How should radiant heating be specified for industrial heating elements?

Radiant heating is specified from surface load and view factor: derive the heated length and tube spacing from the workpiece's absorbed power and furnace geometry, then correct for wall reflectivity and shadowing. Match tube diameter, sheath material and watt density to the furnace temperature; in high-temperature zones the watt density should be reduced to prevent hot spots, oxidation and distortion. Mount tube rows facing the workpiece at even spacing, slightly tighten spacing at edges to offset heat loss, and allow for thermal expansion. Place the sensor where it sees the real workpiece condition, using multiple points averaged if needed. Verify by measured sheath temperature, power tolerance and cold insulation resistance, and record the heat-up curve.