Yttrium-90 radioembolization (RE) is a widely used transcatheter intraarterial therapy for patients with unresectable liver cancer. In the last decade, computer simulations of hepatic artery hemodynamics during RE have been performed with the aim of better understanding and improving the therapy. In this review, we introduce the concept of computational fluid dynamics (CFD) modeling with a clinical perspective and we review the CFD models used to study RE from the fluid mechanics point of view. Finally, we show what CFD simulations have taught us about the hemodynamics during RE, the current capabilities of CFD simulations of RE, and we suggest some future perspectives.

The effectiveness of a close-coupled gas atomisation process largely depends on the operational and the geometric variables. In this study, Computational Fluid Dynamics (CFD) techniques are used to model and simulate the gas flow in the melt nozzle area for a convergent-divergent, close-coupled gas atomiser in the absence of the melt stream. Firstly, a reference case, in which the atomisation gas is nitrogen at 50 bar and a supersonic gas nozzle with a throat width of L0 has been modelled, is presented. Then, the influence of both the inlet gas pressure and this design parameter are investigated, comparing the numerical results provided by simulations varying the inlet pressure from 5 to 80 bar and modelling different convergent-divergent gas nozzles with throat widths of 0.29¿Lo, 0.5¿Lo, 0.77¿Lo and 2¿Lo respectively. The simulation results show how similarly these two parameters modify gas mass flow rates, gas velocity fields, aspiration pressures in the melt delivery tube or the size of the recirculation zones below the melt nozzle. Therefore, it can be stated that this geometric variable of the gas nozzle may be as relevant as the inlet pressure in the atomisation process. The most important novelty of this study is related to experimental validation of the numerical results using the Particle Image Velocimetry (PIV) technique and through direct measurements of gas mass flow rates, with a clear correlation between simulated and measured data. Moreover, some results obtained with experimental atomisations using copper and nitrogen are also presented. The experimental results show that finer powders are produced by increasing the atomising pressure or the throat width of the supersonic gas nozzle, which can be directly related to the gas flow dynamics calculated numerically.

Radioembolization (RE) is a medical treatment for primary and secondary liver cancer that involves the transcatheter intraarterial delivery of micron-sized and radiation-emitting microspheres, with the goal of improving microsphere deposition in the tumoral bed while sparing healthy tissue. An increasing number of in vitro and in silico studies on RE in the literature suggest that the particle injection velocity, spatial location of the catheter tip and catheter type are important parameters in particle distribution. The present in silico study assesses the performance of a novel catheter design that promotes particle dispersion near the injection point, with the goal of generating a particle distribution that mimics the flow split to facilitate tumour targeting. The design is based on two factors: the direction and the velocity at which particles are released from the catheter. A series of simulations was performed with the catheter inserted at an idealised hepatic artery tree with physiologically realistic boundary conditions. Two longitudinal microcatheter positions in the first generation of the tree were studied by analysing the performance of the catheter in terms of the outlet-to-outlet particle distribution and split flow matching. The results show that the catheter with the best performance is one with side holes on the catheter wall and a closed frontal tip. This catheter promotes a flow-split-matching particle distribution, which improves as the injection crossflow increases.

The high demand for quality in the manufacture of absorbent hygiene products requires the adhesive bonds between layers to be as uniform as possible. An experimental study was conducted on two industrial multihole melt blowing nozzle designs used for hot-melt adhesive applications for hygiene products, in order to study two defects that influence the quality of the adhesive bond: fibre breakup, resulting in contamination, and the presence of shots, undesirable lumps that end up in the finished product. To this end, the fibre dynamics were captured at the nozzle exit region by using high-speed imaging. From the results it was observed that die drool is the main source of shot formation, while fibre breakup occurs as a result of applying a sufficiently large force in the direction perpendicular to the fibre. In addition, three dimensionless parameters were defined, the first two being the air-polymer flux ratio and the dimensionless temperature ratio, both of which represent the operating conditions, and the remaining one being the force ratio, which represents the nozzle geometry. The effect of these parameters on fibre breakup and shot formation was studied and the results indicate that both the operating conditions and the nozzle geometry were responsible for the onset of the fibre breakup and for the formation of shots. More precisely, both defects turned out to be dominated by the air-polymer flux ratio and the air tilt angle. The results that emerge from this study are us

Computational fluid dynamics techniques are increasingly used to computer simulate radioembolization, a transcatheter intraarterial treatment for patients with inoperable tumors, and analyze the influence of treatment parameters on the microsphere distribution. Ongoing clinical research studies are exploring the influence of the microsphere density in tumors on the treatment outcome. In this preliminary study, we computationally analyzed the influence of the microsphere concentration in the vial on the microsphere concentration in the blood. A patient-specific case was used to simulate the blood flow and the microsphere transport during three radioembolization procedures in which the only parameter varied was the concentration of microspheres in the vial and the span of injection, resulting in three simulations with the same number of microspheres injected. Results showed that a time-varying microsphere concentration in the blood at the outlets of the computational domain can be analyzed using CFD, and also showed that there was a direct relationship between the variation of microsphere concentration in the vial and the variation of microsphere concentration in the blood. Future research will focus on elucidating the relationship between the microsphere concentration in the vial, the microsphere concentration in the blood, and the final microsphere distribution in the tissue.

The high-quality standards of bodily absorbent hygiene products require that the adhesive bond between layers be as uniform and consistent as possible. The final adhesive pattern of the product is determined by the dynamics of the adhesive fibre, which in turn depends on the nozzle geometry and on its operating conditions. In order to gain a better understanding of the dynamics of adhesive fibres and the deposited application pattern, an experimental study was conducted on two multi-hole melt blowing (MB) nozzles designed for producing hot-melt adhesives. To this end, the fibre dynamics were captured through the use of high-speed imaging (HSI). The main parameters that govern the fibre dynamics, including its frequency of oscillation, were quantified through use of image analysis. The effect of the operating conditions on the fibre's frequency of oscillation at the nozzle exit region was studied and the results indicate that increasing air-polymer flux ratios (m') and decreasing dimensionless temperature ratios (T') both increase the fibre whipping frequency. Additionally, information on the fibre dynamics on the two planes of oscillation is obtained by studying the deposited application pattern of hot-melt applications. Other related matters are also treated throughout the article, such as fibre contact in adhesive patterns, which represent one of the major defects that the melt blowing technology of hot-melt adhesives is trying to mitigate. Experimental measurements are pre

This paper presents a Computational Fluid Dynamics (CFD) model of a pilot scale dissolved air flotation (DAF) tank. A Multiphase Mixture model was used to analyse the influence of bubble sizes on the formation of a stratified flow structure. Critical bubble diameter is defined as the size of the bubble that implies the equality of the bubble rising velocity and flow downward velocity in the separation zone (SZ). The fact as to whether using air bubble sizes which are greater or less than the critical diameter value significantly affects the air content, flow structure and the limit of the whitewater blanket inside the SZ is assessed. The study was carried out using two approaches, namely, mono-and multi-diameter. The results obtained via the mono-diameter approach proved to be closely in line with experimental data when air concentration in the SZ had almost, but not quite, a constant value. However, it failed to predict the case of the progressive decrease in air below half of SZ height. A combined effect of bubbles with different rising speed was required to reproduce a smooth air profile curve, as measured experimentally. In this context, a multi-diameter approach is deemed to be a suitable method for reproducing the stratified structure. In addition, this approach offers the chance to study bubble size distribution inside the SZ domain.

Central blood pressure (cBP) is a highly prognostic cardiovascular (CV) risk factor whose accurate, invasive assessment is costly and carries risks to patients. We developed and assessed novel algorithms for estimating cBP from noninvasive aortic hemodynamic data and a peripheral blood pressure measurement. These algorithms were created using three blood flow models: the two- and three-element Windkessel (0-D) models and a one-dimensional (1-D) model of the thoracic aorta. We tested new and existing methods for estimating CV parameters (left ventricular ejection time, outflow BP, arterial resistance and compliance, pulse wave velocity, and characteristic impedance) required for the cBP algorithms, using virtual (simulated) subjects (n = 19,646) for which reference CV parameters were known exactly. We then tested the cBP algorithms using virtual subjects (n = 4,064), for which reference cBP were available free of measurement error, and clinical datasets containing invasive (n = 10) and noninvasive (n = 171) reference cBP waves across a wide range of CV conditions. The 1-D algorithm outperformed the O-D algorithms when the aortic vascular geometry was available, achieving central systolic blood pressure (cSBP) errors <= 2.1 +/- 9.7 mmHg and root-mean-square errors (RMSEs) <= 6.4 +/- 2.8 mmHg against invasive reference cBP waves (n = 10). When the aortic geometry was unavailable, the three-element 0-D algorithm achieved cSBP errors <= 6.0 +/- 4.7 mmHg and RMSEs <= 5.9 +/- 2.4 mmHg against noninvasive reference cBP waves (n = 171), outperforming the two-element O-D algorithm. All CV parameters were estimated with mean percentage errors <= 8.2%, except for the aortic characteristic impedance (<13.4%), which affected the three-element O-D algorithm's performance. The freely available algorithms developed in this work enable fast and accurate calculation of the cBP wave and CV parameters in datasets containing noninvasive ultrasound or magnetic resonance imaging data. NEW & NOTEWORTHY First, our proposed methods for CV parameter estimation and a comprehensive set of methods from the literature were tested using in silico and clinical datasets. Second, optimized algorithms for estimating cBP from aortic flow were developed and tested for a wide range of cBP morphologies, including catheter cBP data. Third, a dataset of simulated cBP waves was created using a three-element Windkessel model. Fourth, the Windkessel model dataset and optimized algorithms are freely available.

Radioembolization (RE) is a treatment for patients with liver cancer, one of the leading cause of cancer-related deaths worldwide. RE consists of the transcatheter intraarterial infusion of radioactive microspheres, which are injected at the hepatic artery level and are transported in the bloodstream, aiming to target tumors and spare healthy liver parenchyma. In paving the way towards a computer platform that allows for a treatment planning based on computational fluid dynamics (CFD) simulations, the current simulation (model preprocess, model solving, model postprocess) times (of the order of days) make the CFD-based assessment non-viable. One of the approaches to reduce the simulation time includes the reduction in size of the simulated truncated hepatic artery. In this study, we analyze for three patient-specific hepatic arteries the impact of reducing the geometry of the hepatic artery on the simulation time. Results show that geometries can be efficiently shortened without impacting greatly on the microsphere distribution.

Simple Summary Liver cancer is one of the leading causes of cancer-related deaths worldwide and balloon-occluded transarterial chemoembolization (B-TACE) has emerged as a safe and effective treatment for liver cancer. However, the hemodynamic alterations that are responsible for the successfulness of the treatment and are produced by the microballoon catheter used during the treatment are not yet well understood. In this study, we developed an in vitro model (IVM) that can simulate B-TACE. We designed clinically relevant experiments, and we obtained clinically realistic results. We conclude that the IVM allows for a visual understanding of a complex phenomenon (i.e., the blood flow redistribution after balloon occlusion) and it could be used as a base for future sophisticated and even patient-specific IVMs; in addition, it could be used to conduct IVM-based research on B-TACE. Background: Balloon-occluded transarterial chemoembolization (B-TACE) has emerged as a safe and effective procedure for patients with liver cancer, which is one of the deadliest types of cancer worldwide. B-TACE consist of the transcatheter intraarterial infusion of chemotherapeutic agents, followed by embolizing particles, and it is performed with a microballoon catheter that temporarily occludes a hepatic artery. B-TACE relies on the blood flow redistribution promoted by the balloon-occlusion. However, flow redistribution phenomenon is not yet well understood. Methods: This study aims to present a simple in vitro model (IVM) where B-TACE can be simulated. Results: By visually analyzing the results of various clinically-realistic experiments, the IVM allows for the understanding of balloon-occlusion-related hemodynamic changes and the importance of the occlusion site. Conclusion: The IVM can be used as an educational tool to help clinicians better understand B-TACE treatments. This IVM could also serve as a base for a more sophisticated IVM to be used as a research tool.

A perforated plate in an electronic device is typically placed downstream of an axial fan (push cooling) in order to avoid electromagnetic interferences. Because of the swirling component in the flow approaching the screen, determining how the screen affects the flow pattern downstream of the screen is a challenge. It is important to understand this interaction, as the correct location of the electronic components will depend on the flow pattern (the components that dissipate more heat will be located where the maximum magnitude of the velocity is located). This work aims to present an approach of the flow pattern via a compact model based on three directional pressure loss coefficients. The values for the pressure loss coefficients are obtained through different correlations depending on the flow and geometric characteristics for the case that is being modeled. These correlations are obtained through an iterative process that compares different flow patterns obtained through different modeling strategies: the compact one that is presented in this paper and another detailed one, which was validated in previous works. Results show that if this compact model is used, an approximation of the flow pattern could be obtained with a huge decrease in the amount of time invested.

The effect of several operational and geometric variables on the particle size distribution of powders produced by close-coupled gas atomisation is analysed from a total of 66 experiments. Powders of three pure metals (copper, tin and iron) and two alloys (bronze Cu-15 wt% Sn and stainless steel SS 316 L) have been produced. Nitrogen, argon and helium were used as atomising gases. It is shown that the gas-to-metal ratio of volume flow rates (GMRV) is more relevant than the ratio of mass flow rates (GMR) in order to analyse the effect of atomisation variables on the particle size. Kishidaka's equation, originally proposed for water atomisation, is modified to predict the median particle size in gas atomisation. The accuracy of the new equation is compared with that of Lubanska, and Rao and Mehrotra. Kishidaka's modified empirical correlation is the most accurate in predicting the median particle size of the powders produced in this work. The morphology of the produced powders is studied by scanning electron microscopy (SEM) and it is observed that the melt superheat can play an important role in the aggregation of fine particles (< 10 mu m), which increases the fraction of large particles (> 100 mu m). (C) 2020 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Radioembolization (RE) with yttrium-90 (Y-90) microspheres, a transcatheter intraarterial therapy for patients with liver cancer, can be modeled computationally. The purpose of this work was to correlate the results obtained with this methodology using in vivo data, so that this computational tool could be used for the optimization of the RE procedure. The hepatic artery three-dimensional (3D) hemodynamics and microsphere distribution during RE were modeled for six Y-90-loaded microsphere infusions in three patients with hepatocellular carcinoma using a commercially available computational fluid dynamics (CFD) software package. The model was built based on in vivo data acquired during the pretreatment stage. The results of the simulations were compared with the in vivo distribution assessed by Y-90 PET/CT. Specifically, the microsphere distribution predicted was compared with the actual Y-90 activity per liver segment with a commercially available 3D-voxel dosimetry software (PLANET Dose, DOSIsoft). The average difference between the CFD-based and the PET/CT-based activity distribution was 2.36 percentage points for Patient 1, 3.51 percentage points for Patient 2 and 2.02 percentage points for Patient 3. These results suggest that CFD simulations may help to predict Y-90-microsphere distribution after RE and could be used to optimize the RE procedure on a patient-specific basis.

Radioembolization (RE) is a valuable treatment for liver cancer. It consists of administering radioactive microspheres via an intra-arterially placed catheter with the aim of lodging these microspheres, which are driven by the bloodstream, in the tumoral bed. Even though it is a safe treatment, some radiation-induced complications may arise. In trying to detect or solve the possible incidences that cause nontarget irradiation, simulating the particle-hemodynamics in hepatic arteries during RE via computational fluid dynamics (CFD) tools has become a valuable approach. This paper reviews the parameters that influence the outcome of RE that have been studied via numerical simulations. In this numerical approach, the outcome of RE is regarded as successful if particles reach the artery branches that feed tumor-bearing liver segments. Up to 10 parameters have been reviewed. The variation of each parameter actually alters the hemodynamics pattern in the vicinities of the catheter tip, and locally alters the incorporation of the particles into the bloodstream. Therefore, in general, the local influences of these parameters should result in global differences in terms of particle distribution in the hepatic artery branches. However, it has been observed that under some (qualitatively described) appropriate conditions where particles align with blood streamlines, the local influence resulting from a variation of a given parameter vanishes and no global differences are observed. Furth

In the last decades, the numerical studies on hemodynamics have become a valuable explorative scientific tool. The very first studies were done over idealized geometries, but as numerical methods and the power of computers have become more affordable, the studies tend to be patient specific. We apply the study to the numerical analysis of tumor-targeting during liver radioembolization (RE). RE is a treatment for liver cancer, and is performed by injecting radiolabeled microspheres via a catheter placed in the hepatic artery. The objective of the procedure is to maximize the release of radiolabeled microspheres into the tumor and avoid a healthy tissue damage. Idealized virtual arteries can serve as a generalist approach that permits to separately analyze the effect of a variable in the microsphere distribution with respect to others. However, it is important to use proper physiological boundary conditions (BCs). It is not obvious, the need to account for the effect of tortuosity when using an idealized virtual artery. We study the use of idealized geometry of a hepatic artery as a valid research tool, exploring the importance of using realistic spiral-flow inflow BC. By using a literature-based cancer scenario, we vary two parameters to analyze the microsphere distribution through the outlets of the geometry. The parameters varied are the type of microspheres injected and the microsphere injection velocity. The results with realistic inlet velocity profile showed that the par

Conventional cooling systems in large office buildings typically incorporate evaporative cooling towers, despite the drawbacks of direct evaporation. An alternative approach is based on highly selective innovative surfaces capable of daytime radiant cooling, however, prototypes of these cooling radiators have not yet demonstrated a system capable of cooling an actual building. This paper presents a third approach: A hybrid cooling system designed to partly or completely replace a cooling tower using dry heat dissipation panels. Unlike nocturnal cooling radiators, these panels may be integrated into a facade in a vertical position. The hybrid system is described firstly, where two configurations of the system are considered. Then, an evaluation of the hybrid system in comparison to a conventional system is performed by means of a simulation-based study, resulting that the replacement of a cooling tower by cooling panels increases the annual energy consumption by 3.6% compared to a conventional open circuit cooling tower system. However, the decrease in maintenance costs may reduce the annual operational expenses by over 50%. (C) 2020 Published by Elsevier Ltd.

Building envelope systems are rapidly evolving, driven by increasingly stringent requirements for limiting energy consumption. Current trends favour lightweight, prefabricated wall assemblies with high levels of insulation, which have been shown to be particularly sensitive to thermal bridging through anchoring and framing elements. This paper presents a self-supporting multi-layer wall component made from bio-based materials, where novel biocomposite profiles are used instead of conventional metallic frames. The thermal performance of the proposed solution is calculated from numerical modelling and characterised through in-situ measurement of a full-scale prototype. For the plane areas of the wall with continuous insulation, theoretical calculations are broadly in line with results from experimental monitoring (7-15% deviation). Additionally, an area along a framing profile was specifically monitored, and it was found that the numerical model overestimated thermal resistance with a deviation of 121%. The presence of air gaps between the rigid insulation and framing elements, linked to the fabrication process of the prototype, was identified as a plausible cause. A subsequent explanatory numerical assessment, considering the effect of such cavities in the numerical model, provided results that are consistent with measurements from the experiment and previous literature. The study aims at demonstrating the insulation levels achievable with the use of novel bio-based materials of low thermal conductivity, and more generally, contributing to a better understanding of the thermal performance of framed lightweight insulated assemblies in service conditions, by monitoring and modelling the impact of thermal bridges and workmanship at framing elements. (C) 2020 Elsevier B.V. All rights reserved.

The air conditioning systems used in transport vehicles (railway passenger cars) are constrained by two issues: the consumed energy and the occupied space. In order to assess how both restrictions can be fulfilled a parametric analysis and an optimization have been carried out by means of Design of Experiments (DoE) techniques applied to a mathematical model of a real AC system. To evaluate the energy efficiency of the system four parameters have been used: the COP (Coefficient of Performance), the refrigeration power of the system and its dimensionless expression and the effectiveness of the evaporator. The occupied space of the AC system has been characterized through the dimensionless volume of the evaporator. The same compressor has been used in the analysis and the input parameters varied have been the dimensionless evaporator volume and four operating conditions: the evaporator inlet air temperature and mass flow rate, the condenser inlet air temperature and the air temperature increment in the condenser. Through a Central Composite Surface Response design, results show that the dimensionless refrigeration power is the best parameter to assess the energy efficiency because is independent of the operating conditions and only depends on the dimensionless volume of the evaporator: the lower the latter, the higher the former. An optimal dimensionless volume has been identified for the simultaneous optimization of the four output variables of the system that provides an increase of 26% in the dimensionless refrigeration power with respect to the baseline system.

A simple battery thermal management system's control strategy based on reliable battery-pack-level CFD models and numerical optimization methodologies is proposed for vertical elevation applications powered by lithium-ion batteries. A new devised heat generation model named as False Steady has been successfully used to calculate the heat density generated in each cell of the battery pack in a steady simulation without losing the thermal coupling and hence prediction accuracy. The best placement for the temperature sensors to evaluate the thermal dispersion has been decided based on the CFD model results. When the predefined thermal limits are crossed the fans will start operating and they will be regulated depending on the ambient temperature and the measured charge or discharge current level. The optimal values of fans' pulse width modulation level are determined from response surfaces obtained from the simulations.

Balloon-occluded transarterial chemoembolisation (B-TACE) is an intraarterial transcatheter treatment for liver cancer. In B-TACE, an artery-occluding microballoon catheter occludes an artery and promotes collateral circulation for drug delivery to tumours. This paper presents a methodology for analysing the haemodynamics during B-TACE, by combining zero-dimensional and three-dimensional modelling tools. As a proof of concept, we apply the methodology to a patient-specific hepatic artery geometry and analyse two catheter locations. Results show that the blood flow redistribution can be predicted in this proof-of-concept study, suggesting that this approach could potentially be used to optimise catheter location.

Mathematical models describing precipitation processes in one step need to be upgraded. Particle size distribution is a crucial variable and its inclusion in the modelling libraries is necessary if the technology wants to be optimized through simulation. With this objective, a mass based population balance model is presented in this contribution. The model has been constructed using a stoichiometric matrix and a kinetic vector and using mass as the internal coordinate, as it is usually done in wastewater treatment modelling. Identifiability of the parameters of the model was evaluated using a sensitivity and a collinearity analysis for six simulation case studies of struvite precipitation. In addition, parameters in the model were calibrated to represent data from two batch tests in the laboratory. The results of the analysis showed that the identifiability of the parameters depends on the available experimental data and explored scenarios. Identifiability of the parameters could be the reason behind the shifting parameter values describing mechanisms of precipitation in the literature. This contribution helps to understand the possibilities and limitations that the population balance model approach offer.

The maximum diameter criterion is the most important factor in the clinical management of abdominal aortic aneurysms (AAA). Consequently, interventional repair is recommended when an aneurysm reaches a critical diameter, typically 5.0 cm in the United States. Nevertheless, biomechanical measures of the aneurysmal abdominal aorta have long been implicated in AAA risk of rupture. The purpose of this study is to assess whether other geometric characteristics, in addition to maximum diameter, may be highly correlated with the AAA peak wall stress (PWS). Using in-house segmentation and meshing algorithms, 30 patient-specific AAA models were generated for finite element analysis using an isotropic constitutive material for the AAA wall. PWS, evaluated as the spatial maximum of the first principal stress, was calculated at a systolic pressure of 120 mmHg. The models were also used to calculate 47 geometric indices characteristic of the aneurysm geometry. Statistical analyses were conducted using a feature reduction algorithm in which the 47 indices were reduced to 11 based on their statistical significance in differentiating the models in the population (p < 0.05). A subsequent discriminant analysis was performed and 7 of these indices were identified as having no error in discriminating the AAA models with a significant nonlinear regression correlation with PWS. These indices were: D-max (maximum diameter), T (tortuosity), DDr (maximum diameter to neck diameter ratio), S (wall surface area), K-median (median of the Gaussian surface curvature), C-max (maximum lumen compactness), and M-mode (mode of the Mean surface curvature). Therefore, these characteristics of an individual AAA geometry are the highest correlated with the most clinically relevant biomechanical parameter for rupture risk assessment. We conclude that the indices can serve as surrogates of PWS in lieu of a finite element modeling approach for AAA biomechanical evaluation. (C) 2018 IPEM. Published by Elsevier Ltd. All rights reserved.

A computational fluid dynamics (CFD) model representing the effect of wafters in a totally enclosed electric machine is presented, introducing the most relevant theoretical assumptions and simplifications. The validation of the model is conducted through experimental measurements. From the CFD simulation data, a second-order response surface is developed using statistical tools, from which the wafters' influence on the convective heat transfer from the stator end windings is predicted. Wafter design criteria are obtained from the response surface information. Finally, a specific case is analysed, showing through CFD simulations that temperatures in the machine are reduced by including wafters in the design.