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: |
212 150
|
40 30
|
Alkali & selected oakite cleaning solution | 212 | 40 |
Asphalt binder, tar, other viscous compounds | 200 | 8 |
Caustic Soda 2% | 210 | 45 |
Coffee (Direct Immersion) | Boiling | 90 |
Dowtherm A® |
750 |
22 |
Ethylene glycol | 300 | 30 |
±Fuel Oils |
200 |
22 |
Gasoline, kerosene | 300 | 20 |
Glue (heating indirectly using water bath ) | 100 | |
Liquid ammonia plating baths | 50 | 25 |
** Lubrication Oils |
250 |
22 |
* * 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 | 20 |
Molasses | 100 | 2-3 |
Molten salt bath | 800-950 | 40 |
Molten tin | 600 | 20 |
Oil draw bath | 600 | 20 |
Paraffin or wax | 150 | 16 |
Photographic solutions | 150 | 70 |
Plating solutions: |
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 | 500 | 22 |
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.