| Due to environmental factors or city planning, high-power transmission lines overhead are often not suitable for urban areas. Therefore, using directly buried power cable or placing transmission line in underground tunnel is an alternative. Thermal characters of these dense loaded tunnels become a challenge when heat flux generated from the conductor is subjected.This thesis, firstly taking round-shaped underground tunnel into account, offered an effective way of using 2D/3D FDM (Finite Difference Method) to predict the temperature rising in years ahead. Numerical simulation is realized in C++. 2D, unsteady heat conduction model is used to predict the temperature without ventilation. For ventilation anaylsis, model is based on 3D model considering the heat transfer between air and tunnel. Sharp temperature rising happens only during the first 15 years, after which the temperature rising slows down. For ventilation effect analysis, it is predicted that in Shanghai meter condition, ventilation during winter could effectively reduce the temperature rising in tunnel.Then, the thesis gives introduction to our verification work to validate the numerical results. Similarity experiment is designed which reduces the length dimension to 1/100 and time dimension to 1/10,000. Experiment is carried out within lab thanks for this small-scaled design. On-site measurement is also used to verify the results of ventilation simulation. Both similarity experiment and on-site measurement shows good agreements with that of simulation results.Based on the verified simulation code, some predictions are made for with monitored heat load. Effects of tunnel depth, diameter as well as heat load are analysed. Simulation results show that, under current heat load, temperature of tunnels in Shanghai should not exceed that of 35℃. Main reason that caused the temperature rising is heat load. Cutting the tunnel depth while increasing its diameter results in lower temperature rising. Ventilation should be applied during winter when outer temperature is low. High ventilation velocity results in better heat dissipation. Interval ventilation could reduce the time needed for fan working while prolong its life time.Finally, ventilation effect for Expo tunnel is analysed. The Expo tunnel is predicted to have rather dense loads which may result in overheating. Calculation results show that, temperature for dense loads may exceed 35℃and may reach 65℃. Ventilation requirements are given for the management of tunnel. Continuous ventilation could control the temperature well within 35℃with ventilation velocity being 3m/s and ventilation time no less than 120 days. An optimum ventilation algrithm is introduced which control the startup and shut-down of fan according to a close-loop proposal. Time needed for ventilation of the optimum proposal could be kept to be around 100 days per year. Based on the long-term characteristic of tunnel temperture and heat load, a standard is concluded which include the relationship of temperature, load and dimension. This standard could be used by the design or management division for the tunnel.This thesis provides an effective way of solving this problem and could be used as a reliable tool for the design and installation of tunnels.
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