Modeling of hot-point drilling in ice

Abstract

Hot-point drills have been widely used for drilling boreholes in glaciers, ice caps and ice sheets. A hot-point drill melts ice through the thermal head at its bottom end. Penetration occurs through a close-contact melting (CCM) process, in which the ice is melted, and the meltwater is squeezed out by the exerted force applied on the thermal head. During the drilling, a thin water film is formed to separate the thermal head from the surrounding ice. For the hot-point drill, the rate of penetration (ROP) is influenced by several variables, such as thermal head shape, buoyancy corrected force (BCF), thermal head power (or temperature) and ice temperature. In this study, we developed a model to describe the CCM process, where a constant power or temperature on the working surface of a thermal head is assumed. The model was developed using COMSOL Multiphysics 5.3a software to evaluate the effects of different variables on the CCM process. It was discovered that the effect of thermal head shape and the cone angle of conical thermal head on ROP is less significant, whereas the increase in the BCF and the power (or temperature) of the thermal head can continuously enhance the ROP.

Experimental Validation of Cryobot Thermal Models for the Exploration of Ocean Worlds

“…We originally chose a parabolic nose shape based on Shreve (1962), who proposed that nose shape has a significant impact on the efficiency of a thermal probe. However, a recent numerical study (Li et al 2021) subsequently suggested that the shape of the nose might not be as influential on the descent speed as previously hypothesized. In addition, system-level metrics that enable likefor-like comparisons between nose geometries have not yet been developed (e.g., ensuring that different geometries have the same carrying capacity), and the confounding variable of operational efficiency ò has not been sufficiently accounted for in any comparisons.…”

“…Brandt et al (2019) provide two models: the first is a precursor to the numerical model in Durka et al (2022) below, but using a heuristic approach to estimate v; the second is a semianalytical extension of the Aamot model addressing assumption (a) via finite element modeling and includes ò as a model input parameter. Li et al (2021) focus purely on the Startup Phase in warm ice using detailed numerical simulations. Durka et al (2022) introduce two models: the analytical Aamot+ model, which relaxes assumption (a) via an experimental fit to the temperature dependence of the thermophysical properties of pure water ice, and the Aamot++ model, which extends this to address assumption (c) by explicitly positing an (unknown) water jacket thickness to estimate ò.…”

Design and performance of the Hotrod melt-tip ice-drilling system

“…We simulate borehole refreezing using a 1-D radial heat transfer model. This model is relatively simple in comparison to other models describing processes at the interface between the melt tip and surrounding ice (Li et al, 2021b). Our model consists of an enthalpy-based formulation of heat diffusion and latent energy exchange across a moving waterice phase boundary (Greenler et al, 2014).…”

Design and Performance of the Hotrod Melt-Tip Ice-Drilling System

“…We simulate borehole refreezing using a 1-D radial heat transfer model. This model is relatively simple in comparison to other models describing processes at the interface between the melt tip and surrounding ice [Li et al, 2021b]. Our model consists of an enthalpy-based formulation of heat diffusion and latent energy exchange across a moving water-ice phase boundary [Greenler et al, 2014].…”