Numerical investigation of partially-wetted geothermal heat pipe performance

• A transient, 2D model for outer region thermal diffusion is proposed.
• Wetting has strong influence on polyamide heat pipe performance.
• Borehole diameter has a significant influence on performance.
• Borehole filling thermal conductivity has strong influence on performance.
• Soil thermal conductivity is of minor importance in the studied time range.

The influence of different parameters on the performance of partially-wetted geothermal heat pipes is studied in this contribution. For this purpose, a transient, two-dimensional numerical model has been developed, verified against an analytical solution, and series of tests have been conducted with various wetting ratios, tube material (steel and polyamide), borehole radius, and the thermal conductivities of the borehole filling (grout) and the soil. It is found that the wetting ratio has a strong influence on the performance of the polyamide tube, whereby the thermal conductivity of the filling and the borehole radius influence both tubes strongly. The influence of the soil thermal conductivity is of minor importance in the time range under investigation.