Heater Catalog - Watlow

Cartridge/Insertion HeatersMetric FIREROD Cartridge HeatersMaximum Allowable Watt Density (Continued)Watt Density vs. Ambient AirThe Watt Density vs. Ambient Air Temperature graphshows the maximum allowable watt density when onemetric FIREROD heater is operated in air or similar gas.For metric FIRERODs grouped in a single row, with noless than one diameter between elements, multiply valuefrom graph by 0.95. When a reflector is placed behindthe heaters, multiply the maximum allowable watt densityvalue from the graph by 0.85.Ambient Temperature—°C800600400200Maximum Watt Density vs.Ambient Air Temperature0 2 4 6 8Watt Density—W/cm 2Sheath Temperature in Ambient AirThe Sheath Temperature in Ambient Air graph indicates1200the watt density required to bring a metric FIRERODheater to a given sheath temperature when operated in20°C (70°F) ambient air.1000At 7 W/cm 2 (44 W/in 2 ), the sheath temperature will be800790°C (1450°F). At this temperature, one year of heaterlife would be expected, provided cycling is not toofrequent. Higher temperatures would result in reduced600heater life.4002000Watt DensityóW/cm 2Watt Density in Moving AirMaximum Watt DensityThe Watt Density in Moving Air graph gives the maximumin Moving Airallowable watt density of a metric FIREROD heater in22.5Entering Airmoving air.up to 95°C20.5If the volumetric flow rate of air is known in m 3 /s (or CFM),divide this value by the net free area in m 2 (or ft 2 ) around17.5the heater to determine air flow velocity. The net free area15.0is the total area of the enclosure minus the area occupiedby the heater.12.510.07.55.02.55 10 15Watt Density—W/cm 2FIREROD Sheath Temperatureó °CAir Velocity Past Heater—m/sec0Sheath Temperature in 20°C (70°F)Ambient AirNot Pre-OxidizedPre-Oxidized2 4 6 8FIREROD—Parallel to Air FlowFIREROD—Perpendicular to Air Flow2051