How should air heating be specified for industrial heating elements?

For air heating, first size the element from airflow, air velocity and inlet temperature, then back-calculate watt density from the allowable sheath temperature, typically a fraction of liquid-duty values. Match tube diameter, fin pitch and material (carbon steel, stainless or high-temperature alloy) to air cleanliness and temperature, and select protection class and terminal box for the site. A fan interlock with over-temperature cut-off is mandatory: if airflow stops, heating must switch off immediately. Fix installation spacing, airflow direction and sensor location on the drawing, and accept on measured outlet temperature, velocity, insulation resistance and watt density.