Airflow Velocity Distribution Research Articles

Research on the thermal comfort of vertical radiant cold plate coupling with a new dual cold source dehumidification air conditioning system

Radiant cooling provides a completely novel air conditioning terminal that could provide better thermal comfort for the resident. However, the radiative system may encounter condensation issues under high-humidity environments. This article studies a radiant air conditioning system with dual-cold-source dehumidification which comprises a plate heat exchanger, a dual-cold fresh air dehumidifier, a capillary radiant cooling wall, and an air-source heat pump. The experimental results demonstrate a positive correlation between the temperature profile of the indoor air and the temperature distribution of the radiant cooling wall. Simulations were conducted to analyze the office’s air temperature and airflow velocity distributions under different supply air volumes and to assess thermal comfort employing computational fluid dynamics (CFD) software. The comfort levels with different air inlet positions are discussed. The simulation results demonstrate that the air conditioning system can maintain a high standard of comfort under an air supply of 350 m³/h.

Evaluation of supervised machine learning regression models for CFD-based surrogate modelling in indoor airflow field reconstruction

Fast and reliable prediction of indoor airflow distribution is critical for indoor environment control. While neural networks (NN), often interchangeably referred to as Back Propagation Neural Networks (BPNNs), are popular for airflow predictions, optimising these models is challenging due to their ”black box” nature and complex network structures. This study explores alternative robust regression models, including decision-tree-based models (e.g., XGBoost, LightGBM, Random Forest) and Support Vector Regression (SVR), for predicting indoor airflow. Two BPNN structures were initially developed to evaluate feasibility of NN models. BPNN A was trained using airflow velocities from two inlets as input neurons to directly predict the airflow velocity distribution within the domain. BPNN B was trained additionally with spatial information, including space samples and boundary wall data. Higher-dimensional training structures of BPNN B were applied to decision tree-based models and SVR to assess their capability in predicting non-linear airflow patterns. Results indicated that BPNN A achieved the highest accuracy, while the inclusion of higher-dimensional data in BPNN B led to decreased accuracy. Among all decision-tree-based models, XGBoost demonstrated the greatest potential, achieving an R2 above 99.5% and predictive errors below 10%. XGBoost also outperformed both BPNN models in speed, being 15.78 times faster than BPNN A and 252 times faster than BPNN B. The interpretability of XGBoost was further explored by analysing feature importance, which helps identify the most influential input variables while predicting the airflow velocity. This analysis is expected to offer an enhanced understanding of boundary conditions leading to optimised indoor environment strategy.

Coupling adaptive filters with acoustic travel time tomography for indoor climate measurements in occupied room conditions

Acoustic travel time TOMography (ATOM) as a remote sensing technique allows for the measurement of indoor climate parameters, such as air temperature and airflow velocity distributions. The performance of ATOM in monitoring indoor air temperature in empty room conditions was evaluated recently, utilizing a combined analysis approach of room acoustics and tomography. This study shifts focus to the assessment of ATOM in an occupied room condition where fixed objects are introduced to the test area. The presence of objects in a room can result in notable shifts in the travel times of individual reflections. In some cases, these shifts can cause reflections to disappear completely or be replaced by new ones. These partial disruptions in the reflection pattern present challenges in obtaining accurate information about the room's temperature. To ensure the accurate identification of undisturbed reflection paths, an algorithm was developed that can convert distorted signals into a pure reference signal using a suitable adaptive filter. The measurement results confirm the validity of the approach for a temperature interval of 4°C where the system was trained for two temperatures of 20°C and 24°C in a climate chamber.

Oscillatory airflow through the hypopharyngeal and supraglottic airway

Exercise-induced laryngeal obstruction (EILO) is a known cause of exertional dyspnoea, characterised by paradoxical inward collapse of laryngeal tissues. The pathophysiological mechanisms of EILO remain to be fully established, but insufficient mechanical resistance of laryngeal tissues to air-induced loads is hypothesised. It is understood that airflow and anatomic configurations of the airway play a key role in the wall pressure distribution of the larynx. While breathing is a cyclic process with directional changes of airflow, the literature is confined to steady, unidirectional airflow. It is necessary to assess the role of oscillatory airflow on the loads on the laryngeal airway. This study investigates the effect of oscillatory airflow on the laryngeal flow fields and air-induced loads. A computational fluid dynamics model of the upper respiratory tract (URT) is developed using the Reynolds-averaged Navier-Stokes equations. Five oscillatory airflow cases through a single geometry are considered, utilising sinusoidal breathing cycles with different breathing frequencies (24, 32 and 40 breaths per minute) and peak inspiratory flow rates (96, 168 and 240 L/min). Results include the airflow velocity distribution in the URT, and the air-induced pressure and forces. It is demonstrated that inspiratory velocity distribution varies with breathing frequency and intensity. The force acting on the URT walls are in-phase with the airflow rate and therefore exhibit quasi-steady behaviour. These findings are also reflected in the force vectors acting on the aryepiglottic folds and indicate that air-induced closure of the supraglottis in EILO is influenced by the breathing intensity rather than the breathing frequency.

Pneumatic separation and process simulation of waste printed circuit boards pyrolysis residue

In this study, the application of Z-shape pneumatic separator for separating metal and nonmetal particles in pyrolysis residue of waste printed circuit boards was investigated, and the flow field characteristics and particle motion behavior in the separator were revealed through flow field simulation. The pneumatic separation results indicated that pre-screening significantly enhanced the separation efficiency of metals and nonmetals in pyrolysis residue. The simulation results showed that the large gradient of airflow velocity distribution and the turbulent flow field within the Z-shape separation cavity are beneficial for dispersing particles and reducing the influence between particles of different properties, thus enhancing separation efficiency. Using Rocky DEM for modeling of different shapes and properties of particles, and then combined with ANSYS Fluent can better simulate the particle separation behavior in the pneumatic separator.

Design and Evaluation of Face Mask Filtration: Mechanisms, Formulas, and Fluid Dynamics Simulations

The global adoption of face masks as a preventive measure against the spread of the SARS-CoV-2 virus (COVID-19) has spurred extensive research into their filtration efficacy. This study begins by elucidating various mechanisms of particle penetration and comparing filtration efficiency formulas with experimental data from prior studies. This is compared to the filtration efficiency experimental measurement developed in our previous study. Moreover, it delves into fluid dynamics simulations to examine different turbulent airflow models. Specifically, it contrasts the airflow velocity distribution of the k-ω and k-ε turbulent flow models with that of a quadrant-based average velocity model developed within this research. Furthermore, the study conducts fluid dynamic simulations to assess airflow profiles for six distinct medical and non-medical face masks. The results underscore substantial disparities among the simulations, emphasising the criticality of employing accurate fluid dynamics models for evaluating airflow patterns during diverse respiratory activities such as breathing, coughing, or sneezing, thereby enhancing environmental health in the realm of infectious disease prevention.

Numerical Analysis of the Airflow Field and Experiments of Fiber Motion for Solution Blowing.

Solution blowing is a rapidly developing technology for the rapid and large-scale preparation of nanofibers, driven by its advantages, such as wide adaptability to raw materials, simple and safe operation, and ease of scalable production. Most of the research related to solution blowing mainly focuses on the fiber spinning and forming principle, fiber structure and properties, and the development of new materials. Limited studies have focused on the airflow field and fiber motion in solution blowing. In this paper, nine nozzles for solution blowing with varying geometrical parameters were designed by adjusting the outer nozzle diameter, inner nozzle outstretched distance, and inner nozzle diameter. The centerline airflow velocity, turbulence intensity, and velocity distribution of the solution blowing were analyzed using the numerical simulation method. The results showed that the outer nozzle diameter had the greatest influence on the air velocity and turbulence intensity. The airflow velocity increased and the turbulence intensity decreased with the increase of the outer nozzle diameter. The inner nozzle outstretched distance only affected the airflow convergence point and had less effect on the airflow velocity and turbulence intensity. The captured trajectory of the polymer jet initially shows a straight or slightly curved development that eventually diverges from the airflow field. With an increasing distance, dispersed fibers exhibit instability, including loop formation, bonding, and separation. The experimental observation of fiber morphology in the solution-blowing web further verified the instability during the fiber movement.

Numerical Simulation of Airflow Velocity and Temperature Distribution in an Aircraft Cabin

In this work, a computational fluid dynamics (CFD) model is established to calculate the airflow distribution in the cabin of a single-channel Boeing 737-800 airplane. The RNG k-ε model, considering the calculation of turbulence kinetic energy and its rate of dissipation, is adopted to solve turbulence problems in physical field simulation. The proposed three-dimensional model is able to consider the particular physical factors and spatial structures, which can simulate the detailed distributions of complex physical fields, compared with the one-dimensional lumped parameter model. The velocity and temperature fields under different air supply velocities are then numerically investigated. The calculation results show that when the air velocity at the top air supply inlet is 1.4 m/s, the velocity and temperature distribution inside the cabin can both meet the comfort requirements of humans in the airworthiness standards. The results from this work can help to design an aircraft environmental control system.

Research on the Grinding Process of Superhard Particles in the Fluidized Bed Opposed Jet Mill Based on the CFD-DEM Methodology

The process of superhard particle breakage in the grinding zone of the fluidized bed opposed jet mill is investigated using the CFD-DEM (computational fluid dynamics-discrete element method) coupling method with the Tavares UFRJ Breakage Model in the present study. The effects of structural and operational parameters, such as target plate structure, nozzle position, air inlet velocity, and feed rate, on the equipment stress distribution, airflow velocity, pressure field, particle velocity, and cumulative particle size distribution are thoroughly studied to determine the optimal structural and operational parameters. Experimental validation is conducted, including scanning electron microscope (SEM) observation of particle morphology and analysis of particle size distribution of ground product particles. The simulation results indicate that the wear rate of the structure without a target plate is lower than that of the structure with a target plate in the grinding central zone. Therefore, the structure without a target plate is chosen for further investigation. The cumulative particle size distribution after grinding is influenced by nozzle position, air inlet velocity, and feed rate. The particle D50 is positively correlated with nozzle spacing and feed rate, while it is negatively correlated with air inlet velocity. The optimal grinding effect is achieved when the distance between the nozzle and the center of the grinding zone ranges from 52.5 mm to 72.55 mm, the air inlet velocity is 950 m/s, and the feed rate is 10.5 g/s. Through experimental investigation, it has been observed that when the feed rate is 10 g/s, the particle size distribution becomes more uniform. Furthermore, consistent trends in the cumulative particle size distribution in the experiment and simulation results can be found, which validates the present numerical model. It was observed that particles at low feed rates retain certain angular edges, while particle roundness increases at high feed rates.

Influence of deflectors on indoor airflow velocity distribution under natural ventilation conditions

Deflectors offer a cost-effective solution for enhancing airflow distribution. The purpose of this paper is to investigate the effect of the deflector on the indoor airflow velocity distribution under natural ventilation conditions. The results obtained from numerical simulations are validated through experimental measurements using a reduced-scale model. Subsequently, the validated reduced-scale numerical model was extended to full-size rooms. A full-size numerical simulation method is used to analyze the effect of no deflector, deflectors with different opening width-to-height ratios and deflectors with different opening shapes on the percentage of indoor velocity partitions under natural ventilation conditions. The findings reveal that the judicious installation of deflectors can enhance indoor airflow velocity distribution and increase the percentage of the indoor comfort zone. Deflectors with different opening width-to-height ratios exert distinct influences on indoor airflow velocity distribution. When the deflector opening width-to-height ratio is set at 7/6, the indoor comfort zone percentage reaches its maximum at 75.98%. Furthermore, the shape of the deflector’s opening significantly affects indoor airflow velocity distribution, and when the opening shape is a rhombus shape of 4.00 cm × 9.00 cm, the proportion of indoor velocity comfort zone is the largest, which is 75.56%. This study provides a reference for the design and practice of natural ventilation in buildings.

The Optimization of Distribution and Fan Parameters in Heat Treatment Furnaces Through the Integration of Numerical Simulation and Machine Learning

Abstract The present study employed numerical simulation technology to investigate the distribution of workpieces within a low-temperature trolley heat furnace and analyze the influence of circulating fan parameters on heat treatment quality. This analysis was integrated with machine learning technology to guide heat treatment production. The research findings indicate that when the number of workpieces remains constant, their position has a significant impact on airflow velocity distribution, heating rate, and temperature uniformity within the furnace. Additionally, wind pressure from the circulating fan affects both fluid field and temperature field; the increasing wind pressure leads to higher flow rates in the furnace as well as increases heating rates for workpieces. Heating efficiency exhibits a nonlinear relationship with wind pressure increment. By adjusting air pressure distribution from the circulating fan, workpiece temperature uniformity can be improved by 64%. Furthermore, machine learning technique demonstrates excellent performance in predicting workpiece temperatures with a maximum relative error of 2.4%, while maintaining consistent trends in temperature uniformity.

A novel thermal-fluid topology optimization of the frame mold for composite autoclave process

Frame mold serves as an important tool during autoclave process of composite panels. Its temperature uniformity plays a crucial role in guaranteeing the production quality. However, the temperature uniformity of mold usually has to be sacrificed during the design process for ensuring the stiffness of mold. To solve this problem, a novel design strategy is proposed in this study to optimize the heating airflow channels of mold with better temperature uniformity based on thermal-fluid topology optimization method. Firstly, the temperature and the airflow distribution characteristics of mold during autoclave process are investigated systematically based on the Computational Fluid Dynamic (CFD) simulation model. The result indicates that the uneven temperature distribution of the mold during autoclave process is significantly affected by the varying airflow velocity distribution inside the mold. Inspired by this, a thermal-fluid topology optimization method is developed to design the airflow channels of mold to achieve optimal mold temperature uniformity. The optimization result provides a novel configuration of mold in which a ‘wind deflector’ is incorporated inside the mold to alter the airflow pattern. Finally, the simulation results show that the optimized mold with a ‘wind deflector’ significantly improves the mold temperature uniformity by 16%. And experimental validation has applied to confirm the effectiveness of the results. Besides, the configuration of the optimized mold has good industrial application prospects for its convenient installation process and low cost.

Numerical study of snow accumulation on bogies for long marshalling high-speed trains

Current numerical research on snow accumulation on bogies often simplifies train models as 1.5 cars or 3 cars, and there is less research on long marshalling trains with real bogies. In this article, based on the Euler–Lagrange method, the airflow structure and snow accumulation characteristics in the bogie area of an 8-car high-speed train (HST) are studied by numerical simulation. The results show that the airflow velocity and snow distribution concentration inside the bogie cabin vary along the flow direction. The downstream bogie cabin has a lower airflow speed, spatial snow particle concentration, and components snow accumulation. Because of the bogie cabin cover structure, the main airflow direction above the first and second bogie cabin is different, resulting in higher snow concentration and range on the windward side of the first bogie. There is a significant difference in snow accumulation characteristics between powered and nonpowered bogies. The powered bogie gearbox is directly affected by the airflow carrying snow particles, leading to severe snow accumulation on the windward side. This study provides a research foundation and engineering guidance for the snow protection strategy of HST bogies and is important for improving the comfort and safety of HSTs on snow-covered rails.

Numerical study on the airflow characteristics and smoke control condition in stair area of subway stations

As the key facility connecting different floors in subway stations, the smoke control in the stair area has been one of the most important goals of fire protection design. But the detailed airflow field and smoke spread process are rarely discussed. With numerical simulation, this work investigated the airflow velocity distribution and critical condition for smoke control in two critical openings of the stair area, which include the opening beneath the ceiling screen and the opening on the top of the stair. The results indicate that (1) In spatial dimension, the airflow velocity distribution shows a nonuniformity within each opening and a difference between two openings. (2) In the temporal dimension, the airflow velocity shows a normal distribution characteristic. The strong turbulence leads to a dynamic airflow field with an unstable smoke spread process. (3) For the critical opening beneath the ceiling screen, the airflow velocity is dominated by thermal buoyancy or inertia force in different areas. The practical smoke control criterion is to ensure the smoke layer is higher than the edge of the ceiling screen. (4) For the critical opening on the top of the stair, airflow velocity shows an exponential decay distribution. The critical condition could be predicted with a virtual fire source within the stair. This work hopes to present the necessity of dynamic and microscopic modeling of the airflow - smoke flow interaction for an accurate prediction of the smoke control condition in the stair area of subway stations.

Transient Computational Fluid Dynamics Analysis of Passive Cooling in a Building with Diurnal Radiative Cooling Material Coated onto Its Rooftop

Building cooling loads, which continue to increase with increasing global temperatures, are responsible for large quantities of greenhouse gas emissions. Radiative cooling (RC), whereby structures are cooled by emitting radiation in the atmospheric window, from 8–13 μm, to outer space, is a promising clean technology that can be used to meet ever‐increasing building cooling demands. However, the effects of using RC on the airflow velocity and temperature distributions within the occupied zone of buildings are yet to be investigated. Herein, computational fluid dynamics simulations are performed to study the transient airflow velocity and temperature distributions in buildings that are cooled using RC material on their rooftops. For idealized conditions when the thermal mass of the house is neglected, the results show that when the cooling power provided by the RC material is , and the average temperature of the occupied zone in the building is reduced from 295 K to about 293 and 289.7 K after two minutes, respectively. These rapid cooling rates were attained without exceeding head‐to‐ankle temperature differences of about 2.7 °C and with air flow velocities maintained below 19.0 cm s−1, which is consistent with a comfortable environment.

Field study on the through-draught characteristics and its influencing factors in subway carriages

The through-draught effect inside a subway significantly impacts the flow field profile, thus causing a potential threat to pollutant dispersion and human health. This study conducted multiple field measurements to systematically analyze the through-draught characteristics during actual train operation. The results show that the total variation of airflow velocity has a high consistency with train operation parameters, which reaches its peak value at the end of the acceleration period (EAP). And the airflow direction reverses as the running speed falls to nearly 0.45 times the maximum of that. For the whole subway train, the air velocity grows continuously in the first four carriages and then drops from the fifth carriage, with a maximum speed of 2.37 ± 0.12 m/s. Moreover, the airflow velocity distribution in a carriage exhibits an approximate “W-shape”, and the profile of the maximum airflow velocity is equivalent to a “parabolic surface”, with a velocity difference of less than 0.45 m/s. Finally, the through-draught effect is comprehensively affected by train acceleration and station spacing which further impact the air inertia forces and internal pressure difference, respectively; the wind speed peak positively correlates with train acceleration and subjects to an inverse exponential function with the station spacing. The research outcome can provide a valid basis for airflow control and air quality improvement in subway carriages operating in the underground tunnel.

NUMERICAL CALCULATIONS OF WATER DROP USING A FIREFIGHTING AIRCRAFT

The study involved a numerical analysis of the water dropping process by fixed-wing aircraft. This method, also known as air attack, is used for aerial firefighting, primarily in green areas such as forests and meadows. The conducted calculations allowed for the analysis of the process over time. The calculations were performed based on a SolidWorks model of the M18B Dromader aircraft. After defining the computational domain and setting the boundary conditions, the simulations were carried out using the ANSYS Fluent software. The resulting water dropping area was used to analyze the intensity of water distribution. The volumetric distribution and airflow velocity distribution were analyzed for specified time steps. The boundary layer where air no longer mixes with water during the final phase of water dropping was also determined. The obtained results provide an important contribution to further analyses aimed at optimizing the water dropping process by fixed-wing aircraft.

Numerical simulation of using DBD plasma air blower for a proton exchange membrane fuel cell

In this study, a novel air blower by applying the DBD plasma actuator for a PEM fuel cell is proposed for reducing power consumption and air flow saving. For this purpose, the DBD plasma actuators are installed on the bottom surface of the cathode channel of a PEMFC. The impact of the application of DBD plasma and the number of DBDs on the air mass flow rate and performance of PEMFC were numerically investigated. Results show that in comparison to the conventional air blower model, using the DBD plasma air blower at the cathode channel of a PEMFC results in a reduction of velocity magnitude and uniform velocity distribution of airflow within the cathode channel. Also, results indicate that the DBD plasma air blower model with less air flow consumption provides almost the same current density and performance as the conventional model. Results illustrate that the DBD plasma air blower with 3 DBDs can be a suitable candidate to obtain the best design for the DBD plasma air blower. The robust advantages of using the DBD plasma air blower become more underscored when the findings present the 90.31% reduction in the average power consumption.

Innovative concept of splitting water flow rate of cross flow heat exchangers as a solution for reduction of non-uniformity effect – Thermal modelling and feasibility analysis

The water flow rate of water-air cross-flow Heat Exchangers (HXs) is split into various smaller flow rates in this research work, which circulates into several smaller HXs that are put together. In fact, as the non-uniformities in the airflow velocity distributions increase, the thermal performance declines. These non-uniformities, especially in automotive applications, are represented by velocity magnitudes on a part of the HX front area and zero velocities on the remaining part. The innovative idea and the originality of the present study consists on dividing the water flow rates into various passageways as they reach a water-flow HX, where each passage is associated with several smaller HXs. In relation to the air flow, the smaller HXs are sequentially combined. The advantage of such splitting leads to keeping parts of the area of the initial HX from being subjected to low convection heat transfer with zero or negligible velocities and subsequently allows for an increase in the thermal performance globally. Moreover, the dividing idea enables faster but hotter airflow to be applied to each of the individual HXs. Computations for double-split HX utilizing a developed computational code are used to demonstrate the viability of this design. A traditional cross-flow water-air HX's thermal performance can be improved by up to 26.2 % using the novel idea, it has been demonstrated.

Effect of non-uniform incoming flow on the mixing enhancement in a scramjet cavity combustor

Mixing in the combustion chamber is influenced by the velocity distribution of the inlet airflow. Numerical simulations are carried out by using the 3D coupled implicit Reynolds-averaged Navier-Stokes (RANS) equations and the SST k-ω turbulence model. This article compares the flow field characteristics of non-uniform flows with uniform flows. The results show that the penetration depth increases by 22% in the case of a decreasing velocity distribution along the longitudinal direction compared to the increasing velocity condition. The difference in total pressure loss compared to uniform flow is greater than 4%. The mixing coefficient in the cavity is only 81% of uniform flow. The two-hole jet flow approach is able to rapidly reach 90%. The study shows that the non-uniform inlet has a considerable impact on fuel mixing. The high velocity region near the jet hole contributes to the mixing performance of the engine combustion chamber.