Research On Local Ventilation Method And Heat Exchange Effect Of Cable Cabins In The Long-distance Utility Tunnel

Technical code for urban utility tunnel engineering(GB 50838)stipulates that the construction of a utility tunnel every 200 m needs to set a fire interval,and the ventilation interval should overlap with the fire interval.The engineering requirements of projects crossing rivers and mountains have led to extended tunnel ventilation intervals and the placement of fire doors within a single ventilation interval.These new phenomena significantly exacerbate the challenges associated with ventilation and heat dissipation.As the tunnel lengthens,the temperature gradually increases,and the fire doors in tight spaces impede heat dissipation,creating high-temperature areas.In the operation of the utility tunnel,the communication cable cabin requires continuous heat dissipation,which necessitates prolonged and high-volume ventilation,resulting in higher operating and management costs than other cabins.Urgent research is needed to address heat dissipation in the cable cabin to prevent safety hazards caused by elevated tunnel temperatures.Enables the tunnel to control the cabin temperature,even when the ventilation interval is extended.Based on the above-mentioned global ventilation of the tunnel,this paper proposed a method of local ventilation to enhance heat exchange,which reduced the number of air changes by targeting ventilation control to local high-temperature areas.The research targeted ventilation control in specific high-temperature regions,combining numerical computational fluid dynamics(CFD)simulations with scaled-down experimental verification.A comparative analysis was performed between conventional and local ventilation tunnels.The cooling patterns resulting from different local ventilation strategies were studied in detail.A segmental approach was adopted for the qualitative study of both tunnel types,focusing only on the area regulated by the jet fans within the tunnel.An orthogonal experimental methodology was used to quantitatively investigate the various parameters of the jet fans and the fire door area.This methodology helped to determine the optimal arrangement of local ventilation and the ideal size of the fire door area,considering different boundary conditions.The final local ventilation solution was derived by comparing the heat dissipation efficiency of the optimized tunnel with that of the conventional tunnel using three different temperature evaluation criteria.The results of this study demonstrated the feasibility of implementing local ventilation methods in cable cabins within long-distance utility tunnels.Using jet fans and fire doors as part of the local ventilation approach reduced cabin temperatures.Jet fans disrupted the temperature continuity in the upper tunnel area,creating a triangular area with lower temperatures immediately below.There was also a noticeable cooling trend at the air outlet.However,once outside the control range of the jet fan,the tunnel temperatures rose again.There was a significant reduction in temperature behind the fire door and a high-temperature build-up in its upper area.The tunnel’s total air volume interacted with the jet fan’s local air volume.Increasing the number of air exchanges for the same total air volume increased the heat dissipation in the fan control area,resulting in a lower heat exchange rate.Conversely,a higher total airflow would reduce the global heat exchange effect.Optimization of the local ventilation method revealed the optimum operating parameters for cable cabins within the utility tunnels.These parameters include an inlet air volume of 0.7 of the total air volume,a fan air volume of 10% of the total air volume,a fan angle of 5°,a wall temperature set at 15°C,a fan diameter of 300 mm and a duct fire door area of 0.9 times the standard fire door area.Installation of the jet fan at a distance of 50 m behind the fire door allows the cabin to achieve the most effective cooling result.The evaluation of the optimized local ventilation method showed that compared to the conventional tunnel design with 2 air changes per hour,the optimized tunnel achieved similar cooling effects with only 0.7 times the total air volume.Applying the local ventilation method provides effective cooling within the targeted area of the cable cabin while showing variations in other areas.It was observed that increasing the number of air changes leads to reduced heat transfer and lower temperatures at the exit section under optimized working conditions.The local ventilation method is particularly suitable for utility tunnels characterized by low wall temperatures and a reduced number of air changes.The research in this paper successfully addresses the problem of high-temperature regions within the back section of long-distance utility tunnels by spreading the local heat transfer pressure to the global.These findings are of immense significance in reducing the frequency of air changes required in the utility tunnel,improving the operational efficiency,extending the life of the equipment and providing valuable reference and innovative ideas for future ventilation and heat exchange systems in utility tunnel construction.