Do increased flow rates in displacement ventilation always lead to better results?

Indoor ventilation is essential for a healthy and comfortable living environment. A key issue is to discharge anthropogenic air contamination such as CO $_2$ gas or, of potentially more direct consequence, airborne respiratory droplets. Here, by employing direct numerical simulations, we study mechanical displacement ventilation with a wide range of ventilation rates $Q$ from 0.01 to 0.1 m $^3$ s $^{-1}$ person $^{-1}$ . For this ventilation scheme, a cool lower zone is established beneath a warm upper zone with interface height $h$ , which depends on $Q$ . For weak ventilation, we find the scaling relation $h\sim Q^{3/5}$ , as suggested by Hunt & Linden (Build. Environ., vol. 34, 1999, pp. 707–720). Also, the CO $_{2}$ concentration decreases with $Q$ within this regime. However, for too strong ventilation, the interface height $h$ becomes insensitive to $Q$ , and the ambient averaged CO $_2$ concentration decreases towards the ambient value. At these values of $Q$ , the concentrations of pollutants are very low and so further dilution has little effect. We suggest that such scenarios arise when the vertical kinetic energy associated with the ventilation flow is significant compared with the potential energy of the thermal stratification.

Use of Turboprop Fans with the Device for Intensification of Aeration of Open Pits for Ventilation of Mined-Out Space

The application of open-pit fans on the basis of turboprop aircraft engines, working in complex with the devices for intensification of aeration of worked-out space, for ventilation of open-pit mines is considered. The most effective for the open-pit mines ventilation is the use of isothermal jets created by the mine fans with gas-turbine aviation engines. The principle design of the device for intensification of open pits airing represents inclined profiled blades installed on supports. Such a design allows to direct the developed ventilation jet into the quarry, as well as to increase its velocity at the outlet into the mined-out space in the constructions of confusers (blades--top platform of leeward side). The application of the complex, consisting of the ventilation installation and the device of quarries aeration intensification, installed on the surface, allows to increase considerably the volume of the air, supplied to the worked-out space, in comparison with the location of the fan in the pit, to decrease the noise levels in the working zones. By means of modeling qualitative and quantitative aerodynamic characteristics of the offered ventilation scheme (location of the fan and aeration intensifier, pattern of air currents in the quarry, speeds distribution) are defined, its application efficiency and conditions are evaluated

Features of the Working Area Aerogasdynamics with the Direct-Flow Ventilation Scheme

To control rock pressure in the Karaganda coal basin, various technological schemes are used for mining and developing coal seams. At the same time, in order to form healthy and safe working conditions at workplaces in coal mines in the course of mining operations, it is necessary to ensure effective ventilation of the development and breakage faces. When solving the problem of aeration of stopes, the authors of the article propose to take into account air leaks through the collapsed coal-rock mass of the goaf when controlling gas emission of an working area. For this purpose, the gas-dynamic state of the goaf has been studied under various conditions of ventilation: when isolating the longwall face goaf, when demolishing the supported ventilation working, when the amount of air supplied to the longwall face is changed and for refreshing, as well as a combination of these options. Experimental studies have been carried out in the mines of the Karaganda coal basin. This article took into account the features of the working area aerogasdynamics with the direct-flow ventilation scheme. As a result of the study, a quasi-network model of the working area and an algorithm of calculating air leaks through the collapsed goaf massif have been developed.

Research on Indoor Thermal Comfort and Age of Air in Qilou Street Shop under Mechanical Ventilation Scheme: A Case Study of Nanning Traditional Block in Southern China

In hot summers, air conditioning (AC) and mechanical ventilation (such as fans) are used as cooling modes that strongly influence the resultant indoor environment, like thermal comfort and air quality in the shops of a Nanning arcade street (qilou). The air circulation mode in shops greatly affects the indoor thermal environment and level of air freshness. The approaches for effectively improving the indoor thermal comfort and air quality are developed in qilou street shops with air-conditioner in a humid and hot region in southern China. Consequently, the purpose of this study is to assess different ventilation schemes in order to identify the best one. By using two indices, i.e., the predicted mean vote (PMV) and the age of air (AoA), in situ measurement and numerical simulation are conducted to investigate humans’ thermal comfort in extreme summer. Then, the indoor thermal comfort and AoA levels in summer under three different ventilation schemes (upper-inlet–upper-outlet, upper-inlet–bottom-outlet, and side-inlet–side-outlet) are comparatively analyzed through numerical computations of the indoor thermal environment. The results show that the upper-inlet–upper-outlet mode of the AC ventilation scheme led to the creation of a favorable air quality and comfortable thermal environment inside the shop, which will help designers understand the influence of the ventilation scheme on the indoor thermal comfort and health environment.

Research on the construction ventilation scheme of concealed subway station

With the development of underground transportation, in order to reduce the impact on the surrounding environment and traffic, Hejiaying subway island station adopts the concealed excavation method. During the construction process, considering the construction method, tunnel layout, ventilation requirements, and the construction working face as a multi-conductor cave, more stringent requirements are put forward for the construction ventilation of the tunnel. Through the combination of theoretical calculation and numerical simulation, a ventilation method suitable for the actual construction conditions at the site was developed. After applying the scheme to practice, the feasibility of the scheme was verified through the determination of field data, and the improvement of the construction environment for tunnel personnel was achieved, which has certain reference value for similar projects.

Study on ventilation scheme and application during construction of high altitude gas tunnel

It is the key and difficult point to ensure the safety of tunnel construction by ventilation in high gas tunnel construction in high altitude and cold area. Taking ning-chan high gas tunnel as the research object, the ventilation of the tunnel is calculated, the ventilation parameters are optimized, the ventilation equipment is selected according to the calculation results, the location of the ventilation equipment is optimized, and the reasonable construction ventilation scheme is determined. The results show that through the design of the above ventilation scheme and the control of the site, it can not only ensure the ventilation demand of the super long and high gas tunnel construction in the high cold and high altitude area, but also ensure the tunnel construction in winter, and effectively save the construction ventilation cost.

Design features of coal mines ventilation using a room-and-pillar development system

The safety of mining operations in coal mines for aerological factors depends on the quality of accepted and implemented ventilation design solutions. The current “Design Manual of coal mine ventilation” do not take into account the features of room-and-pillar development systems used in Russia. This increases the risk of explosions, fires, and gassing. The detailed study of foreign experience in designing ventilation for the considered development systems e of coal deposits allowed to formulate recommendations on the ventilation scheme organization for coal mines using a room-and-pillar development system and the procedure for ventilation during multi-entry gateroad development. Observations have shown that the use of the existing Russian procedure for airing mining sites with a room-and-pillar development system complicates the emergency rescue operations conduct. Low speeds and multidirectional air movement, difficult heat outflow, and the abandonment of coal pillars increase the risk of occurrence and late detection of endogenous fire. The results of numerical modeling have shown that the installation (parallel to the drifts) of ventilation structures in inter-chamber pillars will increase the reliability of ventilation by transferring the ventilation scheme from a complex diagonal to a complex parallel. It will also reduce the amount of air required for the mine site and the total aerodynamic drag. The research made it possible to formulate requirements for the design procedure for coal mines ventilation using a room-and-pillar development system, which consist in the order of working out blocks in the panel, and also the additional use of ventilation structures (light brattice clothes or blowing line brattice).