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Recurrent epidemics of respiratory infections have drawn attention from the academic community and the general public in recent years. Aircraft plays a pivotal role in facilitating the cross-regional transmission of pathogens. In this study, we initially utilized an Airbus A320 model for computational fluid dynamics (CFD) simulations, subsequently validating the model's efficacy in characterizing cabin airflow patterns through comparison with empirical data. Building upon this validated framework, we investigate the transport dynamics of droplets of varying sizes under three air supply velocities. The Euler-Lagrangian method is employed to meticulously track key parameters associated with droplet transport, enabling a comprehensive analysis of particle behavior within the cabin environment. This study integrates acquired data into a novel PCR (Personal Contamination Rate) equation to assess individual contamination rates. Numerical simulations demonstrate that increasing air supply velocity leads to enhanced stability in the movement of larger particles compared to smaller ones. Results show that the number of potential infections in the cabin decreases by 51.8% at the highest air supply velocity compared to the base air supply velocity, and the total exposure risk rate reduced by 26.4%. Thus, optimizing air supply velocity within a specific range effectively reduces the potential infection area. In contrast to previous research, this study provides a more comprehensive analysis of droplet movement dynamics across various particle sizes. We introduce an improved method for calculating the breathing zone, thereby enhancing droplet counting accuracy. These findings have significant implications for improving non-pharmacological public health interventions and optimizing cabin ventilation system design. [ABSTRACT FROM AUTHOR]

Choledochal cysts (CCs) are an important risk factor for cholangiocarcinoma, though their etiology remains debated. Given the vital role of bile fluid in digestive processes within the biliary system, examining such mechanisms from the perspective of bile fluid dynamics may offer additional insights for clinical use. This study utilized magnetic resonance imaging (MRI)-based patient-specific scans for detailed reconstruction and further employed the computational fluid dynamic method to assess the physiological functions of each system, including refilling and emptying processes. The impact of bile rheological property was also examined. Key biomechanical parameters—pressure and wall shear stress (WSS)—were displayed on a two-dimensional plane via surface mapping for enhanced visualization and comparative analysis. Outcomes demonstrated a significant reduction in bile flow velocity in CCs patients due to common bile duct's anatomical features and bile's shear-thinning, non-Newtonian nature, with a notable increase in pressure drop observed. In healthy biliary systems, WSS variations were minimal; however, in CCs patients, extreme WSS differences were found, with the highest WSS in the segmental bile duct and the lowest in the dilatation area, presenting a magnitude difference of approximately 1000. CCs one showed WSS levels 100–250 times higher than healthy ones in the common bile duct. Bile rheological properties substantially affect pressure and WSS patterns, particularly WSS, where pathological bile caused a tenfold increase in WSS compared to healthy bile. The findings aimed to enhance the understanding of biliary fluid mechanics in CCs and offer insights into selected fluidic variables for future microfluidic chip experiments. [ABSTRACT FROM AUTHOR]

This paper presents a computational fluid dynamics (CFD) study of air-particle flows in the upper tracheobronchial tree. Two respiratory tract models, including a parametrically controlled approximate airway model developed by Kitaoka (KG model) and a CT-based patient specific airway (realistic model) were used. Assuming laminar, quasi-steady, three-dimensional air flow and spherical non-interacting ultrafine particles in sequentially bifurcating rigid bronchial airways, airflow patterns and particle transport/deposition in these two airway models were evaluated and compared. Overall deposition efficiency data was compared with the widely adopted ICRP data published by The International Commission on Radiological Protection. Good deposition efficiency agreements were observed between the present respiratory tract models and the ICRP data, which validated the numerical prediction accuracy of the present computational fluid-particle dynamics (CFPD) model. For the two respiratory models, the comparison showed both difference and similarity between the approximate KG model and the realistic model. Specifically, the realistic model showed more complicated airflow patterns due to the increased surface irregularity. The deposition efficiency data revealed a deposition preference in the first-generation airways compared to the rest regions. For ultrafine particles smaller than 10 nm, Brownian diffusion remains the dominant particle deposition mechanism. However, for ultrafine particles with size ranging from 10 nm to 100 nm, the deposition efficiency decreased dramatically with the 100 nm particles approaching to zero deposition in the present bronchial tree scope. The generation-by-generation deposition data presented in this paper is indispensable to the formulation of new lung inhalation exposure models. [ABSTRACT FROM AUTHOR]

Vortex shedding in the wake flow generated by moving bodies exerts considerable influence on pollutant dispersion. This study investigated the effects of different body shapes using scaled models 1/5th of realistic size, including thin and wide shapes, standing and walking poses. The airflow from moving bodies was simulated using computational fluid dynamics (CFD) with dynamic meshing to account for the manikin movement. Experimental data from a smoke visualisation technique provided validation data for computational simulations which included flow separation angle over the head computed through image processing. Vortex structures were visualised using an Omega vortex identification method and compared with experimental visualisations. The main objective of this study is to verify the CFD simulations with smoke visualisation in terms of predicting motion-induced vortex structures, thus helping identify contaminant transport around different shaped bodies during walking and when coming to a stop. The results showed matching locations and patterns of vortex structures between the smoke visualisation and CFD simulations. After the manikin came to a stop, the flow induced by the larger body was characterised by a longer residence time for airborne contaminants in the breathing region while a reduced flow residence time for the thinner bodied manikin. [ABSTRACT FROM AUTHOR]

Evaluation of nasal spray drug absorption has been challenging because deposited particles are consistently transported away by mucociliary clearance during diffusing through the mucus layer. This study developed a novel approach combining Computational Fluid Dynamics (CFD) techniques with a 1-D mucus diffusion model to better predict nasal spray drug absorption. This integrated CFD-diffusion approach comprised a preliminary simulation of nasal airflow, spray particle injection, followed by analysis of mucociliary clearance and drug solute diffusion through the mucus layer. The spray particle deposition distribution was validated experimentally and numerically, and the mucus velocity field was validated by comparing with previous studies. Total and regional drug absorption for solute radius in the range of 1 − 110nm were investigated. The total drug absorption contributed by the spray particle deposition was calculated. The absorption contribution from particles that deposited on the anterior region was found to increase significantly as the solute radius became larger (diffusion became slower). This was because the particles were consistently moved out of the anterior region, and the delayed absorption ensured more solute to be absorbed by the posterior regions covered with respiratory epithelium. Future improvements in the spray drug absorption model were discussed. The results of this study are aimed at working towards a CFD-based integrated model for evaluating nasal spray bioequivalence. [ABSTRACT FROM AUTHOR]

Based on an experimental sandbox, this article analyzes the heat transfer processes of a ground heat exchanger (GHE) system when adopting two computational fluid dynamics (CFD) modeling approaches. First, the numerical model adopted the measurement recorded inlet temperature of the heat transfer fluid (HTF) as the GHE system input condition, and the predicted HTF outlet temperature was validated against the experimental data. Second, the GHE heating load initiated the numerical simulation, and the HTF outlet temperature was overpredicted by up to 2 °C (3.6 °F), especially for the late stage where discrepancy peaked. The heat transfer analysis showed the heat transfer efficiency of the GHE system adopting the second modeling approach was around 98.5%, due to multiple reasons, including experimental and numerical uncertainties during the tests. It demonstrates the significance of adopting proper thermal boundary conditions in numerical simulations, which can contribute toward the GHE system performance assessment and optimization in real practice. [ABSTRACT FROM AUTHOR]

Bubbly flow in U-bend is widely encountered in two-phase flow systems because of its compactness and high heat transfer coefficient. The modeling of phase distributions, velocity fields, and interfacial area concentration in the U-bend is crucial for the analysis of mass, momentum, and energy transportation processes in the equipment. However, this subject has not received enough attention yet. In this paper, the combination of population balance model and two-fluid model was used in the simulation of air–water bubbly flow in a U-bend with 24 mm inner diameter and 96 mm curvature. The homogeneous multiple size group model was used to solve the population balance equation and reconstruct the bubble size distribution function. The phase distribution at 0°, 90°, and 180° was predicted and the results showed that the superficial velocities of gas and liquid phase were the control parameters. Under higher gas superficial velocity, the buoyant force is dominant and makes the bubbles concentrate on the outer side of the tube wall; while under lower gas superficial velocity, the centrifugal force is dominant and makes the bubbles concentrate on the inner side of the tube wall. These results met well with the experimental results of Usui. [ABSTRACT FROM AUTHOR]

Abstract The theoretical models of Surface-to-Surface (S2S) thermal radiation, including the Monte Carlo model, Discrete Transfer model, Modest model and Heat-Flux-Split approach, are evaluated in terms of the predictive accuracy and CFD computational cost when simulating indoor thermal flows. It is demonstrated that the inclusion of thermal radiation in the CFD model is vital as the air temperature in the lower levels can be underpredicted while the heater surface temperature can be significantly overpredicted if the radiative effects are ignored. In addition, the predicted temperature distribution on the heat-receiving solid surfaces is highly sensitive to the selected radiation model. The comparisons demonstrate that the Monte Carlo model and Discrete Transfer model have comparable predictive capabilities while the latter requires less CPU time and is more computationally efficient. The appropriate number of the representative photons and rays are also recommended for the Monte Carlo model and Discrete Transfer model, respectively. Highlights • Predictive models/approaches of S2S thermal radiation are evaluated. • Importance of indoor radiative heat transfer is demonstrated. • Monte Carlo and Discrete Transfer models are comparably accurate. • Discrete Transfer models are computationally more efficient. [ABSTRACT FROM AUTHOR]

High-temperature gas-cooled reactor is a kind of advanced nuclear reactor in which the core is packed with spherical fuel elements. In high-temperature gas-cooled reactors, the operating temperature is higher than that in ordinary light water reactors. In an attempt to analyze the flow pattern and heat transfer situation to provide reference for the safe operation of the pebble bed reactors, a segment of simplified high-temperature gas-cooled reactor core is simulated with computational fluid dynamics method. Four kinds of arrangement, including simple cubic, body-centered cubic, face-centered cubic, and a combination structure of body-centered cubic and face-centered cubic, are studied, respectively. Based on the simulation results, higher heat transfer capability and lower pebble temperature are obtained in the case with the most compact arrangement. The drag coefficient (Cd) for four arrangements with different inlet Reynolds number (Re) is obtained and relationship between Re and Cd is analyzed. In addition, a simulation with a broken fuel element in the body-centered cubic fluid domain has been performed. The results show that the presence of broken fuel may result in uneven flow, which will change the heat transfer condition. So it is better to avoid broken fuel element in a high-temperature gas-cooled reactor. [ABSTRACT FROM AUTHOR]

Computational fluid dynamics (CFD) is an important and effective tool to study the airflow field and contaminant distribution in aircraft cabins. The accuracy of numerical simulation using the CFD approach could be significantly affected by configurations of the inlet boundary conditions, turbulence model, etc. The core of this study was to assess whether conclusions achieved in simulation of airflow on usual surfaces in buildings like in commercial offices could be applicable to aircraft cabins. Comparative studies involving turbulence models or air supply opening models in aircraft cabin environment are still absent in the literature. Therefore, in this study, two turbulence models (the renormalization group (RNG) k-ɛ model and Reynolds-stress model) and three types of air supply opening models (simple open model, basic model and momentum model) were applied to simulate the airflow and contaminant concentration fields in a mockup seven-row cabin section. Our simulation results were compared with the experimental data. Six indexes based on different criteria were used to quantitatively evaluate the agreement between measurements and modelled results given by turbulence models and air supply opening models. The results show that the RNG k-ɛ and RSM turbulence models have similar accuracy in airflow and contaminant fields in the mockup cabin, and the momentum model has the best accuracy among the three air supply opening models for the aircraft cabin environment. [ABSTRACT FROM AUTHOR]

This study employed a multi-component Eulerian-Lagrangian approach to model the evaporation and dispersion of cough droplets in quiescent air. The approach is featured with a continuity equation being explicitly solved for water vapor, which allows comprehensively considering the effects of inhomogeneous humidity field on droplets evaporation and movement. The computational fluid dynamics (CFD) computations based on the approach achieved a satisfactory agreement with the theoretical models reported in the literature. The results demonstrated that the evaporation-generated vapor and super-saturated wet air exhaled from the respiratory tracks forms a “vapor plume” in front of the respiratory track opening, which, despite the short life time, significantly impedes the evaporation of the droplets captured in it. The study also revealed that due to the droplet size reduction induced by evaporation, both the number density of airborne droplets and mass concentration of inhalable pathogens remarkably increased, which can result in a higher risk of infection. Parametric studies were finally conducted to evaluate the factors affecting droplet evaporation. Summary The study demonstrated the importance of considering inhomogeneous humidity field when modelling the evaporation and dispersion of cough droplets. The multi-component Eulerian-Lagrangian model presented in this study provides a comprehensive approach to address different influential factors in a wide parametric range, which will enhance the assessment of the health risks associated with droplet exposure. [ABSTRACT FROM AUTHOR]

Rats have been widely used as surrogates for evaluating the health effects of inhaled airborne particulate matter. To provide a thorough understanding of particle transport and deposition mechanisms in the rat nasal airway, this article presents a computational fluid dynamics (CFD) study of particle exposure in a realistic rat nasal passage under a resting flow condition. Particles covering a diameter range from 1 nm to 4 µm were passively released in front of the rat’s breathing zone, and the Lagrangian particle tracking approach was used to calculate individual particle trajectories. Detailed particle deposition analysis shows the deposition of inertial particles >2 µm is high in the rat nasal vestibule and more than 70% of all inhaled inertial particles were trapped in this region. While for diffusive nanoparticles, the vestibule filtration effect is reduced, only less than 60% of inhaled nanoparticles were blocked by the anterior nasal structures. The particle exposure in the olfactory region only shows notable deposition for diffusive nanoparticles, which peaks at 9.4% for 5 nm particles. Despite the olfactory deposition remains at a low level, the ratio between the olfactory and the main passage is kept around 30-40% for 10-800 nm particles, which indicates a particle-size-independent distribution pattern in the main nasal passage and olfactory. This study provides a deep understanding of particles deposition features in a rat nasal passage, and the research findings can aid toxicologist in inter-species exposure-response extrapolation study. [ABSTRACT FROM AUTHOR]

Simplified computational thermal manikins are beneficial to the computational efficiency of computational fluid dynamics simulations. However, the criterion of how to simplify a computational thermal manikin is still absent. In this study, three simplified computational thermal manikins (CTMs 2, 3 and 4) were rebuilt based on a detailed 3D scanned manikin (CTM 1) using different simplification approaches. Computational fluid dynamics computations of the human thermal plume in a quiescent indoor environment were conducted. The predicted airflow field using CTM 1 agreed well with the experimental observations from the literature. Although the simplified computational thermal manikins did not significantly affect the airflow predictions in the bulk regions, they strongly influenced the predicted airflow patterns near the computational thermal manikins. The predictive error of the computational thermal manikin was strongly related to the simplification approach. The computational thermal manikins generated from the surface-smoothing approach (CTM 2) was very close to CTM 1, while the required mesh elements for a stable numerical solution dropped by over 75%. Comparatively, the predictive errors of CTMs 3 and 4 were considerable in the near-body regions. This study has illustrated the importance of keeping the key body features when simplifying a computational thermal manikin. The surface-smoothing-based simplification method was shown to be a promising approach. [ABSTRACT FROM AUTHOR]

The impact of human-induced wake flow and particle re-dispersion from floors in an indoor environment was investigated by performing computational fluid dynamics simulations with dynamic mesh of a moving manikin model in a confined room. The manikin motion was achieved by a dynamic layering mesh method to update new grids with each time step. Particle transport from the floors and its re-dispersion was tracked by a Lagrangian approach. A series of numerical simulations of three walking speeds were performed to compare the flow disturbance induced by the walking motion. The significant airflow patterns included: an upward-directed flow in front of the body combined with a high velocity downward-directed flow at the rear of the body; a stagnant region behind the gap between the legs and counter-rotating vortices in the wake region. The airflow momentum induced by the moving body disturbed PM2.5 particles that were initially at rest on the floor to lift and become re-suspended due to its interaction with the trailing wake. The residual flow disturbances after the manikin stopped moving continued to induce the particle to spread and deposit over time. The spatial and temporal characteristics of the particle dispersion and concentration showed that higher walking speed was conducive to reducing human's exposure to contaminants in breathing region. [ABSTRACT FROM AUTHOR]

Computational fluid dynamics computations were conducted to investigate the particle inhalation characteristics of a thermal manikin standing in a horizontal airflow with different orientations, leg postures, wind speeds and particle sizes. The computations revealed that only when the manikin’s thermal plume moves into the breathing zone (namely, the manikin is facing the lee side) could the body heat affect the characteristics of particle inhalation. Further computations demonstrated that, when facing the lee side, the manikin’s particle inhalation is highly sensitive to its leg posture. When the legs are separated, air can flow through the gap, causing more particle entrainment into the breathing zone from the lower level. Although the thermal effect of body heat is gradually suppressed with increasing wind speed or particle size, different leg postures have different environmental sensitivities. [ABSTRACT FROM AUTHOR]

Computational fluid dynamics simulations were conducted in this study to investigate the effects of the buoyancy-driven thermal plume on the airflow pattern and transport characteristics of airborne particles in airliner cabins. A cabin section containing three seats and three passengers was built and numerical simulations were conducted using thermal and isothermal conditions, respectively. Airborne particles were assumed to be released by the passengers through coughing. The predicted airflow field was validated using experimental data available in the literature. Comparison of the computational results revealed that the thermal plume significantly changed both the airflow filed and the trajectories of particle transport. In addition, the spatial distribution characteristics of the particles and their residence time in the passengers’ breathing zones were highly sensitive to the location of released particles. Comparatively, the particles released by the passenger seated close to the window may have the highest health risk to other two passengers. [ABSTRACT FROM PUBLISHER]

This study presented an iterative approach to simplify computer simulated persons (CSPs) based on the mesh decimating algorithm [1]. The approach could largely simplify 3D-scanned manikins while maintaining their key geometrical features. The level of simplification could be quantified through controlling the iteration number of simplification. CFD computations of human thermal plume in a quiescent room were performed using CSPs with different levels of simplification. The numerical results were compared against the experimental data available in the literature. The results demonstrated that within the scope of this study, the CSP simplification only affected the predicted airflow field in the thermally-affected regions where the normalized air velocity was larger than 0.5. The predictive error increased with the dimensionless simplification index ( SI ). When SI was less than 3.5 × 10 −4 , the error induced by CSP simplification could be safely ignored. Contaminant transport in a densely occupied airliner cabin section was also simulated using the simplified CSPs. The results revealed that although the CSP simplification only affected airflow field prediction of the thermal plume regions, it could enlarge the predictive error of contaminant transport in the whole computational domain. In addition, this study found that the CSPs yielded from the algorithm were more numerically stable in terms of CFD computations. [ABSTRACT FROM AUTHOR]

Micron-sized particle deposition in anatomically realistic models of a rat and human nasal cavity was numerically investigated. A steady laminar inhalation flow rate was applied and particles were released from the outside air. Particles showing equivalent total particle deposition fractions were classified into low, medium and high inertial particle. Typical particle sizes are 2.5, 9 and 20 μm for the human model and 1, 2 and 3 μm for the rat model, respectively. Using a surface-mapping technique the 3D nasal cavity surface was “unwrapped” into a 2D domain and the particle deposition locations were plotted for complete visual coverage of the domain surface. The total surface area comparison showed that the surface area of the human nasal model was about ten times the size of the rat model. In contrast, the regional surface area percentage analysis revealed the olfactory region of the rat model was significantly larger than all other regions making up ∼55.6% of the total surface area, while that of the human nasal model only occupying 10.5%. Flow pattern comparisons showed rapid airflow acceleration was found at the nasopharynx region and the nostril region for the human and rat model, respectively. For the human model, the main passage is the major deposition region for micro-particles. While for the rat model, it is the vestibule. Through comparing the regional deposition flux between human and rat models, this study can contribute towards better extrapolation approach of inhalation exposure data between inter-subject species. [ABSTRACT FROM PUBLISHER]

Although desktop computers have been considered in many computational fluid dynamics (CFD) indoor simulations, they were usually simplified as hot boxes. A real desktop computer, however, is not only a heat source but also a momentum source due to the jet airflow generated by the computer case fan. The airflow induced by a desktop case fan could have the same order of magnitude as the ventilation rate of the whole room, and thus is expected to have significant influence upon the indoor airflow field and distribution of contaminants. Obviously, the simplification of desktop computer into a hot box does not sufficiently stand for the actual situation. In this study, a CFD model of a typical office room was built and simulations were conducted to investigate the airflow field and volatile organic compounds (VOC) distribution under two scenarios: (1) computer as a ‘hot box’ without a fan and (2) a more realistic computer model with an operating case fan. The comparison of CFD results yielded from these two scenarios demonstrated that the role of computer fan is very important in terms of airflow field and contaminant distribution and should be included in CFD office simulations for the purpose of improved reliability. [ABSTRACT FROM AUTHOR]

SUMMARY The study of cardiovascular models was presented in this paper based on medical image reconstruction and computational fluid dynamics. Our aim is to provide a reality platform for the purpose of flow analysis and virtual intervention outcome predication for vascular diseases. By connecting two porous mediums with transient permeability at the downstream of the carotid bifurcation branches, a downstream peripheral impedance model was developed, and the effect of the downstream vascular bed impedance can be taken into consideration. After verifying its accuracy with a healthy carotid bifurcation, this model was implemented in a diseased carotid bifurcation analysis. On the basis of time-averaged wall shear stress, oscillatory shear index, and the relative residence time, fractions of abnormal luminal surface were highlighted, and the atherosclerosis was assessed from a hemodynamic point of view. The effect of the atherosclerosis on the transient flow division between the two branches because of the existence of plaque was also analysed. This work demonstrated that the proposed downstream peripheral vascular impedance model can be used for computational modelling when the outlets boundary conditions are not available, and successfully presented the potential of using medical imaging and numerical simulation to provide existing clinical prerequisites for diagnosis and therapeutic treatment. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Our previous study [1] demonstrated that for a thermal manikin in a horizontal airflow, its orientation relative to the free stream has a significant effect on the characteristics of particle transport and inhalation. Based on this conclusion, the previous research [1] was extended and the effect of leg posture (e.g. combined legs and divided legs) on particle inhalation in horizontal free stream was investigated using Computational Fluid Dynamics (CFD) in this study. The numerical results agreed well the experimental data and empirical correlations in the literature. It was revealed that for an occupant standing with its back towards the horizontal airflow, a little change in the leg posture can lead to an obvious variation in the source location of inhaled particles. It was also found that different leg postures have different environment sensitivity since when the manikin legs are divided, the central height of the critical area does not obviously change with increasing wind speed, however, this central height increases significantly with the wind speed when the legs are combined. [Copyright &y& Elsevier]

Abstract: The inhalation of micron particles by a manikin standing in a ventilated indoor environment was numerically investigated using Computational Fluid Dynamics (CFD). Computations were conducted with various combinations of the free stream velocity (0.05–0.25 m/s representing typical indoor wind speeds.), occupant orientation relative to the free stream (back-to-the-wind or facing-the-wind) and heat transfer (isothermal or thermal flow). It was found that the body heat has a significant impact on the airflow field in the vicinity of the manikin by causing an upwards airflow on the downstream side of the manikin. It was also found that the effect of body heat on particle inhalation depends on the manikin orientation relative to the free stream. When the manikin is facing-the-wind, body heat has a little effect on particle inhalation and can be neglected. However for a back-to-the-wind orientation, the situation is much more complicated as the source height of inhaled particles depends on the speed of free stream. When the wind speed is low (0.05 m/s), the critical area is located near the floor level. The central height of the critical area then increases with increasing free stream speed until it reaches the nose height when the wind speed rises up to 0.25 m/s. This indicates that the body heat is an important consideration when investigating contaminant inhalation by human occupants in low-speed (typically less than 0.2 m/s) indoor environment. [Copyright &y& Elsevier]

Computer-aided magnetic resonance (MR) fluid motion tracking and cardiac vorticity quantification of the right atrial flow is implemented in this study to suggest a new method for the diagnosis of an atrial septal defect (ASD). MR signals of blood moving in a cardiac chamber can be represented as an image and vary in intensity at every consecutive cardiac phase. A method was devised to perform flow analysis using MR imaging without modification of scan mode or protocol that allows velocity encoding. A single vortex or multiple vortices may appear in the cardiac chamber. However, velocity fields in any flow scenario are normally unable to reveal information for a concise analysis; therefore, in addition to velocity maps, vorticity flow maps on which the velocity field is superimposed are presented. Through a case study, the difference in vortex strengths pre- and post-atrial septal occlusion can be examined, and the results can be verified using computational fluid dynamics. Based on this framework, the degree of vortical flow was assessed for the right atrium of a subject with atrial septal defect. A relationship can be established between right atrial vorticity and the ASD. As such, there is clear utility of the developed system in its potential as a prognostic and investigative tool for the quantitative assessment of cardiac abnormalities parallel to examining magnetic resonance images. [ABSTRACT FROM AUTHOR]

The purpose of this work is to evaluate numerical modeling techniques for simulation of spray atomization from a nasal spray device to complement experimental measurements previously. In the past, spray breakup models have not been applied to nasal spray applications, but rather for high-pressure applications such as combustion, and industry and agricultural spraying. The parameters in breakup model were not optimized for this kind of low-pressure injection with small-scale atomizer. Thus, there is a need to tune the spray model constants of the linear instability sheet atomization (LISA) model and evaluate its performance for low-pressure applications such as those found in nasal spray devices. Some parameters that were evaluated include the dispersion angle and the liquid sheet constant that influences the droplet size distribution and dispersion. The simulation results were evaluated against experimental data that has been previously performed. It was found that the LISA model provided good comparisons when a dispersion angle of 3° and a liquid sheet constant of 1 were used. In addition, three scenarios were investigated: (i) influence of fluid-droplet coupling; (ii) increase in mass flow rate; and (iii) changing the orientation from downward spray to upward spray. Copyright 2012 American Association for Aerosol Research [ABSTRACT FROM PUBLISHER]

Abstract: Steam-jet vacuum pump is widely used in a range of applications. This paper evaluated the performance of four well-known turbulence models for predicting and understanding the internal flow of a steam-jet vacuum pump first. With the help of a commercial computational fluid dynamics (CFD) code ANSYS-Fluent 6.3, the simulation results obtained from the concerned turbulence models were compared with experimental values, the k-omega-SST model was chosen as a tool model for carrying out numerical simulations. Then, based on the simulation results obtained from specific operating conditions, a method for locating the shock-mixing layer was put forward. The shape of the shock-mixing layer shows that the secondary steam does not mix with the primary steam immediately after being induced into the mixing chamber of the pump; actually, they maintain their independence till the shocking position instead. After the shock happens, the shock-mixing layer disappear, the two fluid in the pump begin to mix with each other and discharge to the next stage with almost the same state. Based on the shape of the shock-mixing layer and the supersonic region of the secondary steam, a detailed analysis for the flow duct of the secondary steam was carried out. It is found that the throat of the secondary steam flow duct plays a crucial role in maintaining a stable operating state and the length of the throat reflects the back pressure endurance for the pump. [Copyright &y& Elsevier]

Abstract: CFD computations of particle flows in a human nasal cavity were conducted, using two types of inlet velocity profiles at the nostril openings respectively. One type is the widely used uniform inlet velocity profile while the other is a realistic inlet velocity profile extracted from the external environment that is influenced by facial features. The latter type of inlet velocity profiles were obtained through CFD computations of indoor gas-particle flows around a human head geometry containing detailed facial features in an enclosed space. Comparisons were made between the predicted results of airflow field, particle tracks and particle deposition efficiency in the nasal cavity. It was revealed that although the effects of facial features exist only in a small region (10–20 mm) in front of the face, they lead to complicated, and non-uniform velocity profiles at the nostril openings. This discrepancy leads to different predictions of airflow fields and local particle deposition efficiency in the nasal cavity, especially in the anterior regions such as the vestibule and nasal valve. The results may further lead to discrepant health-risk assessments associated with particle inhalation. Therefore, for CFD simulations of particle deposition in the nasal cavity, the inlet velocity profiles induced by facial features are important for more realistic results. [Copyright &y& Elsevier]

Aspiration efficiencies from nose and mouth inhalations are investigated at low and high inhalation rates by using the commercial Computational Fluid Dynamics (CFD) software CFX 11. A realistic human head with detailed facial features was constructed. Facial features were matched to represent the 50th percentile of a human male, aged between 20 and 65 years old, based on anthropometric data. The constant freestream velocity was 0.2 ms−1, normal to the face, and inhalation rates through the mouth and nose were 15 liters per minute (LPM) for light breathing and 40 LPM for heavy breathing. It was found that the flow field in the near breathing region exhibited vertical direction caused by the presence of the torso where the airstream diverges as it flows around and over the body. The critical area concept was used as a tool to determine the aspiration efficiency of particles. Comparisons between critical areas for the nose and mouth inhalations show similar geometric properties such as the area’s shape, and its vertical distance location on the x- z plane located at y = 80 cm upstream. The critical area sizes were found to be slightly larger for the mouth inhalation mainly due to the larger mouth area and also the aligned orientation of the mouth to the upstream flow, whereas the nose is perpendicular to the upstream flow. This study was undertaken to establish the flow field in the near breathing region that will help to characterize the flow and particle field for initial boundary conditions leading to a more holistic modeling approach of respiration through the internal nasal cavity and mouth. [ABSTRACT FROM AUTHOR]

The user comfort and energy consumption become two conflicting subjectives leading to pareto-optimal control fronts when designing HVAC systems. Although, indoor air temperature has been extensively used as a primary parameter of HVAC control for many years, it is unable to precisely or fully reflect the perceived thermal comfort. And the set-points of thermal comfort sensors for the conditioned space are generally installed far away from occupants, making them unable to detect real occupant sensations. Computational Fluid Dynamics (CFD) simulations can be used to assist with developing the thermal comfort control strategies. A comparative simulation study between the thermal comfort (Predicted Mean Vote, PMV-based) control and conventional temperature (Temperature-based) control is conducted in a typical glazed office room subjected to solar radiation for the entire occupied time of a day. To achieve the control target of ISO 7730 comfort zone, an iterative procedure was developed to estimate the flow rate of the supply air. The air temperature field and ventilation performance in the work plate and the plate crossing through the middle of the office room were shown in two control strategies by CFD. The thermal environment indices (vertical air temperature difference and draught) and energy saving are analyzed and compared under two control strategies. The results demonstrate that the PMV-based control could provide better thermal comfort in highly glazed office room and it still shows a savings of 1.6% per day of energy usage. • A PMV-based HVAC control strategy is proposed to evaluate the thermal comfort in an office room with solar radiation. • A comparative study between the PMV-based control and the conventional temperature-based control was performed. • The PMV-based control could provide better thermal comfort in highly glazed office room. • Using the PMV as a control objective for the HVAC system, it still shows a savings of 1.6% per day of energy usage. [ABSTRACT FROM AUTHOR]

Highlights: • The SST k-ω model performs best for convection-radiation hybrid thermal airflows. • Surface radiation affects airflow pattern via heating up surfaces. • Surface radiation affects VOC emission and dispersion. Abstract This study presents a computational fluid dynamics (CFD) study on the effects of surface radiation on the emission and dispersion of gaseous contaminants in indoor spaces. Mathematical models are firstly validated against experimental data reported in the literature. It demonstrates that the Shear Stress Transport (SST) k-ω model performs best among other turbulence models when modelling convection-radiation hybrid heat transfer. The study also reveals that surface radiation accounts for 37%–71% of the heat dissipation from the heat sources in a typical office room, which remarkably alters the indoor airflow pattern through cooling and heating the solid surfaces. Beyond that, the emission rate of volatile organic compounds (VOCs) from solid surfaces is also changed due to its dependence on the temperature. Consequently, the VOCs exhibit different dispersion characteristics and distribution patterns in the air, which ultimately results in different evaluations of the indoor air quality (IAQ). This study demonstrates that even in high-momentum indoor spaces such as those equipped with mixing ventilation systems, surface radiation still plays an important role in shaping the overall indoor environment quality (IEQ). [ABSTRACT FROM AUTHOR]

Abstract Intranasal drug delivery has attracted significant attention because of the opportunity to deliver systemic drugs directly to the blood stream. However, the mucociliary clearance poses a challenge in gaining high efficacy of intranasal drug delivery because cilia continuously carry the mucus blanket towards the laryngeal region. To better understand mucus flow behaviour on the human nasal cavity wall, we present computational model development, and evaluation of mucus motion on a realistic nasal cavity model reconstructed from CT-scans. The model development involved two approaches based on the actual nasal cavity geometry namely: (i) unwrapped-surface model in 2D domain and (ii) 3D-shell model. Conservation equations of fluid motion were applied to the domains, where a mucus production source term was used to initiate the mucus motion. The analysis included mucus flow patterns, virtual saccharin tests and quantitative velocity magnitude analysis, which demonstrated that the 3D-shell model results provided better agreement with experimental data. The unwrapped-surface model also suffered from mesh-deformations during the unwrapping stage and this led to higher mucus velocity compared to experimental data. Therefore, the 3D-shell model was recommended for future mucus flow simulations. As a first step towards mucus motion modelling this study provides important information that accurately simulates a mucus velocity field on a human nasal cavity wall, for assessment of toxicology and efficacy of intranasal drug delivery. [ABSTRACT FROM AUTHOR]

In conventional CFD-DEM based on the cell-averaged-volume-fraction (CAVF), mesh size for gas phase is required to be larger than particle size. It is good for fine particles, whereas too coarse for large particles. A conservative virtual volume fraction method is proposed here for sub-particle LES-DEM coupled simulation of large particles. Although still based on CAVF, mesh size is smaller than particle size, and the LES-DEM coupled solution on finer grids incorporating the Smagorinsky sub-grid-scale stress tensor is proposed. The feedback force is redistributed onto the finer grids to perform the four-way coupling on fine scales. It is conservative for the inter-phase interactions between the super-particle (for drag force) and sub-particle (for feedback force) scales through the same distribution function. The 2D case and the 3D cases with or without LES are performed to demonstrate the capability of this model, and validated by an experiment of spouted bed. The important features on gas-phase are illustrated to demonstrate the application for capturing the gas-phase behavior on sub-particle scales. [ABSTRACT FROM AUTHOR]

Human-induced wake flow characteristics and its interaction with thermal conditions was investigated by performing CFD simulations with dynamic-meshing of a moving manikin model. The manikin motion with and without swinging limbs was achieved by the re-meshing method to update the grid with each time step. The results focused on determining what discrepancies are produced in the flow field by a simplified geometry in the form of a cylinder, swinging limbs and thermal conditions; and whether such assumptions can be made for larger multi-body analysis. Using a cylinder showed differences in the velocity field behind the head and leg gap. The flow field between the rigid motion and swinging limb motion, showed significant discrepancies which corresponded to the gait phase. There were increased airflow disturbances at the hands and ankles (furthest body parts from the pivot point). The influence of thermal plume on the wake flow was minor during walking motion because of the walking speed of 1.2 m/s which dominated the buoyant thermal plume velocity. However, after the manikin stopped moving the thermal plume velocity became comparable to the residual wake. [ABSTRACT FROM AUTHOR]

Abstract: Flow over an open side window in a car exhibits similar characteristics as the flow over an open cavity. Computational Fluid Dynamics (CFD) simulation over a cavity was done as a benchmark. The unsteady flow simulation was carried out using Scale Adaptive Simulation (SAS) turbulence model. The benchmark results, frequency and sound pressure levels of feedback and resonance modes, all well matched with the experimental data. Then, with the right rear window, for example, the mechanism of the side window buffeting was investigated. The simulation results show that side window buffeting noise is generated by large scale vortices and in low frequency. Furthermore, buffeting noise characteristics under several patterns of side windows opening were also numerically investigated. As a result, rear window buffeting noise is more severe than that of front window when one window open, and combination pattern of side windows open can reduce buffeting noise. To decrease the interior noise and improve car ride comfort, four suppression measures through adding a side window weather deflector at the A-pillars, constructing a cavity at the B-pillars, combination of the front and rear windows and installing a row of square cylinder deflector at the B-pillars were also studied, respectively. In conclusion, certain noise reduction can be achieved through four passive control methods. [Copyright &y& Elsevier]

Great potential for using low-temperature waste heat for energy savings has been revealed in recent years. In this study, a novel PCM-TES unit integrated into a fresh air system was proposed to effectively utilize low-temperature waste heat to address shortcomings of preheating outdoor air for space heating. An experimental setup was built to investigate the heat storage and release performance of proposed unit. Well-validated CFD simulations further parametrically studied PCM thermal characteristics to HTF's velocity and temperature changes. Energy and thermo-economic analyses were employed to evaluate unit potentials across three Chinese cities with different climate zones. The results showed that charging process was completed in 142–253 min at water temperatures of 55–60 °C; discharging process efficiency increased by 36.10% as the air velocity increased from 2 to 4 m/s. EPI revealed that, theoretically, the system could handle up to 28.2% of the heating demand. Energy and economic analysis indicated the system's significant potential in colder climates, with Harbin achieving average energy savings of 7.93% and 13.48% over Qingdao and Chongqing, respectively, and cost savings up to 67.65% and 229.61% compared to those cities. This study is expected to shed light on the utilization of low-temperature waste sources for indoor space heating. [Display omitted] • Novel PCM-TES system utilizes low-temp waste heat for preheating outdoor cold air. • Thermal performance of unit assessed via experimental and numerical studies. • Energy and economic analyses evaluate unit's potential in varied climate zones in China. • EPI shows unit can cover up to 28.2% of heating demand during heating season. • Unit achieves higher cost substitution rate of up to 40.5% in colder climates. [ABSTRACT FROM AUTHOR]

Thermal performance of the ground source heat pump (GSHP) system can be significantly affected by the complex geological substructures (such as ground stratification and groundwater advection). This study installed a seepage box inside the two-layered laboratory device to investigate the heat transfer processes of the unsaturated, saturated and infiltrated ground. Various operational and geological conditions were designed to study the temperature distributions at various locations and time experimentally and numerically. The groundwater effect on ground heat exchanger (GHE) thermal performance depends on the thermal properties, flow advection and the relationship between temperatures of the groundwater and ground. If the ground was partially saturated during the heat injection period, the cooling seepage will efficiently remove the heat of GHEs in upper-stream rather than those located in the bottom-stream. Meanwhile, the heat transfer can be enhanced if two legs of the U-tube vertical to the direction of groundwater seepage. The groundwater flow can redistribute the heat within the ground and showed a better recovery performance which advance an even temperature distribution by 3 h. The temperature and carried heat load of the cooler groundwater will increase during the heat injection experiment, and further contributed to various temperature distributions of ground at different locations and time. • A laboratory box with two-layered subsurface and groundwater was introduced. • Experiments with various operational and geological conditions were conducted. • Detailed thermal distributions of partially saturated ground were analysed. • Cooling seepage can only efficiently remove the heat accumulated in upper stream. • Heat redistribution brought by groundwater flow gave a better recovery performance. [ABSTRACT FROM AUTHOR]

Thermal performance predictions of ground heat exchangers (GHEs) can be largely affected by the ground stratification and the heat distributions. Based on a validated laboratory device, predictions from numerical models with variable (Q v) and constant (Q c) heat transfer rates along the depth of GHEs were compared against the experimental data. The model with Q v gave a more accurate prediction on the ground temperature, while the Q c model weakened the ground stratification effect and overpredicted the clay temperature by up to 76.6%, especially at the late stage. These models predicted different ground temperature distributions at various locations and time. Specifically, for a two-layered structure in this study, the sand temperature predicted by the model with Q v was higher than the clay one, while the Q c model witnessed an opposite trend and more severe thermal interference in both layers at the end of the 24 h operating period. Furthermore, a comparison of the models with layered and equivalent material reveals that the effect of axial heat load distribution could be more significant on the heat transfer of a stratified subsurface. Therefore, it is recommended to apply the variable axial thermal exchange distributions for heat transfer predictions of GHEs in a layered ground. • Effect of axial heat load distribution on performance prediction was investigated. • The assumption of uniform heat exchange may lead to unacceptable predictions. • Thermal distributions at different time and locations were compared. • Predictions for a layered subsurface should apply variable axial heat load profile. [ABSTRACT FROM AUTHOR]

Abstract In this study, the cause of the boundary layer separation, the determination of the separated region and the effect of the boundary layer separation on ejector performance were comprehensively investigated. The boundary layer separation inside the ejector was studied by using CFD method. A steam ejector refrigeration experimental system was set up to verify the numerical model. The degree of boundary layer separation was determined by back pressure and the ejector geometry parameters. The cause of ejector failure was analyzed. The influence of the boundary layer separation on ejector performance under different throat diameters and the nozzle exit positions (NXP) were investigated in detail. The results indicated that in certain size range of the throat diameter or the NXP, the ejector worked in critical mode and has better pumping performance when the operating conditions were constant. In the case of a small or large throat diameter or a large NXP, the boundary layer separation became more severe, the formation of the shock wave and the choke would be destroyed and the mixed fluid would not overcome the back pressure to discharge from the ejector. The efficiency of the ejector descended to zero, the ejector failed. Highlights • A steam ejector refrigeration system was set up to verify the CFD model. • The GCI method was presented for analyzing the grid density. • Formation and delimitation of the boundary layer separation was investigated. • The boundary layer separation influence on the ejector performance was studied. • Effects of throat diameter and the NXP on the boundary layer separation were analyzed. [ABSTRACT FROM AUTHOR]

Abstract The patterns of primary flow jet core in steam ejector were investigated using computational fluid dynamics (CFD) method. Simulations based on ideal gas model at different operating conditions were performed. The results demonstrate the pattern of primary pseudo-shock flow was affected by the operating conditions obviously when value of operating condition was bigger than that of the critical condition. Compared with the results generated from ideal gas modelling, the primary pseudo-shock flow predicted by wet steam model has a similar pattern and almost the same effective area. But the wet steam model based simulation gives a further downstream choking position and a higher secondary fluid flow velocity at choking position. The above two factors lead to improved entrainment ratio (E m) and increased critical back pressure of steam ejector compared to the results generated from ideal gas modelling. More importantly, the wet steam model predictions show better agreement with the experimental data. Highlights • Study the pumping mechanism of ejector by primary pseudo-shock flow pattern. • The primary pseudo-shock flow pattern affected by the operating conditions. • Secondary fluid flow divided into three modes based on flow pattern analysis. • Operating condition less than critical parameter sustains a stable entrainment process. • Wet steam model captures primary pseudo-shock flow pattern more accurately. [ABSTRACT FROM AUTHOR]

In anaerobic digestion biogas plant industry, high-efficiency agitation system in the Continuously Stirred Tank Reactor (CSTR) is vital for encouraging mixing between substrates and bioliquids with low energy consumption. This study numerically investigated the downward pumping agitation system in an industrial CSTR test site to explore the dynamic characteristics of flow patterns with varied pitched blade turbine (PBT) design. A novel approach was developed to visually distinguish the agitation zone in the CSTR tank, which could be utilised to quantitatively assess the agitation performance and to assist the design of impeller spacing. The numerical approach would vastly improve the cost-efficiency to investigate the close connections among impeller spacing, pitched angle, and agitation intensity The pitched angle was found having more prominent effects on the shape and size of formed circulation loops in the tank. The 45-degree would be the critical pitched angle for PBT since the agitation zone would be rapidly shrunk once the configuration goes beyond this value. • Industrial CSTR is investigated regarding dynamic characteristics of flow patterns. • A novel approach to visually distinguish the agitation zone is developed. • Downward PBT prominently cause primary and secondary circulation loops in the CSTR. • Critical pitched angle for PBT is found at 45-degree. [ABSTRACT FROM AUTHOR]

Despite human exposure to inhaled nanoparticles has been intensively studied, the effect of nasal cavity morphology on the distribution patterns of inhaled particles remains less investigated. This paper compared the total and regional deposition patterns of naturally inhaled nanoparticles among subjects with different vestibule phenotypes (non-notched, unilateral-notched and bilateral-notched vestibules). A sedentary breathing condition with constant flow rate was applied, and the nanoparticle inhalation and transport process were numerically simulated by a computational fluid-particle dynamics (CFPD) approach. The results showed nanoparticle exposure in the nasal cavities was closely associated with anatomical shapes, airflow dynamics, and particle diffusivity. Nanoparticle deposition in the upper passage and olfactory regions was considerably restricted due to the presence of a vestibule notch. However, for the main nasal passage, exposure patterns in all vestibule-notched subjects were similar without significant inter-chamber variations. This indicates the deposition in the main nasal passage was less sensitive to the upstream presence of a notch. This study advances the current understanding of nanoparticle exposure characteristics in human nasal passages with significant inter-subject variations, which play critical roles in assessing particle toxicology following inhalation. [ABSTRACT FROM AUTHOR]