Effective emissivity

A real body at temperature T does not emit with the black body emissive power $\sigma\cdot{T^4}$ but rather with some fraction $\epsilon$.

The total emittances for a variety of surfaces is given in the following table which is an extract from the slides Radiative heat transfer for the course Heat transfer by John Richard Thome (EPFL, 2008).

Symbol

$\epsilon_{rad}$

Related

$K_t$

Effective emissivity of surface

Choices

Material	Type / Treatment	Temperature	nom	min	max	median
Aluminium	Polished, 98% pure	200-600		0.04	0.06	0.05
Aluminium	Commercial sheet	90	0.09
Aluminium	Heavily oxidized	90-540	0.3	0.2	0.33	0.265
Brass	Highly polished	260	0.04
Brass	Dull plate	40-260	0.22
Brass	Oxidized	40-260		0.46	0.56	0.51
Copper	Highly polished electrolyte	90	0.02
Copper	Slightly polished to dull	40		0.12	0.15	0.135
Copper	Black oxidized	40	0.04
Steel	Polished	40-260		0.07	0.1	0.085
Stainless steel	after repeated heating	230-900		0.5	0.7	0.6
Paint	Black gloss	40	0.9
Paint	White paint	40		0.89	0.97	0.93
Paint	Lacquer	40		0.8	0.95	0.875
Paint	Various oil paints	40		0.92	0.96	0.94
Paint	Red lead	90	0.93