the recieved heat from ones legs is absorbed, and 17% of the heat is reflected/transmitted/or re-radiated. Some materials transmit energy at some l while absorbing energy at others; emissivity is a spectral parameter.

In order for the Fluke 45 to read the breath temperature traces, the dancer must wear some type of fabric over the mouth and nose. The "breath mask" will be made from a fabric with a low emissivity factor so the heat absorbs at a low percentage, showing less heat accumulation on the "breath mask" material, and more variation in temperature tracing instead of a gradual gain of heat around the mouth area.

Table 1. Experimentally obtained parameters of different fabrics.


Fabric: max ∆T, °C: Emissivity:
( λ = 2.8 µm )
Polyamide 0.59 0.692 ± 0.012
Factory cloth tape 2.41 0.722 ± 0.012
Crinoline (linen) 2.66 0.732 ± 0.002
Velveteen (thin) 2.90 0.756 ± 0.008
Jean (composite cloth) 3.04 0.813 ± 0.013
Silk cloth 3.22 0.749 ± 0.012
Velveteen (thick) 3.55 0.750 ± 0.015
Polyester 3.86 0.7 (datum point)
Half-woollen cloth 3.98 0.780 ± 0.006
Thick woollen (100%) cloth 4.38 0.762 ± 0.013
Poplin (cotton) 7.75 0.710 ± 0.013
Flannel 8.06 0.668 ± 0.008

body sweat study with infrared thermal imaging