Geothermal field thermal response experiment of large diameter energy shaft: A practical calculation method for thermal property parameters

In the thermal response experiment of energy shafts, an accurate heat transfer model is essential for effectively determining the thermal properties of the surrounding soil in real-time. This paper presents an innovative cylindrical concrete test structure designed for field thermal response experiments of simulated energy shafts, aiming to reduce testing errors and design costs. Based on superposition theory, we have developed an unsteady heat transfer model that accounts for the differences in thermal properties between structures and soil, along with a practical calculation method for field applications. The results indicate that, compared to traditional linear heat source models and hollow column source models, the proposed model more accurately describes the heat transfer process in energy shafts. This improvement helps avoid calculation errors associated with neglecting material differences in the structure. Furthermore, the model effectively calculates the thermal conductivity of the soil surrounding the structure, as well as the thermal resistance within the structure. While maintaining a level of calculation accuracy comparable to that of solid column heat source models, the computational workload is reduced by more than half. Additionally, the practical calculation method is well-suited for various engineering application scenarios, ensuring both the accuracy of data processing and significantly enhancing the convenience of analyzing field thermal physical test data. The findings of this research provide a valuable reference for thermal response testing and the optimal design of energy shafts.