Watlow Heater Catalog

High-Temperature Heaters Ceramic Fiber Heaters Performance Data (Continued) Insulation Effectiveness The graphs below illustrate the effectiveness of adding 6 lb/ft 3 (96 kg/m 3 ) blanket insulation to the backside of standard 2 in. (50 mm) thick ceramic fiber heaters. Total wall thickness of up to 6 in. (152 mm) is shown. Data is for vertical sides without metal sheathing. Top and bottom surfaces and surfaces with metal sheaths covering ceramic fiber insulation will vary.

Heat Loss and Energy Transfer For general calculations of heat loss and energy transfer, the Insulation K-Factors and Emissivity graphs are helpful. The K-Factors graph is for ceramic fiber heaters and the ceramic fiber insulation blanket typically used with the heaters. This blanket is offered as an accessory by Watlow.

Insulation K-Factors

3.0 2.5 2.0 1.5 1.0 0.5

External Surface Temperatures (°F)

Mean Temp. = T Inside + T Outside 2

450 400 350 300 250 200 150 100 External Temperature—°F 1

2200°F Chamber 2000°F Chamber 1800°F Chamber 1600°F Chamber 1400°F Chamber 1200°F Chamber 1050°F Chamber 0850°F Chamber

6 lb/ft 3 Blanket

hr-ft 2 -°F BTU-in

Typical Range for Watlow Molded Fiber

Thermal Conductivity 600

800

1000

1200 1400 1600 1800 2000

Mean Temperature—°F

Insulation K-Factors

2

3

4

5

6

Total Wall Thickness—inches (Includes Standard 2 in. Heater Thickness)

Mean Temp. = T Inside + T Outside 2

40 35 30 25 20 15 10 5

External Surface Temperatures (°C)

96 kg/m 3 Blanket

225 200 175 150 125 100

1200°C Chamber 1100°C Chamber 1000°C Chamber 900°C Chamber 800°C Chamber 700°C Chamber 600°C Chamber

m 2 -C W-cm

Thermal Conductivity

Typical Range for Watlow Molded Fiber

Mean Temperature—°C 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 100010501100

75 50

External Temperature—°C

25

50

75

150

100

125

Total Wall Thickness—mm (Includes Standard 50 mm Heater Thickness)

Application Hints For wall thicknesses (T) in cylindrical situations use the “equivalent thickness” conversion.

r out r in ) (

T cyl. = r out log e

Where r out is outer radius r in is inner radius

Emissivity of Heater Surface The Emissivity graph details the normalized emittance values for the four surfaces most likely to be encountered when planning Watlow ceramic fiber heater applications.

Emissivity Chart

Surface Temperature—°C

600

700

800

900

1000

1100

1.0 0.8 0.6 0.4 0.2

High Emissivity Coating

Oxidized Wire

Std. Hot Face Coating Uncoated Unit Surfaces Ceramic Fiber Blanket

0

Total Normal Emittance 1000 1200

1400

1600

1800

2000

2200

Surface Temperature—°F

423