Study On Ventilation Rate Of Urban Underground Utility Tunnel

With the acceleration of city construction in China,cities over the country have promoted the construction of underground pipe gallery to laying various municipal pipelines,and a series of problems have been solved,like: pipeline easily affected by external force and the occurrence of pipeline rupture,pipeline maintenance,addition of frequent excavation of a series of problems in road construction etc.Ventilation systems are usually required to exclude residual heat and internal storage of harmful gases.However,there is not a set of effective and effective calculation method in determining the amount of ventilation,and further research is needed.This paper summarized the commonly used form of mechanical ventilation pipe gallery.The advantages and disadvantages of all kinds of mechanical ventilation are studied by means of theoretical analysis and numerical simulation.On the basis of the numerical simulation results,the AHP-fuzzy comprehensive evaluation method is used to evaluate and optimize all types of mechanical ventilation.The results show that in a row to form mechanical ventilation optimal choice.Based on the optimal form of mechanical ventilation,according to the characteristics of the pipeline,utility tunnel is divided into the comprehensive tunnel and the gas tunnel,and the ventilation characteristics are studied respectively.Comprehensive tunnel,first studied the influence of outside air temperature,soil temperature,section perimeter,fire partition length,air exchange rate,power cable number and thermal exhaust pipe diameter on the average temperature,and the influence of the above factors as variables,using the orthogonal experiment method to establish a variety of compartment model and the numerical simulation;then the simulated data fitting power tunnel ventilation calculation formula,the verification shows that the relative error is less than 1%,good fitting results;finally proposed and verified by numerical simulation of thermal tunnel keep 2 / hour ventilation frequency can meet the needs of the hypothesis.The gas tunnel,first analyzes the gas under the condition of normal ventilation leakage after different leak sizes corresponding to the corresponding detector alarm time,the alarm response time increases with the gas pipeline pressure decreases with the increase of discharge,and the leakage distance increases,the leakage of small size can trigger the alarm conclusion;and then study the tunnel different concentration of indoor gas pipeline pressure under accident conditions corresponding to the variation of flow rate,the gas concentration control will stabilize at a safe level(<20%LEL)minimum ventilation rate required is 12 times / h respectively(0.4MPa),15 hours(0.8MPa)and 27 hours(1.6MPa).And it is suggested that the ventilation of the gas tank should be adjusted according to the pressure of the gas pipeline.