Watlow Heater Catalog

Air Heaters

Duct Heaters LDH SERIES and D SERIES

To decide watt density requirements, first determine the desired outlet air temperature and velocity in feet per minute. Then, follow the lines on the graph for velocity and process temperature to the watt density Watt Density vs. Air Temperature/Velocity

curve’s intersecting point. This shows the recommended watt density based on a maximum sheath temperature of 1400°F (760°C). For longer heater life, lower watt densities should be chosen.

WATROD Duct Heater Watt Density Vs. Air Temperature Velocity

WATROD Duct Heater Watt Density Vs. Air Temperature Velocity

500

1000 1100 1200 1300 1400 1500 1600

40 W/in 2

30 W/in 2

20 W/in 2

23 W/in 2

6.2 W/cm 2

4.65 W/cm 2

16 W/in 2

8 W/in 2

3.1 W/cm 2

3.5 W/cm 2

2.5 W/cm 2

1.25 W/cm 2

400

300

100 200 300 400 500 600 700 800 900

200

Catalog Duct Heaters

Catalog Duct Heaters

Catalog Duct Heaters

Catalog Duct Heaters

Air Velocity—MPM

Air Velocity—FPM

100

100

700

200

300

400

500

600

100

200 300 400 500 600 700 800 900 1000 1100 1200

Process Temperature—°C

Process Temperature—°F

Estimated Sheath Temperature = 760°C

Estimated Sheath Temperature = 1400°F

The Watt Density vs. Sheath Temperature graph shows the air velocity (FPM or MPM) required to operate a WATROD duct heater at specific watt densities or sheath temperatures. Also depicted is the appropriate watt density vs. sheath temperature at a specified air flow. Watt Density vs. Sheath Temperature

WATROD Duct Heater Watt Density Vs. Sheath Temperature

10

9

Inlet Temperature at 25°C

8

7

Watt Density—W/cm 2 5 4 3 6

WATROD Duct Heater Watt Density Vs. Sheath Temperature

180 MPM

235 MPM

475 MPM

365 MPM

12 16 20 24 28 32 36 40 44 48 52 56 60

Inlet Temperature at 75°F

90 MPM

2

Watt Density—W/in 2

18 MPM or Natural Convection

760 FPM

680 FPM

1550 FPM

1200 FPM

1

100

200

300

400

500

600

700

800

900 1000

300 FPM

Sheath Temperature—°C

60 FPM or Natural Convection

4 8

100 0 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500

Sheath Temperature—°F

377