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Abstract At present, subways (rail transit) are undergoing rapid developments worldwide accompanied by massive energy consumption. Train-induced unsteady airflow (TIUA) generates airflow through the entrances and platform doors, which affects the ventilation and thermal environment of subway stations. Adjustable platform door systems are increasingly being installed in subway stations to reduce the energy consumption by utilising TIUA. In this study, numerical modelling was performed by IDA Tunnel software to analyse the air inflow rate (AIR) through the entrances and adjustable platform doors (APDs). Four key factors, namely, the open and closed systems, bypass ducts, train intervals, and adjustable air vents, were analysed. The results demonstrate that for subway stations with adjustable air vents open, the average AIR through entrances with a closed system was 1.99–4.17 times that of the open system. Moreover, the variations of the average AIR through entrances caused by bypass ducts were less than 9.20%, and turning off the bypass ducts increased the average AIR via the APDs from 35.58% to 65.58%, when the adjustable air vents were open. In addition, the results show that the AIR via the APDs was decreased from 32.48% to 80.45% by shutting the adjustable air vents. Therefore, an innovative energy-saving strategy of environmental control system (ECS) was proposed based on the utilisation of TIUA. A winter case to optimize the ventilation control modes of TIUA is discussed. Compared with the worst mode, the heating requirements of subway stations with optimal ventilation control modes of TIUA can be reduced by 62.85%. Highlights • The air inflow rate of the subway station created by train-induced unsteady airflow is analyzed. • Four factors, including open and closed systems, bypass ducts, train intervals, and adjustable air vents, are discussed. • An innovative energy-saving operational strategy of environmental control system is proposed. [ABSTRACT FROM AUTHOR]

Abstract Currently, subway lines are being increasingly constructed in the northern severe cold regions of China. The average ambient temperature in this region is below −10 °C during winter. Therefore, the extreme climate and piston effect impose challenges for designers for enhancing the thermal environment of a metro station in severe cold season. In this study, one-dimensional modelling is developed using the IDA Simulation Environment (IDA) based on an actual metro line, and the results are validated by experimental data. Moreover, the thermal environment of a typical metro station in the control group, two traditional optimisation measures, and one new method are investigated in severe cold regions. The results indicate that the primary heat loss during winter is attributed to the cold air invasion caused by the piston effect from the entrances. The addition of a warm-air curtain individually at the entrance may not effectively prevent the intrusion of cold air. Furthermore, adding a door curtain can reduce the inlet air volume of the entrance, but reduce the outlet air volume of the entrance. Thus, the heat of the train brake cannot be effectively utilised to improve the station temperature. In addition, one new method using the piston wind principle was presented, and it can effectively prevent the cold wind and more effectively utilise the train braking energy to improve the temperature of the metro station. It serves as a guideline for subway environmental control system (ECS) design. Highlights • The heat loss at subway station is mainly attributed to air invasion caused by the piston effect. • The warm-air curtains method may not effectively prevent the intrusion of cold air. • The door curtains in the entrances may reduce the heat utilization of the train-braking. • A new local component is proposed to improve the station thermal environment. [ABSTRACT FROM AUTHOR]

There is a significant concern about the outdoor particles due to the recurrent smog days around the world. The penetration of outdoor particles through building cracks has a great impact on indoor environment. In this study, various crack models such as straight, L-shaped, Z-shaped and wedge-shaped cracks were investigated. Discrete Particle Model (DPM) in the Lagrangian coordinates was selected to simulate the particle transport through different cracks by employing the Computational Fluid Dynamic (CFD) under different calculation conditions. Moreover, the reliability and practicality of the crack model were well verified by comparing with the literature data. The influence of crack shape, crack size and differential pressure on the particle penetration factor was analyzed and compared in detail. The results showed that increasing crack height ( H ) and differential pressure ( Δ p ) or decreasing crack depth ( L ) can result in a higher particle penetration factor. For particles size less than 3 μm, the penetration factor is higher than 0.93 for cracks with 1 mm height regardless of their depth or differential pressure. For particles size from 3 to 8 μm, the faster penetration factor drops rapidly in the corresponding interval when there is more number of right-angles ( n ). There is a negative correlation between particle penetration factor and wedge-shaped crack tilt angle. The penetration factor decreases along with the increase in wedge-shaped crack tilt angle ( α ). The current study is useful to understand particle penetration through different shapes of building cracks. [ABSTRACT FROM AUTHOR]

High-temperature buoyancy-driven pollutants that generally exist in industrial buildings and kitchens often be eliminated by local exhaust ventilation systems. The high-temperature pollutant plume driven by buoyancy significantly affects the local exhaust process, resulting in the change in the exhaust flow field and reduction of the pollutant capture efficiency. In this study, the effects of thermal buoyancy-driven pollution sources on the vortex flow field and pollutant removal efficiency of a vortex ventilation system are evaluated through experiments and numerical simulations. The results show that with an increase in the buoyancy flux of the pollution source, the minimum negative pressure and maximum tangential velocity in the vortex flow first increase and then decrease, that is, the buoyancy plume first enhances and then weakens the vortex flow. A critical buoyancy flux exists, and the value of the critical buoyancy flux increases with an increase in the vortex ventilation intensity. Furthermore, the capture of high-temperature pollutants by vortex flow can be categorized as "plume-dominated" and "vortex-dominated". These two types exhibit significant differences in pollutant transport paths and pollutant capture times during pollutant removal. In addition, on the basis of the pollutant capture efficiency, the vortex airflow performance with respect to capturing high-temperature buoyancy-driven pollutants can be classified as low-efficiency, transition, high-efficiency, and invalid zones. In the process of capturing high-temperature pollutants, vortex ventilation systems should be avoided in the low-efficiency and invalid zones. • The effects of buoyancy-driven pollution sources on the vortex airflow parameters are shown to be first promoted and then inhibited. • The transport pattern of particles can be classified into "vortex-dominated" and "plume-dominated" types. • It is proposed that the pollutant removal performance of vortex ventilation for buoyancy-driven pollutants can be divided into four zones. [ABSTRACT FROM AUTHOR]

The noise of the plenum chamber plays an important role in the acoustic performance evaluation of ventilation and air condition (VAC) systems. The large eddy simulation (LES) model and Ffowcs Williams & Hawkings (FW–H) equation were used to obtain the transient flow and aerodynamic noise, respectively, and a continuous and uniform impedance boundary condition was introduced to calculate the transmission loss (TL) of the perforated board plenum chamber. The aerodynamic noise, TL, resistance and velocity uniformity distribution characteristics of the plenum chamber were predicted by numerical simulation. A full-scale test bed was built to verify the flow field prediction results, and the acoustic prediction results were verified by analog experiments. In addition, based on the sample entropy theory, the pressure fluctuation on the inner surface of the plenum chamber was evaluated. The results show that the perforated board changes the vortex structure in the plenum chamber and reduces the local resistance and the pressure fluctuation on the inner surface wall, and the local resistance coefficient can be reduced by up to 34%. However, the coefficient of velocity uniformity in the plenum chamber decreases by 4%. Furthermore, the perforated board can significantly reduce the TL and peak sound pressure level (SPL) of the plenum chamber. At the receiving point, the overall SPL can be reduced by up to 2.5 dB. • A low noise plenum chamber with perforated board for VAC system was proposed. • The sound transmission loss effect by perforated board was analyzed. • Sample entropy method was used to analyzed aerodynamic noise of perforated board. • The new plenum chamber can reduce the noise by 2.5 dB and local resistance by 34.4%. [ABSTRACT FROM AUTHOR]

Based on the principle of a column air vortex, a novel curved vortex exhaust system (CVES) is proposed in this study as an alternative for capturing pollutants when a canopy hood cannot be used. Experimental and numerical methods are used to investigate the curved vortex formation process and influencing factors of the CVES, and the effect of geometric parameters and the supply/exhaust flow ratios are investigated to optimise the pollutant capture performance. The evolution of the negative pressure distribution is used to investigate the formation process of the vortex in the CVES. The formation of the curved vortex in the CVES is found to be a top-to-bottom process, and there is a delay of a few seconds before the curved vortex is formed. According to the characteristics of the CVES, the effective pollution source area is proposed as an index to evaluate the performance of the CVES, and the effects of the arc baffle width, back plate angle, exhaust outlet position, and exhaust outlet area on the vortex flow characteristics and effective pollution source area are analysed. The relationship between the supply/exhaust flow ratio and size of the effective pollution source area is investigated with different exhaust outlet flowrates. The results reveal that with an increase in the exhaust outlet flowrate, the optimal supply/exhaust flow ratio of the CVES gradually decreases from 0.4 to 0.2 and then remains stable. Meanwhile, a larger ventilation flowrate is beneficial for increasing the size of the effective pollution source area. • A novel type of curved vortex exhaust system (CVES) was proposed, which could significantly improve the pollutant removal efficiency of side suction exhaust hood. • The evolution process and structure of curved vortex in CVES were studied, and the effective pollution source area of CVES was proposed to evaluate CVES. • The effective pollution source area was used to evaluate the influencing factors of CVES. [ABSTRACT FROM AUTHOR]

Natural ventilation is often used in industrial workshops with high intensity heat sources and pollution sources indoors, because such workshops require large amounts of ventilation. In this study, a numerical simulation of the pollutant dispersion between two adjacent industrial workshops is performed, with a focus on the effects of the downstream workshop's thermal conditions on the flow and pollutant dispersion. The results indicate that there is a significant interaction between the wind and buoyancy generated by the downstream workshop's heat source. And this relationship can be evaluated using the Richardson number (Ri). Firstly, the Richardson number affects the ventilation direction of the downstream workshop. When Ri < 1.6, the airflow is mainly driven by wind, which flows from the leeward of the downstream workshop to the street canyon. When Ri > 1.6, buoyancy's effect begins non-negligible, the ventilation of the downstream workshop comes from the street canyon. There is a low concentration of the pedestrian breathing area and downstream workshop, when the airflow is driven by wind. When the airflow is driven by buoyancy, the pollutants migrate to the pedestrian breathing area and the downstream workshop. • For two adjacent industrial workshops, the buoyancy generated by the indoor heat source of downstream workshop changes the cross-ventilation direction. • For downstream workshops, the lowest volume flow rate through windows occurred when the effect of wind and buoyancy are comparable. • The pollutant concentration of the street canyon breathing zone and downstream workshop is affected by Richardson number of downstream workshop. [ABSTRACT FROM AUTHOR]

For building ventilation, it is often necessary to create airflow in a particular direction and prevent the backflow of pollutants and unnecessary expenditure of energy. At present, most check devices can only be used in small areas, such as pipelines, which cannot fully meet the needs of building ventilation systems. Based on the principle of a Tesla structure, this paper proposes a new type of fluid diode plate (FDP) without moving parts, which can be infinitely extended in terms of area and is suitable for various ventilation environments. A series of experiments and numerical simulations were performed to test the check effect of this FDP under different influencing factors. Two evaluation indices, the pressure loss ratio (F FDP) and minor loss coefficient (ζ), were used to evaluate the flow pressure losses in both forward and reverse directions for the FDP. The results showed that the flow pressure loss in both directions for the FDP were very different. For the fluid diode plate with 4 flow loops, the pressure loss of reverse flow could be more than 6 times that of a forward flow. The pressure loss of a forward flow showed a little increase compared with an orifice plate with the same porosity. Moreover, the check effect of the FDP increased with the inflow velocity and reached a stable value when the flow in the FDP channel became fully turbulent. In future research, the check effect of the FDP will be further improved by further optimizing the structure. • A novel fluid diode plate (FDP) based on Tesla structure was proposed to prevent backflow in building ventilation system. • Inflow velocity, number of flow loop, channel ratio, and porosity, were evaluated by using pressure loss ratio and minor loss coefficient. • The variation trend of pressure loss ratio with the increase of inflow velocity was obtained. [ABSTRACT FROM AUTHOR]