Numerical simulation of heat transfer processes of cone-cylinder pipe and cooling effects of thermosyphon along the Qinghai-Tibet DC Interconnection Project
For studying thermal stability of tower footing along the Qinghai-Tibet DC Interconnection Project, a coupled heat transfer model among air, thermosyphon and soil is established. Based on the model, heat transfer processes around the cone-cylinder pipe and cooling effects of the thermosyphon are simulated by finite element method. Results from the numerical simulation indicate that in cold seasons as thermosyphon works, ground temperatures around the thermosyphon have great gradients and distribute as a spindle, which reveals a remarkable cooling effect of thermosyphon. Meanwhile, cold energy from thermosyphon flows quickly to base of cone-cylinder pipe as high thermal conductivity of the concrete pipe. As a consequence, extensive cold permafrost develops beneath the pipe, which is good for cone-cylinder pipe. In warm season, thermosyphon does not work and shallow ground temperatures are determined by air temperature. Also since high thermal conductivity of the pipe, the maximum seasonal thawing depth near pipe is obviously greater than that beneath original ground with a difference about 35 cm. Ground temperature around the pipe is uniform between profiles with and without thermosyphon. Quickly cooling processes of ground temperature near the pipe occur mainly within the first 5 years after application of the thermosyphon. And then, depth of permafrost table and permafrost temperatures increase slowly as air temperature increase. Overall, under the scenario of climate warming, soil beneath cone-cylinder pipe still keeps frozen, which meet the need of the project.