Freezing of geothermal borehole surroundings: A numerical and experimental assessment with applications

This study examines the thermal consequences of freezing the ground in the immediate vicinity of geothermal boreholes. First, a one-dimensional radial numerical heat transfer model is developed to evaluate heat transfer from the borehole wall to the ground. The model can account for multiple ground layers in the radial direction and phase change is handled using the effective capacity method. The results obtained from the model are in excellent agreement with the results given by analytical solutions for simple cases. A small-scale experimental set-up has also been built to validate the numerical model using temperature measurements. The apparatus mimics the behavior of a geothermal borehole and uses a homogeneous saturated laboratory-grade sand to reproduce unsaturated and saturated conditions. It is shown that the results of the numerical model are in good agreement with the experimental results.