Emissivity of Surfaces Table - Heat Transfer

Heat Transfer Engineering
Thermodynamics

Real objects do not radiate as much heat as a perfect black body. They radiate less heat than a black body and are called gray bodies. To take into account the fact that real objects are gray bodies, Equation 2 is modified to be of the following form.

Q = ε σ A T4

Where:

ε = emmissivity of the grey body (dimensionless)

Emissivity is simply a factor by which we multiply the black body heat transfer to take into account that the black body is the ideal case. Emissivity is a dimensionless number and has a maximum value of 1.0.

Emissivity of Surface Table gives the emittance of various surfaces and emphasizes the variation possible in a single material. The values in the table apply, with a few exceptions, to normal radiation from the surface.

Surface
Temp * C°
Emissivity *
Metals and their oxides
Aluminum:
Highly polished
230–580
0.039–0.057
Polished
23
0.040
Rough plate
26
0.055–0.07
Oxidized at 600°C
200–600
0.11–0.19
Oxide
280–830
0.63–0.26
Alloy 75ST
24
0.10
75ST, repeated heating
230–480
0.22–0.16
Brass
Highly polished
260–380
0.03–0.04
Rolled plate, natural
22
0.06
Rolled, coarse-emeried
22
0.20
Oxidized at 600°C
200-600
0.61–0.59
Chromium
40–540
0.08–0.26
Copper
Electrolytic, polished
80
0.02
Comm’l plate, polished
20
0.030
Heated at 600°C
200–600
0.57–0.57
Thick oxide coating
25
0.78
Cuprous oxide
800–1,100
0.66–0.54
Molten copper
1,080–1,280
0.16–0.13
Dow metal, cleaned, heated
230–400
0.24–0.20
Gold, highly polished
230–630
0.02–0.04
Iron and steel:
Pure Fe, polished
180–980
0.05–0.37
Wrought iron, polished
40–250
0.28
Smooth sheet iron
700–1,040
0.55–0.60
Rusted plate
20
0.69
Smooth oxidized iron
130–530
0.78–0.82
Strongly oxidized
40–250
0.95
Molten iron and steel
1,500–1,770
0.40–0.45
Lead:
99.96%, unoxidized
130–230
0.06–0.08
Gray, oxidized
24
0.28
Oxidized at 190°C
190
0.63
Mercury, pure clean
0–100
0.09–0.12
Molybdenum filament
730–2590
0.10–0.29
Monel metal, K5700
Washed, abrasive soap
24
0.17
Repeated heating
230–875
0.46–0.65
Nickel and alloys:
Electrolytic, polished
23
0.05
Electroplated, not polished
20
0.11
Wire
190–1,010
0.10–0.19
Plate, oxid. at 600°C
200–600
0.37–0.48
Nickel oxide
650–1,250
0.59–0.86
Copper-nickel, polished
100
0.06
Nickel-silver, polished
100
0.14
Nickelin, gray oxide
21
0.26
Nichrome wire, bright
50–1,000
0.65–0.79
Nichrome wire, oxide
50–500
0.95–0.98
ACI-HW (60Ni, 12Cr);
firm black ox, coat
270–560
0.89–0.82
Platinum, polished plate
230–1,630
0.05–0.17
Silver, pure polished
230–630
0.02–0.03
Stainless steels:
Type 316, cleaned
24
0.28
316, repeated heating
230–870
0.57–0.66
304, 42 h at 520°C
220–530
0.62–0.73
310, furnace service
220–530
0.90–0.97
Allegheny #4, polished
100
0.13
Tantalum filament
1,330–3,000
0.194–0.33
Thorium oxide
280–830
0.58–0.21
Tin, bright
24
0.04–0.06
Tungsten, aged filament
25–3,320
0.03–0.35
Zinc, 99.1%, comm’l, polished
230–330
0.05
Galv., iron, bright
28
0.23
Galv. gray oxide
24
0.28
Refractories, building materials, paints, misc.
Alumina
260–680
0.6–0.33
Alumina, 50-mm grain size
1,010–1,570
0.39–0.28
Alumina-silica, cont’g
1,010–1,570
0.4% Fe2O3
-
0.61–0.43
1.7% Fe2O3
-
0.73–0.62
2.9% Fe2O3
-
0.78–0.68
Al paints
(vary with amount
of lacquer
body, age)
100
0.27–0.67
Asbestos
40–370
0.93–0.95
Calcium oxide
750–1,100
0.29–0.28
Candle soot;
lampblack-waterglass
20–370
0.95 6 0.01
Carbon plate, heated
130–630
0.81–0.79
Ferric oxide (Fe2O3)
500–900
0.8–0.43
Magnesium oxide, 1 µm
260–760
0.67–0.41
Oil layers
Lube oil, 0.01 in
on pol. Ni
20
0.82
Linseed, 1–2
coats on Al
20
0.56–0.57
Rubber, soft
gray reclaimed
24
0.86
Silica, 3 µm
260–740
0.7–0.5
Misc. I: shiny black lacquer, planed oak,
white enamel, serpentine, gypsum,
white enamel paint , roofing paper,
lime plaster, black matte shellac
21
0.87–0.91
Misc. II: glazed porcelain, white paper,
fused quartz, polished marble,
rough red brick, smooth glass, hard
glossy rubber, flat black lacquer,
water, electrographite
21
0.92–0.96

* When two temperatures and two emissivities are given they correspond, first to first and second to second, and linear interpolation is suggested.

Reference: Marks Standard Handbook for Mechanical Engineers