Watlow Heater Catalog

Air Heaters

Finned Heaters 375 Finned Strip Heaters Applications and Technical Data

Formulas

Calculating Watt Density Use the graph and formulas to ensure that the maximum allowable watt density for the heater is not exceeded in the application. Open air watt density is calculated for the total heated surface area.

Wattage Heated Area

Watt Density =

Heated Area (Offset Terminals) = [Overall Length (A) - 4 in.] x 3.75 in. = [Overall Length (A) - 102 mm] x 95.3 mm Heated Area (Parallel Terminals) = [Overall Length (A) - 3.12 in.] x 3.75 in. = [Overall Length (A) - 79.3 mm] x 95.3 mm Heated Area (One-on-One Terminals) = [Overall Length (A) - 4.25 in.] x 3.75 in. = [Overall Length (A) - 108 mm] x 95.3 mm

Maximum Allowable Watt Density

Watt Density—W/cm 2 2

4

5

1

3

600

300

15 ft/sec (4.6 m/sec) Air Speed 10 ft/sec (3.0 m/sec) Air Speed 5 ft/sec (1.5 m/sec) Air Speed Still Air

500

400 0 Ambient Air Temperature— ° F 0 5 300 200 100

Ambient Air Temperature— ° C

200

100

30

10

15

20

25

Watt Density—W/in 2

0 ft/sec (0 m/sec) Air Speed

394