Non-Newtonian Droplet Generation in a Cross-Junction Microfluidic Channel

A two-dimensional CFD model based on volume-of-fluid (VOF) is introduced to examine droplet generation in a cross-junction microfluidic using an open-source software, OpenFOAM together with an interFoam solver. Non-Newtonian power-law droplets in Newtonian liquid is numerically studied and its effect on droplet size and detachment time in three different regimes, i.e., squeezing, dripping and jetting, are investigated. To understand the droplet formation mechanism, the shear-thinning behaviour was enhanced by increasing the polymer concentrations in the dispersed phase. It is observed that by choosing a shear-dependent fluid, droplet size decreases compared to Newtonian fluids while detachment time increases due to higher apparent viscosity. Moreover, the rheological parameters-n and K in the power-law model-impose a considerable effect on the droplet size and detachment time, especially in the dripping and jetting regimes. Those parameters also have the potential to change the formation regime if the capillary number (Ca) is high enough. This work extends the understanding of non-Newtonian droplet formation in microfluidics to control the droplet characteristics in applications involving shear-thinning polymeric solutions.

Small-Scale Phenomena in Reactive Bubbly Flows: Experiments, Numerical Modeling, and Applications

Improving the yield and selectivity of chemical reactions is one of the challenging tasks in paving the way for a more sustainable and climate-friendly economy. For the industrially highly relevant gas-liquid reactions, this can be achieved by tailoring the timescales of mixing to the requirements of the reaction. Although this has long been known for idealized reactors and time- and space-averaged processes, considerable progress has been made recently on the influence of local mixing processes. This progress has become possible through joint research between chemists, mathematicians, and engineers. We present the reaction systems with adjustable kinetics that have been developed, which are easy to handle and analyze. We show examples of how the selectivity of competitive-consecutive reactions can be controlled via local bubble wake structures. This is demonstrated for Taylor bubbles and bubbly flows under technical conditions. Highly resolvednumerical simulations confirm the importance of the bubble wake structure for the performance of a particular chemical reaction and indicate tremendous potential for future process improvements.

Characterization of the gas dispersion behavior of multiple impeller stages by flow regime analysis and CFD simulations

Multiple impeller reactors are widely used due to their advanced gas utilization and an increased volumetric mass transfer coefficient. However, with the application of Rushton impellers, gas dispersion efficiency varies between the bottom and the upper impeller levels. The present study analyzes the individual flow regime, power input, and gas hold-up in each compartment of a reactor equipped with four Rushton impellers. The results indicate that the pre-dispersion of the air introduced by the bottom impeller (up to 80%) plays a key role in a better gas retention efficiency of the upper impellers (>300%) and leads to a shift of the cavity and flooding lines in the flow map (Fr- vs Fl-Number) of the upper impellers. A novel analysis of the bubble flow in the dispersed state via a two-phase LES-based CFD model reveals that a more homogenous distribution of air bubbles in the upper compartments leads to high compartment gas hold-up values, but fewer bubbles in the vicinity of the impellers. The measured and simulated data of this study indicate that the upper impellers' efficiency mostly depends on the flow regime of and the pre-dispersion by the bottom impeller rather than on the upper impellers' flow regimes. These results contribute to the understanding of essential mixing processes and scaling of aerated bioreactors.

Numerical simulations of a swimmer's head and cap wearing different types of goggles

The aim of this study was to analyse the effect of swimming goggles on swimming hydrodynamics by numerical simulations. An elite swimmer volunteered for this research. The swimmer's head was scanned both without goggles, and while wearing 3 different types of goggles (Nikko, Ankor and Swedish). Numerical simulations were conducted at 2 m/s with the Fluent code. The condition without goggles showed the highest viscous drag (1.65 N), followed by the Ankor (1.64 N), Swedish (1.63 N) and Nikko (1.62 N) goggles, respectively. The highest pressure drag was found in the situation without goggles (11.34 N), followed by the Ankor (10.87 N), Nikko (10.78 N) and Swedish (10.20 N) goggles. The condition without goggles presented the highest total drag (12.99 N), followed by the Ankor (12.52 N), Nikko (12.40 N) and Swedish (11.83 N) goggles. Thus, Swedish goggles yields the best hydrodynamics, followed by the Nikko and Ankor goggles and lastly without goggles. Thus, goggles minimise the swimmer's drag comparing to not wearing any. The design of the goggles may impose varying drag forces and therefore it is advised to use goggles at least in competition.

Analysis of microparticle deposition in the human lung by taguchi method and response surface methodology

The deposition phenomenon of microparticle and SAR-CoV-2 laced bioaerosol in human airways is studied by Taguchi methods and response surface methodology (RSM). The data used herein is obtained from simulations of airflow dynamics and deposition fractions of drug particle aerosols in the downstream airways of asthma patients using computational fluid dynamics (CFD) and discrete particle motion (DPM). Three main parameters, including airflow rate, drug dose, and particle size, affecting aerosol deposition in the lungs of asthma patients are examined. The highest deposition fraction (DF) is obtained at the flow rate of 45 L min^-1, the drug dose of 200 μg·puff^-1, and the particle diameter of 5 μm. The optimized combination of levels for the three parameters for maximum drug deposition is performed via the Taguchi method. The importance of the influencing factors rank as particle size > drug dose > flow rate. RSM reveals that the combination of 30 L min^-1, 5 μm, 200 μg·puff^- has the highest deposition fraction. In part, this research also studied the deposition of bioaerosols contaminated with the SAR-CoV-2 virus, and their lowest DF is 1.15%. The low DF of bioaerosols reduces the probability of the SAR-CoV-2 virus transmission.

Dataset for transient 3D simulations of turbulent premixed flames of Gas-to-Liquid (GTL) fuel

A fan-stirred combustion vessel is used to study the premixed turbulent combustion of diesel, Gas to Liquids (GTL) and 50/50 diesel-GTL and to generate these datasets. A numerical simulation approach is implemented for modelling the premixed combustion of the three fuels under different thermodynamics and turbulence initial conditions, using Zimont Turbulent Flame Speed Closure (Zimont TFC) model. Different parameters are obtained from these simulation runs such as turbulent eddy viscosity (µ), turbulent kinetic energy (k), Damkohler number (Da), Reynolds number (ReT) and turbulent flame speed (St). The raw, filtered and pre-processed data are imported from ANSYS Fluent and then listed on filtered tables for the ease of accessibility. These datasets can be then used to perform research in different related areas such as chemical kinetic mechanisms, ignition delay time, flame ignition mechanisms and flame extinction and diffusion. Also, they can be employed to further understand trends, patterns, and anomalies in data. In addition, they can be compared with other numerical models to establish a robust knowledge about the modelling of premixed turbulent combustion. For more information and discussion of the dataset creation, the reader is directed to the full-length article, "Abdellatif M. Sadeq, Samer F. Ahmed, Ahmad K. Sleiti, Transient 3D simulations of turbulent premixed flames of gas-to-liquid (GTL) fuel in a fan-stirred combustion vessel, Fuel, Volume 291, 2021, 120,184, ISSN 0016 2361, https://doi.org/10.1016/j.fuel.2021.120184" [1].

An Experimental and Finite Element Approach for a Better Understanding of Ti-6Al-4V Behavior When Machining under Cryogenic Environment

Due to increasing demand in manufacturing industries, process optimization has become a major area of focus for researchers. This research optimizes the cryogenic machining of aerospace titanium alloy Ti-6Al-4V for industrial applications by studying the effect of varying the nozzle position using two parameters: the nozzle’s separation distance from the tool–chip interface and its inclination angle with respect to the tool rake face. A finite element model (FEM) and computational fluid dynamics (CFD) model are used to simulate the cryogenic impingement of cryogenic carbon dioxide on the tool–workpiece geometry. Experiments are conducted to evaluate cutting forces, tool wear, and surface roughness of the workpiece, and the results are related to the CFD and FEM analyses. The nozzle location is shown to have a significant impact on the cutting temperatures and forces, reducing them by up to 45% and 46%, respectively, while the dominant parameter affecting the results is shown to be the separation distance. Cryogenic machining is shown to decrease adhesion-diffusion wear as well as macroscopic brittle chipping of the cutting insert compared to dry turning, while the workpiece surface roughness is found to decrease by 44% in the case of cryogenic machining.

Improving Pulmonary Nanotherapeutics Using Helical Aerosol Streams: An In Silico Study

The increasing prevalence of pulmonary ailments including asthma, chronic obstructive pulmonary disorder, lung tuberculosis, and lung cancer, coupled with the success of pulmonary therapy, has led to a plethora of scientific research focusing on improving the efficacy of pulmonary drug delivery systems. Recent advances in nanoscience and nano-engineering help achieve this by developing stable, potent, inhalable nanosize drug formulations that potentially increase dosages at target sites with significant therapeutic effects. In this study, we numerically analyze a novel methodology of incorporating helical air-nanoparticle streams for pulmonary nanotherapeutics, using a customized version of the open-source computational fluid dynamics (CFD) toolbox openfoam. As nanoparticles predominantly follow streamlines, helical airflow transports them in a centralized core along the human upper respiratory tract, thereby minimizing deposition and hence waste on the oropharyngeal walls, potentially also reducing the risk of drug-induced toxicity in healthy tissues. Advancing our previous study on micron-particle dynamics, helical streams are shown to improve the delivery of nanodrugs, to deeper lung regions when compared to a purely axial fluid-particle jet. For example, an optimal helical stream featuring a volumetric flow rate of 30 L/min, increased the delivery of 300-nm particles to regions beyond generation 3 by 5%, in comparison to a conventional axial jet. Results from regional deposition studies are presented to demonstrate the robustness of helical flows in pulmonary drug delivery, thus paving the way toward successful implementation of the novel methodology in nanotherapeutics.

Numerical Simulation of Nasal Airflow Aerodynamics, and Warming and Humidification in Models of Clival Chordoma Pre and Post-Endoscopic Endonasal Surgery

OBJECTIVES

To study the effect of endoscopic endonasal surgery on nasal function for the treatment of clival chordoma.

METHODS

Pre and post-operative computed tomography (CT) scans of a case of chordoma treated with an endoscopic endonasal approach (EEA) were collected retrospectively, and models of the nasal cavity were reconstructed so that a subsequent numerical simulation of nasal airflow characteristics, warming, and humidification could be conducted.

RESULTS

Middle turbinectomy resulted in redistribution of airflow within the nasal cavity, and the most significant changes occurred in the middle section. Consistent with the results of airflow evaluation, it was found that the change in nasal anatomical structure significantly reduced warming and humidification. Nasal humidification decreased substantially when postoperative loss of mucosa was taken into consideration. The H₂O mass fraction of pharynx in inspiration phase were significantly correlated with airway surface-to-volume ratio (SVR).

CONCLUSIONS

The EEA for chordoma significantly affected nasal function. Attention should be paid to the protection of nasal structure and the associated mucosa.

Comparison of LBM and FVM in the estimation of LAD stenosis

The finite volume method (FVM)-based computational fluid dynamics (CFD) technology has been applied in the non-invasive diagnosis of coronary artery stenosis. Nonetheless, FVM is a time-consuming process. In addition to FVM, the lattice Boltzmann method (LBM) is used in fluid flow simulation. Unlike FVM solving the Navier-Stokes equations, LBM directly solves the simplified Boltzmann equation, thus saving computational time. In this study, 12 patients with left anterior descending (LAD) stenosis, diagnosed by CTA, are analysed using FVM and LBM. The velocities, pressures, and wall shear stress (WSS) predicted using FVM and LBM for each patient is compared. In particular, the ratio of the average and maximum speed at the stenotic part characterising the degree of stenosis is compared. Finally, the golden standard of LAD stenosis, invasive fractional flow reserve (FFR), is applied to justify the simulation results. Our results show that LBM and FVM are consistent in blood flow simulation. In the region with a high degree of stenosis, the local flow patterns in those two solvers are slightly different, resulting in minor differences in local WSS estimation and blood speed ratio estimation. Notably, these differences do not result in an inconsistent estimation. Comparison with invasive FFR shows that, in most cases, the non-invasive diagnosis is consistent with FFR measurements. However, in some cases, the non-invasive diagnosis either underestimates or overestimates the degree of stenosis. This deviation is caused by the difference between physiological and simulation conditions that remains the biggest challenge faced by all CFD-based non-invasive diagnostic methods.

Analysis of Concentration Polarisation in Full-Size Spiral Wound Reverse Osmosis Membranes Using Computational Fluid Dynamics

A three-dimensional model for the simulation of concentration polarisation in a full-scale spiral wound reverse osmosis (RO) membrane element was developed. The model considered the coupled effect of complex spacer geometry, pressure drop and membrane filtration. The simulated results showed that, at a salt concentration of 10,000 mg/L and feed pressure of 10.91 bar, permeate flux decreased from 27.6 L/(m² h) (LMH) at the module inlet to 24.1 LMH at the module outlet as a result of salt accumulation in the absence of a feed spacer. In contrast, the presence of the spacer increased pressure loss along the membranes, and its presence created vortices and enhanced fluid velocity at the boundary layer and led to a minor decrease in flux to 26.5 LMH at the outlet. This paper underpins the importance of the feed spacer’s role in mitigating concentration polarisation in full-scale spiral wound modules. The model can be used by both the industry and by academia for improved understanding and accurate presentation of mass transfer phenomena of full-scale RO modules by different commercial manufacturers that cannot be achieved by experimental characterization of the mass transfer coefficient or by CFD modelling of simplified 2D flow channels.

Effects of head tilt on squeeze-bottle nasal irrigation - A computational fluid dynamics study

Nasal irrigation is a widely recognized treatment for several sinonasal diseases. However, there is a lack of clear evidence-based guidelines for optimal irrigation delivery to improve lavage and topical drug delivery. This study uses computational fluid dynamics (CFD) to assess the effects of different head tilt positions on sinonasal coverage, residence time and shear stresses in squeeze-bottle nasal irrigation. A sinonasal cavity computational model was constructed from a high-resolution CT scan of a healthy, 25-year-old Asian female. The Volume of Fluid method was used to track the interface between the two immiscible fluids (air and water). The direction of gravity was varied to simulate different head tilt-positions (0° Straight, 45° Forward, 45° Left, 45° Right and 45° Backward) during nasal irrigation with 150 mL liquid via a squeeze bottle through the left nostril for 2 s with a 0.1 s acceleration/deceleration time. The results showed that the 45° backward head tilt position was the most effective in delivering irrigation to the ethmoid, frontal and sphenoid sinuses. Altering head tilt had minimal impact on irrigation delivery to the maxillary sinuses. Maximum wall shear stresses seen in localized areas of the sinus mucosa varied significantly with different head tilt angles. However, the difference in mean wall shear stress on the sinus surfaces was marginal with changing head tilt position. The findings suggest that an optimized head tilt position can be identified to improve liquid irrigation to targeted sinuses, as per treatment requirements (lavage and topical drug delivery).

Serum proteomic profiling in patients with advanced Schistosoma japonicum-induced hepatic fibrosis

Background

Schistosoma japonicum is a parasitic flatworm that is the aetiological agent of human schistosomiasis, an important cause of hepatic fibrosis. Schistosomiasis-induced hepatic fibrosis is a consequence of the highly fibrogenic nature of egg-induced granulomatous lesions, which are the main pathogenic features of schistosomiasis. Although global awareness of the association between schistosomiasis-induced hepatic fibrosis and S. japonicum infection is increasing, little is known about the molecular differences associated with rapid progression to schistosomiasis in cirrhotic patients.

Methods

We systematically used data-independent acquisition (DIA)-based liquid chromatography-mass spectrometry to identify differentially expressed proteins in serum samples from patients with advanced S. japonicum-induced hepatic fibrosis.

Results

Our analysis identified 1144 proteins, among which 66 were differentially expressed between the healthy control group and the group of patients with advanced S. japonicum-induced hepatic fibrosis stage F2 (SHF-F2) and 214 were differentially expressed between the SHF-F2 and SHF-F4 groups (up- or downregulation of at least 1.5-fold in serum samples). The results also indicated that two selected proteins (C1QA and CFD) are potential biomarkers for distinguishing between patients with SHF-F2 and those with SHF-F4 due to S. japonicum infection.

Conclusions

We provide here the first global proteomic profile of serum samples from patients with advanced S. japonicum-induced hepatic fibrosis. The proteins C1QA and CFD are potential diagnostic markers for patients with SHF-F2 and SHF-F4 due to S. japonicum infection, although further large-scale studies are needed. Our DIA-based quantitative proteomic analysis revealed molecular differences among individuals at different stages of advanced S. japonicum-induced hepatic fibrosis and may provide fundamental information for further detailed investigations.

Graphic Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-04734-1.

Deposition features of inhaled viral droplets may lead to rapid secondary transmission of COVID-19

Inhaled viral droplets may immediately be expelled and cause an escalating re-transmission. Differences in the deposition location of inhaled viral droplets may have a direct impact on the probability of virus expelling. This study develops a numerical model to estimate the region-specific deposition fractions for inhalable droplets (1-50 μ m) in respiratory airways. The results identified a higher deposition fraction in the upper airways than the lower airways. Particularly for droplets larger than 10 μ m, the relatively high deposition fraction in the oral/laryngeal combined region warns of its easy transmission through casual talking/coughing. Moreover, considering droplet sizes' effect on virus loading capacity, we built a correlation model to quantify the potential of virus expelling hazards, which suggests an amplified cascade effect on virus transmission on top of the existing transmission mechanism. It therefore highlights the importance of considering the instant expelling possibilities from inhaled droplets, and also implies potentials in restricting a rapid secondary transmission by measures that can lower down droplet deposition in the upper airways.

Identification of Novel Biomarker for Early Detection of Diabetic Nephropathy

Diabetic nephropathy (DN) is one of the most common complications of diabetes mellitus. After development of DN, patients will progress to end-stage renal disease, which is associated with high morbidity and mortality. Here, we developed early-stage diagnostic biomarkers to detect DN as a strategy for DN intervention. For the DN model, Zucker diabetic fatty rats were used for DN phenotyping. The results revealed that DN rats showed significantly increased blood glucose, blood urea nitrogen (BUN), and serum creatinine levels, accompanied by severe kidney injury, fibrosis and microstructural changes. In addition, DN rats showed significantly increased urinary excretion of kidney injury molecule-1 (KIM-1) and neutrophil gelatinase-associated lipocalin (NGAL). Transcriptome analysis revealed that new DN biomarkers, such as complementary component 4b (C4b), complementary factor D (CFD), C-X-C motif chemokine receptor 6 (CXCR6), and leukemia inhibitory factor (LIF) were identified. Furthermore, they were found in the urine of patients with DN. Since these biomarkers were detected in the urine and kidney of DN rats and urine of diabetic patients, the selected markers could be used as early diagnosis biomarkers for chronic diabetic nephropathy.

Geometrically induced wall shear stress variability in CFD-MRI coupled simulations of blood flow in the thoracic aortas

Aortic aneurysm is associated with aberrant blood flow and wall shear stress (WSS). This can be studied by coupling magnetic resonance imaging (MRI) with computational fluid dynamics (CFD). For patient-specific simulations, extra attention should be given to the variation in segmentation of the MRI data-set and its effect on WSS. We performed CFD simulations of blood flow in the aorta for ten different volunteers and provided corresponding WSS distributions. The aorta of each volunteer was segmented four times. The same inlet and outlet boundary conditions were applied for all segmentation variations of each volunteer. Steady-state CFD simulations were performed with inlet flow based on phase-contrast MRI during peak systole. We show that the commonly used comparison of mean and maximal values of WSS, based on CFD in the different segments of the thoracic aorta, yields good to excellent correlation (0.78-0.95) for rescan and moderate to excellent correlation (0.64-1.00) for intra- and interobserver reproducibility. However, the effect of geometrical variations is higher for the voxel-to-voxel comparison of WSS. With this analysis method, the correlation for different segments of the whole aorta is poor to moderate (0.43-0.66) for rescan and poor to good (0.48-0.73) for intra- and interobserver reproducibility. Therefore, we advise being critical about the CFD results based on the MRI segmentations to avoid possible misinterpretation. While the global values of WSS are similar for different modalities, the variation of results is high when considering the local distributions.

Kinetics and mechanistic aspects of removal of heavy metal through gas-liquid sulfide precipitation: A computational and experimental study

The production of fine particles from extremely high supersaturation has challenged the application of sulfide precipitation in treating heavy metal wastewater due to the difficulty of solid-liquid separation. To this end, a gas-liquid sulfide precipitation reactor for the removal of Cu²⁺ was designed by controlling the mass transfer and supersaturation levels during sulfidation processes. Particularly, a computational fluid dynamics (CFD) model of the reactor, integrating sulfidation reaction kinetics with two-phase flow hydrodynamics, was first built, followed by examining the effects of H₂S(g) bubble diameter and flow rate. Based on the CFD simulation, the rate-limiting step of the gas-liquid sulfide precipitation reaction is the gas-liquid mass transfer process. Either reducing H₂S(g) bubble diameter or increasing H₂S(g) flow rate can result in the control of reaction rate and supersaturation level in the system. In order to validate the CFD simulations, we measured Cu²⁺ concentrations during the sulfidation process with the batch experiments. The agreement between computational and experimental results indicated that our mechanistic model can provide a protocol for the design and optimization of the reaction system, allowing one to visualize the time-dependent reaction process and evaluate the performance of a reactor.

Numerical Model to Analyze the Physicochemical Mechanisms Involved in CO2 Absorption by an Aqueous Ammonia Droplet

CO2 is the main anthropogenic greenhouse gas and its reduction plays a decisive role in reducing global climate change. As a CO2 elimination method, the present work is based on chemical absorption using aqueous ammonia as solvent. A CFD (computational fluid dynamics) model was developed to study CO2 capture in a single droplet. The objective was to identify the main mechanisms responsible for CO2 absorption, such as diffusion, solubility, convection, chemical dissociation, and evaporation. The proposed CFD model takes into consideration the fluid motion inside and outside the droplet. It was found that diffusion prevails over convection, especially for small droplets. Chemical reactions increase the absorption by up to 472.7% in comparison with physical absorption alone, and evaporation reduces the absorption up to 41.9% for the parameters studied in the present work.

Challenges in hemodynamics assessment in complex neurovascular geometries using computational fluid dynamics and benchtop flow simulation in 3D printed patient specific phantoms

Purpose

Complex hemodynamics assessments, as those related to carotid stenosis, are not always easily straightforward due to multifaceted challenges presented by the collateral flow in the Circle of Willis (CoW) and brain flow autoregulation. Advanced computational and benchtop methods to investigate hemodynamics aspects related to such complex flows are often used, however both have limitations and could lead to results which may diverge. In this study we investigated these aspects by performing correlated computational fluid dynamics (CFD) simulations and benchtop experiments in patient specific 3D printed phantoms.

Materials and Methods

To investigate the flow in patients with carotid stenosis, we built two patient specific phantoms which contained the arterial lesion of interest, all main arteries leading to the brain, the CoW and main arteries branching from it. Each phantom was connected to a generic aortic arch. A programmable pump was connected and flow parameters were measured proximal and distal to the lesion and the contralateral arteries. The patient 3D geometry was used to perform a set of CFD simulations where inflow boundary conditions matched the experimental ones. Flow conditions were recorded at the same locations as the experimental setup. Further exploration into the translation from experimental to CFD was also performed by customizing vascular segmentation and physically manipulating arterial compliance properties.

Results

We initially observed significant differences between the CFD recordings and the experimental setup. Most of the differences were due to changes in phantom geometry when subjected to physiological pressures and simplistic outflow boundary conditions in the CFD simulations which do not account for pulsatility and nonlinear phenomena. Further work confirms the need for dynamic mesh behavior within CFD simulations attempting to computationally mimic 3D-printed benchtop experiments. Additionally, CFD simulation may benefit from considering geometry specific to a 3D-printed vascular phantom.

Assessing and controlling infection risk with Wells-Riley model and spatial flow impact factor (SFIF)

The ongoing COVID-19 epidemic has spread worldwide since December 2019. Effective use of engineering controls can prevent its spread and thereby reduce its impact. As airborne transmission is an important mode of infectious respiratory disease transmission, mathematical models of airborne infection are needed to develop effective engineering control. We developed a new approach to obtain the spatial distribution for the probability of infection (PI) by combining the spatial flow impact factor (SFIF) method with the Wells-Riley model. Our method can be combined with the anti-problem approach, in order to determine the optimized arrangement of people and/or air purifiers in a confined space beyond the ability of previous methods. This method was validated by a CFD-integrated method, and an illustrative example is presented. We think our method can be helpful in controlling infection risk and making the best use of the space and equipment in built environments, which is important for preventing the spread of COVID-19 and other infectious respiratory diseases, and promoting the development of sustainable cities and society.

Lagrangian Trajectory Simulation of Platelets and Synchrotron Microtomography Augment Hemodynamic Analysis of Intracranial Aneurysms Treated With Embolic Coils

As frequency of endovascular treatments for intracranial aneurysms increases, there is a growing need to understand the mechanisms for coil embolization failure. Computational fluid dynamics (CFD) modeling often simplifies modeling the endovascular coils as a homogeneous porous medium (PM), and focuses on the vascular wall endothelium, not considering the biomechanical environment of platelets. These assumptions limit the accuracy of computations for treatment predictions. We present a rigorous analysis using X-ray microtomographic imaging of the coils and a combination of Lagrangian (platelet) and Eulerian (endothelium) metrics. Four patient-specific, anatomically accurate in vitro flow phantoms of aneurysms are treated with the same patient-specific endovascular coils. Synchrotron tomography scans of the coil mass morphology are obtained. Aneurysmal hemodynamics are computationally simulated before and after coiling, using patient-specific velocity/pressure measurements. For each patient, we analyze the trajectories of thousands of platelets during several cardiac cycles, and calculate residence times (RTs) and shear exposure, relevant to thrombus formation. We quantify the inconsistencies of the PM approach, comparing them with coil-resolved (CR) simulations, showing the under- or overestimation of key hemodynamic metrics used to predict treatment outcomes. We fully characterize aneurysmal hemodynamics with converged statistics of platelet RT and shear stress history (SH), to augment the traditional wall shear stress (WSS) on the vascular endothelium. Incorporating microtomographic scans of coil morphology into hemodynamic analysis of coiled intracranial aneurysms, and augmenting traditional analysis with Lagrangian platelet metrics improves CFD predictions, and raises the potential for understanding and clinical translation of computational hemodynamics for intracranial aneurysm treatment outcomes.

A quasi-3D model of the whole lung: airway extension to the tracheobronchial limit using the constrained constructive optimization and alveolar modeling, using a sac-trumpet model

Existing computational models used for simulating the flow and species transport in the human airways are zero-dimensional (0D) compartmental, three-dimensional (3D) computational fluid dynamics (CFD), or the recently developed quasi-3D (Q3D) models. Unlike compartmental models, the full CFD and Q3D models are physiologically and anatomically consistent in the mouth and the upper airways, since the starting point of these models is the mouth-lung surface geometry, typically created from computed tomography (CT) scans. However, the current resolution of CT scans limits the airway detection between the 3rd-4th and 7th-9th generations. Consequently, CFD and the Q3D models developed using these scans are generally limited to these generations. In this study, we developed a method to extend the conducting airways from the end of the truncated Q3D lung to the tracheobronchial (TB) limit. We grew the lung generations within the closed lung lobes using the modified constrained constructive optimization, creating an aerodynamically optimized network aiming to produce equal pressure at the distal ends of the terminal segments. This resulted in a TB volume and lateral area of ∼165 cc and ∼2000 cm², respectively. We created a "sac-trumpet" model at each of the TB outlets to represent the alveoli. The volumes of the airways and the individual alveolar generations match the anatomical values by design: with the functional residual capacity at 2611 cc. Lateral surface areas were scaled to match the physiological values. These generated Q3D whole lung models can be efficiently used for conducting multiple breathing cycles of drug transport and deposition simulations.

The Effect of the Oleophobicity Deterioration of a Membrane Surface on Its Rejection Capacity: A Computational Fluid Dynamics Study

In this work, the effects of the deteriorating affinity-related properties of membranes due to leaching and erosion on their rejection capacity were studied via computational fluid dynamics (CFD). The function of affinity-enhancing agents is to modify the wettability state of the surface of a membrane for dispersed droplets. The wettability conditions can be identified by the contact angle a droplet makes with the surface of the membrane upon pinning. For the filtration of fluid emulsions, it is generally required that the surface of the membrane is nonwetting for the dispersed droplets such that the interfaces that are formed at the pore openings provide the membrane with a criterion for the rejection of dispersals. Since materials that make up the membrane do not necessarily possess the required affinity, it is customary to change it by adding affinity-enhancing agents to the base material forming the membrane. The bonding and stability of these materials can be compromised during the lifespan of a membrane due to leaching and erosion (in crossflow filtration), leading to a deterioration of the rejection capacity of the membrane. In order to investigate how a decrease in the contact angle can lead to the permeation of droplets that would otherwise get rejected, a CFD study was conducted. In the CFD study, a droplet was released in a crossflow field that involved a pore opening and the contact angle was considered to decrease with time as a consequence of the leaching of affinity-enhancing agents. The CFD analysis revealed that the decrease in the contact angle resulted in the droplet spreading over the surface more. Furthermore, the interface that was formed at the entrance of the pore opening flattened as the contact angle decreased, leading the interface to advance more inside the pore. The droplet continued to pass over the pore opening until the contact angle reached a certain value, at which point, the droplet became pinned at the pore opening.

Toward the Next Generation of Passive Micromixers: A Novel 3-D Design Approach

Passive micromixers are miniaturized instruments that are used to mix fluids in microfluidic systems. In microchannels, combination of laminar flows and small diffusion constants of mixing liquids produce a difficult mixing environment. In particular, in very low Reynolds number flows, e.g., Re < 10, diffusive mixing cannot be promoted unless a large interfacial area is formed between the fluids to be mixed. Therefore, the mixing distance increases substantially due to a slow diffusion process that governs fluid mixing. In this article, a novel 3-D passive micromixer design is developed to improve fluid mixing over a short distance. Computational Fluid Dynamics (CFD) simulations are used to investigate the performance of the micromixer numerically. The circular-shaped fluid overlapping (CSFO) micromixer design proposed is examined in several fluid flow, diffusivity, and injection conditions. The outcomes show that the CSFO geometry develops a large interfacial area between the fluid bodies. Thus, fluid mixing is accelerated in vertical and/or horizontal directions depending on the injection type applied. For the smallest molecular diffusion constant tested, the CSFO micromixer design provides more than 90% mixing efficiency in a distance between 260 and 470 µm. The maximum pressure drop in the micromixer is found to be less than 1.4 kPa in the highest flow conditioned examined.

Optimization and parallelization of the discrete ordinate method for radiation transport simulation in OpenFOAM: Hierarchical combination of shared and distributed memory approaches

This paper describes the reduction in memory and computational time for the simulation of complex radiation transport problems with the discrete ordinate method (DOM) model in the open-source computational fluid dynamics platform OpenFOAM. Finite volume models require storage of vector variables in each spatial cell; DOM introduces two additional discretizations, in direction and wavelength, making memory a limiting factor. Using specific classes for radiation sources data, changing the store of fluxes and other minor changes allowed a reduction of 75% in memory requirements. Besides, a hierarchical parallelization was developed, where each node of the standard parallelization uses several computing threads, allowing higher speed and scalability of the problem. This architecture, combined with optimization of some parts of the code, allowed a global speedup of x15. This relevant reduction in time and memory of radiation transport opens a new horizon of applications previously unaffordable.