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"ventilation systems"
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Learning from Nature: Bio-Inspired Designs and Strategies for Efficient On-Earth and Off-Earth Ventilation Systems
Efficient ventilation systems are of paramount importance for maintaining optimal air quality in indoor and enclosed environments, both on Earth and in space. Such environments include buildings, space habitats, international space station crew quarters, tunnels, underground mines and other structures. However, conventional ventilation systems encounter various challenges, including uneven air distribution, energy inefficiency, noise, and limited adaptability to fluctuating environmental conditions. Concurrently, a multitude of organisms in nature have demonstrated the capacity to construct structures that can facilitate efficient air exchange and heat regulation. Illustrative examples of such structures include ant nests, termite mounds and prairie dog burrows. The present study explores, analyses and summarizes the mechanisms, structures and strategies found in nature that can inspire the design of efficient and effective ventilation systems. The purpose of this paper is to highlight the practical implications of the aforementioned designs. To this end, it reviews the progress of research into bio-inspired ventilation, focusing on the following three areas: air regulation, component optimization and environmentally adaptive strategies. A bibliometric analysis and research trend is presented to illustrate the key developments in this field over the past 25 years. The potential of integrating the bio-inspired strategies into ventilation systems, with a particular emphasis on off-Earth habitats and underground mines, is discussed. This study provides a comprehensive overview of the development of bio-inspired ventilation systems, thereby establishing the foundation for the creation of innovative and efficient design solutions.
Journal Article
Heat stress, thermal comfort and control strategy in a warm-humid workplace
The purpose of this study was to design a local ventilation system (LVS) to help reduce the moisture content of a Scalder hall, evaluate its comfort and thermal stress before and after implementation of LVS and introduce an appropriate index to evaluate warm and humid workplaces. The design of the LVS was performed according to the ACGIH standard (VS-30-01). Heat stress and thermal comfort assessment were performed before and after LVS using humidity index (Humidex), discomfort index (DI), heat index (HI), wet-bulb globe temperature (WBGT) and predicted mean vote index (PMV) indices and the results were compared with predicted mean vote index-predicted percentage of dissatisfied (PMV-PPD) subjective indices. The results of heat stress parameters showed that LVS was able to reduce relative humidity (RH) and wet temperature (tnw) by 47% and 7 ° C, respectively. This has caused subjects to feel the heat from hot and very RH hot to warm and the hot and percentage of dissatisfaction has dropped by more than 70%. Design and implementation of a LVS reduced the ambient tnw by decreasing RH. Results also showed in warm and humid workplaces, DI index are highly correlated with subjective evaluation of thermal comfort and this index can be used to evaluate the thermal conditions of the workplaces.
Journal Article
Study on Methane Distribution in the Face Zone of the Fully Mechanized Roadway with Overlap Auxiliary Ventilation System
An overlap auxiliary ventilation system is very often used for driving roadways in methane-rich coal seams. An overlap zone between the outlets of the forcing duct ends with a whirl flow air-duct (WFAD) and the exhaust duct ends with a dust scrubber that is created by applying the overlap system. This study examines the distribution of methane concentrations at various distances in the overlap zone. Maintaining a long overlap zone could increase the advance of the face. Therefore, the impact of overlap zone length on the methane concentration distribution, in and beyond the overlap zone, is investigated. The evaluation of methane concentrations is performed utilizing a well-established computational fluid dynamics (CFD) approach. The mathematical model of methane emissions into the roadway is adopted. Moreover, the CFD model is validated. A vortex of the return air, caused by the free airstream flowing out of the dust scrubber, is found. This air vortex is responsible for higher methane concentrations at the end of the overlap zone. Therefore, the conclusion can be drawn that maintaining the length of the overlap zone at 5 m to 10 m should be done to control permissible methane concentrations.
Journal Article
Research on gas hazard prevention and control of a high-gas fully mechanized mining face based on ventilation system optimization
The gas accumulation in the return corner of a high-gas fully mechanized mining face can easily cause the gas volume fraction to exceed the safety limit, threatening the safety of coal mines. In this study, the unit method was used to analyze the gas sources and emissions based on the actual case. The airflow and gas distribution characteristics of the two-inlet-one-outlet (TIOO) ventilation system and the one-inlet-two-outlet (OITO) ventilation system were studied using CFD numerical simulation. The results show that under the TIOO ventilation system, the “U”-type air leakage in the goaf leads deep gas into the return corner, which causes the gas volume fraction in the return corner to rise to 0.4–2.0%. After the mining face is optimized into the OITO ventilation system, the “J”-type air leakage of the goaf suppresses the high concentration of gas in the deep position of the goaf. Combined with the gas extraction measures, the gas volume fraction in the return corner, exhaust roadway’s outlet, and retaining roadway’s outlet is controlled at 0.28%, 0.34%, and 0.23%. This study will provide new ideas for solving the problem of gas accumulation in the return corner of a high-gas fully mechanized mining face.
Journal Article
Aerodynamic performance of a ventilation system for droplet control by coughing in a hospital isolation ward
Over 766 million people have been infected by coronavirus disease 2019 (COVID-19) in the past 3 years, resulting in 7 million deaths. The virus is primarily transmitted through droplets or aerosols produced by coughing, sneezing, and talking. A full-scale isolation ward in Wuhan Pulmonary Hospital is modeled in this work, and water droplet diffusion is simulated using computational fluid dynamics (CFD). In an isolation ward, a local exhaust ventilation system is intended to avoid cross-infection. The existence of a local exhaust system increases turbulent movement, leading to a complete breakup of the droplet cluster and improved droplet dispersion inside the ward. When the outlet negative pressure is 4.5 Pa, the number of moving droplets in the ward decreases by approximately 30% compared to the original ward. The local exhaust system could minimize the number of droplets evaporated in the ward; however, the formation of aerosols cannot be avoided. Furthermore, 60.83%, 62.04%, 61.03%, 60.22%, 62.97%, and 61.52% of droplets produced through coughing reached patients in six different scenarios. However, the local exhaust ventilation system has no apparent influence on the control of surface contamination. In this study, several suggestions with regards to the optimization of ventilation in wards and scientific evidence are provided to ensure the air quality of hospital isolation wards.
Journal Article
Study on temporal and spatial evolution law for dust pollution in double roadway ventilation system of short wall continuous mining face
To explore the laws of variations in the evolution of dust pollution within a double tunnel ventilation system at a short wall continuous mining face, a numerical simulation of air flow movement was conducted in this study. Results showed that after the wind flowing in the supporting and heading tunnels reached the head, the wind sides returned at speeds of 6.5 and 10.3 m/s, respectively. Affected by the air volume and pressure differences between the two tunnels, part of the air flow entered the connecting tunnel at an average speed of 0.8 m/s and moved to the heading tunnel. Affected by the turbulence at the driving face, a high dust concentration zone with a maximum dust concentration of 1700 mg/m
3
was formed in the tunnels at a distance of 15 m from the heading. Dust blocked by the shuttle car accumulated and settled near it and formed a dust zone with an approximate average concentration of 750 mg/m
3
at a distance of 19–23 m from the heading. The dust produced by the bolt machine formed a dust mass with an average concentration of 900 mg/m
3
at a distance of 0.5–4.5 m from the head. Quantitative analyses of the changes in dust concentration with time at the position of a driver of the continuous mining machine, shuttle car, and anchor bolt machine were conducted, and functional formulae for the quadratic distribution were obtained. Suggestions for dust control were then proposed.
Journal Article
Field measurement and numerical simulation of dust migration in a high-rise building of the mine hoisting system
Dust pollutants generated from the coal transfer process in a high-rise building of the mine hoisting system not only undermine the operating environment but also reduce the surrounding air quality. Therefore, this study aimed to determine the spatiotemporal distribution of coal dust in the high-rise buildings using field measurement and numerical simulation. Based on the discrete phase model (DPM), the dust migration process under the hybrid ventilation system was investigated in detail. Then, the feasibility of the established model to predict the spatiotemporal distribution of dust pollutants was proven through the measurements of both the airflow and the dust concentration. The present study showed that dust distribution is not uniform in time and space, which also differs for different floors. The dust concentration of the 3
rd
floor is relatively larger when compared with those of other floors. The dust concentration increases for the upper floors when the upward air velocity increases, while those of the lower floors are not always low due to the backflows, particularly for the 2
nd
floor. PM
2.5
takes up more than 20% of all discharged particles.
Journal Article
Comparison of Local Mean Age of Air between Displacement Ventilation System and Mixing Ventilation System in Office Heating Conditions during Winter
A novel displacement ventilation system (DVS) was designed using a four-way cassette fan coil unit (FCU) and air purifiers (APs) for supplying clean air. The proposed DVS in this study involved drawing indoor air through the FCU and diffusers installed in the ceiling, controlling air temperature using the FCU, and then discharging it back into the office through the APs placed on the floor. The comparative ventilation system considered was the typical mixing ventilation system (MVS) that intakes and exhausts indoor air using diffusers installed on the ceiling. The local mean age of air was used as an index to compare indoor air quality between DVS and MVS under winter heating conditions. It was found that the DVS was more effective in improving indoor air quality in winter than the MVS. Moreover, compared to the MVS, utilizing the DVS designed in this study resulted in the advantage of a much more uniform air temperature variation in the office space. Therefore, it is anticipated that modifying the structure of an indoor space with an FCU installed in the ceiling and APs on the floor to use the DVS designed in this study would greatly assist in enhancing indoor air quality.
Journal Article
Computational Fluid Dynamics Analysis of Alternative Ventilation Schemes in Cage-Free Poultry Housing
This work investigated alternative ventilation schemes to help define a proper ventilation system design in cage-free hen houses with the goal of assuring bird welfare through comfortable conditions. Computational fluid dynamics (CFD) modeling was employed to simulate indoor and outdoor airflows to quantify the effectiveness of ventilation systems in maintaining suitable and uniform living conditions at the hen level. Four three-dimensional CFD models were developed based on a full-scale floor-raised layer house, corresponding to ventilation schemes of the standard top-wall inlet, sidewall exhaust, and three alternatives: mid-wall inlet, ceiling exhaust; mid-wall inlet, ridge exhaust; and mid-wall inlet, attic exhaust with potential for pre-treatment of exhaust air. In a sophisticated and powerful achievement of the analysis, 2365 birds were individually modeled with simplified bird-shapes to represent a realistic number, body heat, and airflow obstruction of hens housed. The simulated ventilation rate for the layer house models was 1.9–2.0 m3/s (4100 ft3/min) in the desired range for cold weather (0 °C). Simulation results and subsequent analyses demonstrated that these alternative models had the capacity to create satisfactory comfortable temperature and air velocity at the hen level. A full-scale CFD model with individual hen models presented robustness in evaluating bird welfare conditions.
Journal Article