Electric thermal drills for open-hole coring in ice

• Published in: Polar Science
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2018
• Subjects: Thermal drill; Thermal coring head; Meltwater remova; Polar Science
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=15099; http://id.nii.ac.jp/1291/00015009/

Electric thermal drills are more advantageous than electromechanical drills in temperate, near-temperate, and polythermal glaciers because they can avoid problems arising from refreezing of wet chips, which causes drills to become stuck in the borehole. When the refreezing rate of meltwater in borehole is expected to be too high and there is no considerable englacial water flow, thermal drills with meltwater removal system are optional for open-hole shallow (200–300 m) ice coring. To reach a sufficiently high rate of penetration of approximately 6–7 m h−1, the power density of thermal head should be maintained in the range of 100–110 W cm−2, which can be provided by tubular elements cast integrally with an aluminum or copper annulus. To remove meltwater via air reverse circulation, thermal drills can be equipped with a small blower. The safest and most even mode of water removal is lifting in the form of water film on the wall of air sucking tubes. The maximum water removal rate using a single water-lifting pipe via air reverse circulation created by a blower with a sucking power of 110 airwatts was ∼0.35 L min−1. Assuming a penetration rate of 6–7 m h−1 and the outer and inner diameters of 135 and 110 mm, respectively, of the drill head, the meltwater should be removed at a rate not less than 0.8–1.0 L min−1. In this case, at least three water-lifting pipes should be used in the drill.