RADIANT HEATING WITH INFRARED - Watlow

22
Transmission %
Transmission%
Transmission Spectrum for Polyethylene (Fig. 12)
Transmission Spectrum for Polyvinyl Chloride (Fig. 14)
100
80
60
40
20
0
2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0 13.0 14.0 15.0 16.0
Absorption Bands = 3.2 to 3.6 microns, 6.8 to 12.5 microns
2. Determine the optimum heater temperature for most efficient heating of the
plastic.
For maximum absorption, a heater temperature that corresponds to a peak
energy wavelength of 3.4 microns is needed. Use Wien’s Displacement
Law to calculate this temperature, or see Figure 4.
T = 5269 °R micron - 460
Wavelength (microns)
T = 5269 °R micron - 460
3.4 microns
T = 1090°F
In reality, tuning the heater to the proper wavelength is not that critical.
A heater operating in the range of 900-1300°F is acceptable. We choose to
use a heater temperature of 1100°F.
3. Determine how much energy is delivered to the plastic with heaters
operating at 1100°F.
A. Determine the view factor (F)
M = N = 48 = 8
6
From Figure 8:
F = 0.8
Wavelenght (microns)
Wavelength (microns)
B. Calculate the effective emissivity
Emissivity of heater = Eh = 0.85
Emissivity of plastic = Ep = 0.95 (Most plastics reflect about 5%)
E = 1 = 1 = 0.81
1 + 1 - 1 1 + 1 - 1
Eh Ep 0.85 0.95
Polyvnyl Chloride