Borehole Ground Loop 2D: Radial Heat Diffusion

This is the 2D counterpart to the 3D borehole ground-loop simulator, and it models a genuinely different piece of physics: instead of assuming the ground around the borehole is an infinite reservoir at a fixed temperature, it solves the transient radial heat-diffusion equation on a grid of concentric shells running from the pipe wall, through the grout, and out through the native soil to an undisturbed far field. Heat entering or leaving through the fluid-side film and pipe-wall resistance diffuses outward frame by frame, so the temperature right at the borehole wall visibly drifts away from the undisturbed ground temperature under sustained heating or cooling — a real, measurable thermal-depletion effect that a steady-state resistance calculation cannot show. Flow rate, grout conductivity, soil conductivity and simulated time speed are all adjustable, and the model was checked against the analytic logarithmic steady-state temperature profile before shipping.