The Effect of Alignment and Target Material upon Temperature in Halogen Projector Bulb Heating Experiments
Abstract
Incandescent light produced by halogen projector lamps can be used to heat minerals suspended on thermocouples for the purpose of extracting noble gasses under well-known thermal conditions. Experiments were performed to optimize the efficiency of the heat source. An ENX 82 volt, 360 watt bulb with a gold-coated reflector directs more of the infrared spectrum at the sample and is about 65% more efficient than the same bulb with a standard dichroic coating. I used a 3-axis manual positioning device to precisely determine the focal point of the bulb so that it could be best positioned to heat the sample. The focal point is about 25 mm from the filament. Increasing this distance to 45 mm and 65 mm decreases temperature by 27% and 58% respectively. Staying in the focal plane but moving 10 mm from the focal point decreases temperature by about 30%. I also investigated 5 different types of target material (Cu, Al, Ti, Ta, and Mo). A 1 square cm target of a specific metal was placed beneath the lamp at the focal point. Power output was fixed at 2 amps. An inconel-shielded type K thermocouple probe with no target attached produced a temperature of 133°C under these conditions. The target absorbs heat from the lamp but loses it by thermal conduction to the thermocouple. Cu and Al have the highest reflectivity and the highest thermal conductivity and recorded the lowest temperatures (73±3°C and 104±8°C respectively). I found that Ti, Mo, and Ta targets outperformed Cu by 211% (226±19°C), 351% (328±7°C), and 124% (163±13°C) respectively. This variation makes sense in terms of the thermal conductivity and reflectivity of these materials. Coating a Mo target with carbon produced the best results (395°C or 444% more efficient than Cu). Experiments under vacuum produced similar results. In conclusion, samples enclosed in Mo foil and suspended 25 mm from the filament will yield the most efficient arrangement for heating samples with a ENX halogen projector lamp. Although projector bulb heaters can attain temperatures in excess of 900°C under vacuum conditions, extreme caution should be used to shield the window from thermal damage. Mo foil targets should also prove superior for heating with near-infrared lasers that operate at wavelengths similar to that produced by halogen light sources.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFMED41A0485G
- Keywords:
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- 3694 MINERALOGY AND PETROLOGY / Instruments and techniques