Temporal and spatial evolution of temperature field of single freezing pipe in large velocity infiltration configuration

Abstract By accurately controlling the flow velocity and direction of the seepage field and fully considering the influence of the flow and heat-transfer boundary conditions, a large-scale, hydrothermal, coupled-physical-model test system was constructed. The temporal and spatial evolution of the temperature field of single freezing pipe in large velocity infiltration formation was studied by this system. The experimental results were analyzed based on the characteristics of heat conduction and convective heat transfer. The analysis results showed that when the seepage velocity v = 0, 3, 6 and 9 m/d, the time required for the freezing temperature field formed by single freezing pipe to enter the stabilization phase was 28 h, 36 h, 24 h and 20 h, respectively. And when the seepage velocity v = 3 m/d, the temperature drop rate of the frozen region decreased, however, after entering the stable freezing phase, the differences in final shape and extent of the frozen front compared to those of the no-flow state were smaller. When the seepage velocity v = 6 and 9 m/d, the temperature drop rate of the frozen region was further reduced, and the temperature of the upstream region was significantly higher than the downstream region. After entering the stable freezing phase, the extents of the upstream/side/downstream expansion of the freezing front were reduced by 72.27%/52.83%/27.73% and 76.89%/55.89%/39.07%, respectively. And the maximum value that the extended radius Rs could reach on both sides of the freezing pipe was 236/199/110/101 mm, for v = 0/3/6/9 m/d. Based on the results of model tests, an analytical expression of the steady-state temperature field of single freezing pipe under the action of seepage field was derived. The calculation results of the formulas showed that as the seepage velocity increased, the area of the single-pipe freezing zone decreased, the proportion of the low-temperature zone increased, and the average temperature of the temperature field decreased.