Thermal transport in CO2 laser irradiated fused silica: in situ measurements and analysis
In situ spatial and temporal temperature measurements of pristine fused silica surfaces heated with a 10.6 {micro}m CO{sub 2} laser were obtained using an infrared radiation thermometer based on a Mercury Cadmium Telluride (MCT) camera. Laser spot sizes ranged from 250 {micro}m to 1000 {micro}m diameter with peak axial irradiance levels of 0.13 to 16 kW/cm{sup 2}. For temperatures below 2800K, the measured steady-state surface temperature is observed to rise linearly with both increasing beam size and incident laser irradiance. The effective thermal conductivity estimated over this range was approximately 2W/mK, in good agreement with classical calculations based on phonon heat capacities. Similarly, time-dependent temperature measurements up to 2000K yielded thermal diffusivity values which were close to reported values of 7 x 10{sup -7} m{sup 2}/s. Above {approx}2800K, the fused silica surface temperature asymptotically approaches 3100K as laser power is further increased, consistent with the onset of evaporative heat losses near the silica boiling point. These results show that in the laser heating regime studied here, the T{sup 3} temperature dependent thermal conductivity due to radiation transport can be neglected, but at temperatures above 2800K heat transport due to evaporation must be considered. The thermal transport in fused silica up to 2800K, over a range of conditions, can then be adequately described by a linear diffusive heat equation assuming constant thermal properties.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 970141
- Report Number(s):
- LLNL-JRNL-414595; JAPIAU; TRN: US201003%%382
- Journal Information:
- Journal of Applied Physics, Vol. 16; ISSN 0021-8979
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
42 ENGINEERING
BOILING POINTS
CADMIUM TELLURIDES
EVAPORATION
HEAT LOSSES
HEATING
INFRARED RADIATION
LASERS
MERCURY
PHONONS
RADIANT FLUX DENSITY
RADIATION TRANSPORT
SILICA
TEMPERATURE MEASUREMENT
THERMAL CONDUCTIVITY
THERMAL DIFFUSIVITY
THERMODYNAMIC PROPERTIES
THERMOMETERS
TRANSPORT