Upward Airflow Research Articles

Dominant spring precipitation anomaly modes and circulation characteristics in the Tarim Basin, Central Asia

Recently, extreme precipitation has occurred frequently in the Tarim Basin, which has a fragile ecological environment, arousing widespread concern. Using daily precipitation observations from 42 stations in the Tarim Basin during the spring of 1980–2021 and monthly circulation reanalysis data from the European Center for Medium-Range Weather Forecasts Reanalysis v5, as well as statistical analyses and physical diagnostic methods, this study investigated the abnormal modes and the evolution characteristics and differences in atmospheric circulation. The results show that the spring precipitation anomalies in the Tarim Basin can be divided into two independent precipitation modes: the first (EOF1) is a precipitation pattern that is uniform throughout the region and the second (EOF2) is an east–west inverse pattern. Thus, there are distinct differences in the atmospheric circulation characteristics responsible for abnormal spring precipitation modes in the basin. When the precipitation across the entire basin is consistently excessive, the 500 hPa geopotential height is affected by the negative phase of the North Atlantic Oscillation related circulation, and anomalous negative geopotential height at 500 hPa and anomalous cyclone at 700 hPa control the entire Tarim Basin, favoring anomalous upward motion, and western and southwestern water vapor transport. This leaves the Tarim Basin with a net water vapor budget and abnormally high atmospheric precipitable water. The opposite situation occurs when the precipitation across the entire basin is consistently lower than normal. When there is a west-to-east precipitation gradient, the western part of the Tarim Basin is affected by the anomalous cyclone while the eastern part is affected by the amomalous anticyclone, leading to the east-west discrepancy. The western region of the Tarim Basin is dominated by upward airflow, whereas the eastern region is dominated by downward airflow, providing dynamic conditions for the west-to-east precipitation gradient. Under the influence of anomalous water vapor transport from the southwest and water vapor convergence, water vapor conditions favorable for precipitation can occur. The net water vapor in the basin also exhibited an abnormal west-to-east transport pattern. Moreover, the atmospheric precipitable water demonstrated an inverse phase distribution under the EOF2 atmospheric precipitation mode in the Tarim Basin.

Karst cave, a seasonal carbon dioxide exchanger: an example of Sloup-Šošůvka Caves (Moravian Karst)

Part of the gaseous carbon dioxide (CO2) produced in karst soils / epikarst is transported into underground cavities / caves during the growing season by advective flux, diffusive flux, and flux associated with degassing of seeping water. In dynamic caves, accumulated CO2 is released into the outside atmosphere during the autumn-winter period through advective flux associated with ventilation of the cave in the upward airflow mode. This case study from the Moravian Karst (MK) showed that the net weight of CO2 released annually from the Sloup-Šošůvka Caves (total volume of 131,580 m3 and a total area of 17,950 m2) into the external atmosphere was 348 kg. Extrapolating this value to all known MK caves (area about 352,080 m2) yielded a total of CO2 flux of 6820 kg yr−1. This flux is representing only 0.024‰ of the annual soil respiration from entire MK area (about 2.81 × 108 kg CO2 yr−1).

The investigation on the ceiling of inlet velocity regarding to fine particle separation in a cyclone

The maximum efficiency inlet velocity (MEIV) serves as the upper limit for the inlet velocity that defines the separation efficiency in cyclone design and operation. In this paper, a combination of numerical and experimental methods is used to study MEIV. Experimental findings indicate that the MEIV is 22 m/s for a median particle size of 12.39 μm (coarse powder) and 35 m/s for a median particle size of 2.93 μm (fine powder). Meanwhile, the amount of escaped fine powder is reduced by 25% compared to that at an inlet velocity of 22 m/s. Computational fluid dynamics (CFD) simulations have shown that the inconsistency between tangential and axial velocity growth of inlet velocity with respect to various powder diameters can explain this phenomenon. As the inlet velocity increases, the peak axial velocity exhibits a stepwise increase. When the peak value remains constant, the peak width increases. This phenomenon is called stagnation of the axial velocity. During the axial velocity stagnation step, the residence time of back-mixed particles vary. In contrast, the tangential velocity increases linearly with the inlet velocity, resulting in an enhanced secondary separation of the inner vortex. Both factors hinder the escape of fine particles due to entrainment by a rapid upward airflow. The inlet velocity range corresponding to the stagnation step of the fine powder is larger than that of the coarse powder. Therefore, the MEIV of the fine powder is higher.

Investigating the impact of air distribution on spray dryer operability using CFD simulations and pilot-scale experiments

Fouling reduces spray dryer operability. The impact of different configurations of a spray dryer on operability and nozzle-zone agglomeration stimulated by dry powder dosing was investigated through a combination of CFD simulations and pilot-scale experiments. Included were two positions of the nozzle and dry powder introduction, and two degrees of air swirl. Air flows and droplet trajectories were simulated and a particle collision model was built in. The experiments were executed using a single stage co-current spray dryer with concentrical fines return. A high nozzle position (6 cm below the air inlet) resulted in undesired fouling due to an upward air flow causing wet droplets to collide with the roof. The operability was improved by lowering the nozzle position 25 cm as there was less fouling. With a low nozzle position, the degree of air swirl only had a limited effect on fouling. Surprisingly, agglomeration did not seem to be significantly affected by air distribution in both the simulations and the experiments. This means that there is some freedom in the design of a spray dryer in terms of agglomeration. Overall, the findings highlight the importance of well-designed spray drying operations to reduce fouling and thus minimize product waste.

Summer long-lived heatwaves in Northeast Asia promote heavy precipitation in South China

Heatwaves interact with various extreme weather events, amplifying their impacts beyond the risks associated with high temperatures alone. However, previous research has often overlooked the extent to which heatwaves influence regions beyond their origin. In this study, we introduce a classification of heatwaves in Northeast Asia, distinguishing between long-lived heatwaves (LHWs) lasting five days or more and short-lived heatwaves (SHWs) lasting less than five days. The study highlights the significant role of LHWs in triggering heavy precipitation in South China. The anticyclonic anomalies associated with LHWs are influenced by a slow-moving wave train, initiating and sustaining cyclonic anomalies over South China, resulting in upward airflow anomalies. Additionally, easterly wind anomalies in the southern region of the anticyclonic anomalies facilitate moisture transport to South China, creating favorable conditions for precipitation. The findings underscore that LHWs could account for a noticeable portion (17.6%) of total summer extreme precipitation days in South China. The study highlights the significant role of LHWs-related circulations in triggering heavy precipitation in South China.

The effect of cave ventilation on carbon and oxygen isotopic fractionation between calcite and drip water

Rapid CO2 degassing and calcite precipitation driven by cave ventilation influence the speleothem δ18O and δ13C. However, the drivers of cave ventilation are not completely understood due to the lack of monitoring of multiple environmental factors. Furthermore, the understanding of isotope fractionation caused by the dissolution of speleothem in undersaturated drip water is limited during the cave air stagnation. In this study, we displayed four years of cave microenvironment monitoring in Shawan Cave, Southwestern China, and analyzed the δ13CDIC and δ18O of drip water, and calcite precipitation δ18O and δ13C. The results show that the ventilation process is attributed to buoyancy airflow between external atmosphere, fissure air, and cave air. This causes that the higher (lower) cave air pCO2 in the summer (winter) is associated with upward airflow mode (downward airflow mode). Furthermore, cave ventilation could control the isotopic fractionation. Specifically, when cave air pCO2 is lower, the carbon isotopic disequilibrium between calcite and dissolved inorganic carbon (DIC) is controlled by the degassing of CO2 associated with calcite precipitation. The disequilibrium fractionation in carbon isotopes is less pronounced at slower drip-rate sites. The oxygen isotope fractionation between calcite and the drip water is found to be close to equilibrium. However, the high cave air pCO2 (exceeding 10,000 ppm) may result in drip water undersaturation to drive the dissolution of speleothem calcite. The δ18O values of drip water are pulled away from their original values to disequilibrate to the calcite because the exchange time of oxygen in the dissolved carbonates with the oxygen in the water is sufficiently long. Hence, the dissolution of speleothems may be a new mechanism to explain the oxygen isotopic disequilibrium between the calcite and drip water during the cave air stagnation. The carbon isotope fractionation between calcite and drip water is close to equilibrium.

The role of the cold pool in a mountain-to-plain and plain-to-mountain squall line case in the south of the Yangtze River in China

A squall line event that occurred in the south of the Yangtze River in China on 4 May 2020 was simulated using the WRF model and 3DVAR data assimilation. The radar radial wind, reflectivity, and conventional observation data were assimilated in a cycling interval of 15 min. The main findings from the examination of the development mechanisms of the squall line are as follows. The simulation effectively reproduced the development and evolution of the squall line. The squall line strengthened from the Wuling Mountains to the Dongting Lake Plain, moved eastwards and developed to its strongest stage over the plains, before weakening from thereon to the Mulianjiu Mountains. When the squall line moved from the mountains to the plains, the convergence of the airflow in front of the squall line increased because of the strengthening of the near-surface easterly airflow over the plains. Concurrently, the intensity of the cold pool behind the squall line decreased, while the low-level vertical wind shear over the plains increased. This reduced the gap between the cold pool and vertical wind shear. The low-level upward airflow in front of the cold pool tended to be vertical, which was conducive to the development and maintenance of the squall line. When the squall line moved eastwards from the plains to the mountains, the convergence of the airflow in front of the squall line weakened because of the weakening of the surface easterly airflow over the mountains. Concurrently, the intensity of the cold pool behind the squall line increased, while the low-level vertical wind shear in front of the squall line significantly declined. The intensity of the cold pool significantly exceeded the low-level vertical wind shear, inducing a tendency for the low-level upward airflow in front of the cold pool to tilt towards the cold pool, which was not conducive to the development and maintenance of the squall line. This was a reason why the squall line moved eastwards faster after going up the mountains. Based on these observational and simulation results, physical conceptual models for the enhancement of squall lines from the mountains to the plains and their weakening from the plains to the mountains have been preliminarily developed.

Aerodynamic performance comparison of wind-driven turbine ventilators: A numerical investigation

Wind-driven roof ventilator is a cost-effective and environmentally sustainable solution for improving indoor ventilation and reducing energy use. This study aims to compare the ventilation performance of turbine ventilators with curved and straight blades of various sizes, utilizing both computational fluid dynamics (CFD) methods and experimental validation. Additionally, a mathematical expression is derived based on the aerodynamic principles of turbomachinery. The results indicate that both types of ventilators exhibit two streams of rotating airflow and an upward airflow. The angular velocity and ventilation rate demonstrate an approximately linear increase with higher wind speeds, and ventilators with smaller outer diameters experience a greater rate of increase in angular velocity. Larger-sized ventilators, despite having lower angular velocities, achieve higher ventilation rates for geometries of similar proportions. However, it should be noted that reducing the throat diameter may result in inadequate ventilation rates. In general, straight blade ventilators outperform curved blade ventilators, yielding 10%–38% higher ventilation rates due to their lower flow resistance. The discharge coefficients for the former and the latter are 0.32–0.37 and 0.25–0.32, respectively. The derived mathematical expression based on aerodynamics agrees well with the simulation results, providing a means for predicting ventilator performance. The objectives of this study are to enhance understanding of the ventilation performance of two types of turbine ventilators, aid in the selection and design of wind-driven roof ventilators, and promote improved indoor ventilation and energy efficiency.

Influence of environmental parameters on workers' dust inhalation in underground mines.

Much dust is generated in underground coal mining processes, posing threats to workers' health and safety production. Dust enters the human body mainly through inhalation, primarily determined by the dust concentration around workers. In this study, the airflow field and dust distribution in the tunnel are simulated with FLUENT software. The breathing zone for a worker was defined to clarify the extent of external dust distribution influencing dust inhalation. The effects of human respiration, dust production rates, air supply velocities, and workers' positions on dust concentration in the breathing zone were investigated. The results show that there is upward airflow around the worker standing in the center of the air circulation. Human breath barely influences the airflow distribution and respirable dust concentrations in the breathing zone. Reducing the dust production rate in the tunnel can decrease the respirable dust concentration in the breathing zone by almost the same proportion. While increasing the air supply velocity by 50% would reduce only 20% of dust in the breathing zone. The dust concentrations vary along the roadway, in which the low concentration zone is located in the middle, more than 1.0m away from the dust-producing surface and the wind surface. The research contributes to reducing workers' dust exposure with suggestions regarding ventilation optimization and working position selection.

Research on snow prevention in the bogie region based on active blowing method

To reduce excessive snow accumulation on bogie surfaces during high-speed train operations in cold regions, two active blowing schemes are designed in this study based on the shape of the bogie cavity and the relative position of the brake caliper. The unsteady Reynolds-averaged Navier–Stokes algorithm coupled with a discrete phase model was used to calculate the airflow and snow flow under the train. Moreover, the algorithm is employed to explore the impact of active blowing on the flow field characteristics and snow accumulation in the bogie region. Results show that active blowing changes the upward airflow in the bogie region, causing air at the bottom of the train to flow outwards, carrying off numerous snow particles from the bogie region. Active blowing accelerates the surface friction velocity on the bogie, increases the shear force on snow particles, and effectively reduces the snow accumulation on the bogie surface. The foregoing observation indicates that active blowing has considerable potential for snow accumulation prevention.

Automated- closed canopy chamber for measuring photosynthesis and transpiration responses of ornamental plants to soil aeration

A system was developed for measuring the time course of photosynthesis and transpiration. The system was applied to ornamental plants in an office under different root environmental conditions: soil and non-soil aerations. This system composes an automated-closed chamber and a sensing unit. The shoot part of a fully grown ornamental plant enclosed by a transparent film in the chamber. Two circulation fans are installed at the center of the chamber to continuously stir the air. One ventilation fan located at the bottom of the chamber to exhaust air and create an upward airflow in the chamber. When the ventilation fan is turned off, the chamber becomes a closed space. The changes in the concentrations of CO2 and H2O during the period over which the chamber is closed are used to calculate the photosynthesis and transpiration rates of the plant. Two types of ornamental indoor plants were observed under the aforementioned root conditions. Soil aeration was found to produce an increase in the photosynthetic rate, transpiration rate, and total conductance. These results indicate that the measuring system could be a particularly helpful tool for evaluating temporal changes in the photosynthesis and transpiration of ornamental plants in an indoor environment.

A novel personal comfort system for older adults in hot conditions: Design, modelling, and performance

This study introduces a novel personal comfort system aimed at establishing a relatively uniform thermal microclimate around the body to meet the thermal needs of seated elderly individuals under hot conditions. The system integrates cool air supply vents into a chair to provide thermal comfort by i) generating upward airflow by colliding jets to disperse cool air across the upper body; and ii) releasing air flow targeting the lower body by relying on buoyancy for air confinement.A computational fluid dynamic model was developed to predict the flow and thermal fields around the occupant who is seated on a chair equipped with the proposed system. The model was experimentally validated in a climatic chamber using a thermal manikin. An elderly bioheat and thermal sensation models were used to predict skin temperatures and corresponding sensation of elderly users. The microclimate was assessed in terms of effective confinement of cool air around users and improvement in elderly thermal sensation. At a total chair supply flow of 17 l/s, microclimate air confinement was attained. At 29 °C room temperature, the proposed system lowered the mean skin temperature from 34.15 °C to 33.33 °C and improved the whole-body TS, which decreased from slightly warm to neutral. At 33 °C room temperature, the mean skin temperature decreased from 35.6 °C to 33.99 °C and the sensation improved, decreasing from above warm to below slightly warm.

Field application of bio-foam spray to reduce ammonia emission from ammonia-rich swine manure piles

In this study, the first field-scale application of a bio-foam spray (a mixture of microbes and a surfactant) for the reduction of ammonia emitted from manure was investigated on six field swine manure piles. The objective of this study was to evaluate the odor suppression ability of bio-foam and odor degradation ability of odor-degrading bacteria loaded in the surfactant foam after covering manure piles. The size of field manure piles tested in this study ranged from 27 to 300 m3. Bio-foam spraying completely suppressed the release of the major odor component, ammonia (NH3), and odor-degrading bacteria in the bio-foam aided in the degradation of NH3 in field swine manure piles. On average, 85.7–100% of NH3 was reduced after 24–48 h of serial bio-foam spray application on the swine manure surface, while the control showed 25–42%. The reduction efficiency of NH3 by the bio-foam application was affected by the bio-foam spray frequency, ambient temperature, ventilation of the field facility, and upward airflow to the pile. The reduction in surface emission of NH3 also reduced the ambient air concentration of NH3 at the gate of the compost facility. NH3 gas measurements at a depth of 50 cm indicated that NH3-degrading bacteria infiltrated the manure and were active in biodegradation. Finally, the measured effectiveness of bio-foam application as shown by this study indicates that sprinkling bio-foam via specialized rotating sprinklers may be an efficient and uniform method for the delivery of bio-foam to wide field areas within composting facilities.

Optimizing window ventilation strategies for high-rise residential buildings with U-shaped lightwell: Simulating gaseous pollutant cross-room transmission

The lightwell structure widely used in high-rise residential buildings becomes a pathway for the cross-room transmission of gaseous pollutants. In order to devise effective strategies for window ventilation, it is necessary to conduct research on the transmission characteristics of pollutants in the lightwell. The unsteady-state characteristic of the temperature in natural conditions is represented using a sine function. The transmission of pollutants in the lightwell during the 24 h was simulated by computational fluid dynamics (CFD) employing the RNG k-ε turbulence model and continuous phase model. Three pollution sources were considered at three typical building heights: low floor (5 floors), middle floor (18 floors), and high floor (32 floors). Moreover, the window ventilation time was accurately determined by calculating the room's re-entry ratio near the pollution sources. The results show that the day (24 h) can be divided into three time periods based on the airflow pattern in the lightwell: the downward airflow time (17:00 to 2:30), the upward airflow time (5:00 to 15:00), and the transition time (2:30 to 5:00 and 15:00 to 17:00). During the transition time, pollutant is transmitted both horizontally and vertically, and all rooms around the pollution source are unsuitable for window ventilation.

Prolonged facemask wearing among hospital workers and dry eye – a mixed-methods study

BackgroundProlonged facemask wearing may have negatively affected essential workers with dry eye. We conducted a mixed-methods study to examine and understand the associations of the ocular surface, periocular environment, and dry eye-related symptoms among hospital workers across the job spectrum with prolonged facemask use.MethodsWe recruited clinical and non-clinical hospital workers with self-reported symptoms of dry eye and prolonged facemask use. We measured symptoms using the 5-item Dry Eye Questionnaire and the Ocular Surface Disease Index (OSDI). Objective ocular signs included corneal and conjunctival staining, fluorescein tear break up time (TBUT), meibography, tear film interferometry, and periocular humidity. We compared symptoms and signs across levels of periocular humidity, dry eye severity, facemask type, and job type. Participants with moderate or severe dry eye symptoms (OSDI > = 23) were invited for a semi-structured, one-on-one interview.ResultsWe enrolled 20 clinical and 21 non-clinical hospital workers: 27% were 40 years or older, 76% were female, 29% reported a race other than White, and 20% were Hispanic. Seventeen individuals participated in the semi-structured interviews. From the quantitative analyses, we found that 90% of participants reported worsened severity of dry eye at work due to facemasks. Although wearing facemasks resulted in higher periocular humidity levels compared with not wearing facemasks, 66% participants reported increased airflow over their eyes. Findings from the qualitative interviews supported the finding that use of facemasks worsened dry eye symptoms, especially when facemasks were not fitted around the nose. The data did not suggest that non-clinical hospital workers experienced a greater impact of dry eye than clinical workers.ConclusionsHealthcare providers and patients with dry eye should be educated about the discomfort and the ocular surface health risks associated with inadequately fitted facemasks. Wearing a fitted facemask with a pliable nose wire appears to mitigate the upward airflow.

Feedback control applied to a low cost ball-in-tube air levitation plant

Commercial educational tools for teaching feedback concepts in control systems engineering and mechatronics are generally expensive, large, complexand sensitive instruments; therefore, it cannot be used in universities with budget constraints, which greatly hinders the teaching of basic concepts of control theory and application. The mathematical tools that are taught in the disciplines of control theory in the undergraduate course are often abstract, especially in terms of practical application in an industrial setting, which makes it necessary to use didactic control plants to complement teaching and hands-on experimentation. This paper presents a low-cost ball and tube air levitation laboratory system as a teaching tool for engineering. Ball and tube laboratory setup is a dynamic benchmark system, designed to control the position of the ball on a vertical upward airflow that counteracts the gravitational force exerted on the ball without mechanical support. A blower feeds airflow, and the position of the ball is measurable by using an ultrasonic distance meter. As the purpose of the article is to serve as support material for undergraduate students who are taking their first steps in the study of control theory and feedback control, detailed modeling by the laws of physics are presented, followed by classic tools for the study of linear control and then a proportional-integral-derivative (PID) control system is developed. A modified structure of the classic PID is used and the results are compared with the classic structure.

Correction: Experimental and numerical study of forced convection heat transfer in a upward two-phase flow of air–water/SiO2 nanofluid with slug flow regime

Correction: Experimental and numerical study of forced convection heat transfer in a upward two-phase flow of air–water/SiO2 nanofluid with slug flow regime

Experimental and numerical study of forced convection heat transfer in a upward two-phase flow of air–water/SiO2 nanofluid with slug flow regime

Experimental and numerical study of forced convection heat transfer in a upward two-phase flow of air–water/SiO2 nanofluid with slug flow regime

The research on the interfacial area transport equation in rectangular channels: Interfacial characteristics distribution and bubbles interaction mechanism

The interfacial area transport equation (IATE) is employed to describe the evolution of interfacial structure and evaluate the interfacial area concentration of two-phase flow. However, the interaction mechanisms among bubbles change in different rectangular channels, significantly impacting interfacial characteristics and source terms in IATE. In order to study the interface characteristics and mechanism of bubble interaction in rectangular channels with different gap sizes, an experimental study was conducted on the upward mixture flow of air and water in an adiabatic vertical channel under atmospheric pressure. Two channels with cross-sections of 4 × 66 mm and 8 × 66 mm were selected. The superficial velocities of water and air were 0.5–3 and 0–1.12 m/s, respectively, almost at the transitional region of bubbly to slug flow. Flat electrodes and the four-sensor probes measured the interfacial characteristics. This study analyzes the development of interface and mechanism of interaction among bubbles. The result shows that the evolution in the distribution of void fraction and interfacial area concentration significantly depends on the flow regime, flow rate, and cross-sectional geometric size of channels. Under the condition of a lower liquid flow rate, the gap size of the channel plays a vital role in the efficiency of bubble coalescence, influencing the mechanisms of the random collision and wake entrainment among bubbles. However, the interfacial parameter distribution under higher liquid rate conditions is dominated by turbulence intensity and flow regime, and the mechanisms of bubble interaction become identical. Finally, the mechanisms of interaction among bubbles (random collision and wake entrainment) are analyzed based on the development of interfacial characteristics. In a word, based on the conclusions specified in this research, the new models of source terms of ITAE in rectangular channels will be predictably established in the future.

Improving advantages and reducing risks in increasing cyclone height via an apex cone to grasp vortex end

• Introduction of a cone leads to maintain the cyclone efficiency with an excessive height. • It is found that the vortex turning is forced to occur at the location of apex cone. • The added apex cone can stretch the vortex length to protect the efficiency. • The stagnant upward airflow in the centre is helpful to protect the efficiency. • The cone enhances the tangential velocity of inner vortex rather than outer vortex. For a cyclone, it is possible to improve separation efficiency and reduce pressure drop by increasing the cyclone height. However, an exceeded height increase could result in a dramatical drop in separation efficiency. In this study, experimental and computational fluid dynamics simulation results exhibit that the introduction of an apex cone at the dust outlet could avoid the risk of separation efficiency drop but lead to a continuous reducing of the pressure drop. Generally, the optimal cyclone height should be closely related to the natural vortex length. While, when the vortex end contracts into the separation space in the cyclone with an exceeded height, severe back-mixing of particles always occurs, which will result in the decrease of separation efficiency. Herein, it is found that when an apex cone is installed at the dust outlet, the vortex end can be grasped by the cone so as to weaken the back-mixing of particles. Meanwhile, the introduction of this apex cone can enhance the secondary separation to capture the back-mixed particles again so as to protect the efficiency. In addition, it is found that the enhanced secondary separation could come from either the stagnant current of axial velocity in the center or the improved tangential velocity of inner vortex whereas the forcibly extending the length of vortex to exceed its natural length will not significantly increase efficiency.