Simulation Research And Optimization Of Ventilation System Of Long Distance Cable Tunnel

In the previouselectric cable tunnel projects,due to the small cross-section of the tunnel,short laying distance and relative low voltage level,the ventilation requirements are generally not considered.Even in hot areas,when the process major clearly requires,natural ventilation is often used.With the continuous deepening of urban development today,in order to adapt to the restrictions of urban landscape and planning,more and more high-voltage lines are now required to be laid with cable tunnels.It is characterized by a complicated tunnel path and a large cross-section.The construction mostly adopts methods such as digging and pipe jacking,and the voltage level of the internally laid cable is relatively high,the number of cables is large,and the cable itself generates a large amount of heat.Therefore,the standards requirements for the design of such cable tunnel ventilation are also getting higher and higher.Restricted by geographical conditions,more and more long-distance high-voltage cable tunnel projects are being built across the rivers in China,and there is little research on the ventilation system applied to the cooling of the tunnel and the industrial stardardfor cable tunnel ventilationare also relatively simple.In general,the air supply and exhaust fans are designed only according to the number of air changes to eliminate the heat dissipation of the tunnel.The design of this ventilation system can meet the requirements of tunnel use when the ventilation interval is short.However,for the ultra-long ventilation zone of 500 meters or even more than 1000 meters,whether such ventilation system can meet the requirements of the tunnel temperature yet not exceeding the standard needs further study.First thermal environment factors in the cable tunnelare analyzed,that is,the main heat gain in the tunnel comes from the heat generated by the cable itself.The heat dissipation inside the tunnel is mainly the heat exchange heat dissipation through the tunnel enclosure and soil.The ventilation system is mainly to take away the remainingheat.On the other hand,the ventilation system also needs to consider the amount of fresh air required for personnel maintenance and the amount of smoke exhausted after the accident.In this paper,the cable tunnel project across the Bahe River on the East Third Ring Road in Xi’an City is selected as an example for calculation and simulation study.The three-dimensional modeling of Fluent is used to simulate the effect of outdoor ventilation system and the water cooling and ventilation system of the cable tunnel on the temperature field and velocity field in the tunnelunder the outdoor high temperature in summer.It is concluded that when the outdoor air temperature exceeds 30 ° C,the air supply and exhaust fans alone cannot meet the requirement that the temperature in the tunnel does not exceed 40 ° C.In the water cooling and ventilation system,the cooling water reduces the temperature of the supply air and increases the temperature difference between the supply and exhaust air.Therefore,it can meet the internal temperature requirements of the tunnel under the high outdoor temperature in summer.Combined with the project cases,the economic and energy saving of the two ventilation schemes are compared and analyzed.Although the initial investment of the water cooling ventilation system is relatively increased,the future operating costs will be lower than the ordinary ventilation system.In order to make the comparison more intuitive,this article uses a comprehensive cost analysis method,that is,a unit heat dissipation cost comparison method.It is concluded that the water cooling ventilation system is superior to the ordinary ventilation system.In terms of energy saving,since the water cooling and ventilation system uses natural water for cooling,it belongs to the renewable energy utilization system,so it has significant energy saving benefits.Finally,it is hoped that through the research in this paper,it can provide a certain reference for the design of the ventilation system of long-distance power cable tunnels in the actual engineering design work in the future.It provides a valuable reference for the further research work in the cable tunnel ventilationsystem.