tunnel

A model tunnel (approximately ten hydraulic diameters) with different designs of the tunnel mouth has been placed in a wind tunnel and has been subjected to the effects of external wind by varying the wind direction at the mouth of the tunnel. In the experimental oriented study pressures have been measured and the airflow has been made visible with smoke and by the sand erosion method (semolina). The relation between the flow ratio and the direction of the wind has been explored.

In this study, we monitored the carbon dioxide (CO2) concentration in a high-speed train passengercabin by the in-situ non-dispersive infra-red (NDIR) method in order to investigate the effects of variousfactors, such as number of passengers and the presence of tunnels on the CO2 concentration levels.We found that the CO2 concentration was strongly related with the number of passengers andcorrelated with the presence of tunnel regions. The CO2 concentration increased with increasingnumber of passengers and increasing tunnel residence time.

Longitudinal ventilation systems are commonly installed in new tunnels in big cities of the Far Eastincluding Mainland China, Hong Kong and Taiwan. Many tunnels are found and some of them areinclined at an angle to the horizontal. However, smoke movement in those tilted tunnels is not fullyunderstood. Some longitudinal ventilation was designed based on presumed smoke movementpattern without experimental demonstration.Smoke movement pattern in a tilted tunnel model was studied by scale modeling technique.

Ventilation requirements for vehicular tunnels in the Hong Kong Special Administrative Region are discussed. For vehicle emissions, carbon monoxide is considered to be important for vehicles running on petrol engines, and suspended particulates for diesel engines. Other environmental control parameters are temperature, air speed and air pressure. Codes, regulations and design guides for ventilation systems are reviewed. Different ventilation designs adopted in local vehicular tunnels are described.

A concept of mixing ratio of piston air is developed to evaluate the portion of the injecting air from tunnel mixed with the air in platform space of metro system. And a 3- dimensional turbulent model is used to simulate the airflow in metro platform resulted by the ventilation system and moving trains. Field measurement has been conducted to verify the 3-dimensional model. This experiment is performed during the normal operation time of a metro station with constant tracer-gas injection method. The results agree well with the numerical solution.