Modification on constant temperature boundary considering conjugate heat transfer of brine turbulent flow in brine artificial ground freezing method

Abstract

The brine artificial ground freezing (AGF) method is an effective construction technique extensively employed in underground engineering reinforcement. In the numerical simulation of soil temperature field associated with the brine-AGF method, researchers typically impose a constant temperature boundary on the surface of the freezing pipe. This approach circumvents the need to simulate brine flow, thereby simplifying the numerical simulation and enhancing computational efficiency. However, questions arise regarding the accuracy of these simulations: Is the soil temperature field consistent with a constant temperature boundary model when considering brine flow? These concerns remain unresolved at present. Consequently, based on the conjugate heat transfer mechanisms, this paper establishes a numerical model for coupling brine-freezing pipe-soil to analyze variations in soil temperature fields under brine turbulent conditions. Compared to the constant temperature boundary model, it was observed that overall soil temperatures in the brine turbulent flow model are generally lower. However, they are 4 °C higher at the bottom of the freezing pipe. Therefore, this paper proposes a modified temperature boundary that incorporates both Reynold's number of brine and freezing pipe depth considerations. Results indicate that this modified temperature boundary yields a soil temperature field closely aligned with that produced by brine flow models. Furthermore, compared with the model test, the modified temperature boundary can respectively reduce the temperature difference from 3.4 °C to 2.1 °C and from 1.5 °C to 0.3 °C when the different brine flow velocities are considered. The proposed modified temperature boundary not only retains advantages such as simplified modeling and rapid computation inherent in constant temperature boundary but also enhances calculation accuracy significantly. This work provides valuable insights for advancements in brine-AGF engineering.