Numerical evaluation of ice borehole PCM problem and temperature field in RECoverable Autonomous Sonde (RECAS) system

When the RECoverable Autonomous Sonde (RECAS) penetrates ice, hot point drilling drives ice water phase change that governs borehole closure and cavity formation above the sonde. This study develops a Stefan problem-based numerical model for ice-water phase change material (PCM) under RECAS conditions with ice ambient temperature from −60 °C to −2 °C and meltwater at 0 °C. An implicit finite difference scheme tracks the phase interface and the temperature field to quantify the closure process. During the freezing process, the average and minimum closure rate range from 0.33 to 23.30 mm/h and from 0.24 to 17.39 mm/h. The minimum closure rate occurs from 2.00 to 88.75 h, and appears at radii from 52.48 to 74.91 mm. The average closure rate is 1.34 to 1.39 times the minimum value across the ambient temperature range. Using three detection resolutions, the maximum values of the Thermal Influence Boundary (TIB) during freezing and cooling are 10.48 and 12.26 times the initial radius, respectively. Accordingly, empirical fitting formulas are established to parameterize characteristic closure rates, their radial positions and occurrence time, and cavity height, providing the guidance for RECAS engineering decisions. • RECAS-oriented Stefan PCM model predicts borehole refreezing and closure behavior. • Fitting formulas link ambient temperature to borehole freeze and closure metrics. • Spatiotemporal evolution of the temperature field is quantified during freezing/cooling.