Revistas
Revista:
JOURNAL OF VASCULAR AND INTERVENTIONAL RADIOLOGY
ISSN:
1051-0443
Año:
2023
Vol.:
34
N°:
1
Págs.:
21 - 22
Revista:
JOURNAL OF VASCULAR AND INTERVENTIONAL RADIOLOGY
ISSN:
1051-0443
Año:
2023
Vol.:
34
N°:
1
Págs.:
21 - 22
Revista:
INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING
ISSN:
2040-7939
Año:
2022
Vol.:
38
N°:
4
Págs.:
e3577
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.
Revista:
MATHEMATICS
ISSN:
2227-7390
Año:
2022
Vol.:
10
N°:
2
Págs.:
4280
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.
Autores:
Formoso, I. (Autor de correspondencia); Rivas, Alejandro; Beltrame, G.; et al.
Revista:
JOURNAL OF INDUSTRIAL TEXTILES
ISSN:
1528-0837
Año:
2022
Vol.:
51
N°:
3
Págs.:
3895S - 3922S
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
Autores:
Formoso, I. (Autor de correspondencia); Rivas, Alejandro; Beltrame, G.; et al.
Revista:
JOURNAL OF INDUSTRIAL TEXTILES
ISSN:
1528-0837
Año:
2022
Vol.:
51
N°:
3
Págs.:
3923S - 3948S
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
Revista:
EKAIA
ISSN:
0214-9001
Año:
2022
Vol.:
42
Págs.:
339 - 348
Erradioenbolizazioa (RE) gibeleko minbizia tratatzeko metodoetako bat da. Bertan, mikrokateter bidez gibeleko arterian mikroesfera erradioaktiboak injektatzen dira, hauek tumoreak enbolizazio eta erradiazio bidez erasotzeko. Mikroesferen ibilbidea ordenagailu bidezko fluido dinamika simulazioekin (CFD) aztertu daiteke. Kalkulu hauen iraupen luzea arazo bat da medikuntzaren egunerokotasunean simulazioak erabili ahal izateko. Kalkuluak azkartzeko asmoz, odolaren biskositatearen izaera ez¿newtondarra izaera newtondarrera sinplifikatu da. Emaitzek erakutsi dute mikroesferen banaketan eta odolaren hemodinamikan biskositate aldakorraren eragina mespretxagarria dela, odola fluido newtondar bezala aztertzearen sinplifikazioa ontzat emanez.
Revista:
CARDIOVASCULAR AND INTERVENTIONAL RADIOLOGY
ISSN:
0174-1551
Año:
2022
Vol.:
45
N°:
7
Págs.:
970 - 971
Revista:
SCIENTIFIC REPORTS
ISSN:
2045-2322
Año:
2021
Vol.:
11
N°:
1
Págs.:
3895
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.
Revista:
MATHEMATICS
ISSN:
2227-7390
Año:
2021
Vol.:
9
N°:
8
Págs.:
839
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.
Revista:
APPLIED SCIENCES
ISSN:
2076-3417
Año:
2021
Vol.:
11
N°:
5
Págs.:
1999
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.
Revista:
BIOLOGY
ISSN:
2079-7737
Año:
2021
Vol.:
10
N°:
12
Págs.:
1341
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.
Revista:
DYNA
ISSN:
0012-7361
Año:
2020
Vol.:
95
N°:
6
Págs.:
640 - 645
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.
Revista:
INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING
ISSN:
2040-7939
Año:
2020
Vol.:
36
N°:
6
Págs.:
e3337
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
Revista:
COMPUTER METHODS IN BIOMECHANICS AND BIOMEDICAL ENGINEERING
ISSN:
1025-5842
Año:
2019
Vol.:
22
N°:
5
Págs.:
518 - 532
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.
Autores:
Martin-Martin, L.; Gastelurrutia, J. (Autor de correspondencia); Larraona. Gorka S.; et al.
Revista:
APPLIED THERMAL ENGINEERING
ISSN:
1359-4311
Año:
2019
Vol.:
147
Págs.:
155 - 166
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.
Autores:
Urrutia, J. ; Roy, A.; Raut, S. S. ; et al.
Revista:
MEDICAL ENGINEERING AND PHYSICS
ISSN:
1350-4533
Año:
2018
Vol.:
59
Págs.:
43 - 49
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.
Revista:
INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING
ISSN:
2040-7939
Año:
2018
Vol.:
34
N°:
7
Págs.:
e2983
Revista:
JOURNAL OF BIOMECHANICS
ISSN:
0021-9290
Año:
2017
Vol.:
57
Págs.:
161 - 166
An Abdominal Aortic Aneurysm (AAA) is a permanent focal dilatation of the abdominal aorta at least 1.5 times its normal diameter. The criterion of maximum diameter is still used in clinical practice, although numerical studies have demonstrated the importance of biomechanical factors for rupture risk assessment. AAA phantoms could be used for experimental validation of the numerical studies and for pre intervention testing of endovascular grafts. We have applied multi-material 3D printing technology to manufacture idealized AAA phantoms with anisotropic mechanical behavior. Different composites were fabricated and the phantom specimens were characterized by biaxial tensile tests while using a constitutive model to fit the experimental data. One composite was chosen to manufacture the phantom based on having the same mechanical properties as those reported in the literature for human AAA tissue; the strain energy and anisotropic index were compared to make this choice. The materials for the matrix and fibers of the selected composite are, respectively, the digital materials FLX9940 and FLX9960 developed by Stratasys. The fiber proportion for the composite is equal to 0.15. The differences between the composite behavior and the AAA tissue are small, with a small difference in the strain energy (0.4%) and a maximum difference of 12.4% in the peak Green strain ratio. This work represents a step forward in the application of 3D printing technology for the manufacturing of AAA phantoms with anisotropic mechanical behavior. (C) 2017 Elsevier Ltd. All rights reserved.
Revista:
JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME
ISSN:
0148-0731
Año:
2017
Vol.:
139
N°:
1
An abdominal aortic aneurysm (AAA) is a permanent focal dilatation of the abdominal aorta of at least 1.5 times its normal diameter. Although the criterion of maximum diameter is still used in clinical practice to decide on a timely intervention, numerical studies have demonstrated the importance of other geometric factors. However, the major drawback of numerical studies is that they must be validated experimentally before clinical implementation. This work presents a new methodology to verify wall stress predicted from the numerical studies against the experimental testing. To this end, four AAA phantoms were manufactured using vacuum casting. The geometry of each phantom was subject to microcomputed tomography (lCT) scanning at zero and three other intraluminal pressures: 80, 100, and 120 mm Hg. A zero-pressure geometry algorithm was used to calculate the wall stress in the phantom, while the numerical wall stress was calculated with a finite-element analysis (FEA) solver based on the actual zero-pressure geometry subjected to 80, 100, and 120 mm Hg intraluminal pressure loading. Results demonstrate the moderate accuracy of this methodology with small relative differences in the average wall stress (1.14%). Additionally, the contribution of geometric factors to the wall stress distribution was statistically analyzed for the four phantoms. The results showed a significant correlation between wall thickness and mean curvature (MC) with wall stress.
Revista:
INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING
ISSN:
2040-7939
Liver radioembolization (RE) is a treatment option for patients with unresectable and chemorefractory primary and metastatic liver tumours. RE consists of intra-arterially administering via catheter radioactive microspheres that locally attack the tumours, sparing healthy tissue. Prior to RE, the standard practice is to conduct a treatment-mimicking pretreatment assessment via the infusion of Tc-99m-labelled macroaggregated albumin microparticles. The usefulness of this pretreatment has been debated in the literature, and thus, the aim of the present study is to shed light on this issue by numerically simulating the liver RE pretreatment and actual treatment particle-haemodynamics in a patient-specific hepatic artery under two different literature-based cancer scenarios and two different placements of a realistic end-hole microcatheter in the proper hepatic artery. The parameters that are analysed are the following: microagent quantity and size (accounting for RE pretreatment and treatment), catheter-tip position (near the proper hepatic artery bifurcation and away from it), and cancer burden (10% and 30% liver involvement). The conclusion that can be reached from the simulations is that when it comes to mimicking RE in terms of delivering particles to tumour-bearing segments, the catheter-tip position is much more important (because of the importance of local haemodynamic pattern alteration) than the infused microagents (i.e. quantity and size). Cancer burden is another important feature because the increase in blood flow rate to tumour-bearing segments increases the power to drag particles. These numerical simulation-based conclusions are in agreement with clinically observed events reported in the literature. Copyright (c) 2016 John Wiley & Sons, Ltd.
Revista:
JOURNAL OF MECHANICS IN MEDICINE AND BIOLOGY
ISSN:
0219-5194
Revista:
AEROSOL SCIENCE AND TECHNOLOGY
ISSN:
0278-6826
Año:
2017
Vol.:
51
N°:
2
Págs.:
168 - 177
Surfactant aerosol delivery in conjunction with a noninvasive respiratory support holds the potential to treat neonatal respiratory distress syndrome in a safe manner. The objective of the present study was to gain knowledge in order to optimize the geometry of an intracorporeal inhalation catheter and improve surfactant aerosol delivery effectiveness in neonates. Initially, a mathematical model capable of predicting the aerosol flow generated by this inhalation catheter within a physical model of the neonatal trachea was implemented and validated. Subsequently, a numerical study was performed to analyze the effect of the aerosol liquid droplet size and mass flow rate on surfactant delivery and on the required aerosolization time period. Experimental validation of the mathematical model showed a close prediction of the air axial velocity at the distal end of the physical model, with an absolute error between 0.01 and 0.15 m/s. Furthermore, an admissible absolute error between 0.2 and 2 mm was attained in the prediction of the aerosol mean aerodynamic diameter and mass median aerodynamic diameter in this region. The numerical study highlighted the beneficial effects of generating an intracorporeal aerosol with a mass median aerodynamic diameter higher than 4 mm and a surfactant mass flow rate above 8.93 mg/s in order to obtain effective surfactant delivery in neonates with minimal airway manipulation.
Revista:
JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME
ISSN:
0148-0731
Año:
2017
Vol.:
139
N°:
8
Págs.:
081006 - 081006-7
The maximum diameter (MD) criterion is the most important factor when predicting risk of rupture of abdominal aortic aneurysms (AAAs). An elevated wall stress has also been linked to a high risk of aneurysm rupture, yet is an uncommon clinical practice to compute AAA wall stress. The purpose of this study is to assess whether other characteristics of the AAA geometry are statistically correlated with wall stress. Using in-house segmentation and meshing algorithms, 30 patient-specific AAA models were generated for finite element analysis (FEA). These models were subsequently used to estimate wall stress and maximum diameter and to evaluate the spatial distributions of wall thickness, cross-sectional diameter, mean curvature, and Gaussian curvature. Data analysis consisted of statistical correlations of the aforementioned geometry metrics with wall stress for the 30 AAA inner and outer wall surfaces. In addition, a linear regression analysis was performed with all the AAA wall surfaces to quantify the relationship of the geometric indices with wall stress. These analyses indicated that while all the geometry metrics have statistically significant correlations with wall stress, the local mean curvature (LMC) exhibits the highest average Pearson's correlation coefficient for both inner and outer wall surfaces. The linear regression analysis revealed coefficients of determination for the outer and inner wall surfaces of 0.712 and 0.516, respectively, with LMC having the largest effect on the linear regression equation with wall stress. This work underscores the importance of evaluating AAA mean wall curvature as a potential surrogate for wall stress.
Revista:
INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING
ISSN:
2040-7939
Liver radioembolization is a promising treatment option for combating liver tumors. It is performed by placing a microcatheter in the hepatic artery and administering radiation-emitting microspheres through the arterial bloodstream so that they get lodged in the tumoral bed. In avoiding nontarget radiation, the standard practice is to conduct a pretreatment, in which the microcatheter location and injection velocity are decided. However, between pretreatment and actual treatment some of the parameters that influence the particle distribution in the liver can vary, resulting in radiation-induced complications. The present study aims to analyze the influence of a commercially available microcatheter with an angled tip and particle injection velocity in terms of segment-to-segment particle distribution. Specifically, four tip orientations and two injection velocities are combined to yield a set of eight numerical simulations of the particle-hemodynamics in a patient-specific truncated hepatic artery. For each simulation, four cardiac pulses are simulated. Particles are injected during the first cycle, and the remaining pulses enable the majority of the injected particles to exit the computational domain. Results indicate that, in terms of injection velocity, particles are more spread out in the cross-sectional lumen areas as the injection velocity increases. The tip's orientation also plays a role because it influences the near-tip hemodynamics, therefore altering the particle travel through the hepatic artery. However, results suggest that particle distribution tries to match the blood flow split, therefore particle injection velocity and microcatheter tip orientation playing a minor role in segment-to-segment particle distribution.
Revista:
BIOMEDICAL PHYSICS AND ENGINEERING EXPRESS
ISSN:
2057-1976
Año:
2016
Vol.:
2
N°:
1
Págs.:
015001
The analysis of the progression of cardiovascular diseases is an active area of ongoing research. This paper develops an image registration-based methodology to quantify the patient-specific local blood vessel shape variations that occur in the radial direction (i.e. expansion or shrinkage) over an imaging follow-up period, and an example is presented as proof of principle. The methodology can be used for complex vessels with bifurcations, and it is able to identify and address vessel deformations if changes in tortuosity or longitudinal direction are small. The methodology consists of (a) overlapping the baseline and follow-up vessel surfaces by matching the lumen centerline, (b) dividing the region of interest into slices perpendicular to the centerline and centering each slice, and (c) dividing each centered slice into sectors. The local approach consists of analyzing a representative point in each sector of each slice (i.e. each patch). In this paper the algorithm is applied to a patient-specific abdominal aortic aneurysm (AAA) as a proof of principle of the method. Six patient-specific image reconstructions from a single subject followed for 28 months are analyzed in pairs, yielding five time spans to which the algorithm was applied. The algorithm was able to quantify the AAA radial growth. The average AAA radial growths for the five case studies are ¿2.13 mm, 3.43 mm, ¿0.25 mm, 1.41 mm, and 0.84 mm, whereas the maximum local growths are 4.76 ± 0.15 mm, 9.30 ± 1.13 mm, 2.08 ± 0.05 mm, 4.10 ± 0.14 mm, and 4.16 ± 0.45 mm. The tolerance of the geometric local measurements is related to the matching processes (i.e. overlapping the geometries and centering each slice) because of the vessel deformation that took place over time. Thus, this methodology has been used to quantify the average AAA growth and the maximum local AAA growth (± the tolerance) as metrics of the vessel's radial growth.
Revista:
MEDICAL ENGINEERING AND PHYSICS
ISSN:
1350-4533
Año:
2016
Vol.:
38
N°:
12
Págs.:
1505 - 1512
An Abdominal Aortic Aneurysm (AAA) is a permanent focal dilatation of the abdominal aorta at least 1.5 times its normal diameter. The criterion of maximum diameter is still used in clinical practice, although numerical studies have demonstrated the importance of other biomechanical factors. Numerical studies, however, must be validated experimentally before they can be clinically implemented. We have developed a methodology for manufacturing anisotropic AAA replicas with non-uniform wall thickness. Different composites were fabricated and tested, and one was selected in order to manufacture a phantom with the same properties. The composites and the phantom were characterized by biaxial tensile tests and a material model was fit to the experimental data. The experimental results were compared with data from the literature, and similar responses were obtained. The anisotropic AAA replicas with non-uniform wall thickness can be used in benchtop experiments to validate deformations obtained with numerical simulations or for pre-intervention testing of endovascular grafts. This is a significant step forward considering the importance of anisotropy in numerical simulations.
Revista:
JOURNAL OF BIOMECHANICS
ISSN:
0021-9290
Año:
2016
Vol.:
49
N°:
15
Págs.:
3705 - 3713
Radioembolization, which consist of the implantation of radioactive microspheres via intra-arterially placed microcatheter, is a safe and effective treatment for liver cancer. Nevertheless, radioembolization-related complications and side effects may arise, which are an active area of ongoing research. The catheter design has been claimed as an option in reducing these complications. In this paper, the influence of catheter type and location are investigated. The study was undertaken by numerically simulating the particle¿hemodynamics in a patient-specific hepatic artery during liver radioembolization. The parameters modified were cancer scenario (30% liver involvement in the right lobe, `scenario A¿, and in both lobes, `scenario B¿), catheter type (standard end-hole microcatheter, SMC, and antireflux catheter, ARC), and the location of the tip in the proper hepatic artery (in the straight part, `inlet¿, and near the bifurcation, `bifurcation¿). Comparing ARC with SMC, the maximum and average (over segments) absolute difference in the percentage of particles that reached each segment were 19.62% and 9.06% when injecting near the inlet for scenario A; 3.54% and 1.07% injecting near the bifurcation for scenario A; and 18.31% and 11.85% injecting near the inlet for scenario B. It seems, therefore, that the location of the catheter tip in the artery is crucial in terms of particle distribution. Moreover, even though the near-tip blood flow was altered due to the presence of a catheter, the particle distribution matched the flow split if the distance between the injection point and the first bifurcation encountered enabled the alignment of particles with blood flow.
Revista:
INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING
ISSN:
2040-7939
Año:
2016
Vol.:
32
N°:
11
Págs.:
e02764
Some of the latest treatments for unresectable liver malignancies (primary or metastatic tumours), which include bland embolisation, chemoembolisation, and radioembolisation, among others, take advantage of the increased arterial blood supply to the tumours to locally attack them. A better understanding of the factors that influence this transport may help improve the therapeutic procedures by taking advantage of flow patterns or by designing catheters and infusion systems that result in the injected beads having increased access to the tumour vasculature. Computational analyses may help understand the haemodynamic patterns and embolic-microsphere transport through the hepatic arteries. In addition, physiological inflow and outflow boundary conditions are essential in order to reliably represent the blood flow through arteries. This study presents a liver cancer arterial perfusion model based on a literature review and derives boundary conditions for tumour-bearing liver-feeding hepatic arteries based on the arterial perfusion characteristics of normal and tumorous liver segment tissue masses and the hepatic artery branching configuration. Literature-based healthy and tumour-bearing realistic scenarios are created and haemodynamically analysed for the same patient-specific hepatic artery. As a result, this study provides boundary conditions for computational fluid dynamics simulations that will allow researchers to numerically study, for example, various intravascular devices
Revista:
JOURNAL OF BIOMECHANICS
ISSN:
0021-9290
Año:
2016
Vol.:
49
N°:
15
Págs.:
3714 - 3721
Liver radioembolization is a treatment option for patients with primary and secondary liver cancer. The procedure consists of injecting radiation-emitting microspheres via an intra-arterially placed microcatheter, enabling the deposition of the microspheres in the tumoral bed. The microcatheter location and the particle injection rate are determined during a pretreatment work-up. The purpose of this study was to numerically study the effects of the injection characteristics during the first stage of microsphere travel through the bloodstream in a patient-specific hepatic artery (i.e., the near-tip particle¿hemodynamics and the segment-to-segment particle distribution). Specifically, the influence of the distal direction of an end-hole microcatheter and particle injection point and velocity were analyzed. Results showed that the procedure targeted the right lobe when injecting from two of the three injection points under study and the remaining injection point primarily targeted the left lobe. Changes in microcatheter direction and injection velocity resulted in an absolute difference in exiting particle percentage for a given liver segment of up to 20% and 30%, respectively. It can be concluded that even though microcatheter placement is presumably reproduced in the treatment session relative to the pretreatment angiography, the treatment may result in undesired segment-to-segment particle distribution and therefore undesired treatment outcomes due to modifications of any of the parameters studied, i.e., microcatheter direction and particle injection point and velocity.
Revista:
INTERNATIONAL JOURNAL OF ENGINEERING EDUCATION
ISSN:
0949-149X
Año:
2015
Vol.:
31
N°:
1
Págs.:
209 - 219
Formula Student (also known as Formula SAE) is an international competition for universities that challenges the students with a comprehensive engineering problem. Most of the participant universities and all the companies involved in the organization of the competition have identified this event as the most suitable tool for hard and soft skills development. This paper evaluates this development by means of two different objective assessments in the frame of a specific team, identifying the potential of the competition and showing a particular approach to enhance soft skills development.
Autores:
Antón, R; Chen, C.-Y.; Hung, M.-Y.; et al.
Revista:
COMPUTER METHODS IN BIOMECHANICS AND BIOMEDICAL ENGINEERING
ISSN:
1025-5842
Año:
2015
Vol.:
18
N°:
9
Págs.:
981 - 992
The objective of the present manuscript is three-fold: (i) to study the detailed pressure field inside a patient-specific abdominal aortic aneurysm (AAA) model experimentally and numerically and discuss its clinical relevance, (ii) to validate a number of possible numerical model options and their ability to predict the experimental pressure field and (iii) to compare the spatial pressure drop in the AAA before and after the formation of intraluminal thrombus (ILT) for a late disease development timeline. A finite volume method was used to solve the governing equations of fluid flow to simulate the flow dynamics in a numerical model of the AAA. Following our patient-specific anatomical rapid prototyping technique, physical models of the aneurysm were created with seven ports for pressure measurement along the blood flow path. A flow loop operating with a blood analogue fluid was used to replicate the patient-specific flow conditions, acquired with phase-contrast magnetic resonance imaging, and measure pressure in the flow model. The Navier-Stokes equations and two turbulent models were implemented numerically to compare the pressure estimations with experimental measurements. The relative pressure difference from experiments obtained with the best performing model (unsteady laminar simulation) was ~1.1% for the AAA model without ILT and ~15.4% for the AAA model with ILT (using Reynolds Stress Model). Future investigations should include validation of the 3D velocity field and wall shear stresses within the AAA sac predicted by the three numerical models.
Revista:
INTERNATIONAL JOURNAL OF ENGINEERING EDUCATION
ISSN:
0949-149X
Año:
2015
Vol.:
31
N°:
5
Págs.:
1299 - 1308
This paper presents what we call the Multiple Approach Experimental Project (MAEP), a project based on the model-building approach to learning. The MAEP complements theoretical lectures by placing students in a real situation where they design and build a physical structure. A total of 65 students divided into 24 teams voluntarily took part in the competition. Assessments from students who participated in the MAEP along with assessments from the instructors who implemented it are presented. Results show that the MAEP was welcomed and that the objective of engaging students in the subject was met.
Revista:
PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART H-JOURNAL OF ENGINEERING IN MEDICINE
ISSN:
0954-4119
Año:
2015
Vol.:
229
N°:
4
Págs.:
291 - 306
Physiological outflow boundary conditions are necessary to carry out computational fluid dynamics simulations that reliably represent the blood flow through arteries. When dealing with complex three-dimensional trees of small arteries, and therefore with multiple outlets, the robustness and speed of convergence are also important. This study derives physiological outflow boundary conditions for cases in which the physiological values at those outlets are not known (neither in vivo measurements nor literature-based values are available) and in which the tree exhibits symmetry to some extent. The inputs of the methodology are the three-dimensional domain and the flow rate waveform and the systolic and diastolic pressures at the inlet. The derived physiological outflow boundary conditions, which are a physiological pressure waveform for each outlet, are based on the results of a zero-dimensional model simulation. The methodology assumes symmetrical branching and is able to tackle the flow distribution problem when the domain outlets are at branches with a different number of upstream bifurcations. The methodology is applied to a group of patient-specific arteries in the liver. The methodology is considered to be valid because the pulsatile computational fluid dynamics simulation with the inflow flow rate waveform (input of the methodology) and the derived outflow boundary conditions lead to physiological results, that is, the resulting systolic and diastolic pressures at the inlet match the inputs of the methodology, and the flow split is also physiological.
Revista:
INGENIERIA E INVESTIGACION
ISSN:
0120-5609
Año:
2015
Vol.:
35
N°:
3
Págs.:
115 - 120
This paper presents a change made to the lecturing approach used within a specific course. The new lecturing approach is based on a non-linear structure where each lesson combines concepts from different topics, in contrast to the traditional linear structure in which each topic is treated separately. The objective of the non-linear approach is to increase student dynamism and motivation and to foster teacher-student dialog. Assessments from students who were taught according to the traditional linear structure along with assessments from students who were taught under both the linear and non-linear approaches are presented. Results show that the non-linear lecturing approach was welcomed and led to a higher degree of student dynamism and motivation and to more tea-cher-student dialog.
Autores:
Chen, C.-Y.; Antón, R; Hung, M.-Y.; et al.
Revista:
JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME
ISSN:
0148-0731
Año:
2014
Vol.:
136
N°:
3
Págs.:
031001 - 031001-9
Autores:
Goikoetxea, E.; Murgia, X.; Serna-Grande, P.; et al.
Revista:
PLOS ONE
ISSN:
1932-6203
Objective: Aerosol delivery holds potential to release surfactant or perfluorocarbon (PFC) to the lungs of neonates with respiratory distress syndrome with minimal airway manipulation. Nevertheless, lung deposition in neonates tends to be very low due to extremely low lung volumes, narrow airways and high respiratory rates. In the present study, the feasibility of enhancing lung deposition by intracorporeal delivery of aerosols was investigated using a physical model of neonatal conducting airways. Methods: The main characteristics of the surfactant and PFC aerosols produced by a nebulization system, including the distal air pressure and air flow rate, liquid flow rate and mass median aerodynamic diameter (MMAD), were measured at different driving pressures (4-7 bar). Then, a three-dimensional model of the upper conducting airways of a neonate was manufactured by rapid prototyping and a deposition study was conducted. Results: The nebulization system produced relatively large amounts of aerosol ranging between 0.3 +/- 0.0 ml/min for surfactant at a driving pressure of 4 bar, and 2.0 +/- 0.1 ml/min for distilled water (H(2)Od) at 6 bar, with MMADs between 2.61 +/- 0.1 mu m for PFD at 7 bar and 10.18 +/- 0.4 mu m for FC-75 at 6 bar. The deposition study showed that for surfactant and H(2)Od aerosols, the highest percentage of the aerosolized mass (similar to 65%) was collected beyond the third generation of branching in the airway model. The use of this delivery system in combination with continuous positive airway pressure set at 5 cmH(2)O only increased total airway pressure by 1.59 cmH(2)O at the highest driving pressure (7 bar). Conclusion: This aerosol generating system has the potential to deliver relatively large amounts of surfactant and PFC beyond the third generation of branching in a neonatal airway model with minimal alteration of pre-set respiratory support.
Revista:
ENGINEERING APPLICATIONS OF COMPUTATIONAL FLUID MECHANICS
ISSN:
1994-2060
Año:
2014
Vol.:
8
N°:
4
Págs.:
623 - 638
A perforated plate placed downstream of an axial fan in order to avoid electromagnetic interferences (push cooling) is a common assembly in electronic systems. Because of the swirling component that the flow approaching the screen has, there is no accuracy in knowing how the screen affects the flow pattern downstream of the screen and the pressure drop through the screen. Since cooling capacity is related to velocity, the placement of the components downstream of the screen will be related to the velocity magnitude. Thus, properly predicting the flow pattern is highly important, and the results of this work may serve a good guideline for thermal designers to surmount this challenge. In order to establish how the screen affects the flow pattern, a parametric study is carried out. This study is performed by a central composite face-centered (CCF) Design of Experiment (DoE), which demanded 81 Computational Fluid Dynamics (CFD) simulations and for which the Reynolds Stress Transport Model was used as a turbulence model. Thanks to the numerical results, the influence that different operational and geometrical parameters have on the flow pattern downstream of a screen and on the total pressure drop is analyzed. The swirl that the flow has at the inlet is found to be related to the screen's capacity to homogenize the flow downstream of the screen, as its thickness plays an important role in the flow's tangential component destruction. The main effects of the parameters and the interactions between them are shown. At the same time, through DoE techniques, different reduced models that predict how the flow pattern changes because of the screen are presented as useful tools for thermal designers.
Revista:
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
ISSN:
0142-727X
Año:
2014
Vol.:
46
Págs.:
43 - 60
A perforated plate placed behind an axial fan (push cooling) is a common assembly in electronic systems. The flow approaching the screen will have a swirling component, and therefore, there is uncertainty in the prediction of the flow pattern at the outlet of the screen and the pressure drop through the screen. Correctly predicting the flow field is important in order to properly place the electronic components. This work tries to give some insight into these issues. A wind tunnel was manufactured in order to produce the typical flow field at the outlet of an axial fan and to measure the field at the inlet and at the outlet of the perforated plate using the Particle Image Velocimety (PIV) technique; the pressure drop through the screen was also measured. The velocity contours measured at the screen inlet were used as boundary conditions for computational fluid dynamics (CFD) simulations. Several turbulence models (k-epsilon, k-omega and RSTM) and their variations were used for the simulations and the results at the outlet of the perforated plate are compared with the Particle Image Velocimetry results. Two screens with very different geometrical characteristics were used. Results show that if k-e models are used a significant error is made in the prediction of the velocity field and in the pressure drop. Although the k-omega models predicted better than the k-e models, the RSTM were shown to be the most reliable. (C) 2014 Elsevier Inc. All rights reserved.
Autores:
Antón, R; Ayala,Gabriel; Mouzo, Francisco; et al.
Revista:
INTERNATIONAL JOURNAL OF ENGINEERING EDUCATION
ISSN:
0949-149X
Año:
2014
Vol.:
30
N°:
2
Págs.:
495 - 504
Revista:
APPLIED THERMAL ENGINEERING
ISSN:
1359-4311
Año:
2014
Vol.:
62
N°:
1
Págs.:
215 - 228
An algebraic thermal zonal model of the ventilation of underground transformer substations during a standardised temperature rise test is presented in this paper. The development and adjustment of the proposed model rely on the analysis of the air flow pattern and temperature distributions obtained by a more complex model numerically solved by means of CFD techniques. The flow domain of the model represents a section of the substations divided into several interrelated zones where the mass and the energy conservation equations are formulated and the generated system of nonlinear algebraic equations is solved. The model is validated by comparing its results with the ones obtained by the CFD model and with the experimental results of eight temperature rise tests under different conditions. A parametric analysis was carried out on the model to prove its utility as an efficient tool to improve and optimise the thermal performance of transformer substations during the design process. From the parametric study it has been inferred that the main parameters affecting the ventilation of the substations are the pass area between the LV-MV zone and the transformer zone, the surface area of the ventilation grilles in the substation with horizontal ventilation, and the perimeter of the protruding ventilation vents in the substation with vertical ventilation. (c) 2013 Elsevier Ltd. All rights reserved.
Revista:
JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME
ISSN:
0148-0731
Año:
2013
Vol.:
136
N°:
1
Págs.:
014502 - 014502-5
The goal of this work is to develop a framework for manufacturing nonuniform wall thickness replicas of abdominal aortic aneurysms (AAAs). The methodology was based on the use of computed tomography (CT) images for virtual modeling, additive manufacturing for the initial physical replica, and a vacuum casting process and range of polyurethane resins for the final rubberlike phantom. The average wall thickness of the resulting AAA phantom was compared with the average thickness of the corresponding patient-specific virtual model, obtaining an average dimensional mismatch of 180 lm (11.14%). The material characterization of the artery was determined from uniaxial tensile tests as various combinations of polyurethane resins were chosen due to their similarity with ex vivo AAA mechanical behavior in the physiological stress configuration. The proposed methodology yields AAA phantoms with nonuniform wall thickness using a fast and low-cost process. These replicas may be used in benchtop experiments to validate deformations obtained with numerical simulations using finite element analysis, or to validate optical methods developed to image ex vivo arterial deformations during pressure-inflation testing.
Revista:
APPLIED THERMAL ENGINEERING
ISSN:
1359-4311
Año:
2013
Vol.:
52
N°:
2
Págs.:
428 - 438
A parametric study based on design of experiments (DoE) techniques was carried out by computational simulation in order to evaluate the effect that design parameters have on heat transfer and pressure loss of an impinging jet in a cross-flow configuration. The main effects of each parameter and the interactions between parameters were analyzed in detail through the Response Surface Methodology (RSM). Additionally, the potential of the impinging jet in a cross-flow configuration was assessed by calculating the optimal values of the parameters and comparing the cooling efficiency of the resulting configuration with the efficiency of the conventional cross-flow configuration. It was found that the degree to which the average heat transfer coefficient is enhanced as the result of adding an impinging jet depends on the height of the cooled component. Specifically, it was found that the higher the component, the more significant the enhancement. (C) 2013 Elsevier Ltd. All rights reserved.
Revista:
EXPERIMENTAL THERMAL AND FLUID SCIENCE
ISSN:
0894-1777
Año:
2013
Vol.:
50
Págs.:
127 - 138
Spray cooling experiments were performed to study the effect of the spray cone angle on heat transfer and film thickness. The experiments were carried out for three different types of nozzles. Results for heat transfer and film thickness for different flow rates are presented working with the dielectric refrigerant R134a and on a heater with low surface roughness. The behavior of the heat transfer with respect to the spray cone angle shows that as the spray cone angle decreases, there is a delay in the onset of the nucleated boiling regime. As a result, thermal performance worsens as the spray cone angle decreases. On the other hand, in the nucleate boiling regime film thickness increases as the spray cone angle decreases. The qualitative analysis of these variations serves to better understand the heat transfer mechanisms that occur during the spray cooling technique. (c) 2013 Elsevier Inc. All rights reserved.
Revista:
EUROPEAN RESPIRATORY JOURNAL
ISSN:
0903-1936
Año:
2013
Vol.:
42
N°:
57
Págs.:
2062
Background: Aerosolized surfactant is a promising technique to treat neonatal Respiratory Distress Syndrome (RDS). However, aerosol delivery to neonates is complex and few studies have addressed its feasibility in vitro.
Methods: A computer-design of an infant airway model was drawn in CAD, and 3D pieces were printed by means of rapid prototyping. Natural surfactant aerosols were produced by a pneumatically-driven intratracheal inhalation catheter (driving pressure range 4-6bar). Characterization of surfactant aerosols (particle size and distribution) was performed using Time of Flight technology. Further, deposition of surfactant aerosols within the thermoplastic model of the upper airways was measured.
Results: The printed neonatal tracheobronchial airway model successfully passed the quality control. Maximum surfactant aerosol production rate was achieved at 6bar (0.39±0.01ml/min; 31.54±0.52mg/min). Although a high percentage of deposition of the aerosolized mass (between 23.75±6.45% 4bar and 26.48±11.43% 6bar) was deposited within the printed model, the highest percentage of mass (between 64.95±7.40% 4bar and 66.43±11.46% 6bar) was measured beyond the distal exit of the model. The Mass Median Aerodynamic Diameter (MMAD) ranged between 8.52±0.16µm (6bar) and 9.36±0.35µm (4bar); higher MMAD values (13.26±3.41µm) where measured at the exit of the printed model.
Conclusion: Surfactant aerosolization seems to be feasible and holds potential as a treatment for RDS; however, further research is needed to adapt current technology to the requirements of the neonatal population.
Revista:
EXPERIMENTAL THERMAL AND FLUID SCIENCE
ISSN:
0894-1777
Año:
2013
Vol.:
46
Págs.:
183 - 190
Experimental measurements in a spray cooling test rig were carried out for two different heater surface roughnesses and for two different types of nozzles with the dielectric refrigerant R134a. In this paper, results of the heat transfer measurements are presented. The analysis of the results explains the influence of the volumetric flow rate, the surface roughness and the type of nozzle (through the spray parameters) on the spray cooling boiling curve, on the Nusselt number and on the efficiency. It has been found that the effect of a smooth roughness is to delay the onset of the nucleate boiling, but once this regime has started, boiling is so fast that the CHF (Critical Heat Flux) is reached at lower heater temperatures and lower heat fluxes. In a companion paper the sprayed refrigerant film thickness measurements and its relation with the heat transfer measurements are presented. (C) 2012 Elsevier Inc. All rights reserved.
Revista:
EXPERIMENTAL THERMAL AND FLUID SCIENCE
ISSN:
0894-1777
Año:
2013
Vol.:
48
Págs.:
73 - 80
Experimental measurements in a spray cooling test rig were carried out for two different heater surface roughnesses and for two different types of nozzles with the dielectric refrigerant R134a. In this paper, results of the sprayed refrigerant film thickness measurements are presented. The influence of the volumetric flow rate, the surface roughness and the type of nozzle (through the spray parameters) on the total average film thickness is analyzed and discussed. In a companion paper, results of the heat transfer measurements are presented. It has been found that there is a relation between the variations of the average Nusselt number and of the film thickness along the spray cooling boiling curve. The heat transfer regimes along that curve are related not only to a variation in the average Nusselt number but also to changes in the film thickness. The qualitative analysis of those variations served to better understand the heat transfer mechanisms occurring during the spray cooling. (C) 2013 Elsevier Inc. All rights reserved.
Revista:
APPLIED THERMAL ENGINEERING
ISSN:
1359-4311
Año:
2013
Vol.:
51
N°:
1-2
Págs.:
852 - 863
Ventilation by natural convection of two underground transformer substations has been numerically modelled. The model has been verified in terms of discretization errors and it has been validated with the experimental results of eight temperature rise tests carried out under different conditions of ventilation and transformer power losses. The results of the simulations serve to analyse the air flow pattern and the air temperature distributions inside the substation. A correlation for the air mass flow rate as a function of the ventilation conditions (discharge coefficient and area of the grilles) and the heat dissipated by the transformer has been fitted. The heat transfer coefficients on the surfaces of the transformer and the walls of the enclosure can also be obtained from the simulations of the model. All this information will be used in a future paper to develop a zonal thermal model of the ventilation of the substations that can be employed as a design and optimisation tool. (C) 2012 Elsevier Ltd. All rights reserved.
Revista:
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
ISSN:
0142-727X
Año:
2012
Vol.:
38
Págs.:
50 - 71
The air flow around a cubic obstacle mounted on one wall of a rectangular channel was studied experimentally. The obstacle represents an electronic component and the channel the space between two parallel printed circuit boards (PCBs). The flow was produced by the combination of a channel stream and a jet which issued from a circular nozzle placed at the wall opposite from where the component is mounted. With this aim, a test rig was designed and built to carry out experiments with both the above mentioned configurations and other cooling arrangements. Planar Particle Image Velocimetry (PIV) was employed to measure the instantaneous flow velocity on several planes covering the space around the component. The mean velocity and the Reynolds stresses were obtained from averaging the instantaneous velocity, and the mean flow showed a complex pattern with different features such as recirculation bubbles, vortices, detachment and reattachment zones. The influence of two parameters, namely the channel Reynolds number and the jet-to-channel Reynolds number ratio, on these flow features was studied considering nine cases that combined three values of the channel Reynolds number (3410, 5752 and 8880) and three values of the ratio (0.5, 1.0 and 1.5). The results show that the Reynolds number ratio determines the drag produced on the jet and the deflection from its geometric axis due to the channel stream. In all the cases corresponding to the lowest value of the ratio, the jet was dragged and did not impact the component. This fact accounts for the non-existence of the Upper Horseshoe Vortex and changes in the flow characteristics at the region over the component. (C) 2012 Elsevier Inc. All rights reserved.
Revista:
ATOMIZATION AND SPRAYS
ISSN:
1044-5110
Año:
2012
Vol.:
22
N°:
9
Págs.:
733 - 755
This paper presents a combined experimental and theoretical investigation of the disintegration of fan-shaped liquid sheets produced by industrial fan-spray atomizers. The disintegration regimes observed for different geometries and operating conditions are described, proving the paramount role of nozzle flow on the final characteristics of the spray produced. The concept of breakup length is redefined to account for the stochastic nature of liquid stream disintegration. An analogy is established between the breakup of a liquid sheet dominated by the wave mode and a radial sheet, obtaining good agreement with the experiments. However, in those cases where several disintegration regimes coexist, the breakup length cannot be given by an analytical expression. Finally, the influence of the disintegration regime on both the droplet size and the spatial distribution of the droplets is investigated, confirming the strong influence of rim breakup.
Revista:
JOURNAL OF ELECTRONIC PACKAGING
ISSN:
1043-7398
Año:
2012
Vol.:
134
N°:
1
Págs.:
011004 - 011004-8.
The performance of axial fans in close proximity to the electromagnetic compatibility (EMC) screens was analyzed by means of an experimental parametric study. The following geometrical parameters were studied: the hub-to-tip ratio, the ratio between fan thickness and fan diameter, the porosity and thickness of the perforated plate, and finally, the distance between the perforated plate and the inlet and the outlet of the fan. Screen porosity was found to be the most important parameter. Fan performance degradation is expressed by means of two correlations: one for the deterioration in the fan pressure at the no-flow point and the other for the flow rate reduction at the free delivery point. Both correlations were formulated as functions of screen porosity and the distance between the fan and the screen. We believe that the correlations can serve as a good guide for correct fan placement in a telecommunications cabinet. [DOI: 10.1115/1.4005913]
Revista:
JOURNAL OF ELECTRONIC PACKAGING
ISSN:
1043-7398
Año:
2011
Vol.:
133
N°:
1
Págs.:
011002-1 - 011002-11
Experimental measurements in a spray cooling test rig have been carried out for several heat fluxes in the heater and different spray volumetric fluxes with the dielectric refrigerant R134a. Results of the heat transfer and the sprayed refrigerant film thickness measurements are presented. The film thickness measurements have been made with a high speed camera equipped with a long distance microscope. It has been found that there is a relation between the variation in the average Nusselt number and the film thickness along the spray cooling boiling curve. The heat transfer regimes along that curve are related not only with a variation in the average Nusselt number but also with changes in the film thickness. The qualitative analysis of those variations has served to understand better the heat transfer mechanisms occurring during the spray cooling. [DOI: 10.1115/1.4001857]
Revista:
INTERNATIONAL JOURNAL OF ENGINEERING EDUCATION
ISSN:
0949-149X
Año:
2011
Vol.:
27
N°:
4
Págs.:
805 - 812
A Multiple Approach Competing Practical Exercise (MACPE), is an open exercise that confronts a group of students with a practical engineering problem using their own resources and choosing among multiple approaches in a competing environment. A case study with a teacher's assessment and a student's assessment has shown that this sort of exercise is able to motivate the students' learning process. It has also been found that it is a fun way to foster team work and constitutes an open door to innovation.
Revista:
PHYSICS OF FLUIDS
ISSN:
1070-6631
Año:
2010
Vol.:
22
N°:
7
Págs.:
074103-01 - 074103-11
The present paper focuses on the linear spatial instability of a viscous two-dimensional liquid sheet bounded by two identical viscous gas streams. The Orr-Sommerfeld differential equations and the boundary conditions of the flow configuration are numerically solved using Chebyshev series expansions and the collocation method. The strong dependence of the instability parameters on the velocity profiles is proven by using both quadratic and error functions to define the base flow in the liquid sheet and the gas shear layer. The sensitivity of the spatial instability growth rate to changes in the dimensionless parameters of the problem is assessed. Regarding the liquid sheet Reynolds number, it has been observed that, when this parameter increases, both the most unstable growth rate and the corresponding wavenumber decrease, whereas the cutoff wavenumber increases. The results of this analysis are compared with temporal theory through Caster transformation. The effects liquid and gas viscosity have on instability are studied by comparing the instability curves given by the presented model with those from an inviscid liquid sheet and a viscous liquid sheet in an inviscid gaseous medium. The model presented in this paper features a variation in the cutoff wavenumber with all the governing parameters of the problem, whereas that provided by cases that account for an inviscid surrounding gas depends only on the liquid sheet Weber number and the ratio of gas to liquid densities. Results provided by the presented model have been experimentally validated and show that quadratic profiles have a greater capacity to predict the disturbance wavelength. (C) 2010 American Institute of Physics. [doi:10.1063/1.3460348]
