RADIANT HEATING WITH INFRARED - Watlow

Note: The spacing between source
and load can also affect uniformity.
Generally, the closer the heater is to
the load, the more pronounced will
be the effects of heater nonuniformity.
Increased distance allows
the radiant energy to “spread” and
become less focused, but at the
possible loss of efficiency due to
greater edge losses.
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Some methods of grouping heaters to reduce the effects of no-heat zones are
given below.
• Staggered Units
By shifting alternate units a few
inches sideways, the no-heat
between units can be spread out
and its effects reduced in
magnitude. (All units are the
same.)
• Alternate Size Units
Combinations of long and short
units can be used to spread out
the effects of the no-heat area. A
minimum of two designs are
required.
• Diagonal Positioning
By setting all units in the assembly
at an angle, as shown, the gap
between heaters is shifted across
a greater width, relative to the
product flow. This reduces the
differential heating in that area.
• Zoning
The shaded areas represent where
the extra power could be applied
to offset the edge losses and nonuniformity
at the center. The
heaters must be built with special
higher watt densities or separate
control zones in these areas. The
size of zoned area and the higher
power differential used depend on
the specific application and the
heater design.
Mounting
Panel heaters are available with threaded studs welded to the back sheet
metal for mounting purposes. The studs are typically located approximately on
12 inch centers.
All metal cased radiant heaters expand as they heat up, and room must be
provided at the ends and sides of the unit for about one percent (1%) growth.
Holes for mounting studs must be oversized or slotted. The mounting studs
must be free to move in the oversized hole. On long units, if the studs are
tightened firmly to the mounting frame, either the panel will warp or the studs
will be bent.