Research Of Heat Dissipation And Ventilation On Thermal Cabin Of Urban Underground Utility Tunnel

The urban underground utility tunnel refers to the public tunnel used for centralized laying of municipal pipelines including electric power,heat pipelines and etc,which is equipped with corresponding monitoring and maintenance systems to implement integrated management of underground construction.Utility tunnel solves the problem of repeated excavation of roads in direct burial laying and prolongs the service life of pipelines.It has become an effective means and an inevitable trend to solve the contradiction between pipelines and space in urban development.In recent years,it has been widely concerned and popularized in China.As the main heat source in the pipe gallery,the heat pipe affects the urban central heating efficiency.Meanwhile,the continuous heat dissipation of the pipeline leads to the increase of the cabin temperature,and the enclosed space causes insufficient oxygen.These issues not only threaten the safety of pipelines and operations,but also relate to ventilation system design and operating costs.However,there are still few studies on the heat dissipation of heat pipelines and ventilation of thermal cabin in the utility tunnel,and the corresponding standard is not perfect.Therefore,this paper has carried out research on this subject in order to provide a basis for the future engineering design and specification of the corridor.In this paper,the heat dissipation problem of the heat pipelines of thermal cabin in the utility tunnel is studied firstly.Based on the research of heat transfer and pipe trenching,the theoretical calculation process of heat loss of the pipeline is determined.With reference to the study of the temperature field of the buried heat source such as the cable trench,and the related literature of the thermal cabin pipeline,the numerical analysis model of the heat dissipation of the cabin heating pipeline is determined.The model can reflect the heat exchange flow of the cabin air,and it provides new ideas for future research on pipeline insulation design.Based on theoretical calculation and numerical simulation,the effects of soil thermal conductivity and other factors on the heat dissipation of pipelines are studied.Based on the theoretical and simulation error analysis,the applicability of the empirical formula of soil thermal resistance is further explored,and the corresponding correction coefficient is obtained by data fitting.In addition,the influence of the multi-cabin structure with cable heat source on the heat dissipation of the heating pipeline is studied.The results show that due to the shallow depth of the pipe gallery,the heat loss of the pipeline is affected by atmospheric temperature,soil depth and soil thermal conductivity,and the variation range is large.The average error of theoretical and simulated values of pipeline heat loss is less than 3%,mainly caused by the formula of soil thermal resistance.the shallower the soil cover and the larger the aspect ratio,the greater the empirical error of soil thermal resistance.The multi-cabin structure has little effect on the heat dissipation of the heating pipeline,but when considering the cable current carrying,the temperature rise of the cable compartment will inhibit the heat dissipation of the heating pipe to the soil.Secondly,based on the CFD numerical analysis,the airflow organization law under the mechanical ventilation condition of the thermal cabin is studied,and the air age and other indicators are introduced to evaluate the ventilation effect.On this basis,the influence of inlet air temperature and exhaust air volume on airflow organization is further analyzed,and the feasibility of regulating the inlet air temperature through the exhaust heat recovery of the pipe gallery is discussed.The results show that there is recirculation on the air inlet side of the cabin.The heat lift generated by the heat dissipation of the pipeline hinders the vertical circulation of the fresh air.When the temperature of inlet air increases,the air volume that participates in the air circulation of the working surface increases,and the flow form is closer to the piston flow.The sewage discharge capacity of the breathing surface is significantly improved.The inlet air temperature can be controlled by the recycling of the exhaust heat from the thermal or power cabin ventilation to achieve double-effect energy saving for ventilation and energy recovery.