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In this study, the dynamic process of a droplet moving with a substrate until blocked by air flow is investigated experimentally and theoretically. A sequence of experiments has been conducted to investigate the impacts of wetting properties, droplet volumes, air flow velocities, and droplet velocities. The substrate is driven by a linear motion motor to ensure the droplet moves at a certain velocity alongside the substrate. The air flow that is vertically injected from the nozzles toward the substrate is known as an impinging jet. After the air flow impacts the substrate, it will blow horizontally. When the direction of air flow is opposite to that of the droplet movement, a force will be exerted on the surface of the droplet. This action incurs the deformation of the droplet and the cessation of its movement, eventually resulting in an equilibrium state. The droplet shape and motion processes are recorded by a high-speed camera. A mathematical model considering the effect of droplet contact angle, droplet size, droplet moving velocity, and air flow velocity is established in the state of equilibrium. Correlation factors are used in the model for the drag coefficient and air average velocity acting on the droplet. It is found that the air flow rate required to stop the motion of the droplet increases with the droplet moving velocity and the droplet size but reduces with the increase in the static contact angle. The mathematical model, when equipped with suitable correlation factors, exhibits good agreement with experimental data and could potentially be utilized as a predictor of critical velocity for the cessation of the droplet motion. [ABSTRACT FROM AUTHOR]

Considering that nearly 39% of the total CO2 emission released into the atmosphere today are thought to be due to the energy consumed by buildings, the importance of taking measures through buildings to combat global warming is evident. Therefore, the concept of nearly zero‐energy buildings (NZEB) is come to the forefront. Building integrated photovoltaic thermal (BIPV/T) systems are used to enable buildings to generate their own energy. However, buildings have limited facade and roof areas required for BIPV/T systems. Therefore, in this study, various configurations of bifacial (double‐sided) and monofacial (single‐sided) panels were compared to investigate ways to enhance the efficiency of BIPV/T systems. Different air flow velocities and varying air gap distances were tested for both panel types. By placing a reflective surface on the wall behind the bifacial panel, the electrical efficiency of the bifacial panel was increased and proven through PVsyst analysis. Both panels provided maximum heat efficiency at the shortest air gap distance under high air flow conditions. In addition, it was shown in both the experimental setup and Comsol CFD analysis that it provides significant benefit in the thermal energy load of the building when heating the interior environment in winter. In terms of electrical power production surplus, the bifacial panel outperformed the monofacial panel in all configurations, with a minimum advantage of 8.33% and a maximum of 12.73%. Additionally, the maximum electrical efficiency was obtained from the bifacial panel in configurations with the longest air gap distance. Using the bifacial panel in the BIPV/T system with the shortest air gap distance during the heating season and the longest air gap distance during other seasons can provide the highest efficiency for the building throughout the year. [ABSTRACT FROM AUTHOR]

To meet the requirements of achieving higher efficiency and lower NOx pollution, the flame temperature in gas turbine combustors increases continually; thus, the effusion-cooling technology has been used to ensure the combustor liner remains within the allowed temperature, by which the combustion characteristics and emission behavior are possibly influenced. In order to investigate the effects of dome cooling air flow on combustion characteristics and NOx emissions, three-dimensional combustion simulations for a swirl-stabilized can-type gas turbine combustor are carried out in this work by using the computational fluid dynamics (CFD) method. Through adjusting the ratio of the dome cooling air flow and the dilution cooling air flow, the characteristics of flow field, temperature distribution and NOx emissions under each work condition are analyzed. At different ratios of the dome-cooling air flow to the total air flow, the flow velocity field in the region near the center of the combustion chamber is not changed much, while the velocity field near the chamber wall shows a more significant difference. The temperature in the outer recirculation zone within the combustion chamber is effectively reduced as the dome cooling air flow increases. By analyzing the distribution characteristics of the concentration of OH*, it is demonstrated that the dome cooling air flow does not have a direct effect on the reaction of combustion. It is also found that as the ratio of the dome cooling air flow to the total air flow increases from 0 to 0.15, the value of the NOx emissions drops from 28.4 to 26.3 ppmv, about a 7.4% decrease. The distribution of the NOx generation rate in the combustion chamber does not vary significantly with the increasing dome cooling air flow. Furthermore, by calculating the residence time in different stages, when the the ratio of the dome cooling air flow to the total air flow varies from 0 to 0.15, the residence time in the pilot stage decreases obviously, from 42 ms to 18 ms. This means that reduction in residence time is the main factor in the decrease of NOx emissions when the dome cooling air flow increases. [ABSTRACT FROM AUTHOR]

With the increasing demand for the resilient capacity of transformers in high-proportion renewable energy grids, the overload capacity of transformers and the thermal conductivity of winding insulation materials have been put forward as important requirements. In response to these requirements, a novel ceramic high temperature tolerance insulation winding is proposed in this paper and is applied in a ceramic insulated winding transformer. A combination of simulation and experimentation is used to analyze the thermal-flow characteristics of this transformer. The temperature and flow field distribution characteristics of transformers with both winding insulation methods (ceramic and Nomex paper) are compared. The internal mechanism of reflux near the iron core and high voltage winding under forced air cooling is clarified. A superior outside cooling condition is obtained. A prototype ceramic insulated winding transformer is developed and tested to verify the accuracy of the simulation model. The results show that the hotspot temperature of the ceramic insulated winding transformer under natural cooling is 10.7% lower than that of the Nomex paper insulated winding transformer. With forced air cooling of 2, 3, 4, 5, and 6 m/s applied at the bottom, the hotspot temperature of the ceramic insulated winding transformer is 11.4%, 10.5%, 9.7%, 14.0%, and 17.8% lower than that of the Nomex paper insulation winding transformer, respectively. Under forced air cooling, a reflux phenomenon is observed in both transformers in the vicinity of the iron core and high voltage winding due to the formation of adverse pressure gradient region and wall viscous force blocking. The strength of the reflux is affected by the magnitude of the forced air cooling flow velocity and the construction of the transformer. The optimal range of the external cooling flow velocity for the ceramic insulated winding transformer is 3–4 m/s. The errors between the simulated temperature and the measured temperature at the nine monitoring points of the prototype are all less than 5%, which verifies the effectiveness of the simulation model. The experimental and theoretical basis for the design and application of resilient capacity dry type transformers is provided by this research. [ABSTRACT FROM AUTHOR]

This study focuses on the hibernation behavior of the western barbastelle bat (Barbastella barbastellus) in underground systems in Poland from 2006 to 2011, specifically during the peak hibernation months of December to February. The impact of climate parameters, namely temperature (T), humidity (Rh), and air flow velocity (v), on the clustering behavior of bats during hibernation was investigated. The climate parameters varied within specific ranges: T fluctuated between 6.0 and 12.4 °C, Rh ranged from 56.4 to 91.8%, and v varied from 0.01 to 1.17 m/s. The quantile linear regression method for statistical analysis of the results was employed. This study found that certain combinations of climate parameters influenced the grouping behavior of bats during hibernation. The model structural parameters revealed the following relationships: 1. An increase in the product of T and v led to an increase in the bats' group size. 2. For pairs of variables such as T and Rh, and Rh and v, an increase in their product resulted in a decrease in the bats' group size. 3. When considering the product of T, Rh, and v, a decrease in the bats' group size was also observed. [ABSTRACT FROM AUTHOR]

Mechanized agriculture is the foundation of large-scale agriculture. However, in current mechanized corn cultivation, the cleaning efficiency during the cleaning phase is poor due to design defects, which in turn reduces its yield. Therefore, this study proposed an optimization of the corn screening device based on high-precision aerodynamic models. 3D modeling was used to explore the parameter optimization of the corn cleaning devices from an aerodynamic point of view, and certain improvements were made to the fish scale sieve structure. The results indicated that the cleaning efficiency was related to airflow velocity, vibration frequency, and the opening of the fish scale sieve. The optimal wind speed was 16 m/s, and the separation efficiency currently was 94.27%. The optimal vibration frequency was 8 Hz, and the separation efficiency currently was 97.24%. The optimal opening of the fish scale sieve was 26 mm, at which point the screening efficiency reached 100%. The optimized fish scale sieve reduced blockage by 63.7% compared to the traditional fish scale sieve, and ultimately achieved an impurity content of 1.4% with an improvement of 81.3%. In summary, the optimization plan proposed by this research can effectively improve the cleaning efficiency of corn and promote agricultural production and efficiency. [ABSTRACT FROM AUTHOR]

A numerical investigation of the influence of the compressibility of the air flowing around a disk–cylinder–disk set with an outward-projecting disk of diameter 0.4 and a clearance between this disk and the cylinder of 0.98, close to the optimum one as to the profile drag for the movement with a transonic velocity at Mach numbers of 0–2, on the circulation air flow in the clearance and on the frontal resistance of the set has been performed. The adequacy of the numerical estimates made was substantiated by their comparison with the corresponding results of experiments in a wind tunnel. It was established that in the transonic Mach number range 0.7–0.8, the structure of a vortex in the clearance between the outward-projecting disk and the front edge of the cylinder is rearranged. Because of this, unlike the axisymmetric flow of air around a disk–cylinder–disk set optimum for an incompressible medium, normal and oblique shocks are not formed over the shear layer of the detached flow in the indicated clearance, and, at M = 0.9, a lambda-like shock is formed over the side surface of the cylinder. The wave drag of a disk–cylinder–disk set, optimum for transonic velocities, increases at a smaller rate with increase in the Mach number and appear to be smaller by almost two times compared to the wave drag of a disk–cylinder–disk set optimum for the deep subsonic velocities. [ABSTRACT FROM AUTHOR]

When air flows through the mirrors, A-pillars, and other surfaces of a passenger car, airflow separation occurs to generate vorticity and generates aerodynamic noise. The dipole noise source is the main source of aerodynamic noise when the passenger car is travelling at high speed. In order to reveal the relationship between the physical quantities in the flow field and the intensity of the dipole noise source, this paper equates each dipole noise source to a sphere radiating noise to the outside. The acoustic wave fluctuation equations expressed as spherical coordinates are combined with the acoustic boundary conditions and the equations of motion of an ideal fluid medium to obtain the relationship between the intensity of the dipole noise source and the flow velocity and vorticity in the flow field. Then, through flow field simulation, we establish a method of identifying the dipole noise source and its distribution area, and analyze the generation mechanism of the dipole noise source. Through the analysis, it is concluded that the dipole noise sources are mainly concentrated in the airflow separation areas, which easily generate vortices. The size of the vorticity is the key factor affecting the intensity of the dipole noise source. When the intensity of the dipole noise source reaches its peak, the direction of the flow vorticity is perpendicular to the direction of the flow velocity and the peak of the flow velocity occurs before the peak of the dipole noise source, which indicates that the angle between the flow vorticity and the flow velocity, as well as the flow velocity, also has a certain effect on the generation of the dipole noise source. [ABSTRACT FROM AUTHOR]

In order to predict the regular temperature change in tuna during the freezing process for cold chain transportation, improve the quality of frozen tuna, and reduce the energy consumption of freezing equipment, a three-dimensional numerical model for freezing tuna of different sizes was established. An unsteady numerical simulation of the air velocity and flow field was combined with an analysis of the freezing process of tuna. This paper also studied the effect of air velocity, temperature, and tuna size on the freezing process. The numerical results show that there was a positive correlation between the cold source environment and the tuna-freezing process. Lower temperatures and higher air increased the velocity at which the tuna moved through the maximum ice crystal formation zone, maintaining a better aquatic product quality. In some cases, however, the smaller tuna models achieved a longer freezing time. Due to the difficulty of obtaining the whole tuna sample, the temperature curve and freezing rate over time obtained during the freezing process were tested using a tuna block of a specific size. The maximum error did not exceed 6.67%, verifying the authenticity and feasibility of the simulation. [ABSTRACT FROM AUTHOR]

The detailed understanding of heat transfer in the pulsating airflow in the pipe is critical to reducing heat losses in the engine exhaust stream and improving catalyst performance. In the present investigation, we have scrutinized the impact of pulsation frequencies ranging from 0-90 Hz on the flow velocity field and the consequent heat transfer through a horizontal pipe wall. The Nusselt numbers were evaluated at three distinct cross-sectional points moving from upstream to downstream, by systematically modulating the frequency. Temporal variations in the velocity field and temperature were captured utilizing particle image velocimetry (PIV) and dual-thermocouple probes, respectively. Intriguingly, while the Nusselt number for steady flow at 0 Hz closely adhered to Gnielinski's equation, the pulsating flow demonstrated a peak between 25-35 Hz, a pattern not predicted by the prevailing quasi-steady-state theory. The observed frequency response of turbulence was found to be congruous with the Nusselt number, indicating that the heightened heat transfer at frequencies of 25-35 Hz could be attributed to the enhanced turbulence and the temperature gradient between the fluid and the wall surface during the deceleration phase in the hysteresis of turbulence in the pulsating flow. The unique frequency characteristics of heat transfer that were uncovered in this study, with respect to both flow velocity and temperature, offer valuable insights for devising strategies to mitigate heat loss during ignition and idling. Furthermore, these findings provide robust benchmarks for validating numerical simulations of pulsating flows in real-life automotive engines. [ABSTRACT FROM AUTHOR]

Citrus orchards in Southeast Asia are commonly grown in hilly areas, where the terrain is unsuitable for the operation of crop protection machinery. Conventional spraying equipment used in hilly orchards have a poor deposition effect. In this paper, a new air-assisted electrostatic sprayer was designed for hilly citrus orchards. The orthogonal method was conducted to determine the optimal spray parameters of the sprayer. To evaluate the spray performance of the optimized air-assisted electrostatic sprayer, field tests were carried out on a citrus orchard with various cultivation patterns. Based on the data of the field tests, a comprehensive evaluation model was constructed to quantitatively analyze the performance of the sprayer. Results indicate that the optimal parameters are a spray pressure of 0.5 MPa, applied voltage of 9 kV and air flow velocity of 10 m/s. The optimized air-assisted electrostatic sprayer has the best performance in the citrus under dense fence cultivation pattern, followed by dense dwarf cultivation pattern. Comparing to the other sprayers tested, the air-assisted electrostatic sprayer greatly improves the spray coverage on the leaf surfaces (abaxial and adaxial) under various cultivation patterns. [ABSTRACT FROM AUTHOR]

For the problem that when wheat is sucked up by the air suction method, the seeds are aligned in a small area, making it difficult for the contact seed cleaning mechanism to clean the seeds. The mechanism of seed cleaning airflow on wheat seed was studied, the flow velocity distribution relationship of the jet section was defined, the mathematical model of the jet velocity of circular and plane sections was established, and the key factors that could have a significant influence on seed cleaning effect were explored. A non-contact positive pressure air flow seed cleaning method was proposed. After theoretical calculations, it is concluded that the core section lengths of the circular section jet and the inline jet are 24.8 mm and 28.8 mm, respectively. The clearing distance is set to 20 mm. Through the single-factor test, the best air tube nozzle shape was clarified as a vertical inline nozzle. The angle of seed cleaning, the air velocity of seed cleaning, and the negative supply pressure were selected as influencing factors, and the seed leakage index, seed reabsorption index, and seed qualification index as the evaluation indicators to conduct a 3-factor 5-horizontal rotation test. A mathematical regression model of influencing factors and evaluation indexes was established to analyze the influence of these factors and indexes. The optimal operation parameters were obtained as the seed cleaning Angle of 19°, the seed cleaning air velocity of 58 m/s, and the negative pressure of 8.5 kPa. Under the optimal parameters, the seed leakage suction index is 8.23%, the seed reabsorption index is 0.33%, and the seed qualification index is 91.44%, which meets the design requirements. [ABSTRACT FROM AUTHOR]

In this study, the performance of a novel method where an antibacterial solution is pressurized and sprayed into recirculated air through nozzles, is investigated numerically. This resembles a jet in a cross-flow problem where the antibacterial solution mixes with ventilation air and further adheres to the inner surfaces of the duct. The motion of particles dispersed in antibacterial solution is described as the advection of a passive scalar, i.e., temperature, allowing for a single-phase flow solution. The effectiveness of the coating is evaluated by the temperature distribution on the inner surfaces of the duct. Single phase 3-D turbulent flow of air at two different temperatures is modeled and the velocity and temperature fields in the ventilation duct were calculated using the commercial code ANSYS FLUENT. The numerical model is validated by experiments conducted on a full-scale test rig, in terms of temperature. The numerical calculations were conducted in four series: where the effect of the nozzle arrangement, the jet injection angle, the jet-to-cross- flow velocity ratio, and a time-dependent jet velocity profile of a sinusoidal wave form are investigated. The numerical solutions show that the coating is highly inefficient for velocity ratios less than 3.3, and the period of time-varying jet stream has little effect on the coating performance. [ABSTRACT FROM AUTHOR]

In this paper, a nonlinear energy sink (NES) and a giant magnetostrictive-piezoelectric (GMP) energy harvester (NES-GMP) are investigated to suppress the nonlinear aeroelastic responses and to absorb the mechanical energy of an embedded plate interacting with external subsonic airflow. The analytical model of the embedded plate attaching the NES-GMP is established by using the Hamilton's principle based on the Kirchhoff plate theory and incompressible subsonic aerodynamic model. The natural frequencies of the plate with the NES-GMP and with the NES are analyzed by solving the generalized eigenvalue problems. The global amplitude-frequency responses of the pure plate, the plate with NES, and the plate with NES-GMP are compared to show the vibration suppression effects of the proposed method. Based on the energy analysis, the energy transfer mechanisms of the plate with the NES-GMP are studied. The results reveal that the input energy of the NES-GMP converts into the strain energy by the Terfenol-D layer and then transforms into the electric energy by the piezoelectric layer. Furthermore, numerical simulations also indicate that the maximum harvested energy is obtained when the airflow velocity approaches the critical divergence flow velocity of the plate, and the most effective harvesting installation position is in a specific annular region near the edge of the plate. [ABSTRACT FROM AUTHOR]

Air-assisted boom sprayer is proven to be one of the best pesticide application methods to achieve uniform deposition of droplets in the canopy and improve the effective utilization of pesticides. However, the air flow velocity, air flow volume and air flow direction of the orchard sprayer should match the characteristic parameters of the target canopy, equipment spraying parameters and meteorological conditions so as to improve the spraying quality and reduce environmental pollution. This paper elaborates on the research status of air-assisted field sprayers and orchard sprayers, summarizes the research methods of air-assisted sprayers in four aspects, including experimental verification, theoretical analysis, simulation and structural optimization, and clarifies the advantages and disadvantages of these methods. It also presents two future research and development trends, including the intelligent, precise dynamic regulation of air flow velocity, air flow volume and air flow direction and the instant feedback of spraying quality, hoping to provide a reference for the research of air-assisted spray technology and equipment. [ABSTRACT FROM AUTHOR]

In the process of tea plucking and leaf gathering, the structure optimization design of the leaf collecting mechanism is the key element responsible for collecting fresh leaves. The unreasonable design and manufacture of leaf collecting mechanisms will cause the smooth collection of fresh leaves, the quality of the collected fresh leaves will be damaged, and the commodity value will be reduced. In order to further study the structural characteristics of the leaf collecting mechanism, an air outlet model of the leaf collecting mechanism was established for the phenomena of internal vortex rotation and impact in the leaf collecting mechanism process. The internal flow field of the leaf collecting mechanism, the movement trajectory of fresh leaves, and the non-homogeneous flow are calculated using computational fluid dynamics (CFD). Based on Box-Behnken's central combinatorial design theory, the velocity inlet and outlet air structure factors are taken as the influencing factors to carry out response surface test research. The effect of different parameters such as engine rotation, shape of the blowing cavity and air outlet parts, and velocity on the flow is determined. The optimal parameter combination is as follows: the height of the outlet end, the length of the inlet end, and the velocity inlet are 0.01 m, 0.03 m, and 25 m/s, respectively. Furthermore, it was found that when the number of plates increases from 1 to 4, the non-homogeneity decreases all the time, and the distribution of blowing air is improved without a sharp decrease in velocity. The average velocity outlet was larger than the velocity inlet, which meets the requirements of blade gathering. Considering comprehensively, the flow field simulation of the blade collecting mechanism with four baffles was consistent with the test results of the velocity outlet. The validation results showed that the model can successfully simulate the air flow inside the leaf-collecting mechanism, and the reasonable structure design was conducive to reducing the number of collisions between tea buds and improving the quality of tea buds. This research has certain theoretical and practical implications for the accurate plucking of high-quality tea. [ABSTRACT FROM AUTHOR]

A theoretical study of the formation of water build-up, or water blanketing, and its influence on the ventilation of mine upcast shafts was carried out. Two scenarios for droplet moisture accumulation in the shaft were considered: condensation from saturated air rising up the shaft and groundwater inflows through the leaky shaft lining. Analytical dependencies of the pressure drop due to the influence of water build-up versus the outgoing air flow velocity and the height of the groundwater source were obtained, taking into account the fractional composition of the droplet moisture. Practical arrangements are proposed to reduce the influence of the effect of water build-up in upcast shafts in the case of groundwater inflows through the leaky shaft lining. [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]

Anatomical airways parameters, such as length, diameter and angles, have a strong effect on the flow dynamics. Aiming to explore the effect of variations of the bifurcation angle (BA) and carina rounding radius (CRR) of lower human airways on respiratory processes, numerical simulations of airflow during inhalation and exhalation were performed using synthetic bifurcation models. Geometries for the airways models were parameterized based on a set of different BA's and several CRR's. A range of Reynolds numbers (Re), relevant to the human breathing process, were selected to analyze airflow behavior. The numerical results showed a significant influence of BA and the CRR on the development of the airflow within the airways, and, therefore, affecting the following relevant features of the flow: the deformation of velocity profiles, alterations of pressure drop, flow patterns, and, finally, enhancement or attenuation of wall shear stresses (WSS) appearing during the regular respiratory process. The numerical results showed that increases in the bifurcation angle value were accompanied by pressure increases of about 20%, especially in the regions close to the bifurcation. Similarly, increases in the BA value led to a reduction in peak shear stresses of up to 70%. For the ranges of angles and radii explored, an increase in pressure of about 20% and a reduction in wall shear stress of more than 400% were obtained by increasing the carina rounding radius. Analysis of the coherent structures and secondary flow patterns also revealed a direct relationship between the location of the vortical structures, the local maxima of the velocity profiles and the local vorticity minima. This relationship was observed for all branches analyzed, for both the inhalation and exhalation processes of the respiratory cycle. [ABSTRACT FROM AUTHOR]

With the aid of the COMSOL program, the laminar mixed convection heat transfer in a channel-open cavity with two heat sources of constant 20 W each and varying input air velocity ranges (0.1, 0.5, 1.0, and 1.5 m/s) is numerically determined. In this study, the effect of varying inlet air velocity on the heat transfer characteristics is investigated. Numerical results show that the temperature starts to fall steadily as one moves farther and further away from the site of the two heat sources and closer to the horizontal channel. The higher the velocity of the air entering the cavity, the greater the natural convection that will be created by the heated heat sources. The increase in inlet air velocity will increase the turbulence of airflow and thus increases the pressure distribution. The increase in absolute y-direction decreases the velocity distribution. The rise in the inlet velocity of air will increase the transfer of heat; thus, the Nusselt number will be great when increasing air flow velocity. The maximum Nusselt number is at the interface and reduces with increasing the absolute value of y. A reduction in air temperature and an increase in air density result from an increase in natural convection from the cavity into the air stream caused by an increase in air input velocity. [ABSTRACT FROM AUTHOR]

To improve air quality, it is customary to apply technological measures to isolate or retain pollutants by influencing the polluted stream in various ways to effectively remove the pollutants. One of the most commonly used measures is a filter, in which the air flow passes through a porous aggregate. A variety of filter materials allows very selective and precise cleaning of the air flow in non-standard or even aggressive microclimate conditions. In this paper, the environmental aspect of the used materials is discussed, and a theoretical model of an adapted mycelium is proposed as an alternative to the use of filter materials to predict air flow purification. In the created numerical model of an idealized filter, several cases are considered when the pore size of the mycelial fillers reaches 1.0, 0.5 and 0.1 mm, and the feed flow velocity reaches 1–5 m/s. Moreover, in the mycelium itself, the flow velocity can decrease and approach the wall to a value of 0.3 m/s, which is estimated for additional numerical studies of interaction with the surface. These preliminary studies are aimed at establishing indicative theoretical parameters for favorable air flow movement in the structure of the mycelium. [ABSTRACT FROM AUTHOR]

In order to investigate the flow characteristics and distribution law of airflow in multi-branch pipe of pneumatic rice precision direct seeder and obtain the mathematical model between airflow parameters and pipe geometry structure. In this study, the airflow flow law of the multi-branch pipeline of the pneumatic system was studied, the mechanism of airflow flow in the multi-branch pipe was analyzed, and it was clarified that the main factors affecting the airflow flow in the pipe, namely, air density, air dynamic viscosity, the total flow rate of the inlet branch pipe, the length of the closed end of the header, the inner diameter of the outlet branch pipe, and the outlet branch pipe spacing. Numerical simulations were carried out using Fluent simulation software to elucidate the cause of multi-branch pipes of uneven distribution of airflow in multi-branch pipes, the empirical equation among these factors and the flow velocity of the outlet branch pipe are established by dimensional analysis method. The bench test results show that the established empirical equations are applicable in the following ranges: 0.018 m³/s≤Q≤0.054 m3/s, 0.045 m≤d≤0.05 m, 0.075 m≤L≤0.125 m, 0.7 m≤Y1≤0.875 m (0.5 m≤Y2≤0.75 m, 0.36 m≤Y3≤0.45 m), the prediction accuracy can be controlled within 10% of the empirical formula, which can provide a reference for the prediction and optimization design of outlet velocity of the multi-branch pipe. [ABSTRACT FROM AUTHOR]

The wave drag coefficient is a significant part of drag coefficient at speeds higher than the speed of sound and it depends on body shape and flow velocity. Elliptical cone and semi-ellipsoid in air flow with velocity from 1 to 2 Mach are studied by computational fluid dynamics. Fineness ratio of cone is chosen so that oblique shock wave is generated at the tip of the body. A semi-ellipsoid has a rounded tip so a detached bow shock wave is formed ahead of the body. Different ratios of semi-axis of elliptic base and different lengths of forebodies are considered and their influences to wave drag coefficient are analysed. It was confirmed that the wave drag coefficient decreases if the fineness ratio of forebody increases. The influence of semi-axis ratio of the elliptic base to wave drag coefficient is present for a cone in the entire interval of considered speeds and it is decreased with the fineness ratio increasing for a cone and for a semi-ellipsoid the influence is inversed. [ABSTRACT FROM AUTHOR]

This study serves as a basic study of the indoor dispersion of pollen particles, simulating the flow field and discussing the behavior of particles of different diameters in different rooms. By comparing the vertical velocity components of particles (w¯p$$ {\overline{w}}_{\mathrm{p}} $$) and the mean flow velocity of z‐direction component (wf$$ {w}_{\mathrm{f}} $$) plus the terminal settling velocity in a gravitational field (Vg$$ {V}_{\mathrm{g}} $$), the differences between w¯p$$ {\overline{w}}_{\mathrm{p}} $$ values and wf$$ {w}_{\mathrm{f}} $$ plus Vg$$ {V}_{\mathrm{g}} $$ values are found to occur mainly at locations close to the opposite wall of the inlet. The location of the differences between w¯p$$ {\overline{w}}_{\mathrm{p}} $$ values and wf$$ {w}_{\mathrm{f}} $$ plus Vg$$ {V}_{\mathrm{g}} $$ values is important findings of this study, which facilitates the improvement of the simulation method at a later stage and the rational design of indoor ventilation patterns to easily remove particles from the room. [ABSTRACT FROM AUTHOR]

A tube-integrated flow sensor is proposed in this study by integrating a micro-electro mechanical systems (MEMS) flow-sensing element and electrical wiring structure on the same copper on polyimide (COP) substrate. The substrate was rolled into a circular tube with the flow-sensing element installed at the center of the tube. The signal lines were simultaneously formed and connected to the Cu layer of the substrate during the fabrication of the sensing structure, thus simplifying the electrical connection process. Finally, by rolling the fabricated sensor substrate, the flow sensor device itself was transformed into a circular tube structure, which defined the airflow region. By implementing several slits on the substrate, the sensing element was successfully placed at the center of the tube where the flow velocity is maximum. Compared to the conventional sensor structure in which the sensor was placed on the inner wall surface of the tube, the sensitivity of the sensor was doubled. [ABSTRACT FROM AUTHOR]

In this paper, we discuss the problem of estimating the unknown parameters of the Gompertz distribution and the acceleration factor under constant-stress partially accelerated life test model. Based on adaptive Type II progressive hybrid censored samples, the maximum likelihood estimates of the model parameters and acceleration factor are derived. From Bayesian aspect, the Bayes estimates of the unknown parameters are obtained using the Gibbs sampler together with Metropolis-Hastings (GMH) algorithm. Based on the interval estimation viewpoint, the asymptotic, Bayesian credible and bootstrap confidence intervals for model parameters and acceleration factor are also constructed. In order to investigate the impact of estimation procedures and methodologies adopted, a simulation study is performed. Finally, a real life example contains the persistence of the virus-containing micro droplets is analyzed to illustrate the application of the partially accelerated life test model. It is observed that the GMH algorithm is superior for estimating the parameters of partially accelerated life test model after comparison. The results of real example analysis show that the proposed model can be applied to the engineering problem and the considered methods are suitable for the modeling of the virus-containing micro droplets lifetime data under two co-current air flow velocities. [ABSTRACT FROM AUTHOR]

This paper analyzes a piezoelectric system made of a smart lead zirconate material. The system is composed of a monolithic PZT (piezoelectric ceramic) plate made of a ceramic-based piezoelectric material. The experiment was conducted on a test stand with a GUNT HM170 wind tunnel and a special measurement system. The developed bluff-body shape mounted on an elastic beam with a piezoelectric was mounted on a mast with arms. Springs were fixed on the arms to limit the movement of the test object. Air flow velocity in the wind tunnel and forced vibration frequencies were changed during the tests. The recorded parameters were an output voltage signal from the piezoelectric element and linear accelerations at selected points of the test object. The highest energy efficiency of the tested system was specified from mechanical vibrations and air flow. The results of the tests are a resonance curve for the tested system and a correlation of RMS voltage and acceleration as a function of the velocity of air flow for the excitation frequency f ranging from 1 to 6 Hz. The tests specified the area where the highest output voltage under the given excitation conditions is generated. [ABSTRACT FROM AUTHOR]

Air-doors are important facilities for regulating the air flow in a mine ventilation network. It is of value to study the influence of air-doors, which are adjacent to a fire source on smoke back-layering in order to build a rational ventilation system. By regulating air-doors in a mine ventilation network test platform, two typical mine ventilation networks, with parallel branches and a diagonal branch, were constructed. During the study, into the closing degree of the air-doors adjacent to a fire source in a ventilation network with parallel branches, the back-layering length is up to 3.70 m when the ventilation velocity is 1.40 m/s. When the air-door on the return side of the adjacent branch is closed, the back-layering subsides within 1 min and the upstream temperature drops rapidly to normal. When the air-door is half closed, there is still a back-layering flow within 5 min. Smoke control, with the air-door is closed, is better than when the air-door is half closed. Based on this, tests into the influence of the closing position of air-doors, which are adjacent to a fire source, were carried out in a ventilation network with a diagonal branch. Results indicate that when the ventilation velocity is 1.70 m/s, the back-layering flow spreads to the diagonal branch, and the air flow velocity of both the adjacent branch and the diagonal branch increases. When closing the air-door on the return side of the adjacent branch, the back-layering rapidly subsided. The wind velocity on the intake side of the adjacent branch is stabilized after a rapid decrease, and the wind velocity of the diagonal branch is stabilized after a rapid increase. When closing the air-door on the intake side of the adjacent branch, the smoke from the diagonal branch spreads. Compared with closing the intake side air-door, closing the air-door on the return side of the adjacent branch is more effective in preventing back-layering. This work provides a reference for preventing back-layering and guiding the evacuation of people from the upstream of a fire source. [ABSTRACT FROM AUTHOR]

Smoldering, characterized as a slow, low-temperature, and flameless reaction process, represents one of the most persistent types of combustion phenomena. While oxygen supply is one of the governing mechanisms controlling smoldering, the specific oxygen threshold or smothering limit remains inadequately investigated. Herein, we built a physics-based 1-D computational model integrating heat-and-mass transfer and 5-step heterogeneous chemistry to investigate the oxygen threshold or smothering limit of smoldering propagation in porous pine needle beds subjected to forced internal oxidizer flow. Simulation results revealed that, the required oxidizer flow velocity or oxygen supply rate increased as the oxygen concentration decreased, and the predicted limiting oxygen concentration (LOC) was about 3 %, agreeing well with the experimental observations and theoretical analysis. Moreover, the required airflow velocity was predicted to increase as the fuel density and environmental temperature decreased, or the moisture content increased, and the predicted maximum moisture content capable of supporting smoldering was about 110 %. At the smothering limit, the modeled minimum smoldering temperature and propagation rate were around 300 °C and 0.5 cm/h. This work helps deepen our understanding of the limiting conditions of smoldering combustion, thus improving the mitigation strategy of smoldering fire and the efficiency of applied smoldering systems. Oxygen supply is one of the key mechanisms governing the smoldering propagation. In the literature, scattered studies have examined the limiting oxygen concentration (LOC) of smoldering under different conditions, leading to disparate results even for the same fuels. In our previous work, for the first time, we developed a tubular smoldering reactor capable of precisely controlling the flow of oxidizer, and successfully quantified the exact oxygen supply limit of smoldering combustion. However, no computational model was established specifically for the oxygen threshold of smoldering with forced internal oxygen supply. The novelty of this research is the establishment of the first-ever computational model to investigate the oxygen threshold or smothering limit of smoldering propagation in porous pine needle beds subjected to forced internal oxidizer flow. It is significant because (1) it contributes to a fundamental understanding of smoldering combustion; (2) it investigates the role of fuel properties and environmental conditions in smoldering dynamics and the oxygen supply limits; (3) it assists in optimizing the applied smoldering systems and enriching prevention strategies for smoldering fires. [ABSTRACT FROM AUTHOR]

Horizontal well air sparging (AS) technology is an efficient method for removing volatile organic compounds (VOCs) contamination from groundwater. However, there are insufficient theoretical explanations for the air flow velocity inhomogeneity in the AS process, and there are fewer studies on how the structural parameters of AS tubes affect the gas migration behavior. In this study, the air distribution characteristics of three types of AS tubes at different heights (20, 30, and 40 cm) were investigated through three-dimensional modeling experiments, and the effects of different AS pressures (30–90 kPa) on gas distribution were analyzed. The results showed that the total flow velocity output of the AS tube gradually increased with the increase of AS pressure. The 8-hole AS tube had the highest flow velocity with a peak value of 550 cm/min at 90 kPa. Dimensionless analysis showed that the 8-hole AS tube exhibits an approximately Gaussian distribution, the 25-hole AS tube had a fingered distribution, and the 25-slit AS tube had an approximate trapezoidal distribution. The 25-slit AS tube exhibited a more uniform flow velocity distribution than the other two. The internal flow velocity characteristics of the AS tube can be analyzed using the theory of homogenization of fluids. Its homogeneity is related to its structural parameters (e.g., pore spacing S and the ratio of the open area to the lateral area of the AS tube nd2/4DL, etc.). This study provides a valuable reference for the structural design of horizontal well AS. [Display omitted] • Conducted 3D model experiments on AS in horizontal wells. •Observed lateral airflow variations among different AS tubes. •Identified correlation between airflow patterns and orifice pressure. •Investigated pressure drops along AS tube flow direction. [ABSTRACT FROM AUTHOR]

In restricted space, fuel combustion is often constrained by sidewalls and corners, which can alter the air entrainment compared to unrestricted scenarios. To investigate the impact of sidewalls and corners, this paper presents numerical simulations of rectangular propane gas fires under sidewall and corner restricted conditions. The burner had an area of 300 cm2, with 5 different aspect ratios (n = 1, 1.5, 2, 3, and 4) and 4 heat release rates of the fire source (12 kW, 18 kW, 24 kW and 30 kW). The results demonstrate variations in the distribution of the flow field under different restricted conditions. For wall fires, when the long side of the burner is against the wall, the velocity in the X direction (u) approaches 0, and the lateral flow velocity on the X – Y plane (V) and the velocity in the Y direction (v) are nearly identical near the short side of the burner. Velocity V near the burner side can be divided into three zones: the high-velocity zone, the low-velocity zone, and the locally high-velocity zone. For corner fires, V increases as it gets closer to the wall. With the increase of n , the streamline where the velocities u and v are equal moves to the long side of the burner. Additionally, the fire entrainment rates of rectangular wall and corner fires at different heights from the burner surface were quantitatively studied. On the basis of the fire entrainment model for square and circular fires in open space, by introducing the equivalent diameter D eff * , a modified entrainment rate model at different heights from the burner surface is proposed, which can well predict the entrainment rate of rectangular wall or corner fires when the aspect ratio of the rectangular burner ranges from 1 to 4 and Q ˙ eff * ranges from 0.97 to 6.79. • Numerical study on the rectangular gas fires under restricted conditions was conducted. • Flow field and entrainment behavior of the rectangular fire plume were studied. • Air entrainment rate models under restricted conditions were established. [ABSTRACT FROM AUTHOR]

Thermochemical heat storage has attracted significant attention in recent years due to potential advantages associated with very high-energy density at the material scale and its suitability for long-duration energy storage because of almost zero loss during storage. Despite the potential, thermochemical heat storage technologies are still in the early stage of development and little has been reported on thermochemical reactors. In this paper, our recent work on the charging and discharging behavior of a fixed-bed thermochemical reactor is reported. Silica gels were used as the sorbent for the experimental work. An effective model was established to numerically study the effect of different charging conditions on the discharging behavior of the reactor, which was found to have a maximum deviation of 10.08% in terms of the root mean square error compared with the experimental results. The experimentally validated modelling also showed that the discharging temperature lift increased by 5.84 times by changing the flow direction of the air in the discharging process when the charging level was at 20%. At a charging termination temperature of 51.25 °C, the maximum discharging temperature was increased by 2.35 °C by reducing the charging flow velocity from 0.64 m/s to 0.21 m/s. An increase in the charging temperature and a decrease in the air humidity increased the maximum discharging outlet temperature lift by 3.37 and 1.89 times, respectively. [ABSTRACT FROM AUTHOR]

The scope of the research comprises an analysis and evaluation of samples of rape, barley and wheat seeds. The experiments were carried out using the author's original research object. The air flow velocities to transport seeds, were set at 15, 20 and 25 m s−1. A database consisting of images was created, which allowed to determine 3 classes of kernels on the basis of 6 research variants, including their transportation way via pipe and the speed of sowing. The process of creating neural models was based on multilayer perceptron networks (MLPN) in Statistica (machine learning). It should be added that the use of MLPN also allowed identification of rape seeds, wheat seeds and barley seeds transported via pipe II at 20 m s−1, for which the lowest RMS was 0.05 and the coefficient of classification accuracy was 0.94. [ABSTRACT FROM AUTHOR]

In order to suppress the irregular diffusion of dust in the unloading process of grab ship unloaders, an air curtain soft-sealing system was designed that can effectively block the air flow and restrict the diffusion of pollutants and reduce the average mass fraction of pollutants outside the air curtain plane by 70.02%. The grab unloading model was constructed using the Computational Fluid Dynamics–Discrete Element Method (CFD-DEM) coupling method, and the diffusion law of the gas–solid two-phase flow field of the falling bulk material was studied. Moreover, the motion trajectory and velocity distribution of the particle flow field and air flow field were obtained, as well as the maximum air flow field velocity of five planes above the hopper. The three-dimensional model of the air curtain jet was used and simplified, and the air curtain parameters were set based on the maximum air flow field velocity. The barrier performance of the air curtain under different air curtain jet modes, jet widths, jet velocities and induced wind velocities was simulated by the control variable method. The results show that selecting the appropriate jet widths and jet velocities can significantly reduce dust diffusion; under different jet modes, the order of influence was blow and suction, unilateral blowing and bilateral blowing; under a certain range of induced wind velocities, the air curtain had an obvious blocking effect. These results can provide a reference for the design and improvement of dust suppression of the air curtain soft-sealing system. [ABSTRACT FROM AUTHOR]

Social hibernation of animals is one of the most important physiological and ecological behaviours. The purpose of the study was the investigation of the influence of the roostsite climate parameters: temperature (T), humidity (Rh) and air flow velocity (v) on the clustering of the Barbastella barbastellus (western barbastelle) during hibernation. The research was carried out in the underground systems of Poland (Central Europe) over a period of 6 years. The range of air parameters changes ranged for T from 6.0 to 12.4 °C, for Rh from 56.4 to 91.8% and for v from 0.01 to 1.17 m/s. The quantile linear regression method was used for the statistical analysis of the results. The study indicated that the increase in the number of individuals in the hibernaculum occurs with an increase in the product (correlation result) T and v, while a decrease in the size of the group occurs with an increase in the products T and Rh, v and Rh as well as T, v and Rh. [ABSTRACT FROM AUTHOR]

Reverse-flow combustor is widely used for small engines to overcome high speed shaft whirling problem and to provide a low frontal area. An experimental investigation was carried out to research the flow field characteristics of a reverse-flow combustor in this paper. Different aerodynamic conditions were studied using PIV to reveal the characteristics of both the nonreacting and reacting flow fields. The structure of the nonreacting flow field in the central section shows similarity as the total pressure loss coefficient increases. The penetrating depth, jet angle, recirculation zone position, and the flow streamlines are similar, while the velocity value of the flow field increases. The structure of the reacting flow field on the central section is different from that of nonreacting flow field, but the variation trend of the reacting flow field under different pressure loss coefficient is similar to that of the nonreacting flow field. By examining the nonreacting and reacting flow fields under the same total pressure loss conditions, marked differences were observed in the primary zone close to the swirler outlet. The relative motion between fuel injection, airflow, and combustion affects the flow field in this zone. The velocity with combustion is faster than that of the nonreacting flow because of the increased temperature and heat release. [ABSTRACT FROM AUTHOR]

With the advancement of agricultural mechanization and the development of combine harvesters, cleaning devices play a very important role in the grain harvesting process. In this study, the DFPF-25 type material floating velocity measuring device was used to measure the suspension velocity of each component of the grain material. Secondly, the DFQX-3 cleaning device was used to conduct the airflow field test, then the fluid simulation of the cleaning shoe was carried out. The results showed that the simulation and experimental results were in a good agreement under the conditions of single fan and double fan. The high-speed flow velocity formed by the double fan system at the tail of the cleaning shoe was 4.76 m/s (simulation) and 4.03 m/s (experiment), which had outstanding cleaning effects on unfilled grains, long stems, and short stems. To sum up, the installation of the cross-flow fan at the rear of the cleaning shoe has a positive effect on the cleaning effect of the combine harvester, and the double-fan cleaning structure composed of the cross-flow fan and the centrifugal fan can significantly improve the cleaning effect. [ABSTRACT FROM AUTHOR]

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Measurements of air flow velocity are essential at every stage of the design, construction and operation of wind turbines. One of the basic measurement tools in this area is the tachometric anemometer, which is based on the simple physical phenomenon of the air kinetic energy exchange with a rotating measuring element. Tachometric anemometers have favorable operational features and good static metrological parameters. However, in the case of fast-changing flows, the measurement is burdened with a significant dynamic error, and the measured average value of the velocity is overestimated. This article presents the concept and results of pilot studies of a dynamic error correction method of tachometric anemometers. The correction consists of the precise measurement of the rotor's rotational velocity and determination of the measured air velocity, taking into account the dynamics of the instrument. The developed method can be used in tachometric anemometers intended for laboratory, technical and industrial measurements in time-varying flows. One of the important application areas is the measurement of wind energy. [ABSTRACT FROM AUTHOR]

• A numerical model considering interaction between airflow and melt was built. • Melt peeling off process induced by airflow was directly simulated and obtained. • The mass loss at 0.5 Ma was 26.87 % higher than that at 0.3 Ma. • The melt peeling off at 0.8 Ma occurred 64.15 % earlier than that at 0.5 Ma. • The cooling effect on melt with the increase of airflow velocity was discussed. In this paper, a computational fluid dynamics model considering the interaction between subsonic tangential airflow and centimeter-level molten pool was established to investigate the melt peeling off behavior during laser ablation process. The results showed that the airflow resulted in violent fluctuations on the surface of molten pool and then flowed upward at a velocity of 2–10.5 m/s, accelerating the surface melt to move upward. A liquid column was formed and elongated slender along the metal surface pushed by the subsonic tangential airflow. An upward-bending tail appeared at the end of the liquid column, which was accelerated up to 6 m/s and then cut off by the airflow, making the melt peel away from the molten pool. Compared with the partial melt peeling off at 0.3 Ma, almost all of the melt was pushed out of the molten pool to peel off when the airflow velocity was increased to 0.5 Ma. When the airflow velocity was further increased to 0.8 Ma, the metal on the surface was accelerated in short time, leading to the peel-off occurring in advance. In addition, the melt temperature decreased due to the forced convection cooling effect of airflow. When the melt solidified, the solid-liquid interfacial tension generated in the liquid column provided tangential force conducive to cutting off the liquid column and peeling off. The decrease rate of the melt temperature with time accelerated significantly and then expedited the melt solidifying and peeling off when the airflow velocity was increased to 0.5 Ma. The decrease rate further accelerated and the temperature decrease occurred earlier at 0.8 Ma, reaching a stable state in a shorter time. [ABSTRACT FROM AUTHOR]

Similarly to a harmonica reed, a piezoelectric MEMS cantilever is self-excited by an airflow. An airflow-induced self-excited vibration can be utilized as an energy source for energyharvesting devices. In this study, with the aim of reducing the cut-in flow velocity, which is the lowest flow velocity required for resonant vibration, a thin MEMS structure with an intentionally warped shape was exploited in an energy harvester based on the principle of harmonica reeds. By compensating for the residual stresses of PZT and Pt electrode films, the cantilever warpage of the harvester structure can be controlled. The thin-film nature and the warped PZT/Si laminated MEMS structure enabled energy harvesting from an airflow at low flow velocities. Moreover, the cut-in flow velocity of the airflow-induced MEMS harvesting device was very low (1.2 m/s, one-tenth of that of a conventional device), and an output power of 3.84 μW was obtained at a flow velocity of 3.7 m/s. [ABSTRACT FROM AUTHOR]

Experiments of microfiltration enhanced with air dispersion were carried out through a sub-merged flat sheet membrane using commercial yeast suspension. In the experiments, the effect of hydrodynamic parameters like liquid flow velocity, air flow rate and aerator size were examined on flux control of fouling for different feed concentrations at constant transmembrane pressure. The classical heat and mass transfer analogy was applied to get an insight into the mechanism of fouling control in single and two-phase flow systems. The experimental results show that: (a) air dispersion reduced the particle fouling on membrane surface thus causing permeate flux enhancement for any value of air flow rate and for any feed concentration. A maximum flux enhancement factor of 270% was achieved for feed concentration of 25 g/L whereas as it was 60% for feed concentration of 1 g/L at an optimum air flow rate of 64 L/min. (b) Convective back transport of solids from membrane surface due to shear forces generated during two-phase flow was found to the be most significant phenomena of fouling control in submerged flat sheet microfiltration membranes. (c) The classical heat and mass transfer analogy successfully provided the explanation of phenomena of convective back transport of solids due to gas-liquid two-phase flow. [ABSTRACT FROM AUTHOR]

A new dynamic air classifier was designed to address the problems of uneven material dispersion and high dust concentration in industrial applications of turbo air classifiers. This paper presents a study on the use of guide cones in the new dynamic air classifier. The ANSYS-Fluent 19.2 software was implemented to simulate the airflow in the dynamic air classifier, and the impact of the guide cone size on the flow field and classification performance of the dynamic air classifier was investigated. The simulation results indicated that with the increase in the guide cone height, the flow field distribution becomes reasonable and the velocity distributions become uniform. When the guide cone height is greater than twice the distance between the guide cone and the bottom of the rotor cage, there is no discernible change in the flow field distribution and classification efficiency. When the guide cone diameter is approximately 0.9 times the diameter of the rotor cage, the airflow pathline is more reasonable, and the flow field and velocity distributions are more uniform. An improper guide cone diameter and height will worsen the classification environment, resulting in a significant decline in classification performance. The material experimental and discrete phase simulation (DPM) showed that DPM can anticipate the changing trends of the cut size and classification accuracy. This study provides theoretical assistance for the structural design and optimization of an air classifier. [ABSTRACT FROM AUTHOR]

The BSL k-ω turbulence model was used to numerically simulate the inspiratory airflow of the airway with foreign bodies using a real CT scan human airway model. The paper selects three foreign bodies with different diameters, three different foreign body positions, and three different breathing intensities, and the FLUENT software is used to perform numerical simulation. This study has found that the increase in the diameter of the foreign body and flow velocity will make the flow structure in the airway more complicated. The airway pressure will increase so that the resistance of breathing will increase, and the shear force will also increase, which hurt the airway. The impact of the foreign body on the left side on the flow structure in the airway is less than that of the foreign body on the right side. The foreign body on the left side causes the pressure drop in the airway to be higher than that on the right side. Moreover, sharp changes in pressure driving force and airway curvature will affect the airflow pattern of the central airway. We concluded that foreign matter has a great influence on the characteristics of the airflow structure, and more research is needed to increase the understanding of the airflow pattern under the condition of foreign matter in the airway, and the research helps doctors avoid the influence of airflow when removing foreign bodies in the airway. [ABSTRACT FROM AUTHOR]

The intake air preheating is an effective method to improve the cold start performance of diesel engines. The combustion process and ignition probability were investigated in the present study. The average flame area (AFA) during the steady stage of the combustion process was used to evaluate the effects of various factors on combustion. The increase of voltage was found to enhance the combustion process, while the increased diesel flow rate first promoted the combustion before deteriorating it. The increased intake air flow velocity enhanced the combustion within 2.64 m/s, and excessive air flow velocity hindered the combustion from 2.7 to 3 m/s. The cross-distributed vortex clusters in the combustion chamber, periodic diesel evaporation and vortexes with opposite rotation directions in the vicinity of the intake manifold burner were believed to be the main reasons for flame stripping and swirl motion. The temperature rise in the exhaust pipe was recorded to investigate the thermal distribution. The warm air was concentrated in the upper region because of the buoyancy effect of the flame. With the air flow velocity increasing from 1.4 to 10 m/s, the average temperature rise increased first before decreasing, while the combustion efficiency increased due to the increased air flow volume. [ABSTRACT FROM AUTHOR]

In the present work, a three-dimensional computational fluid dynamics (CFD) model was established to simulate the heat transfer process at different air-inflow velocities, and to predict the spatial and temporal variations of temperature distribution during forced-air cooling (FAC). Based on the conventional evaluation system, a more comprehensive multiparameter evaluation system was proposed to determine an optimal precooling strategy of various air-inflow velocities. The current system employed a novel heterogeneity index to quantify the overall uniformity (OHI), and added a detailed theoretical calculation procedure of the cumulative moisture loss during the forced-convection cooling (M, mg). By analysing the effect of different airflow rates on SECT, precooling uniformity, moisture loss, and energy requirement, an airflow rate in the range of 1.5 - 2.5 m·s-1 was recommended as optimum for harvested peach precooling. Any further increase in air-inflow velocity led to excessive energy cost since it generated a relatively low decrease in SECT and overall heterogeneity index, so as moisture loss. At the same time, the moisture loss of peach primarily occurred in HCT, which was inversely proportional to airflow rate and cooling uniformity. An increasing power-law function relationship existed between energy consumption and airflow rate. The present work demonstrated the effect of various air-inflow velocities on peach precooling efficiency, and provided an integral evaluation system to optimise the precooling strategy of other horticultural fruits. [ABSTRACT FROM AUTHOR]

In the context of aircraft aerodynamics, the compressibility of air flowing around the aircraft must always be considered. This fact brings with it one inconvenience: to evaluate the velocity of the flowing air (airspeed), it is necessary to know its temperature as well. Unfortunately, direct measurement of the temperature of air flowing at high speed (usually at Ma > 0.3) is practically impossible without knowledge of its velocity. Thus, there are two unknown quantities in the problem that depend on each other. The solution is achieved by a method that uses temperature probes composed of multiple sensors with different properties (different recovery factors). The comparison of rendered temperatures subsequently allows the elimination of the necessary knowledge of static temperature and the evaluation of velocity. In this paper, one of such probes is described together with its thermodynamic properties and possible applications. [ABSTRACT FROM AUTHOR]

Modeling has been carried out for the aerodynamics of air flow past the windwheel with three cylinder blades rotating around their axis using the Ansys suite. A system of equations in approximation of a realizable k–ε turbulence model was solved by the method of finite volumes using the approach of multiple (imbeddable) systems of coordinates. Patterns have been constructed for vortex zones near cylinder blades. Analysis is given of the aerodynamic characteristics of flow past rotating cylinders under the conditions of the operation of a wind turbine using the Magnus effect depending on the velocity of cylinders' rotation and the Reynolds number. Dependences have been obtained for the drag force of the windwheel, the lift force of the cylinder, and also the force moment on the velocity of approach flow. [ABSTRACT FROM AUTHOR]

This article presents a bidirectional thermoresistive micro calorimetric flow (TMCF) sensor implemented by a 0.18-μm complementary metal–oxide–semiconductor microelectromechanical systems (CMOS-MEMS) technology, while the sensor thickness is thinned to 2.7 μm through an in-house developed MEMS fabrication process. For the bidirectional airflow of −6 to 6 m/s, the TMCF sensor achieves the highest sensitivity of 453 mV/(m/s), and its highest normalized sensitivity with respect to the signal amplification gain (gain = 250) and the input heating power (1.58–1.72 mW) is 1150 mV/(m/s)/W. By reducing the heating power to the sub-mW of <220 μW, the TMCF sensor can still give a remarkable sensitivity of 87.4 mV/(m/s). In addition, the developed TMCF sensor has an intrinsic minimum detectable flow velocity of 99 μm/s and a response time of 4.8 ms. The performance achieved by this flow sensor enables accurate indoor airflow measurements even when dealing with the extremely low-speed flow (<0.05 m/s). Furthermore, the high-performance TMCF sensor is applied for remote human motion detection, where different walking speeds and moving patterns of the occupants can be captured. Therefore, this developed CMOS-MEMS sensor will not only be a promising flow sensing node in the HVAC system, but also potentially be used for the nonvisible and private occupant counting in buildings/rooms. [ABSTRACT FROM AUTHOR]

In deep mines, thermal disasters pose a serious threat to the health and production efficiency of underground workers. It is of certain safety and economic significance to numerically simulate the thermal environment of hot mines. The existing studies are limited in that they only consider a single air flow velocity field or thermal field, or a single heat source. To overcome the limitation, this paper collects the big data on the temperature and humidity of smart coalmines, and numerically simulates the thermal environment in hot mines. Firstly, the authors analyzed the heat sources, including relative heat sources like the hot surrounding rock and hot water, and absolute heat sources like electromechanical equipment, chemical reactions, and the self-compression of the airflow. Next, the thermal environment of the hot mine was simulated by the Lattice Boltzmann method, and the flow state of the hot fluid in the roadways was analyzed in details. The proposed numerical simulation approach was proved effective through experiments, providing a reference for the safety prewarning of hot mines. [ABSTRACT FROM AUTHOR]