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The strong flow field in a hoistway will cause a significant piston effect during the operation of high-speed/ultra-high-speed elevator. Thus, studying the airflow in the hoistway and the reasonable opening of ventilation holes is important. First, a three-dimensional geometric model of the ventilation holes (VHs) and elevator car was established. Based on this model, a multi-region dynamic layering method was proposed. The movement of the unsteady airflow in hoistways with different numbers of VHs and the interaction between the VHs were then analyzed. The correctness of the numerical simulation method was verified by comparing the results of the simulation, experiments and theoretical calculations. Finally, the influence of the number, location and cross-sectional area of the VHs on the airflow movement was analyzed, and the optimal opening positions of one and two pairs of VHs were discussed. The results showed that the variations of the number, location and cross-sectional area of the VHs had a significant influence on the airflow movement. According to the quantitative analysis of the ventilation efficiency, the optimal positions of one and two pairs of VHs were located in the middle of the hoistway and the upper and lower sides of the middle position, respectively. [ABSTRACT FROM AUTHOR]

Based on the Reynolds-averaged Navier–Stokes (RANS) method, a modified standard k-ϵ turbulence model with a source term rooted on Monin–Obukhov similarity theory was used to investigate the effects of temperature stratifications on the flow field and pollutant dispersion in 3D street canyons. The results showed that airflow and pollutant transport was highly dependent on temperature stratifications. The vortex velocity in the canyon varied with temperature stratifications. With the more unstable conditions, the centre of the vortex was closer to the ground, and the intensity and turbulent kinetic energy of the eddy increased. Because the source of pollution was located on the ground, the pollutants migrated to the leeward side of the building with the eddy and then moved upstream or downstream with the airflow. Under neutral conditions, the pollutants migrated to the leeward side first with the eddy in the canyon and then mainly migrated downstream with the airflow but rarely migrated to the upstream street canyons. However, under unstable conditions, the pollutant concentration in the upstream street canyons also increased, mainly because the intensity of the vortex increased, which made the pollutant easier to transport upstream. According to the results of the pollutant flux analysis, the turbulent fluxes on the top plane of the buildings were positive and increased significantly with the more unstable conditions, indicating that turbulent fluxes play a positive leading role in the dispersion of pollutants. The transverse transport of the pollutants was mainly dominated by convective motion, and turbulent transport was relatively minor. [ABSTRACT FROM AUTHOR]

Measurement of air flow is a vital concern in diverse domains. Piezoresistive micro-cantilever-based air flow sensing is a promising research domain within MEMS technology due to its several advantages. Displacement, bending stress, sensitivity, resolution and stability are significant challenges in the design of this sensor. These parameters are also affected by the cantilever profile and its materials. Hence, the purpose of this study is to investigate the performance of a piezoresistive multilayer polymer variable width profile micro-cantilever structure and propose its materials, fabrication process flow, optimisation of geometric dimensions, piezoresistors placement and piezoresistors circuit connections to address challenges in the design. Methodical steps towards design optimisation of the proposed sensor under the applied pressure due to its interaction with air flow comprise preliminary approximation of geometrical dimensions through analytical models developed using Conjugate Beam and Rayleigh methods, subsequently, 3D modelling numerical simulation using the COMSOL Multiphysics FEM tool. It is observed that numerical simulation results agree with the results of analytical modelling. It is concluded that the proposed study contributes to the development of accurate analytical models and design optimisation of a low-cost and stable micro-cantilever-based air flow sensor that performs yet equally well compared to previously published designs in terms of sensitivity. [ABSTRACT FROM AUTHOR]

In this paper, the performance of an integrated variable refrigerant flow (VRF) system with the stratum ventilation (SV) system was numerically examined and compared with the experimental measurements in terms of temperature distribution and airflow patterns. In total six different configurations were designed and analyzed. The results suggest that configuration 5 was greatly satisfied the airflow movement needs. The positive thermal gradient with a modest airflow velocity (< 0.8 m/s) was setup in the entire breathing zone. The indoor temperature in the range of 20°C–22°C was seen throughout the occupied space, except for some places near the walls. Furthermore, a very strong airflow throw from the SV supply terminals was observed with the recommended value of face velocity. Hence, the VRF-SV hybrid system could achieve a better thermal comfort (TC) and indoor air quality (IAQ) in large ACMV applications. [ABSTRACT FROM AUTHOR]

This paper presents a numerical simulation of a ventilated roof based on a novel plastic support especially designed to reduce the solar heat gains by improving the airflow distribution as compared to a traditional one. In order to evaluate the benefits of the new configuration, a 3 D numerical model was developed allowing for a deep understanding of the airflow distribution inside the ventilated roof channels. The simulations were performed by varying the solar irradiance from 600 to 1000 W m−2 assuming buoyancy-driven airflow. The investigation was conducted by comparing the new proposed ventilated roof assembly to the traditional layouts. In particular, two roof types were considered as benchmarks: an insulated roof and a non-insulated one. When compared to the traditional ones, the results revealed that the innovative ventilated roof led to a great reduction (up to 70%) of the total amount of solar heat gains for all the simulated scenarios. [ABSTRACT FROM AUTHOR]

Cell exposure experiments at the air-liquid interface (ALI) are used increasingly as indicators for health effects and for the impact of aerosols on the lung. Thereby the aerosol particles are kept airborne and can deposit on a cell surface area similar to the human respiratory tract (RT). However, geometry and air flow rates of an ALI system deviate considerably from the RT. As the tissue-delivered particle dose to the lungs (TD) can hardly be measured, computer models of particle deposition are used here to mimic both the particle deposition at ALI and in the RT. An ALI exposure setup (VitroCell GmbH) for an airflow rate of 100 cm3 min−1 is selected, where the particle deposition model has been verified experimentally. For the RT we use the hygroscopic lung deposition model of Ferron et al. (2013). Model runs are performed for the particle deposition and for the deposited particles per surface area in both the ALI and the RT. The results show that the ALI-deposited mass is 1-2 orders of magnitude higher than in the alveolar region, because the surface area of the lung region is substantially larger. A particle size range from 40 to 450 nm is identified, where the ratio of both the deposition in a lung region and the deposition at the ALI varies by a factor less than two. Mean values for this ratio are 31 and 101 for the tracheo-bronchial and the alveolar region, respectively. The same size range is found for the ratio of the deposited particles per surface area in a lung region and at the ALI. For this range the mean surface deposition at the ALI is 23- and 1575-times larger than in the tracheo-bronchial and the alveolar lung region, respectively. The effect is partly compensated by different flow rate and cell size. Copyright © 2020 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

This article presents the results of numerical simulation and experimental study of a multi-pin electrohydrodynamic (EHD) dryer. Combined effect of EHD flow and the external air cross-flow on drying performance was investigated with 3-D numerical model, which accounts for electric field, electric charge transport, external air cross-flow and material-gas moisture transport. Effect of cross-flow air stream on drying was positive in the range of low velocities, changing to negative at high velocities due to counteracting with EHD flow. Numerical simulation predicted previously unknown effect of EHD flow on the cross-flow air stream, which was quantified as an increase of airway resistance. This prediction was fully validated by experiments. Both numerical simulation and experiment proved that for given intensity of EHD flow there is an optimum value of the cross-flow, resulting in maximum drying performance. The numerical model can be applied to determine the optimal operating parameters for multi-pin EHD dryer. [ABSTRACT FROM AUTHOR]

In this paper, numerical simulation study was carried out to study the combustion rule and the flow field characteristics of propane-air premixed gas in different angle bending pipes with Realizable model and turbulent flame closure combustion model. The results show that the bending structure of the pipe has a significant effect on the flame front and the surrounding flow field. With the increase of the bending angle, the resistance effect of the bending pipes on the airflow becomes stronger, and the separation of the flame and the concave wall is more obvious. However, the flame propagation velocity increases first and then decreases with the increase of the bending angle. When the bending angle is 120°, the incentive effect of the concave wall side reflected wave on the combustion reaction is the strongest and the attenuation effect of the convex wall side sparse wave on the combustion reaction is the weakest. Meanwhile, flame propagates the fastest, which is increased by 80% compared with that in straight pipe. When the shock wave passes through the bending pipes, the analysis on characteristics of pressure field shows that under bending pipes with different angles, the distance recovered from the curved shock wave to the plane shock wave is 3-5 times of the equivalent diameter. [ABSTRACT FROM AUTHOR]

This study evaluates effects of building form and wind direction on urban ventilation using a large-eddy simulation (LES) model. Numerical simulations of air flow in 80 sets of parametric scenarios are conducted and the results are cross-compared. Main findings and potential recommendations for urban planning are: First, high mean building height is generally not good for ventilation, as vertical momentum is prevented from penetrating inside the street canyon. Second, inhomogeneous building heights tend to decrease the variance of site-averaged velocity ratios compared to homogeneous scenarios. Horizontal ventilation is moderated by the vertical momentum generated by inhomogeneous building heights. Third, rectangular (1:2 horizontal size) building arrays may allow better ventilation than square (1:1 horizontal size) building arrays. Moreover, given a moderate ground coverage ratio in square building arrays, 45° wind input allows better ventilation than 0° wind input. Finally, in cases of square arrays, higher ground coverage ratios result in lower site-averaged velocity ratios. But in the case of rectangular arrays, this negative relationship may be reversed. [ABSTRACT FROM AUTHOR]

Twisting is one of the most important steps in the yarn spinning, which influences the geometry of spinning triangle and determines the properties of spun yarns. Airflow is one of the most important measures on improving yarn spinning. In this paper, a kind of air nozzle with vortex guiding channel was designed and used on the modification of ring spinning system, and the spun yarn qualities was studied by analyzing the airflow field in the nozzle. Firstly, the three-dimensional physical model of nozzle was given using CAD software according to the geometrical size of the practical nozzle model. Then, the numerical simulations of the three-dimensional flow field in the nozzle were given using Fluent software. Finally, two different kinds of yarns 10Ne and 20Ne were spun in the modified ring spinning system with the nozzle installed. The airflow pressure 0.01 Mpa and two different swirling directions, anticlockwise and clockwise, were chosen. The qualities of spun yarns, hairiness, strength, evenness, and number of snarling were measured and analyzed. It is shown that the high vortex airflow can be produced in the nozzle, and then corresponding twist can be produced. For the Z(S) twisting spun yarn, under the effects of the clockwise (anticlockwise) vortex airflow, the pre-twisting would be produced and the yarn twist can be strengthened, while under the effects of the anticlockwise (clockwise) vortex airflow, the untwisting effect would be produced, and the yarn twist can be decreased. [ABSTRACT FROM AUTHOR]

In the paper, using finite element method (FEM), the effects of lattice apron density on yarn qualities in Four-line compact spinning system were studied by analyzing the numerical simulations of the airflow velocity. Firstly, three different kinds of yarns, 18.2tex (32S), 9.7tex (60S), and 5.8tex (100S), were spun on FA507B spinning frame equipped with lattice aprons of mesh size 150, 120, and 100, respectively. The hairiness, breaking strength, and evenness of spun yarns were tested and comparatively analyzed. Secondly, using FEM, the numerical simulations of the airflow velocity in the condensing zone were presented. The finite element model of condensing zone was constructed according to the physical parameters of the practical system. Then, the simulation of airflow velocities on five straight lines located in the front, middle, and back of condensing zone were given. It is shown that, in the whole condensing zone, for the lattice apron with mesh size 100, the direct transverse condensing force is high, but the assisted condensing force is low and disorder, which is not beneficial for yarn qualities. Compared to the lattice apron with mesh size 150, the usage of lattice apron with mesh size 120 may be beneficial for the high-count yarn condensing or the yarn condensing under the relatively lower negative pressures. Furthermore, taking the 9.7tex as an example, the trajectory of yarn movement in the condensing zone was given using high-speed camera system OLYMPUS i-speed3. Corresponding airflow velocities along the yarn movement path were presented. [ABSTRACT FROM AUTHOR]

This paper presents a comparative assessment of two urban morphologies representing the urban transformations that occurred between 1976 and 2013 in downtown Rio de Janeiro. The work documents the impact of the city morphology changes on the air flow pattern, which is known to change the energy needs at the scale of the city. Special attention is dedicated to the comfort at pedestrian level and the potential for natural ventilation in a building of reference. The study was performed by means of numerical simulations based on the RANS k-ϵ turbulence model. The results show an increment in wind velocity at pedestrian level and a pressure difference rise between the building facades. New high-rise buildings increase the stagnation area in the leeward region, the boundary layer height, and the turbulence level. [ABSTRACT FROM AUTHOR]

Two-phase flow is studied numerically one-dimensionally using a two-fluid equation system. A hyperbolic type of governing equation is applied in our simulation. The segregated solution method is promoted and adopted in this article. By establishing mass conservation-based pressure correction, the SIMPLE algorithm is extended to two-phase flow simulations. Numerical results for well-known two-fluid air/water flow benchmark problems are presented and discussed. [ABSTRACT FROM AUTHOR]

This study investigates the fine particle behavior in the laminar airflow past a triangular cylinder. To track particles in motion for the investigation, a visualization system integrated with an effective postprocessing method is developed. Then it is perhaps for the first time that several individual fine particles moving in the flow near the base corners of the cylinder are tracked both simultaneously and continuously. These particles are found to follow closely the airflow pathlines, except very near the corners where the microscopic Stokes number is high. It is also revealed that all the particle tracks vacillate discernibly due to the Brownian motion. Taking this into account, an improved numerical simulation is conducted based on CFD software package FLUENT, with which dithering tracks of the moving particles are reproduced. Copyright 2013 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

A computational model for the analysis of natural flow of air through a ventilation system has been presented. The model has been validated and applied for the analysis of solar heat driven flow of air through a typical ventilated room space. Computations have been performed for Rayleigh number (dimensionless number characterizing this flow) ranging from . The details of the flow and temperature distributions in the room have been extracted corresponding to air as the working medium. This paper presents the details of the computational model and results corresponding to different conditions. The numerical method used is a hybrid finite element-finite volume method. [ABSTRACT FROM PUBLISHER]

In this paper, a method combining the orthogonal array design and the numerical simulation is proposed to optimize the geometry parameters of the melt-blowing slot die. An index, the stagnation temperature, is used to evaluate the performance of the slot die. The stagnation temperature is obtained by simulating the subsonic compressible air jet from the melt-blowing slot die, whereas the optimization is accomplished by the orthogonal array method. Three geometry parameters of the slot die: slot width, nose piece width, and slot angle are investigated. The results show that smaller slot angle and larger slot width will result in a higher stagnation temperature, which is beneficial to the air drawing of the polymer melt and thus to reducing fiber diameter, whereas the effect of nose piece width is insignificant. The optimal geometry parameters of the melt-blowing slot die achieved in this study are: slot width of 1.5 mm, slot angle of 30°, and nose piece width of 2 mm. [ABSTRACT FROM AUTHOR]

Steady-state, three-dimensional numerical simulations for airflow through large-scale sparse tubular heat exchangers are performed using Fluent (2006). A new porous media approach, semiporous media, is developed to simplify the computational fluid dynamics (CFD) modeling. In this approach, the tube bundle is simplified to a porous media zone that has half real tubes on both sides of it. Three CFD approaches, the real tube one, the semiporous media one, and the conventional porous media one, are compared in the predictions of the tubular heat exchanger airflow distributions. The comparison shows that the semiporous media approach predicts airflow distribution similar to the real tube distributions, reduces computational cost significantly, and can be easily implemented. The heat exchanger pressure drops predicted by the semiporous media approach are compared with the experimental data for eight designs. The results show that this new approach gives reasonable agreement with the experiments. [ABSTRACT FROM AUTHOR]

The objective of this study is to investigate the mechanism of inter-flat airborne disease transmission under the condition of single-sided natural ventilation. The focus is on one of the typical designs in residential buildings with a rectangular plan layout and having a common corridor separating the two sides, each of which has a flat facade with openable windows. When the wind speed is extremely low, with doors closed and windows opened, the flats become single-sided naturally ventilated driven by buoyancy effects. The air pollutants can travel from a lower flat to a vertically adjacent upper flat through open windows, caused by indoor/outdoor temperature-difference induced buoyancy. Computational fluid dynamics is employed to explore the characteristics of this process. Based on the comparison with experimental data about the air flow distribution in and around a single-sided naturally ventilated room, the renormalization group based k-ε model, together with carbon dioxide used as a tracer, is chosen to reveal this air cross-contamination. The simulation results are in agreement with our prior on-site tracer-gas measurements, revealing that the windows flush with a flat facade can be a major route of the air cross-contamination in high-rise residential buildings. Finally, an assessment index is proposed to evaluate the potential infection risks associated with this inter-flat air flow occurring in high-rise residential buildings. [ABSTRACT FROM AUTHOR]

Dispersion of airborne contaminants in indoor air was evaluated employing physical measurement, empirical models, and computer simulation methods. Field data collected from a tray of evaporating solvent in the laboratory were compared with computational fluid dynamics (CFD) simulations coupled with evaporation models. The results indicated that mathematical models of evaporation can be coupled with CFD simulations to produce reasonable qualitative predictions of airborne contaminant levels. The airflow pattern within a room is primarily determined by the room layout and the position of the air supply diffusers. Variations in ventilation rate did not alter the airflow pattern, thus generating a characteristic concentration profile of the airborne contaminants. [ABSTRACT FROM AUTHOR]

Properties of air are interrelated in a drying process. Equations of psychrometrics and fluid dynamics developed by previous researchers enable the development of simulation models, which become an indispensable tool for the study of drying technology. A Windows based software, entitled SAPGD (Simulation of Air Properties and Grain Drying), written in MATLAB, was developed to simulate the equations/models related to the following four aspects: The equilibrium moisture content of grains under the diverse conditions of atmosphere. The pressure drop to airflow of various grains. The relationship between drying time and moisture content under the model of thin layer drying of grains. The relationships among drying time, moisture content, grain depth, and grain temperature under the logarithmic model of deep bed drying of grains. [ABSTRACT FROM AUTHOR]

Representative double bifurcation airway models with asymmetric branch flow rate ratios, caused by spatially different downstream impedances or a carinal tumour in one branch, have been considered. For steady laminar inhalation of a dilute micron-particle suspension, i.e. 500 < or = Re < or = 2000 and 0.02 < or = St < or = 0.12, air flow fields, aerosol distributions, and wall particle concentrations have been simulated with a user-enhanced finite-volume code and an off-line particle tracking routine. Particle deposition efficiencies are shown for both asymmetric branch flow rate cases, i.e. unobstructed and tumour-induced. [ABSTRACT FROM AUTHOR]