Heater Catalog - Watlow

High-Temperature HeatersCeramic Fiber HeatersPerformance Data (Continued)Insulation EffectivenessThe graphs below illustrate the effectiveness of adding6 lb/ft 3 (96 kg/m 3 ) blanket insulation to the backside ofstandard 2 in. (50 mm) thick ceramic fiber heaters. Totalwall thickness of up to 6 in. (152 mm) is shown. Data isfor vertical sides without metal sheathing. Top and bottomsurfaces and surfaces with metal sheaths covering ceramicfiber insulation will vary.External Temperature—°FExternal Temperature—°C4504003503002502001501002252001751501251007550External Surface Temperatures (°F)2200°F Chamber2000°F Chamber1800°F Chamber1600°F Chamber1400°F Chamber1200°F Chamber1050°F Chamber0850°F Chamber1 2 3 4 5 6Total Wall Thickness—inches (Includes Standard 2 in. Heater Thickness)External Surface Temperatures (°C)1200°C Chamber1100°C Chamber1000°C Chamber900°C Chamber800°C Chamber700°C Chamber600°C Chamber25 50 75 100 125 150Total Wall Thickness—mm (Includes Standard 50 mm Heater Thickness)Heat Loss and Energy TransferFor general calculations of heat loss and energy transfer,the Insulation K-Factors and Emissivity graphs are helpful.The K-Factors graph is for ceramic fiber heaters andthe ceramic fiber insulation blanket typically used withthe heaters. This blanket is offered as an accessory byWatlow.Thermal ConductivityThermal ConductivityBTU-inhr-ft 2 -°FW-cmm 2 -C3.02.52.01.51.00.5403530252015Mean Temp. = T Inside + T Outside2Mean Temp. = T Inside + T Outside2Insulation K-FactorsInsulation K-Factors6 lb/ft 3 BlanketTypical Range for Watlow Molded Fiber600 800 1000 1200 1400 1600 1800 2000Mean Temperature—°F96 kg/m 3 Blanket105250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 100010501100Mean Temperature—°CTypical Range for Watlow Molded FiberApplication HintsFor wall thicknesses (T) in cylindrical situations use the“equivalent thickness” conversion.Tcyl. = rout logeroutrin )Where rout is outer radiusrin is inner radius(Emissivity of Heater SurfaceThe Emissivity graph details the normalized emittancevalues for the four surfaces most likely to be encounteredwhen planning Watlow ceramic fiber heater applications.WATLOW ®Total Normal Emittance1.00.80.60.40.201000Emissivity ChartSurface Temperature—°C600 700 800 900 1000 1100High Emissivity CoatingOxidized WireCeramic Fiber BlanketStd. Hot Face CoatingUncoated Unit Surfaces1200 1400 1600 1800 2000 2200Surface Temperature—°F439