Catalogue - Application Guide catalog - Watlow - (Version JPG)

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Application Guide

Some Material Emissivities/Metals—Ref. 10

Electric Data

Heat Loss Factors

and Graphs

Continued

Helpful Hint: The graphs for losses from uninsulated and insulated

surfaces are hard to read at low temperatures close to ambient. Here are two easy-to-use calculations that are only rule-of-thumb approximations when used within the limits noted.

Rule #1: Losses from an uninsulated

surface (with an emissivity close to 1.0): (This applies only to temperatures between ambient and about 250°F)

Losses (W/in2) =

AT (°F) rise above ambient 200

Rule #2: Losses from an insulated

surface: (This insulation is assumed to be one inch thick and have a K-value of about 0.5 Btu-in/hr - ft2-°F. Use only for surfaces less than 800°F.)

Losses (W/in2) =

AT (°F) rise above ambient

950


	Specific	Emissivity
Material	Heat	Polished		Medium	Heavy
	Btu/lb-°F	Surface		Oxide	Oxide
Blackbody				0.75	1.00
Aluminum	0.24	0.09		0.11	0.22
Brass	0.10	0.04		0.35	0.60
Copper	0.10	0.04		0.03	0.65
Incoloy® 800	0.12	0.20		0.60	0.92
Inconel® 600	0.11	0.20		0.60	0.92
Iron, Cast	0.12	—		0.80	0.85
Lead, solid	0.03	—		0.28	—
Magnesium	0.23	—		—	—
Nickel 200	0.11	—		—	—
Nichrome, 80-20	0.11	—		—	—
Solder, 50-50	0.04	—		—	—
Steel
mild	0.12	0.10		0.75	0.85
stainless 304	0.11	0.17		0.57	0.85
stainless 430	0.11	0.17		0.57	0.85
Tin	0.056	—		—	—
Zinc	0.10	—		0.25	—
Some Material Emissivities/Non-Metals—Ref. 11
	Specific
Material	Heat
	Btu/lb-°F
Asbestos	0.25^H
Asphalt	0.40^H
Brickwork	0.22^H
Carbon	0.20^H		Most non-metals:
Glass	;:;.20ifal		0.90
Paper	0.45^H
Plastic	0.2-0.5^1
Rubber	0.40^H
Silicon Carbide	0.20-0.23M
Textiles	—
Wood, Oak	0.57^\|

O i-*

0) i-*

Additional information on emissivities is available from Watlow.

Incoloy® and Inconel® are registered trademarks of the Special Metals Corporation.

Application Guide catalog - Watlow - #27

Thermocouple, Thermocouple wire, Cable, Band heater, Heating element