Thermal tips for ice hot-point drilling: Experiments and preliminary thermal modeling

Electrically heated hot points are widely used for drilling in glaciers and ice sheets. To study the effect of input power, axial load, ice temperature, shape, and material of the thermal tip on the hot-point rate of penetration (ROP), a 0.8-m-long drill with 18 changeable thermal tips was designed. The ROP increased with input power for all the thermal tips. Seven tip shapes (cylinder, cosine, ogive, sphere, catenary, parabola, and cone) were tested at the same power level, axial load, and ice temperature, and they exhibited the same ice contact area. The 60° cone-shaped tip demonstrated the highest ROP. The horizontal ring and longitude grooves on the surface of the thermal tips did not improve the drilling performance. The ROP decreased linearly with decreasing ice temperature. Increases in the axial load resulted in increase in the ROP only within the limited range (<20 N or < 8.2 kPa). The ROP of the thermal tip made of copper was more than twice that of the aluminum thermal tip of the same shape. All tested tips were also modeled for temperature distribution inside the thermal tips, and the temperature and heat flux distribution along the outside operating surface of the tips.