Increasing Oxygen Mass Fraction in Blind Headings of a Plateau Metal Mine by Oxygen Supply Duct Design: A CFD Modelling Approach

Hypoxia problem has always been a difficult point in plateau tunneling projects. To solve this problem, a blind heading face in a plateau metal mine in western China was taken as the physical model, and the computational fluid dynamics was used to analyze the oxygen mass fraction distribution and oxygen-increasing effect in 1 m, 3 m, and 5 m roadway sections from the heading face. The optimal ventilation system was first built to obtain the optimum height and length of the airflow ducts. Then different cases with various oxygen supply duct designs were built in 2 scenarios. The results found that different oxygen supply duct design has significant influence on the oxygen distribution in the heading face. Also, each design has different optimal height of oxygen outlet. The oxygen supply effect is best when some small holes are made in the oxygen supply duct to diffuse oxygen to the working surface. The finding of this paper is helpful for effective and economical oxygen supply in roadway excavation of plateau metal mine and tunnel.

Static balance duct design method and temperature dependent variable air volume systems

In hot and humid tropical countries, the air-conditioning system has a high energy usage in commercial buildings. This study introduces a static balance duct design method for a temperature dependent variable air volume system. Ducts are looped together, which cause the air to self-balance and minimize the pressure loss across the duct network. The static balance duct network can easily identify the critical zone of highest pressure loss. This zone appears at the longest duct length from the air source and is always consistent for different load conditions. The air supplied to this critical zone is controlled by the zone temperature sensor, which directs feedback to the variable frequency drive fan of the air-handling unit. The rest of the variable air volume terminal units are zone temperature controlled. The duct looping design mitigates the problems in pressure variations and complements the temperature dependent control strategy. An open office case study is carried out to demonstrate the merit of the static balance duct design method. An actual installation was completed in a shopping mall. The recorded temperature readings verified that the static balance duct network and temperature dependent variable air volume air-conditioning system is operational and functional. Approximately 27% energy savings is achieved compared to the constant air volume system. Practical application: The static balance duct design method is a combination of equal friction duct design method and a loop duct network. This static balance duct network can identify the critical zone of highest pressure loss and this zone is always consistent. In this temperature-dependent variable air volume (TDVAV), the variable air volume (VAV) terminal unit at the critical zone is eliminated. The zone temperature sensor at the critical zone provides direct feedback to the variable frequency drive fan. All other terminal units are temperature dependent. The static balance TDVAV system enhances energy savings, improves the performance of VAV system and reduces the faults for VAV systems.