Experimental investigation of water freezing and estimating refreezing time in ice boreholes

Borehole closure owing to the refreezing of meltwater poses a serious limitation in ice thermal drilling, and estimates of the refreezing rate are essential for determining safe drilling rates. In this paper, we describe the results of water cooling and freezing experiments in cylindrical ice holes with a diameter of 200 mm at a setup temperature within the range of −20 to −50 °C. These experiments represent a new means of estimating cooling/refreezing rates using two mutually perpendicular diametric sets of thermoresistors installed inside the holed ice sample. In a colder environment, water cooled/froze faster than in the warmer setup: the cooling rates for a hole diameter of 200 mm were 33.3 to 38.5 °C h⁻¹ at −50 °C and 8.5 to 9.5 °C h⁻¹ at −20 °C, while the average freezing rates were 32.3 to 35.1 mm h⁻¹ at −50 °C and 14.9 to 20.9 mm h⁻¹ at −20 °C. Data from the refreezing rates are applied for practical ice drilling purposes, and a method for predicting safe hot-point drilling performance in cold ice is suggested.