Heater Catalog - Watlow

Reference DataPower CalculationsConduction and Convection HeatingRadiant HeatingWhen the primary mode of heat transfer is radiation, weadd a step after Equation 5.Equation 6 is used to calculate the net radiant heattransfer between two bodies. We use this to calculateeither the radiant heater temperature required or (if weknow the heater temperature, but not the power required)the maximum power which can be transfered to the load.Equation 6—Radiation Heat TransferBetween Infinite Size Parallel SurfacesP RA=S (T 4 1 - T 4 2)( 1 ef)(144 in 2 /ft 2 ) (3.412 BTU/Wh)ffFEmissivity Correction Factor (e f )e 1 1f = +e S e - 1 Le1 f = +e SD SD L1- 1( e L )( )1 De f = + S - 1e 1S D xe L Lplane surfacesconcentric cylindersinner radiating outwardconcentric cylindersouter radiating inwarde S = heater emissivity (from material emissivity tables)e L = load emissivity (from material emissivity tables)D S = heater diameterD L = load diameterP R = power absorbed by the load (watts) - fromequation 4 or 5A = area of heater (in 2 ) - known or assumedS = Stephan Boltzman constant= 0.1714 10 • -8 (BTU/hr. sq. ft. °R 4 )T 1 (°R) = emitter temperature (°F + 460)T 2 (°R) = load temperature (°F + 460)e F = emissivity correction factor - see EmissivityCorrection Factor information to the rightF = shape factor (0 to 1.0) - see Shape Factor forRadiant Application graph to the rightShape Factor FShape Factor for Radiant Application1.00.70.50.40.30.2Shape Factor for Radiant Application10.04.00.10.20.070.050.10.040.030.020.010.1 0.2 0.3 0.4 0.5 1 2 3 4 5 10 20M2.01.00.60.4NFor Two Facing Panels:N =(Heated LengthDistance to Material)M =(Heated WidthDistance to Material)WATLOW ®547