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| Always consider proper watt density for your electric heater application. |
Reprinted with permission from Hotwatt
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 Lead-Stereotype pot) | 600 | 35 on casting |
| 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 BCE for limitations.
Important: The above values are estimates. It is strongly suggested that you discuss your requirement with an application expert before you apply any electric heating element in to a process where the proper watt density is unknown.