Coiled Resistance Wire Wound Elements

Keith Company manufactures wire wound (aka coil resistance wire) heating elements
that work best for air velocities of 5 to 2,000 SFPM. Higher air velocities could cause the
coils to touch each other and short out, so tubular air heaters may have to be considered.
A successful installation of air heating elements consists of the heater itself, an airflow switch
which turns off the power to the heating element if air flow is outside the specs, a high limit
temperature controller installed close to the heating element and the process 
temperature sensor  at the right location in the air stream. Wire wound heating elements are
made from resistance wires like Nichrome 80/20, Kanthal A1, APM and others and fixed onto
a supporting ceramic or porcelain element. We recommend solid state relays or SCRs for
power control for this low mass heaters. 

The low pressure drop due to the large open space makes open coil heating elements the best
choice for applications where large air volumes need to be moved. (example: convection ovens)

We don't recommend wire wound heating elements for glass applications because they can be
the number one cause of contamination because of oxidation at high temperatures. Expansion
and contraction of the heating wire causes small oxidized particles to be ejected into the work space.