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The proton exchange membrane fuel cell (PEMFC) air supply system is a complex nonlinear system with strong coupling of air flow and pressure. To avoid oxygen starvation and unstable output performance during rapid load changes, the oxygen excess ratio (OER) and air pressure need to be controlled effectively. To cope with the nonlinearity, coupling and uncertainty of the PEMFC air system, this paper puts forward a coordinated controller regulating OER and air pressure based on the input-output linearization and sliding mode methods. Firstly, a control-oriented third-order model is proposed to describe the dynamic behavior of the air supply system. Secondly, this paper decouples the flow and pressure of the PEMFC air system by using an input-output linearization method to obtain two independent linear subsystems. Moreover, a sliding mode method, effectively coping with the uncertainty of the system model, is designed to regulate the OER and air pressure of the PEMFC, which enhances the robustness of the control system. The overall simulation outcomes show that the proposed controller regulates OER and cathode pressure with smaller root mean square error (RMSE) and mean absolute percentage error (MAPE) compared with the combined proportional integral (PI) and feedforward controller. • A modified model oriented to control of air supply system is proposed. • Input-output linearization and sliding mode are used to develop coordinated control strategies. • The outcomes illustrate that the air supply affects the output performance of the fuel cell. • Control performance in the presence of model uncertainty is verified. [ABSTRACT FROM AUTHOR]

As an efficient, clean and pollution-free power generation device, proton exchange membrane fuel cell (PEMFC) has been widely applied in transportation, distributed power generation and other fields. However, the performance of PEMFC cannot be separated from appropriate cathode gas supply, for example, it is prone to oxygen starvation under frequent variable load conditions. This is due to the mismatch between the air supply rate and the electrochemical reaction rate, making it difficult for the system to meet the air flow requirement instantaneously when subject to the load changes abruptly. Thus, oxygen starvation control has become a particularly challenging nonlinear control problem because of the great difficulty in achieving an accurate system identification model and an efficient controller. To this end, a long short-term memory (LSTM) neural network-based model predictive control (MPC) is developed to model and control the PEMFC air supply system, which combines the advantages of LSTM and MPC. Firstly, LSTM is utilized to train an online control-oriented model from the measured dataset. Secondly, a sparrow search algorithm (SSA) is utilized to update the hyper-parameters of LSTM model, which can obtain more accurate predictive model in MPC. Thirdly, the MPC with LSTM-SSA model is solved online using different high efficiency solvers. Fourthly, the proposed LSTM-SSA based on MPC is adopted to model and control a PEMFC air supply system. Finally, the stability proof of the proposed method is illustrated in the Appendix. The simulation results reveal that the data-driven learning method and MPC method have significant advantages in modeling and improving the system performance. • Machine learning-based MPC framework is proposed to regulate air supply system. • LSTM as the predictive model in MPC is developed to describe the dynamic system. • Sparrow search algorithm is used to update the hyper-parameters of the LSTM model. • The control effects of proposed controller based on different solvers are compared. [ABSTRACT FROM AUTHOR]

Summary: In this paper, a robust adaptive vibration control method for gantry crane system is proposed considering unknown parameters brought by unknown payload, cable length and tension. The control objective is to transport the cargo to the desired position while suppressing the vibration of the cable in the presence of unknown parameters. For this purpose, a boundary controller is designed with an adaptive law to compensate the parameter uncertainty of the system. The well‐posedness of the closed‐loop system is proved by means of operator semigroup theory and the asymptotic stability of the closed‐loop system is analyzed. Finally, the effectiveness of the proposed control approach is demonstrated through both numerical simulation comparisons and physical experiments. [ABSTRACT FROM AUTHOR]

Existing research of non-unidirectional cleanrooms generally suggests that lower-side return air outlets provide better control effect on indoor particle concentration. As a result, there has been relatively less focus on return air outlets. However, installing return air outlets oriented towards operators as particle emission sources can reduce the impact on process layout and improve space utilization, while also provide less impact from upper particle emission sources on the workbench area. To investigate the characteristics of return air outlet for operators (abbreviated as H), this study compared the particle concentration distribution, non—uniformity, and purification efficiency of return air oultet H and the traditional lower-side (abbreviated as L) return air outlets by experiments and CFD simulations. Based on the theory of mass conservation, the expression of required air supply volume under equivalent cleanroom conditions was derived. Under corresponding experimental and simulation conditions, the particle concentration differences range from 2.0% to 12.7% for return air outlet H and from 12.4% to 33.2% for return air outlet L, and these differences gradually decrease with the air exchange rate (ACH) increases. The results show that ACH = 20 is sufficient for cleanliness requirements with return air outlet H when there is one person in the cleanroom, while a higher rate of ACH = 35 is needed when there are two persons. Although lower-side return air outlets have certain potential for reducing particle concentration in the cleanroom, increasing the air exchange rate remains the most effective method to control indoor particle concentration. Compared to the traditional lower-side return air outlet L, the ranges of the non-uniformity coefficients for return air outlet H and L are 0.50 to 0.67 and 0.45 to 0.53, respectively. The average non-uniformity coefficient differs by 11.9%, and there is not a significant difference in uniformity with more than 20 air changes per hour. The use of return air outlets H only requires an additional 11% of air supply volume to achieve the same cleanliness, demonstrating its effectiveness in controlling particle concentration. It is suitable for cleanrooms with higher requirements for workbenches and for cleanrooms with restricted floor usage or requiring flexible layouts. The study also explores the impact of width of return air outlet oriented towards operators as particle emission sources, the results show that the larger-sized outlets facilitate the particle discharge and control the particle distribution inside the room. [ABSTRACT FROM AUTHOR]

Guaranteeing rapid management of oxygen excess ratio (OER) for proton exchange membrane fuel cells (PEMFC) under load variations is a challenge with practical significance. To improve the controller response of PEMFC air supply system, a fixed time fault-tolerant control strategy is proposed in this paper. A fixed convergence time of PEMFC air supply control system is quantified and guaranteed by the proposed method and the control response can be accelerated by reducing the setting time. The contributions of this paper is fourfold. Firstly, the manifold leakage fault is estimated by fixed time fault observer, which can improve the real-time fault tracking performance of the control system. Secondly, a hierarchical fixed time sliding mode controller is proposed to regulate the OER rapidly. Furthermore, a novel adaptive term is employed to reduce the effects of the chattering from fault observer in the outer loop. Finally, the effectiveness of the proposed method is verified on a real-time PEMFC simulation platform. Experimental results on a Hardware-in-the-loop (HIL) platform show that the proposed fixed time fault tolerant control strategy has the characteristics of fast response and high robustness. [Display omitted] • Fixed time fault observer is employed to monitor the manifold leakage. • Fixed time control framework guarantees a quantified stabilization time of OER. • An adaptive term reduces the chattering effects of the fault observer. • The FTC method is validated on a high-fidelity HIL platform. [ABSTRACT FROM AUTHOR]

This study demonstrates the applicability of an explicit model predictive controller (ExMPC) to the air mass flow control in a fuel cell electric vehicle. The two control tasks comprise the supply of air to the fuel cell stack for the electrochemical reaction as well as the dilution of hydrogen in the outlet gas flow of the cathode subsystem. With the aim of achieving zero control deviation for steady states, the linear model in the state observer is extended with two perturbations. During the experimental validation of the proposed controller, fast dynamics are achieved with the ExMPC, which generally exploits the limits of the control variables. After the calibration of the ExMPC, the final comparison to a set of reference PI controllers reveals a significant improvement in the closed-loop behavior of the cathode subsystem during step changes in the controller setpoints. • An explicit model predictive controller is applied to a fuel cell electric vehicle. • Delays for control and controlled variables are considered. • The operating limits of the control variables are exploited during dynamic operation. • Improved closed-loop behavior is achieved in comparison to reference PI controllers. [ABSTRACT FROM AUTHOR]

In order to obtain high power and efficiency while operating PEM fuel cells in airborne applications, pressurizing the inlet air is necessary. The control strategy for dynamic operation of an air supply module was developed in order to provide cathode inlet air at optimal conditions (mass flow, pressure, humidity and temperature) for different ambient conditions and varying power demand. A surge avoidance strategy without additional surge control valves was successfully implemented. The system was successfully tested statically and dynamically and afterwards connected to a fuel cell system. The air supply module was able to provide cathode pressure, mass flow and humidity dynamically as requested and the developed control strategy was able to avoid unstable operation. •Air supply system for pressurized hydrogen fuel cells in aviation was developed. •Control strategy for varying mass flow, pressure and power demand was developed. •Statically and dynamically stable operation over complete compressor map is achieved. •Measurement data from a combined system with a fuel cell stack is presented. [ABSTRACT FROM AUTHOR]

Tracking control of the oxygen excess ratio (OER) and keeping the cathode air pressure relatively stable are essential for the operation of polymer electrolyte membrane fuel cell (PEMFC). In automotive fuel cell air supply systems, the cathode air pressure and OER are usually unmeasurable parameters, which makes the air supply system control and fault analysis very difficult. To solve this problem, this paper proposes an extended state observer based on the hyperbolic tangent function (HTF-ESO) to estimate the cathode air pressure of the fuel cell gas supply system, and indirectly obtains the OER according to the estimated cathode pressure, and designs the sliding mode control (SMC) and a first-order active disturbance rejection control (ADRC) for the tracking control of the OER. The simulation results show that the improved HTF-ESO effectively mitigates the initial differential peak phenomenon and reduces the initial estimation error of the cathode air pressure, and the RMSE of the cathode pressure and supply manifold pressure observation errors are reduced by 68% and 20%, respectively, compared with the present unimproved ESO. Compared with the PI, the RSME of the control error after convergence of the designed SMC and ADRC is reduced by 4.3%, and the OER can be restored to the reference value within 1 second, with good dynamic response. [ABSTRACT FROM AUTHOR]

The COVID-19 pandemic has emphasized the crucial role of ventilation systems in mitigating cross-infections, especially in infectious-disease hospitals. This study introduces a dual-design operation ventilation system that can operate under two sets of ventilation conditions for normal and epidemic times. A challenge is optimizing duct diameters for required airflow while maintaining hydraulic balance. We designed an improved genetic algorithm with an adaptive penalty factor and velocity constraint, as well as the improved crossover probability and mutation probability. The improved genetic algorithm is suitable for ventilation system networks, which can find a better combination of air duct diameters to improve the hydraulic balance rate and reduce the usage of air valves, resulting in efficient hydraulic balancing commissioning. A supply air ventilation system of an actual hospital in China was selected as a case study, and the number of imbalanced air ducts was reduced from 14 to 4. Compared with the traditional genetic algorithm, it has a faster search speed and a better global search ability, which is effective for the optimal design of ventilation system networks. [ABSTRACT FROM AUTHOR]

When installed in deep tunnel systems, the cover of the vortex dropshaft may be partially or fully sealed. With air exchange restricted through the cover, the air supply to the dropshaft through the inflow channel might not be adequate. Hence, further investigation is required to examine the effect of the restricted air passage through the cover on the flow regimes and hydraulic performance of the scroll vortex dropshaft. This study aims to quantify the head-discharge relationship, air-water distribution, and minimum air core size with different cover opening conditions. The 3D model of a fully open scroll vortex dropshaft is constructed, and numerical simulations are carried out and validated using experiment data. The results show that the effect is generally small when the ratio of the opening and dropshaft area is larger than 1%. When the cover is fully sealed, the minimum air core size reduces by 5% of the dropshaft area which can have a serious implication to the design of the scroll vortex dropshaft. The present study provides a practical evaluation of the effect of the opening condition in the cover of the vortex chamber on the performance of scroll vortex dropshafts for underground water drainage systems.. [ABSTRACT FROM AUTHOR]

The ventilation system significantly affects the energy saving, thermal comfort, and pollutant dispersion characteristics of high-speed trains. Using Computational Fluid Dynamics (CFD), the effects of combining side-wall air supply with side roof or ceiling air supply, on the performance of a highspeed train ventilation system is studied. The results show that the addition of side-wall air supply aids energy saving and emission reduction, resulting in an increase in energy utilisation coefficient of between 5% and 30%. The number of measurement points with wind speed less than 0.3 m/s increases by 3%~9%, which can improve passenger comfort. Also, the concentration of pollutants can be reduced by 6%~29%, and the diffusion distance along the length of the train can be reduced by 18%~45%, which means more efficient ventilation and a shorter diffusion range of pollutants. However, it reduces temperature uniformity. The results of this study can be used for ventilation optimisation of high-speed trains, to reduce ventilation energy consumption, improve thermal comfort, and increase ventilation efficiency. [ABSTRACT FROM AUTHOR]

Low-level outlets are essential flood discharge structures for high-head dams. High-speed free-surface flows releasing into tunnels lead to substantial air discharge, and the air supply is important for gate vibration mitigation, cavitation protection by aeration, and slug flow transition phenomena. An additional challenge is the excessive wind noise due to low air supply efficiency, threatening staff working conditions in flood discharge operations. However, the current understanding of the effects of air vent sizes and locations on the air supply efficiency is still limited. In the present study, based on a series of experimental tests, air vent designs of long flood discharge tunnels, including a single vent and two combined working vents, are analyzed with respect to the air discharge variation. For air vent designs with a small vent size and an installation location downstream, the air discharge into the tunnel is low, and the air supply efficiency is low even for two combined working vents. Equations for the air supply efficiency are proposed, which enables quantifying the ventilation performance, and related vent parameters are recommended for favorable air ventilation designs. The present investigation provides a reference for the flood discharge tunnel design and ventilation operation assessment in hydraulic engineering. Air ventilation design is an important part of flood discharge tunnels and water supply and drainage systems. The single air vent sizes, locations, and combined working vents are considered in the present studies. The single air vent sizes, air vent downstream locations, and two vent distances are effect factors, providing reasonable assessment methods to predict the air supply efficiency for different structural and hydraulic conditions. A reasonable hydraulic design can obtain high air supply efficiency and regulate air discharge distributions in multiple air vents. The guidelines in the present analyses are effective to optimize the multiple air ventilation system and to obtain safety operations and acceptable staff working conditions. [ABSTRACT FROM AUTHOR]

This research is conducted to study the effect of air-flow rate to the smoldering combustion dynamics and transition flaming. Test is done using peat extracted from Papua Provinces, Indonesia. The combustion is conducted on natural, 1.33 cm/s, 3.98 cm/s, and 6.63 cm/s of air-flow, respectively, representing the oxidation with lack and excess of air as calculated by stoichiometric equilibrium. Test result show that smoldering spread rate tends to increase with increasing the air supply. Differences in physical properties yield the different of the smoldering dynamic behavior. In general, the higher the air-flow velocity leads to a higher smoldering temperature, spread rate, and mass loss rate. Combustion with natural air and lack of oxygen will result in smoldering whereas in excess air led to transition flaming. [ABSTRACT FROM AUTHOR]

A stockpile heated and ambient air dryer (SHAD) was developed as an alternative to conventional almond windrow drying. Previous experiments showe that the drying air produced by SHAD was undesirably distributed through the almond stockpile. Therefore, an air distributor was developed containing 12 outlets, arranged in 4 rows of 3 outlets each. This study describes the comprehensive process of the air distributor design, manufacturing, and its optimization. The optimization process employed both computational fluid dynamics simulations and in-field airflow validation measurements. Initial 4-row air distributor in-field validation measurements indicated airflow distribution percentages were 4.1%, 30.8%, 44.9%, and 20.2% for the outlets in rows 1 through 4. This showed that almonds located around row 1 would not receive sufficient air to properly dry. Thus, an optimized 3-row air distributor configuration was developed and validated to yield an airflow distribution percentage of 31.3%, 44.4%, and 24.3% for outlets in the second to fourth rows, respectively. The 3-row air distributor configuration is therefore desirable, as the middle and tallest section of the stockpile will receive the highest airflow. The air distributor therefore markedly enhanced the SHAD's air supply distribution. • Drying air supplied by SHAD was unevenly distributed in the almond stockpile. • A multi-outlet air distributor was developed to improve air delivery. • Optimized air distributor design contained 3 rows, with 3 outlets on each row. • Air supply was highest in the middle row, where there are most almonds to dry. • The SHAD with air distributor significantly improved the air distribution supply. [ABSTRACT FROM AUTHOR]

By designing an office with window shutters and setting different window sizes, the indoor wind and thermal environments were investigated at different heights. Opening windows improved the thermal conditions in the office, especially in high temperature rooms. Despite generation of high ventilation rates at many locations, the ventilation rates were good within the main areas. It appeared critical to supply air through opening of the windows. A novel simulation method was explored. Meanwhile, an appropriate numerical simulation scheme was chosen to evaluate the effects of various office structures on thermal comfort, which can thus provide an important reference for the office building design. [ABSTRACT FROM AUTHOR]

In airlift systems, the difference in gas holdup (εg) between the riser and the downcomer creates the driving force for liquid circulation. This feature can be an interesting approach to using an airlift pump instead of the conventional paddlewheels for simultaneous mixing between phases and supply of air to microalgae in the biomass culture ponds. Before any biomass cultivation, the hydrodynamic behavior of the system must be recognized. Therefore, cold model hydrodynamic characteristics in the air–water system of a novel oval airlift open pond (AOP) are presented by studying gas holdup and riser liquid velocity (Ulr) at different ratios of baffle clearances from the top and bottom (ht/hb) in the AOP. The gas holdup is one of the key parameters to describe the performance of airlift systems, so the effect of riser superficial gas velocity (Ugr), riser liquid velocity, and ht/hb ratios on gas holdup are investigated in this research. The results of this study indicate that superficial gas velocity, riser liquid velocity, and ht/hb ratio have a pronounced effect on the gas holdup. Moreover, due to the lack of gas holdup correlations in the AOP system, new empirical correlations have been developed to predict total gas holdup, riser gas holdup (εgr), and downcomer gas holdup (εgd) with satisfactory accuracy. [ABSTRACT FROM AUTHOR]

This study investigates the behavior of air supply in tunnels with multiple vertical shafts during fire incidents, focusing on natural ventilation dynamics. Numerical simulation is utilized to analyze the effect of different variables on air supply within vertical shafts. The findings reveal that the position of the smoke front significantly influences the direction and flow rate of gases during fire development. The mass flow rate of air supply during the stable fire development stage is influenced by the geometric size and positioning of vertical shafts, with shafts closer to the fire source exhibiting higher air flow rates. To address this issue, this study introduces a predictive model for estimating air flow rates in vertical shafts. This model exhibits a high level of accuracy when compared to simulations, offering a reliable method for predicting air flow rates based on the geometric characteristics of vertical shafts. Overall, this research contributes to understanding the complexities of air supply in tunnels with multiple vertical shafts, aiding in the improvement of natural ventilation strategies during fire incidents. [ABSTRACT FROM AUTHOR]

Novel ultrasonic bat deterrents based on aerodynamic whistles are proposed and investigated experimentally and numerically for their ability to generate ultrasound. The baseline deterrent, a single-whistle design inspired by Beeken ["Fluid ultrasonic generator," U.S. patent 3,432,804 (1969)], is examined first. It consists of two resonating cavities/chambers. The whistle is "powered" by a regulated high-pressure air supply, and the performance of the whistle is examined for a range of supply pressures. Far-field acoustic measurements in the 20 Hz–50 kHz frequency range are made in an anechoic chamber. The noise measurements are supplemented with two- and three-dimensional unsteady Reynolds-averaged Navier–Stokes (uRANS) simulations to investigate the mechanisms of ultrasound generation. The Ffowcs Williams–Hawkings acoustic analogy is used with the three-dimensional uRANS results to predict the far-field radiation. The far-field acoustic predictions are in good agreement with the measurements in the anechoic chamber. The peak frequency (fundamental) of the radiated ultrasound of the baseline deterrent is approximately 23 kHz. Harmonics and a sub-harmonic of the fundamental tone are also observed. The numerical simulations show that the two resonating chambers of the baseline deterrent operate out-of-phase and Helmholtz resonance determines the whistling frequency over the range of supply air pressure considered. A six-whistle deterrent targeting a broad spectral coverage in the 20–50 kHz frequency range is designed, fabricated, and tested in the anechoic chamber. Each whistle in the deterrent is obtained by geometrically scaling the baseline whistle. Measurements show that the six-whistle ultrasound deterrent generates ultrasound with six dominant peaks in the designed frequency range when the supply air pressure exceeds 5 psig. The proposed ultrasound devices can be used for a variety of purposes including bat deterrence at wind turbines. [ABSTRACT FROM AUTHOR]

This paper compares four commonly used air supply methods, namely hot and cold aisle open air supply systems, hot aisle sealed air supply systems, under-rack cold aisle air supply systems and cold aisle sealed air supply systems. For each air supply method, the effects of geometric factors, including static pressure box height (0.4–0.6 m in steps of 0.1 m), perforation rate (10%-40% in steps of 10%), baffle position shape (\/-shaped and /\- shaped) and baffle angle (30°/45°/60°), on the thermal environment of the data center are numerically calculated (288 cases in total). Thereafter, the numerical calculation results of the optimal structure were verified through comparison with the results of measurement of the average rack temperature, the average hot spot temperature, the thermal performance evaluation index and the return temperature index on site. The results show that by increasing the height of the static pressure box or reducing the perforation rate within range of 10–30%, the thermal performance of the static pressure box can be improved. Taking into account the room temperature profile and the evaluation indicators (β, RTI), the best overall performance is achieved in the case of cold aisle containment. Finally, \/-shaped and /\-shaped baffles are compared in the model with cold aisle contained, and the results show that the perforation rate is 20% for both \/-shaped and /\-shaped baffles, and the optimum static pressure heights are 0.5 m and 0.6 m for \/-shaped and /\-shaped baffles, respectively. Overall, \/-shaped baffles have better temperature uniformity than /\-shaped baffles. It is found that the best performance for the CACS model is the configuration with \/-shaped baffle at the angle of 60°, the plenum height of 0.5 m and a perforation rate of 20%. [ABSTRACT FROM AUTHOR]

The COVID-19 pandemic caused a paradigm shift in our way of using heating, ventilation, and air-conditioning (HVAC) systems in buildings. In the early stages of the pandemic, it was indeed advised to reduce the reuse and thus the recirculation of indoor air to minimize the risk of contamination through inhalation of virus-laden aerosol particles emitted by humans when coughing, sneezing, speaking, or breathing. However, such recommendations are not compatible with energy saving requirements stemming from climate change and energy price increase concerns, especially in winter and summer when the fraction of outdoor air supplied to the building needs to be significantly heated or cooled down. In this experimental study, we aim at providing low-cost and low-energy solutions to modify the ventilation strategies currently used in many buildings to reduce the risk of respiratory disease transmission. Measurements of the indoor air bacterial concentration in a typical office building reveal that ultraviolet germicidal irradiation (UVGI) modules added to the HVAC system are very efficient at inactivating pathogens present in aerosols, leading to indoor concentrations as low as outdoor concentrations, even with significant indoor air recirculation. Moreover, measurements of the CO2 and aerosol air concentration reveal that, with air supply vents placed in the ceiling, placing the air exhaust vents near the floor instead of on the ceiling can improve the ventilation capacity in terms of effective flow rate, with significant consequences in terms of energy savings. [ABSTRACT FROM AUTHOR]

The factors affecting purification of concentrated extracts obtained from the aerial parts of two Hypericum species (H. scabrum L. and H. perforatum L.) using 80% EtOH were studied. A five-fold treatment with extraction naphtha followed by six-fold extraction with EtOAc was shown to provide a dry extract with a hypericin content of at least 0.29%. The recommended conditions for obtaining a spray-dried extract of Hypericum were coolant temperature at the inlet, 160 – 180°C; at the outlet, 80 – 90°C; solution delivery rate, 5 L/h; air pressure supplied to the nozzle, 0.15 MPa; and solution concentration, 15%. A unified technology for production of Hypericum dry extract substance from the aerial parts of H. scabrum and H. perforatum was developed and could produce a finished product that met the requirements of foreign pharmacopoeias. [ABSTRACT FROM AUTHOR]

Virtually dividing thermal zones into micro-zones and conditioning them using occupant-centric control (OCC) has emerged as a significant method in reducing cooling energy. Hence, the need arises to study time-sensitive thermal behaviour within micro-zones under OCC as thermal coupling from adjacent micro-zones significantly influences cooling patterns. This will explain possible variations in cooling time and energy consumption under different occupancies and aid in analysing the feasibility of micro-zoning as an efficient strategy. This study aims at exploring the key parameters that influence cooling patterns under micro-zonal OCC. Effects of four factors, namely indoor ambient temperature, supply air velocity, thermostat location and occupancy are explored using validated transient state CFD simulations for a hypothetical open-plan office. Results indicate that compared to zone conditioning, micro-zonal OCC can reduce about 20%–70% overall cooling energy while maintaining setpoint conditions and show the following three patterns: rate of cooling in occupied micro-zones decreases as they start to cool unoccupied zones through thermal coupling; supply air velocity and ambient temperature impact thermal coupling and the size of a chosen micro-zone influences energy load. This study is the first attempt at transient exploration of thermal developments within micro-zones under the influence of relevant parameters and is a necessary precursor to experimental studies on micro-zonal OCC. HIGHLIGHTS • Dividing thermal zones into micro-zones under the OCC saves 20%–70% energy. • First attempt at transient exploration of thermal developments within micro-zones. • The supplied air velocity, ambient temperature and micro-zone size influence HVAC energy. [ABSTRACT FROM AUTHOR]

As the heat hazard problem in the deep mine becomes more prominent, it is difficult to alleviate the high-temperature problem by increasing the air supply and adjusting the ventilation mode alone. In order to solve the issue of heat damage in the Linglong Gold Mine, a cooling system based on water source heat pump technology and utilizing the return air system to exhaust heat was constructed, and each system was rationally arranged in conjunction with the mine's actual conditions. The reasonable critical threshold of cooling system parameters is then determined by numerical simulation and field application verification. The results indicate that the closed cycle adopted by the cooling system can effectively solve the problem of groundwater shortage. The heat can be discharged directly to the return air shaft to prevent the impact of secondary heat hazards. The temperature near the working face can be reduced from 35°C to below 28°C. This system effectively resolves the issues of water shortage, heat release, and cold transfer in the water source heat pump technology and provides a reference for the application of other mines. [ABSTRACT FROM AUTHOR]

In the hope of reducing the air supply flow of the powered air-purifying respirator (PAPR) and extending the service life of the filter, a breath-following powered air-purifying respirator (BF-PAPR) that can dynamically adjust the air supply flow according to the breathing flow is proposed. The BF-PAPR changes the air supply flow by adjusting the speed of the variable-frequency centrifugal fan according to the air velocity at the half mask outlet (vhm) monitored by the modular wind speed transmitter. In the study, the air supply flow adjustment model of the BF-PAPR is developed. It is found that the filtration resistance barely influences vhm. In addition, under the same mean inhalation flow, the minimum outlet air velocity increases first and then decreases with the increase of the duty cycle variation coefficient (λ), while the maximum outlet air velocity decreases first and then increases. Moreover, the minimum air supply flow of the BF-PAPR is achieved when the standard value of the air velocity is 13.4 m/s and the value of λ is 1. The BF-PAPR can reduce the air supply flow by 6.5%-8.6% and the energy consumption by approximately 20% compared with the PAPR, which is beneficial for reducing the usage cost and extending the continuous working time. [ABSTRACT FROM AUTHOR]

This review article presents a summary of currently used and proposed methods of manufacturing fir tree slots of discs in turbine engines. The production of aircraft, including aircraft engines during times of overlapping global economic crises related to the COVID-19 pandemic or the war in Eastern Europe requires a quick response to the changing numbers of passengers and cargo. Similarly, the aviation industry must adapt to these conditions, and thus utilize flexible production methods allowing for a quick change in the design or type of a given part. Due to the constant adoption of new materials for the most critical aero engine parts and the necessity of complying with environmental regulations, it is necessary to search for new methods of manufacturing these parts, including fir tree slots. As an alternative to currently used expensive and energy-intensive broaching, many manufacturers try to implement creep feed grinding CFG or contour milling. However, other manufacturing methods, thus far rarely used for crucial machine parts such as WEDM, ECDM or AWJ, are gaining more and more popularity in the aviation industry. This article presents the advantages and shortcomings of these methods in the context of manufacturing fir tree slots. [ABSTRACT FROM AUTHOR]

Due to energy constraints and people's increasing requirements for indoor thermal comfort, improving energy efficiency while ensuring thermal comfort has become the focus of research in the design and operation of HVAC systems. This study took office rooms with few people occupying them in Wuhan as the research object. The EnergyPlus-Fluent co-simulation method was used to study the impact of 12 forms of air distribution on the thermal environment and air-conditioner energy consumption. The results indicate that 3 m/s supply air velocity and 45° supply air angle are more suitable for the case model in this study. The EnergyPlus-Fluent co-simulation method used in this paper provides a reference for the study of indoor environments in offices with few people occupying them. [ABSTRACT FROM AUTHOR]

During the cold-start process of a PEMFC, the supply of air and hydrogen in the gas supply system has a great influence on the cold-start performance. The cold-start of a PEMFC is a complex nonlinear coupling process, and the traditional control strategy is not sensitive to the real-time characteristics of the system. Inspired by the strong perception and decision-making abilities of deep reinforcement learning, this paper proposes a cold-start control strategy for a gas supply system based on the MADDPG algorithm, and designs an air supply controller and a hydrogen supply controller based on this algorithm. The proposed strategy can optimize the control parameters of the gas supply system in real time according to the temperature rise rate of the stack during the cold-start process, the fluctuation of the OER, and the voltage output characteristics. After the strategy is trained offline according to the designed reward function, the detailed in-loop simulation experiment results are given and compared with the traditional control strategy for the gas supply system. From the results, it can be seen that the proposed MADDPG control strategy has a more effective coordination control effect. [ABSTRACT FROM AUTHOR]

A fabric air dispersion system (FADS) is a type of flexible air supply system that integrates air transmission and distribution. This innovative system has the potential to address common issues such as uneven air supply and surface condensation, which are often associated with traditional ventilation systems. Existing numerical simulation studies on fiber ducts have encountered problems with mesh generation and simulation accuracy. This work develops a simulation method based on the equivalent discounting method to overcome these challenges. The proposed method is utilized to investigate the flow and heat transfer characteristics inside fiber ducts while also examining the effects of various shapes and opening configurations. The findings indicate that the temperature rise inside the duct is positively correlated with flow rate, with higher temperatures resulting from faster flow speeds. The temperature rise of FADS with four rows of openings increased by 0.4 k compared to other opening methods. Additionally, the study shows that increasing the number of rows of openings in the fiber duct leads to a faster decay of flow velocity and a higher temperature rise. At the same time, increasing the number of openings in the duct slightly reduces flow velocity while slightly increasing the temperature rise. The presence of more fiber duct elbows leads to greater local resistance, which accelerates the decay of the flow velocity and increases the temperature rise. Compared to the "1"-shaped FADS, the temperature rises of the "L"-shaped and "U"-shaped systems have increased by 0.9 k and 2.9 k, respectively. [ABSTRACT FROM AUTHOR]

Stratum ventilation (SV) for heating with proper operation can effectively reduce the energy consumption of the system on the premise of meeting the requirements of thermal comfort. Previous studies mainly focused on the influence of non-human factors on ventilation performance (i.e., thermal comfort and energy consumption), such as multiple ventilation operation parameters (i.e., supply air temperature and supply vane angle) and outdoor temperature. Existing studies show that metabolic rate also greatly influences thermal comfort. Therefore, this study carried out multi-criteria dynamic optimization for the operation of SV for heating that considers the factors of metabolic rate, air supply parameters, and outdoor temperature. Firstly, 25 specific operation cases corresponding to combinations of different levels of factors are determined via the Box–Behnken design. Then, using computational fluid dynamics to simulate the above-mentioned operation cases, so as to construct the response surface model of ventilation performance. Finally, the multi-criteria performance of heating ventilation is optimized through the technique of order preference by similarity to ideal solution based on the set pair analysis (SPA-TOPSIS) method. The results show that after the optimization of SV for heating considering different metabolic rates, the dynamic optimization effect of ventilation performance is significant. The vertical air temperature difference between head and ankle levels, the energy consumption, and the predicted percentage of dissatisfied for 21 different metabolic rates decrease by 19.112%, 3.597%, and 21.289% on average, respectively. The draft risk increases slightly, with an average increase of only 4.736%, and still satisfies the requirements of the standard ISO-7730. [ABSTRACT FROM AUTHOR]

Most of the thermal management for the battery energy storage system (BESS) adopts air cooling with the air conditioning. However, the air-supply distance impacts the temperature uniformity. To improve the BESS temperature uniformity, this study analyzes a 2.5 MWh energy storage power station (ESPS) thermal management performance. It optimizes airflow organization with louver fins and simulates its heat transfer behavior. To improve the flow rate distribution along the airflow passage, the air-supply organization of louver fins for the overhead air conditioner is optimized. It indicates that the air-supply angle (A) for louver fins and the battery spacing (D) impacts greatly on BESS thermal management performance. The air supply optimal organization with the A of 90° and the D of 18mm was determined, of which the average temperature (TA) rise of the battery can be reduced by 18%, and the temperature difference (TD) is decreased by 23%. Furthermore, a multi-parametric sensitivity analysis is conducted, and the different heat-flow parameter influential sequence for the TA and TD are revealed. The air supply volume flow rate (L) and the air supply temperature (AST) has a significant effect on the TA reduction, and the AST shows significance on the TD decreasing. When AST is reduced to 290 K, the TA rise of batteries decreased by 71%. When the L is increased 10 times, the TA rise of batteries decreased by 227%. When the AST is decreased to 290 K, the TD is reduced by 39%. When the L for air supply is increased by 10 times, the TD will increase by 28%. In this research, the louver fins are firstly adopted for orifices air supply organization to improve thermal field uniformity for BESS. [ABSTRACT FROM AUTHOR]

While there have been numerous comparative case studies involving air-lift- dependent situations, this study takes a novel approach and assesses the available evidence supporting six unique airlift anecdotes in military history. These case studies are either moments for celebration or moments for reflection on the role moral hazard plays in airlift operations. [ABSTRACT FROM AUTHOR]

The landing phase of an airdrop process is prone to accidents, and thus, it is important to assess the landing reliability for an airdrop system. However, full field tests to assess the reliability are unacceptable due to their cost and the time required. As such, it is necessary to estimate the reliability in the design stage. To address this problem, a method based on vine-Bayesian Network (vine-BN) is proposed to assess the landing reliability by fusing multisource information. First, the network structure is determined by the relationship between data of simulation or ground tests and failure modes. Then, nodes are defined as random variables on [0, 1] based on the definition of the performance metric. Finally, the dependence between nodes is quantified by expert opinions. To illustrate the effectiveness of the method, a particular ground test or simulation is chosen to establish a network for a typical heavy cargo airdrop system (HCADS). Forward and backward propagation is carried out on the network. The forward analysis predicts the landing reliability in the design stage through multisource information fusion. Beta distribution is applied to fit the fusion result, so Bayesian inference is made to perform field test times decision-making. The backward analysis works to identify the key performance metrics related to landing reliability. The results and analysis manifest that vine-BN is feasible for fusing multisource information. Through the network, the reliability of the current design can be predicted effectively, and the field test times can be remarkably reduced. This method plays a crucial role in airdrop system design and reducing test time and labor. [ABSTRACT FROM AUTHOR]

Despite the high cost and low efficiency, compressed air is mostly used in underground mining for ore extraction, hoisting, and mineral processing operations. Failures of compressed air systems not only threaten the health and safety of workers but also contribute to inefficient control of airflow and stopped all equipment that operates by compressed air. In such uncertain conditions, mine managers are faced with the big challenge to supply enough compressed air, and therefore, the reliability evaluation of these systems is essential. This paper aims to analyze the reliability of the compressed air system using the Markov modeling approach as a case study, Qaleh-Zari Copper Mine, Iran. To achieve this, the state space diagram was constructed considering all relevant states for all compressors in the main compressor house of the mine. The failure and repair rate of all main and reserve compressors were calculated for all possible transitions between states to obtain the probability of being of the system in each of the states. Moreover, the probability of failure at any time period was considered to study the reliability behavior. The results of this study show that there is 31.5% probability that the compressed air supplying system is in operating condition with two main and one standby compressors. The system probability that two main compressors are remain in the operation without failure for one months is 92.32%. Furthermore, the lifetime of the system is estimated 33 months when at least one main compressor is active. [ABSTRACT FROM AUTHOR]

The airflow distribution in an operating room plays a vital role in preventing surgical site infection by diluting and removing particles released by medical staff, lowering particle settlement on a patient. This study aims to computationally examine the efficiency of a ceiling-mounted air curtain in reducing particle distribution in a surgical zone. A computational fluid dynamic (CFD) software simulated an operating room's airflow and particle movements using the corresponding Re-Normalisation Group (RNG) k-ε model and a Lagrangian model. The baseline case and case 1 simulations were equipped with air supply diffusers, while cases 2 to 5 utilised combined air supply diffusers and air curtains. The results revealed that an air curtain fails to reduce particle settlement on a patient. In fact, the use of air curtain in cases 2, 3, 4, and 5 led to an unwanted 3.3-, 4.3-, 3.0-, and 6.7-fold increased particle settlement, respectively. On a positive note, the study found that increasing the area of the air supply diffuser from 4.32 to 7.74 m2 favourably reduced the number of particles by 33.3%. [ABSTRACT FROM AUTHOR]

In the parachute high-speed airdrop test, the parachute is affected by the attitude of the dummy while doing non-uniform acceleration and unsteady motion. The parachute opening dynamic load data obtained from the conventional airdrop test are often discrete, which can not truly reflect the parachute opening performance. According to the influence characteristics of the front body of the parachute, this paper proposes a method of adding a stable parachute to control the attitude of the dummy in the free flight stage, and the motion process of dummy under different working conditions is simulated and analyzed. By using airdrop test of three working conditions, this paper researches the dummy attitude effect on opening shock of parachute, and analyses the test data to obtain the relationship between dummy attitude and opening time, opening speed, opening shock, opening speed loss of parachute, dummy angular velocity. The results show that dummy attitude control does not affect the parachute opening procedure. Compared with the situation without controlling dummy attitude, it is closer to the actual parachute opening procedure in front body for this type life-saving parachute. Based on the results analysis, it is concluded that dummy attitude control can improve the discreteness and the validity of opening shock data, and the maximum parachute opening shock data can be reduced by 8.9%. [ABSTRACT FROM AUTHOR]

Active adjustment of the airflow organization in data centers (DC) has been increasingly applied due to its superior adjustment performance. But for now, the main focus is on the airflow distribution optimization in the horizontal direction, while few research has been conducted to investigate the additional energy consumption of active method. This paper introduced the jet-induced ventilation into under-floor air distribution (UFAD), then the coupling air supply system (CASS) was established. Taking the CASS data center as an example, this paper focuses on the impact of the active adjustment method on both airflow organization and energy consumption of the DC, and analyzes the energy consumption of the system while meeting the security operations of the thermal environment. The results showed that the incorporation of jet-induced ventilation effectively improved the airflow distribution uniformity, while the active adjustment of the airflow organization in the DC has little effect on the overall energy consumption. On the premise of meeting the demand of thermal environment, the energy consumption of the CRAC (Computer room air conditioning) units in the CASS is reduced and the change of the overall energy consumption is small, while the total energy consumption increased with the increase of airflow uniformity. [ABSTRACT FROM AUTHOR]

Two 75 t/h medium-temperature separated circulating fluidized bed boilers burning Fujian anthracite were upgraded with low NOx combustion (LNC). By reducing the effective cross-sectional area of the air distributor (from 13.43 m2 to 11.38 m2), improving the secondary air rate (from 40% to 45%), adjusting the secondary air supply method (adding a layer of upper secondary air, raising the height of the lower secondary air nozzle (0.4 m), and increasing the secondary air speed (from 48 m/s to 54 m/s), the reform of low nitrogen combustion was carried out. The transformation achieved remarkable results, i.e., the original NOx emission concentration can be controlled between 140–160 mg/m3 after the transformation, and the lowest value is below 120 mg/m3. [ABSTRACT FROM AUTHOR]

Conical diffusers of various configurations are used in many kinds of technical equipment and manufacturing processes. Therefore, it is a relevant objective to obtain reliable experimental and mathematical data on the aerodynamic characteristics of diffusers. This article presents experimental data on the aerodynamics of stationary flows in a vertical conical diffuser when air is supplied through tubes with various cross sections (circle, square, and triangle). Instantaneous values of air flow velocity are measured with a constant-temperature hot-wire anemometer. Data are obtained on the velocity fields and turbulence intensity along the height and the diameter of the diffuser's cylindrical part when air is supplied through tubes of various configurations. It is established that air supply through profiled tubes has a significant effect on the shape of the velocity field and turbulence intensity in a vertical conical diffuser. For example, higher values of turbulence intensity are typical of air supplied through profiled tubes (the differences reach 50%). A mathematical formulation (linear and exponential equations) of the change in the average speed and intensity of air flow turbulence along the height of the diffuser's cylindrical part for various initial conditions and supply tube configurations is presented. The obtained findings will make it possible to refine mathematical models and update algorithms for engineering the design of diffusers for various engineering processes and pieces of technical equipment. [ABSTRACT FROM AUTHOR]

A three-dimensional numerical simulation of a combustion chamber with a continuous rotating detonation wave was studied. A nozzle-type main system feeding was located at the end part of the chamber, and an additional feeding from the inner and outer walls of the annular channel was considered. A hydrogen-oxygen mixture was considered as a fuel. A detailed kinetic mechanism by Z. Hong (2010) consisting of 20 reactions with 9 components was used to simulate chemical processes. Various relations of the fuel were considered: lean mixture [H 2 ]:[O 2 ] = 1:1, stoichiometric mixture [H 2 ]:[O 2 ] = 2:1, and rich mixture [H 2 ]:[O 2 ] = 3:1. Besides, either the same mixture, or additional oxygen, or air was supplied from the side-wall feeding system. For all the considered feeding options, a detonation mode was obtained, and the traction characteristics were calculated. • A simulation of an engine powered by a hydrogen-air mixture was carried out. • Hong's kinetic mechanism was considered. • The influence of the fuel concentration on the processes in the chamber was studied. • Traction characteristics were obtained and analyzed for all cases. [ABSTRACT FROM AUTHOR]

In recent years, proton exchange membrane fuel cell (PEMFC) has received growing attention as a new sustainable energy source because of its high-power density and zero-emission. In the PEMFC system, the air supply control has a significant impact on the efficiency and lifetime of the PEMFC stack. However, external disturbances and output constraints regularly have negative effects on air supply control. This paper aims to investigate a novel system analysis and advanced strategy control for the oxygen-excess ratio of a PEMFC system under the variant load current disturbance. The air-supply dynamic model is established which takes into account the supply manifolds, compressor, and the PEMFC stack. The proposed control method is designed based on finite-time command-filter control (FTCFC) to improve the tracking performance and ensure the finite-time convergence. Moreover, owing to the suggested prescribed performance function, the oxygen-excess ratio output remains in the pre-boundedness. Theoretical analysis exhibits that the closed-loop system stability is guaranteed by the Lyapunov theory. Finally, the simulation and hardware-in-loop (HIL) experiments are carried out on MATLAB environment and a 100 W power PEMFC system to validate the effectiveness of the suggested methodology. [ABSTRACT FROM AUTHOR]

When burning fuel in grate furnaces, supplying the right amount of air to them is as important as the method of air supply. In a furnace with a fixed grate, the supply method of primary air is determined by the distribution of the supplied air stream over time, and in a furnace with a movable grate, the said method involves the distribution of the stream along the active length of the grate. The need to account for air distribution is attributable to complex processes that occur during the combustion process. The paper describes experimental studies aimed at determining the influence of the distribution of the supplied primary air on the emission of CO2, CO, SO2, NOx, and on the content of combustible parts in the slag. In all cases, the total amount of primary air supplied to the process as well as other process control parameters was identical, and only the distribution of primary air was different. The paper proposes the use of a generalized function to describe the distribution of air, defined by its total demand and the relative time R that fuel remains on the grate until the maximum air stream is obtained. The quantity R was accepted at the value ranging from 1/6 to 2/3. With the rise of R, the emissions of CO2, CO, and SO2 increased by 53%, 125%, and 27%, respectively, and the emissions of NOx and the share of combustibles in the slag decreased by 12% and 79%, respectively. [ABSTRACT FROM AUTHOR]