Airflow Behavior Research Articles

Flow field characteristic in a novel cyclone-granular bed coupled separator

The three-dimensional flow field in a novel cyclone-granular bed coupled separator was discussed experimentally with a five-hole probe system. The airflow behaviors in the annular space, separation space, and central outlet were addressed. Several significant phenomena (the squeezing effect, the top flow loop, and the rectification effect) were observed and analyzed. By comparing the three-dimensional velocity distribution in the coupled separator with different structure parameters (the coupling space index, rc = 0.37/0.44), the combined effect between the two efficient gas purifiers was demonstrated and the importance of the tangential velocity was clarified. For this purpose, the equations for the tangential velocity at four circumferential positions were fitted using regression analysis with a wide array of experimental data and effectively characterized prior experimental outcomes.

Influence and optimization of dual-orifice jet nozzles on oil capture performance of under-race lubrication with a radial oil scoop for high-speed bearings in aero-engine

The objective of this research is to determine the influence of dual-orifice jet nozzles on the oil–air flow dynamics and oil capture performance in the under-race lubrication for high-speed bearings and to identify the optimal design parameter combinations for optimizing the oil capture performance. An experimental setup for under-race lubrication is specifically designed, complemented by a multiphase computational fluid dynamics model to elucidate the oil–air flow behavior. The response surface methodology is combined with a multi-objective particle swarm optimization algorithm to perform multi-objective optimization of the oil capture performance. The findings indicate that oil capture efficiency initially rises to a peak and subsequently declines with increasing orifice spacing, identifying an optimal orifice spacing that maximizes efficiency. While the oil flow rate from dual-orifice jet nozzles is lower than twice that of single-orifice jet nozzles, appropriate parameter matching allowed for an increase in both captured lubricant oil and efficiency. Optimized configurations achieved substantial enhancements in oil capture efficiency, with the greatest improvement exceeding 16%, all while maintaining precise oil supply to the high-speed bearings.

CFD modeling of gas−liquid flow phenomenon in lead smelting oxygen-enriched side-blown furnace

A validated numerical model was established to simulate gas−liquid flow behaviors in the oxygen-enriched side-blown bath furnace. This model included the slip velocity between phases and the gas thermal expansion effect. Its modeling results were verified with theoretical correlations and experiments, and the nozzle-eroded states in practice were also involved in the analysis. Through comparison, it is confirmed that the thermal expansion effect influences the flow pattern significantly, which may lead to the backward motion of airflow and create a potential risk to production safety. Consequently, the influences of air injection velocity and furnace width on airflow behavior were investigated to provide operating and design guidance. It is found that the thin layer melt, which avoids high-rate oxygen airflow eroding nozzles, shrinks as the injection velocity increases, but safety can be guaranteed when the velocity ranges from 175 to 275 m/s. Moreover, the isoline patterns and heights of thin layers change slightly when the furnace width increases from 2.2 to 2.8 m, indicating that the furnace width shows a limited influence on production safety.

Heat transfer within a multi-package: Assessing the impact of package design on the cooling of strawberries

Perishable horticultural products may necessitate multi-packaging for preservation. The optimized primary and secondary packaging designs allow to reduce cooling time and ensure uniform product temperature, thereby enhancing fruit quality. This study examined how the secondary package design impacts the cooling of strawberries in airtight clamshells (AC) during precooling. The AC design simulates heat transfer within Modified Atmosphere Package (MAP) where there is no direct interaction between the external cooling air and the internal environment of the clamshell. Laboratory experiments were conducted to simulate one level of a pallet, using artificial material instead of real strawberries in order to have a better control of thermophysical properties and thus to better investigate heat transfer mechanisms. The thermal performance of an existing tray design was compared to three new alternative designs. The effect of air headspace, vent holes area and inlet airflow rate on the cooling efficiency was investigated.Experimental results revealed significant cooling heterogeneities among different AC positions, with the largest observed disparities being 1.8 h for half cooling time (HCT) and 3.7 h for seven-eight cooling time (SECT) in the current tray design. Incorporating vent holes into the current commercialized tray design demonstrated superior cooling performance, with 8% improvement of the overall average HCT. Analysis showed increasing the thickness of the air headspace above the AC increased 91% and 113% the overall average HCT and SECT, respectively. The research found that airflow distribution in a tray has a critical effect on the heat transfer between the AC walls and the surrounding air temperature. Thus, the packaging design is crucial in ensuring proper ventilation around the ACs.The alternative designs or operating under a lower airflow rate revealed a potential to cut down on energy use for ventilation. Specifically, when the airflow rate was reduced by one-quarter, there was a remarkable 94% decrease in energy usage. However, this benefit is counterbalanced by a 100% increase in the overall average HCT, which might adversely affect the product quality. Hence, optimizing the packaging design is essential to ensure the right balance between energy efficiency and product quality.The HCT exhibited a linear correlation with the external resistance, which is influenced by the airflow behavior, whatever the AC positions and tray designs.

Airflow detailed analysis through a face mask using the schlieren technique

This work presents an exhaustive visualization of the airflow expulsed by a person while breathing, talking, exhaling, and blowing inside a closed room wearing a disposable face mask like those used in hospitals for patient protection and those who care for them. An optical schlieren experimental arrangement was used to obtain some of the relevant physical characteristics of the airflow, such as its refractive index gradient, the distribution of temperature, and the associated velocity field for all the tests developed. We tested three face masks, one of the surgical types and the others of the N95 series with denominations KN95 and 3MN95 (Aura TC-84A-8590). The results show appreciable differences between the masks evaluated; the surgical mask was the one that allowed the most abrupt output airflow through it in the field of view of the experimental setup. However, were also found some differences in the performance of the KN95 and 3MN95 masks. The KN95 face mask had the best performance since it expulsed to its surroundings the lowest airflow with different physical properties to the input airflow. The results obtained are relevant since it was possible to estimate the expulsed airflow velocity as a function of the distance for every face mask tested, which allows for understanding its filtering capacity by restricting the flow of potential pathogens from the mouth or nose of one person to another. Undoubtedly, the airflow behavior determination around a face mask can help to reduce the risk of spreading infectious airborne particles.

Analysis of the alternative air ductwork by Numerical airflow behavior combined with the New Economic index and standard

This research studies the numerical modelling using computational fluid dynamics with a k-Epsilon turbulence model to analyze airflow behaviors inside the alternative compared with conventional air ductwork combined with a comprehensive analysis of the economic parameter created by the author called Reveal Comparative Advantage Cost index. All alternative air ductwork has lower pressure drop and a higher ability to maintain the temperature inside, showing that alternative air duct systems have a significant advantage over conventional air ductwork. The fabric ductwork has a lower pressure drop than galvanized steel perforated ductwork, which is 69.15 %. The pre-insulated ductwork can keep the best temperature inside, with a different temperature value between the air inlet and air outlet of 0.06°C. The Reveal Comparative Advantage Cost of construction costs of the galvanized steel ductwork and the galvanized steel perforated ductwork are 1.02 and 1.06, which means the conventional air ductwork is initially cost-effective in terms of investment and operating costs. However, alternative air ductwork is the better option for long-term use. They have cost-effective electrical energy and maintenance costs with a high Reveal Comparative Advantage Cost index. Significantly, the pre-insulated ductwork has the Reveal Comparative Advantage Cost index of maintenance, electrical energy, and construction costs of 1.38, 1.09, and 0.95, respectively. The results of the airflow behaviors study combined with the Reveal Comparative Advantage Cost index study show that the galvanized steel perforated ductwork is not a selectivity that qualifies either for airflow behaviors or is unsuitable for investment. Pre-insulated ductwork is the appropriate option due to the high airflow behaviors and cost, which makes it suitable for investment. However, the Thailand Authority should develop alternative air ductwork Thai standards for engineering design and safety building.

A Numerical Simulation of the Coal Dust Migration Law in Directional Air Drilling in a Broken Soft Coal Seam

Abundant industrial experiences have shown that directional air drilling technology is effective for gas drainage when drilling broken and soft coal seams. In this paper, the Eulerian–Eulerian model was used to simulate the gas–solid two-phase flow behavior of compressed air transporting coal dust in broken soft coal seams. The relationship between the degree of coal dust deposition, annular air pressure law, transportation of coal dust, aforementioned factors of rotational speed, particle size, and air volume could be determined. The results indicate that the particle size plays a significant role in the transport capacity of coal dust. Smaller particle sizes and a higher airflow result in a lower deposition degree of coal dust. When the particle size of coal dust is 1.69 mm and the airflow is 300 m3/h, in the case of coal dust generation at a rate of 0.24 m3/h, the deflection angle of the coal dust collection zone is increased by 130% as the rotational speed of the drill rod is increased from 0 to 120 rpm. Similarly, the deflection angle of the coal dust collection zone is increased by 12.8% in a 500 m3/h airflow under the same condition. Additionally, fine particle-sized coal dust is transported in a spiral line. The coal dust with larger particle sizes tends to be in the middle and lower parts of the hole and move along a specific trajectory. Industrial experiences of medium-air-pressure drilling confirm that a rotary drilling speed between 80 and 120 rpm, with a minimum air volume of 400 m3/h and preferably 500 m3/h, can promote a smooth hole drilling effect and enhance the construction safety in the gas drainage process.

Static and dynamic study of the airflow behavior generated by two air assisted sprayers commonly used in 3D crops

Air-assisted sprayers, which are commonly used for pesticide application in three dimensional (3D) crops, are evolving towards increasingly innovative designs in terms of pneumatic system regulation with the aim of providing an adjusted amount of airflow to the target. As a result, it is currently possible to modify the characteristics of the airflow by remote control from the cab or manually. In this sense, characterizing the behavior of airflow in agricultural sprayers has become crucial to understand how the characteristics of the air velocity vector vary before reaching the crop when the main application parameters change. Therefore, the present study focuses on characterizing the airflow generated by both a multirow and an axial air-assisted sprayer as a function of different configurations associated with both the pneumatic system (fan gearbox position and diffuser air outlet section) and the application conditions (height, horizontal distance and forward speed) with the final objective of obtaining mathematical models to estimate the air speed in the vicinity of the crop as a function of these parameters (pneumatic system configurations and application conditions). Air velocity maps were generated for each sprayer in both static and dynamic situations under laboratory conditions and in the absence of wind. Airflow rate (m3 h−1) generated by the sprayers was first quantified in accordance with the ISO 9898: 2000 standard using a vane probe anemometer. Then, static and dynamic measurements were carried out using a 3D ultrasonic anemometer to analyze module and direction of the air velocity vector for all configurations. Results showed some similarities in the airflow behavior between sprayers under static conditions. As horizontal distance increased, the vertical distribution of airflow became more homogeneous across different heights. Furthermore, the adjusted deflectors of the Twister sprayer and the multirow design resulted in minimal variation in the direction associated with the lower magnitude components of the air velocity vector. As the forward speed increased, main factors had different effects on the response variables among the sprayers. Models with a high goodness of fit when predicting the air velocity module were achieved for both sprayers.

Effect of Septum Deviation on the Airflow Distribution for a Patient Specific Model using Numerical Methods

Septal deviation (SD) in nasal cavity plays a crucial role in symptoms related to nasal obstruction, aesthetic appearance of the nose, and increase in nasal resistance, and may induce snoring. The aim of the present study was to evaluate the significance of SD on the air flow behaviour and compare its deviation with a healthy nasal cavity by using CFD. A 3D CAD model of subject specific nasal cavity was generated from CT images of patient with septal deviation. The variation of maximum WSS observed in the present study was higher when compared with that of normal subjects. In contrast to the healthy subject, the airflow in the septal deviation models showed asymmetry in bilateral nasal cavities. The maximum velocity inside the nasal cavity exceeded the value that was usually found at the nasal valve region. The findings from this study help understand the basic aerodynamics in a severely deviated septum.

Assessment of Airflow Patterns Induced by a Retractable Baffle to Mitigate Heat Stress in a Large-Scale Mechanically Ventilated Barn

In large-scale dairy farming, heat stress remains a primary concern, and cross-ventilated barns have become increasingly prevalent in order to tackle this issue. Such barns employ energy-intensive electrical fans to enhance airflow and regulate temperature. To optimize this system, air baffles are often placed above the animal-occupied zones (AOZ) to direct airflow toward the cows. Although previous studies have suggested that baffles can substantially amplify the system’s cooling effect, the comprehensive impact of baffles on airflow patterns in a full-scale barn is less understood. Traditional measurement techniques, involving physical sensors, are both technically demanding and costly. Moreover, they often fall short in accounting for the dynamic microenvironmental changes induced by fluctuating weather, animal movement, and operational machinery. This study leverages computational fluid dynamics (CFD) to model airflow behaviors within a cross-ventilated barn, specifically examining the influence of a retractable baffle. CFD not only offers a reliable and efficient method for simulations but also allows for accurate assessments by validating the generated data against empirical observations. The results verify that, when properly configured, air baffles can significantly enhance airflow at cows in large barns. Additionally, the study establishes the reliability of CFD for designing large-scale dairy barns.

Study of Airflow Behavior for Duplex Circular Cylinders

Study of Airflow Behavior for Duplex Circular Cylinders

Heat transfer characteristics of charging and discharging encapsulated PCMs (SP24, SP26 & SP29) for free cooling: impact of geometry and nanomaterials addition

Herein, free cooling an application of thermal energy storage is investigated through theoretical observations of air being cooled after passing over encapsulated phase change material (PCM). The impact of encapsulation geometry changes from circular to; rectangular, square, and elliptical shapes is studied for the PCM solidification and melting cycles. The study is performed for sp24, sp26, and sp29 PCM types with and without the inclusion of CuO and Al2O3 nanoparticles (NPs). A transient mathematical model for heat transfer behavior of airflow over the encapsulation is constructed and solved using Ansys 20.2 software. It is found that the rectangular-shaped PCM encapsulation with CuO nano-enhanced PCM has the shortest complete melting (~ 1–2 h) and complete solidification times (~ 3–9.3 h). Nanoparticle enhancement improves the rate of melting by a maximum of 11.56% with Al2O3 NPs and by 6.12% with CuO NPs at an inlet airflow temperature of 313 K. A maximum outlet air-temperature drop of ~ 3.1 K occurs in the cylindrical geometry with CuO nano-enhancement and the highest Nusselt number is obtained at similar conditions. From this study it is recommended to use either sp24 or sp26 PCMs mixed with nano-alumina and encapsulated within rectangular containers for free cooling applications.

Effects of wavy structure, ambient conditions and solar intensities on flow and temperature distributions in a mini solar flat plate collector using computational fluid dynamics

Mini solar flat plate collectors have gained traction due to their cost-effectiveness, high efficiency in converting solar radiation to heat energy, and versatility in residential and commercial applications, offering long lifespans with minimal maintenance. Optimizing the thermal performance of solar flat plate collectors using numerical simulations helps enhance their efficiency, making them even more appealing for small-scale heating and hot water applications. This study investigates the flow behavior and temperature distribution of air within a small-sized solar collector (286 × 800 × 70 mm) and optimizes its design for achieving the highest outlet air temperature. The optimization process included varying geometric parameters, such as the wavy structure hole diameter, and considering a range of operating conditions, including ambient conditions and solar intensities. This analysis aimed to understand the flow behavior and temperature distributions within the solar collector. The numerical studies provided valuable insights into the thermal and flow characteristics of the collector. The velocity distribution of the fluid within the collector aided in understanding the flow behavior, optimizing the flow path to minimize pressure drop, and maximizing heat transfer. Additionally, calculations were performed to determine total useful heat, outlet temperatures, and efficiencies. The study also discusses the optimal design and operating conditions for the collector.

Modeling and Thermal Simulation of 2U-Rack Servers Applying Computational Fluid Dynamics Techniques

The data center industry consumes between 196 and 400 terawatt-hours annually, between 1% and 2% of the world's energy consumption. A high percentage of data center energy consumption is associated with air conditioning and cooling systems. The optimization of the data center cooling process can occur at multiple scales, being one of the most relevant to the generation and heat transfer processes within servers. In this approach, we must study the temperature fields of each server’s components and understand airflow behavior within the server chassis. The present work, in its first stage, performs a thermal and cooling analysis for a two-unit rack server (2U-Rack) using computational fluid dynamics (CFD) techniques via Ansys Fluent code. A geometric server model was developed, considering heat generation in the main electrical components and heat and air mass transfer with the data center. The model was validated by comparing simulation results with the server's sensor values and the results of thermography testing. Following CFD simulation, airflow velocity fields, temperature contours, and sensitivity scenarios were obtained, with the goal of proposing an optimization model that would allow us to improve server heat transfer processes in the following steps.

Computational fluid dynamics simulation and optimization of the fluid flow behaviour in a multi‐stage solar updraft tower using a new chimney design

AbstractThis work proposes a new chimney design that allows for the development of a multi‐stage solar updraft tower (SUT). The new design consists of two successive divergent chimneys. A 3D model was established to inspect the air flow behaviour within the SUT in six configurations: four multi‐stage systems with four divergence angles of the second stage were compared to the simple conventional SUT and the simple SUT with a divergent chimney. The new SUT performs better than the conventional one, while the two‐stage solar tower multiplied the system efficiency. Two high‐velocity zones appeared for the two‐stage SUT, whereas one zone occurred for the conventional system. The velocity in the two zones achieved a significant value, like that of the conventional system. In addition, the second stage's divergence angle directly impacts the velocity value inside the two stages. The static pressure distribution varies with the change in chimney design. The depression area occurs twice for the multi‐stage SUT in the inlet of each stage.

Impact of eave and roof pitch on cross ventilation for an isolated building with sawtooth roof

An eave refers to an extension attached to the building roof to protect the interior space from direct solar radiation and improve the performance on cross ventilation. In this study, the impact of eave inclination angle and roof pitch of an isolated sawtooth roof building on cross ventilation were investigated. The eave configurations at either windward or leeward openings were included. 3D steady Reynolds-Averaged Navier-Stokes (RANS) equation in combination with the Shear-Stress Transport model (SST k-ω model) was used for the Computational Fluid Dynamics (CFD) simulations. Grid sensitivity study was carried out and the performance of cross ventilation was evaluated based on the non-dimensional velocity magnitude, spatial distribution of pressure coefficient as well as the ventilation rate of the building. For the simulation model with 55° roof pitch, it is observed that a region with high velocity magnitude formed on top of the leeward eave due to the higher roof pitch and presence of the leeward eave. Results also indicated that the building model with 90° leeward eave and 55° roof pitch has the highest increment in ventilation rate which is 7.16%. On the other hand, the building model with 90° windward eave has the highest pressure coefficient because more blockage of airflow is caused by a steeper roof as the roof pitch of the building increases. Furthermore, the building model with 90° leeward eave shows a larger region with negative pressure at the leeward façade indicating higher airflow leaving the leeward opening. Therefore, the airflow behavior and characteristic are both dependent on the roof pitch and eave inclination angle for a naturally ventilated building.

Experimental Investigation of Fluid Flow through Zinc Open-Cell Foams Produced by the Excess Salt Replication Process and Suitable as a Catalyst in Wastewater Treatment

The “excess salt replication process” is a new simple method of fabrication of open-cell metal foam based on the commonly known salt replication method. Porous materials with porosity between 46% and 66% result when the employed alloy is 25% antimonial lead alloy and when it is 58% to 65% zamak 5. These foams are proposed as structured catalysts instead of packed beds in the treatment of wastewater. The local regimes influencing macroscopic air flow behaviour through these foams are delimited and boundaries are analysed in terms of sample length. Most of the experimental tests in this work exhibited a general trend of air flow in ESR foams dominated by the “strong inertia regime”. It was established that the law governing the unidirectional air flow through these foams was the full cubic law. The permeability and inertia coefficient of five samples with a cell diameter between 2.5 and 4.5 mm were calculated, and an empirical correlation was fitted. The irregular cuboid shape of salt grains used in the ESR foam was the origin of the special cell form of ESR foams leading to an anisotropic ordered porous media. This can explain the macroscopic turbulence of air flow because there were many dead zones present in the corner of each cubic cell, thus causing kinetic energy loss starting at earlier regimes.

Analysis of the particle collision behavior in spiral jet milling

Collision behaviors of particles in spiral jet milling were analyzed by using a simulation. The motion of the particles was tracked by the discrete element method (DEM), and the air flow was represented by the computational fluid dynamics (CFD). The DEM was coupled with the CFD by a one-way coupling method. The simulated air flow was validated by comparing the fluid velocity field with the measured one in a model experiment. Furthermore, the air flow and particle behaviors in a spiral jet mill used commercially were analyzed by using the simulation. As a result, the particles with a region balancing between centrifugal and radial drag forces could be mainly ground by the high-speed collisions between the particles circulating near the top and bottom walls of the grinding chamber.

Density and Small Disturbance Equation-Based Simulation of Designed Bipalne Airfoil Under Supersonic Flow

For inviscid airflows, the small disturbance equation (SDE), as a condensed form of the full potential equation, is an effective approach for characterising the behaviour of this type of airflow in the presence of thin obstacles in its path. Density-based solutions (DBS) are frequently used by ANSYS to model the airflow behavior under the same environment. Through the impact of shock interference between the target wings, special Bussemann-type supersonic biplane designs can be effective in restricting sonic booms and wave drags in particular supersonic conditions. The modeling investigations of the shock oscillations produced between the wings are quite rare, nevertheless. Therefore, in order to replicate the behavior of the airflow over the target wing in supersonic settings and to compare the results more closely to reality, the Small Disturbance Equation (SDE) and the Density Based Solution (DBS) will be employed as efficient simulation tools in this study. The SDE results are vulnerable to inaccuracies because of the constraints of the simulation settings, whereas the DBS results are more accurate when compared to the exact simulation results. Overall, the DBS simulation results and the legit results are consistent, indicating that the inviscid airflow hypothesis is a feasible option for modelling the effectiveness of shock oscillations between wings. The SDE approach, which is implemented in Python and is a condensed version of the en-tire potential equation, offers a lot of space for development as it only does simulations in terms of velocity in this article and ignores the pressure and density elements.

Influence of Morphological Parameters on the Flow Development within Human Airways

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.