delta t - charts for infrared heating

8/3/2019 Delta T - Charts for Infrared Heating

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PROCESS INFRARED HEATING


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SPECTRAL ABSORPTION OF VARIOUS

MATERIALS

100%

80%

60%

40%

20%

1 2 3 4 5 6 7 8 9

WAVE LENGTH (MICRONS)

ABSORPTION

ALUMINUM: Anodized Polished Sandblasted

100%

80%

60%

40%

20%

1 2 3 4 5 6 7 8

WAVELENGTH (MICRONS)

ABSORP

TION

PURE LINEN COTTON CELLULOSE WOOD

100%

80%

60%

40%

1 2 3 4 5 6 7 8

WAVELENGTH (MICRONS)

ABSORPTION

26T: Water

27T: Aluminum

28T: Pure Linen, Cotton and Cellulose Wood

produce uniform radiant distribution. Specific application con-siderations may require the distance to be adjusted.

Materials are selective as to the wavelength accepted toabsorb infrared energy. As can be seen on 38T, PVC willabsorb best at 3.5 microns. The wavelength produced by theheat source is dependent upon the source temperature. It ispossible then to adjust the source temperature and thus the

peak wavelength to match the best spectral absorption rate orwavelength. The formula is:

C =2897

-273F =

5215-459

=5215

459 + F =

2897

273 + C

Thus, if the element temperature is known and thewavelength is desired:

By applying the formula to PVC, based upon 3.5 micronsbeing the desired wavelength, 1025F (550C) would be theemitters surface temperature for the best heat transfer to theprocess. This principle holds true no matter what the con-struction of the heat source. An Incoloy tubular heater, the

resistance wire of a quartz heater, an FP Flat Panel heater ora Black Body Ceramic Infrared heater operating at 842F(450C) would all have the same peak energy wavelength of4 microns. Other characteristics such as penetration andcolor sensitivity would also be the same.

Other common methods of temperature control in infraredprocesses is by varying the voltage input to the elements oradjusting the amount of on-time versus off-time of theelements. These are open-loop control systems and usuallyrequire the constant attention of an operator. A closed loopcontrol system would consist of infrared sensors orthermocouples attached or integral to the heat source, thatwould monitor the temperature of the process or heater,signal a control which in turn would signal an output device todeliver current (or turn off) the heat source. For complete

information, see each respective catalog section, the ThermalSystem Design section or consult OGDEN.

OGDEN offers a number of choices of heating elements forinfrared applications. The advantages, limitations andadaptability of each will determine which is most suitable.For instance, the emissivity/conversion ratio of an Incoloy

sheath tubular heater is about 55%, a quartz heater's is 60%,an FP Flat Panels is about 80% and the Black BodyCeramics is over 90%. This indicates that close to all of theinfrared energy produced by the ceramic heater will beabsorbed by the process. This type of efficiency may be themost important consideration. But the process may require aheat source with a quick response time. The quartz heaterwill likely be chosen, or an expensive retraction system maybe necessary should a line stoppage occur. The Incoloy

sheath tubular heater could be the best selection because ofits ruggedness and ability to be formed to suit spacing orconfinement requirements. An FP Flat Panel heater may beselected because of the wide area coverage.

Although much technical information is available in this andother sources, trial and pilot testing are often necessary toestablish if a process is suitable for infrared. The wattagerequired, watt density, process time cycle, distance from theheat source to the material and how well the materialabsorbs infrared can perhaps only be determined by thismethod. Should any uncertainty exist, contact OGDEN. Theinformation necessary may already be on file, becauseOGDEN has successfully solved scores of infrared heatingproblems.


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delta t - charts for infrared heating

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