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Emissivity

The emissivity of a material (usually written ε or e) is the relative ability of its surface to emit energy by radiation. It is the ratio of energy radiated by a particular material to energy radiated by a black body at the same temperature. A true black body would have an ε = 1 while any real object would have ε < 1. Emissivity is a dimensionless quantity.

Emissivity table

Metal

Item Smooth Rough corrosion
Aluminum 0.04 0.05 0.11~0.19
Brass 0.03 0.06 ~ 0.2 0.6
Copper 0.02 0.57
Gold 0.2 ~ 0.4
Iron 0.13 ~ 0.3 0.25~0.45 0.8~0.95
Lead 0.06~0.08 0.63
Nickel 0.04~0.09 0.37~0.48
Silver 0.02~0.4
Tin 0.04~0.07
Zinc 0.04~0.05 0.11
Yellow calcite 0.23 0.23

Nonmetal

Name of article Emissivity
Asbestos 0.93~0.96
Brick 0.75~0.93
Carbon 0.93~0.97
Glass (soft) 0.94
Plaster 0.9
Marble 0.93
Oak 0.9
Paper 0.92~00.94
Lime 0.91
Ceramic 0.92~0.93
Crystal (coarse side) 0.93
Roofing paper 0.91
Rubber 0.86~0.95
Water 0.95~0.96

Paint Emissivity shown in rough figures depends on the surfaces.

Name of article Emissivity
Black lacquer
White lacquer 0.8~0.95
Enamel 0.85~0.91
Oil paint 0.92~0.96
Aluminum paint 0.27~0.67
Varnish 0.89~0.93

Applications

Infrared rays Industry Deterioration diagnosis Electricity, machinery, electronics, buildings and civil engineering
Energy Heat transfer, radiant heat, heat insulation property and test
Non-destructive test Wholesomeness evaluation and structural analysis
Process monitoring Quality control & monitoring
Safety/Environment Fire Fire watch, firefighting & rescue and analysis of source
Gas detection Inspection of contamination and leak
Quarantine Airport inspection
Medicine Body diagnosis Nervous system, musculoskeletal system, blood vascular system and metabolic disorders
Veterinary science
Security Military Night guard and trace
Night watch Night watch