Use graph (English or Metric) to plot Outlet Air Temperature vs. Outlet Air Velocity to determine Element Watt Density.
The recommended watt density is based on a maximum element sheath temperature of 1400°F (760°C). Air and other gases that are poor conductors of heat require watt densities matched to the velocity of the gas flow to prevent element overheating. Selecting a lower watt density for the heating elements will extend heater life expectancy.
Element Watt Density is the wattage dissipated per square inch of the element sheath surface and is calculated with the following formula.
Air Velocity (feet per minute)
English
Process Temperature °F – Approximate Sheath Temperature 1400°F
Air Velocity (meters per minute)
Metric
Process Temperature °C – Approximate Sheath Temperature 760°C