Watlow Heater Catalog

Reference Data (SI Unit)

Power Calculations Heat Loss Curves

Ref. 5

1. Based upon combined natural convection and radiation losses into 21°C environment. 2. Insulation characteristics k = 0.097 W/m K @ 93°C k = 0.120 W/m K @ 538°C 3. For molded ceramic fiber products and packed or tightly packed insulation, losses will be lower than values shown. For 50.8 or 76.2 mm insulation multiply by 0.84. For 102 or 127 mm insulation multiply by 0.81. For 152 inches insulation multiply by 0.79.

Heat Losses from Vertical Insulated Surfaces

1400

1200

4 in. Insulation

5 in. Insulation

6 in. Insulation

3 in. Insulation

1000

2 in. Insulation

800

1 in. Insulation

600

400

200

0 in. Insulation

200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 0 0 Temperature of Insulated Surface - °C Loss - W/m 2

Ref. 6

Heat Losses from Horizontal Metal Surfaces

*For losses of molten metal surfaces, use the curve e=0.40.

700

e = 0 . 2 0

n d R a d i a t i o n o n v e c t i o n a n d

600

R a d i a t i o n e = 0 . 4 0 *

N a t u r a l C o n v e c t i o n

t i o n a

500

o n v e c

n e d C

a d i a t i o n e = 1 . 0

400

C o m b i

C o m b i n e d C

n v e c t i o n a n d R

300

C o m b i n e d C o

200

100

Temperature of Surface - °C

Loss - W/m 2 2000 4000 6000 8000 10000 12000 1400016000 18000 20000 22000 24000 26000 28000 30000 0 0

Ref. 7

300 Combined Convection and Radiation—Losses from Oil or Paraffin Surfaces

250

200

150

100

50

1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 11000 12000 13000 0 0 Temperature of Surface - °C

Loss - W/m 2

538