Millimeter-Wave Heating, Radiometry, and Calorimetry of Granite Rock to Vaporization

• Published in: Journal of infrared, millimeter and terahertz waves Vol. 33; no. 1; pp. 82 - 95
• Main Authors: Woskov, Paul, Michael, Phil
• Format: Journal Article
• Language: English
• Published: Boston Springer US 2012
• Subjects: Calorimetry; Classical Electrodynamics; Electrical Engineering; Electronics and Microelectronics; Emissivity; Engineering; Granite; Heating; Infrared; Instrumentation; Radiometry; Rock; Vaporization; Calorimeter; Heterodyne receiver; Molten granite; Millimeter-wave drilling; Rock vaporization; Thermal dynamics; Engineered geothermal systems; Gyrotron; Radiometer
• DOI: 10.1007/s10762-011-9851-0
• EISSN: 1866-6906
• ISSN: 1866-6892

Millimeter-wave (MMW) technologies can provide unique heating and diagnostic capabilities to research the thermal dynamics of materials to extreme temperatures. The MMW properties of rocks in the molten state up to their vaporization temperatures are not well known. Using a 28 GHz gyrotron beam collinear with a 130 GHz radiometry view in a calorimetric chamber, the transitions of granite rock specimens through solid phases, melting, and vaporization were observed, including release of trapped trace gas (<0.07%). The 28 GHz emissivity of molten granite was observed to be approximately constant at 0.66 ± 0.03 up to vaporization where it increased to 0.70 ± 0.03 at an equilibrated temperature of 2710 ± 120°C. An analysis of the thermal power balance during a 76 s steady state vaporization time period indicates that the MMW emissivity of the molten granite is larger than in the infrared. The observations support the possibility that MMW thermal ablative penetration into hot crystalline rock formations could be a more practical approach than infrared laser drilling to access deep resources.