TECHNICAL: SUGGESTED WATT DENSITIES

Suggested Watt Densities

The rates below are recommended watt densities for use with various materials. Safe values vary with operating temperature, flow velocity, and heat transfer rates. In general,the higher the material temperature, the lower the watt density should be, especially those materials which coke or carbonize, such as oils. Watt densities should be low if a material is being heated to a temperature near where the change of state to a vapor occurs (water to steam @ 212°F) since the vapor state has much poorer heat transfer capabilities.

Material being heated

Maximum Operating Temp.°F

Maximum Watts Per Sq. In.*

Acid Solutions:
Acetic
Chromic (5%)
Citric
Ferric Chloride (40%)
Hydrochloric
Nitric (50%)
Sulphuric

 

 

212
Boiling
Boiling
Boiling

150
Boiling
Boiling

 

 

 

40
40
40
40

30
40
30

 

Alkali & selected oakite cleaning solution

212

40

Asphalt binder, tar, other viscous compounds

200
300
400
500

8
7
6
5

Caustic Soda 2%
10%
75%

210
210
180

45
25
25

Coffee (Direct Immersion)

Boiling

90

Dowtherm A®
flowing at 1 ft/sec or more
Non-flowing

 

750
750

 

22
10

Ethylene glycol

300

30

±Fuel Oils
Grades 1 & 2 (Distillate)
Grades 4 & 5 (Residual)
Grade 6 & Bunker C (Residual)

 

200
200
160

 

22
13
8

Gasoline, kerosene

300

20

Glue (heating indirectly using water bath )

100


Liquid ammonia plating baths

50

25

** Lubrication Oils
SAE 10, @ 130°F
SAE 20, @ 130°F
SAE 30, @ 130°F
SAE 40, @ 210°F
SAE 50, @ 210°F

 

250
250
250
250
250

 

22
22
22
13
13

* * Some oils contain additives that will boil or carbonize at low watt densities. Where oils of this type are encountered, a watt density test should be made to determine a satisfactory watt density.

Material being heated

Maximum Operating Temp.°F

Maximum Watts Per Sq. In.*

Metal melting pot

500 to 900

20-27

Mineral oil

200
400

20
16

Molasses

100

2-3

Molten salt bath

800-950

40

Molten tin

600

20

Oil draw bath

600
400

20
24

Paraffin or wax

150

16

Photographic solutions

150

70

Plating solutions:
Cadmium plating
Chrome plating
Copper plating
Nickel plating
Tin plating
Zinc plating


 

40
40
40
40
40
40

Salt Bath

900

30

Sea Water

Boiling

90

Sodium cyanide

140

40

Steel tubing cast into aluminum

500 to 750

50

Steel tubing cast into iron

750 to 1000

55

Heat transfer oils
flowing at 1 ft/sec or more

500
600
650
750

22
22
22
15

Trichloretylene

150

20

Vapor degreasing solutions

275

20

Vegetable oil (fry kettle)

400

30

Water (process)

212

60

Water (washroom)

140

80-90

* Maximum watt densities are based on heated length,and may vary depending upon concentration of some solutions. Watt density should be kept as low as possible in corrosive applications since higher watt densities accelerate corrosive attack on element sheaths. Consult factory for limitations.