Nuestros investigadores

Raúl Antón Remírez

Departamento
Líneas de investigación
Mecánica de Fluidos, Biofluídica, Electronics cooling
Índice H
6, (WoS, 03/09/2017)
10, (Google Scholar, 01/09/2017)

Publicaciones científicas más recientes (desde 2010)

Autores: Goikoetxea, E., ; Rivas Nieto, Alejandro; Murgia, X. , ; et al.
Revista: AEROSOL SCIENCE AND TECHNOLOGY
ISSN 0278-6826  Vol. 51  Nº 2  2017  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.
Autores: Aramburu Montenegro, Jorge; Antón Remírez, Raúl; Rivas Nieto, Alejandro; et al.
Revista: INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING
ISSN 2040-7939  2017  págs. e02895
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.
Autores: Ruiz de Galarreta Moriones, Sergio; Cazón Martín, Aitor; Antón Remírez, Raúl; et al.
Revista: JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME
ISSN 0148-0731  Vol. 139  Nº 1  2017 
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.
Autores: Ruiz de Galarreta Moriones, Sergio; Antón Remírez, Raúl; Cazón Martín, Aitor; et al.
Revista: JOURNAL OF BIOMECHANICS
ISSN 0021-9290  Vol. 57  2017  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.
Autores: Ruiz de Galarreta Moriones, Sergio; Cazón Martín, Aitor; Antón Remírez, Raúl; et al.
Revista: JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME
ISSN 0148-0731  Vol. 139  Nº 8  2017  págs. 081006 - 081006-7
Autores: Aramburu Montenegro, Jorge; Antón Remírez, Raúl; Rivas Nieto, Alejandro; et al.
Revista: INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING
ISSN 2040-7939  Vol. 33  Nº 2  2017 
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.
Autores: Aramburu Montenegro, Jorge; Antón Remírez, Raúl; Rivas Nieto, Alejandro; et al.
Revista: JOURNAL OF BIOMECHANICS
ISSN 0021-9290  Vol. 49   Nº 15   2016  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.
Autores: Aramburu Montenegro, Jorge; Antón Remírez, Raúl; Borro Yagüez, Diego; et al.
Revista: BIOMEDICAL PHYSICS AND ENGINEERING EXPRESS
ISSN 2057-1976  Vol. 2  Nº 1  2016  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.
Autores: Aramburu Montenegro, Jorge; Antón Remírez, Raúl; Rivas Nieto, Alejandro; et al.
Revista: JOURNAL OF BIOMECHANICS
ISSN 0021-9290  Vol. 49  Nº 15  2016  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.
Autores: Ruiz de Galarreta Moriones, Sergio; Antón Remírez, Raúl; Cazón Martín, Aitor; et al.
Revista: MEDICAL ENGINEERING AND PHYSICS
ISSN 1350-4533  Vol. 38  Nº 12  2016  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.
Autores: Aramburu Montenegro, Jorge; Antón Remírez, Raúl; Rivas Nieto, Alejandro; et al.
Revista: JOURNAL OF BIOMECHANICS
ISSN 0021-9290  Vol. 49   Nº 15   2016  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.
Autores: Aramburu Montenegro, Jorge; Antón Remírez, Raúl; Rivas Nieto, Alejandro; et al.
Revista: INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING
ISSN 2040-7939  Vol. 32  Nº 11  2016  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
Autores: Pradera Mallabiabarrena, Ainara; Merideño Labayen, Iñaki; López de Arancibia, Aitziber; et al.
Revista: INTERNATIONAL JOURNAL OF ENGINEERING EDUCATION
ISSN 0949-149X  Vol. 31  Nº 5  2015  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.
Autores: González Prada, Jorge; López de Sabando, A., ; Antón Remírez, Raúl; et al.
Revista: INTERNATIONAL JOURNAL OF ENGINEERING EDUCATION
ISSN 0949-149X  Vol. 31  Nº 1  2015  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: Merideño Labayen, Iñaki; Antón Remírez, Raúl; González Prada, Jorge
Revista: INGENIERIA E INVESTIGACION
ISSN 0120-5609  Vol. 35  Nº 3  2015  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: Aramburu Montenegro, Jorge; Antón Remírez, Raúl; Bernal, N., ; et al.
Revista: PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART H-JOURNAL OF ENGINEERING IN MEDICINE
ISSN 0954-4119  Vol. 229  Nº 4  2015  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.
Autores: Antón Remírez, Raúl; Chen, C.-Y., ; Hung, M.-Y., ; et al.
Revista: COMPUTER METHODS IN BIOMECHANICS AND BIOMEDICAL ENGINEERING
ISSN 1025-5842  Vol. 18  Nº 9  2015  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.
Autores: Goikoetxea, E., ; Murgia, X., ; Serna-Grande, P., ; et al.
Revista: PLOS ONE
ISSN 1932-6203  Vol. 9  Nº 9  2014 
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.
Autores: Bengoechea García, Asier; Antón Remírez, Raúl; Sánchez Larraona, Gorka; et al.
Revista: INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
ISSN 0142-727X  Vol. 46  2014  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: Bengoechea García, Asier; Antón Remírez, Raúl; Sánchez Larraona, Gorka; et al.
Revista: ENGINEERING APPLICATIONS OF COMPUTATIONAL FLUID MECHANICS
ISSN 1994-2060  Vol. 8  Nº 4  2014  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.
Autores: Chen, C.-Y., ; Antón Remírez, Raúl; Hung, M.-Y., ; et al.
Revista: JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME
ISSN 0148-0731  Vol. 136  Nº 3  2014  págs. 031001 - 031001-9
Autores: Antón Remírez, Raúl; Ayala, Gabriel; Mouzo, Francisco; et al.
Revista: INTERNATIONAL JOURNAL OF ENGINEERING EDUCATION
ISSN 0949-149X  Vol. 30  Nº 2  2014  págs. 495 - 504
Autores: Beiza Silva, Maximiliano Patricio; Ramos González, Juan Carlos; Rivas Nieto, Alejandro; et al.
Revista: APPLIED THERMAL ENGINEERING
ISSN 1359-4311  Vol. 62  Nº 1  2014  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.
Autores: Martínez Galván, Eduardo; Ramos González, Juan Carlos; Antón Remírez, Raúl; et al.
Revista: EXPERIMENTAL THERMAL AND FLUID SCIENCE
ISSN 0894-1777  Vol. 48  2013  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.
Autores: Martínez Galván, Eduardo; Antón Remírez, Raúl; Ramos González, Juan Carlos; et al.
Revista: EXPERIMENTAL THERMAL AND FLUID SCIENCE
ISSN 0894-1777  Vol. 50  2013  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.
Autores: Martínez Galván, Eduardo; Antón Remírez, Raúl; Ramos González, Juan Carlos; et al.
Revista: EXPERIMENTAL THERMAL AND FLUID SCIENCE
ISSN 0894-1777  Vol. 46  2013  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.
Autores: Sánchez Larraona, Gorka; Rivas Nieto, Alejandro; Antón Remírez, Raúl; et al.
Revista: APPLIED THERMAL ENGINEERING
ISSN 1359-4311  Vol. 52  Nº 2  2013  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.
Autores: Ramos González, Juan Carlos; Beiza Silva, Maximiliano Patricio; Gastelurrutia Roteta, Jon; et al.
Revista: APPLIED THERMAL ENGINEERING
ISSN 1359-4311  Vol. 51  Nº 1-2  2013  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.
Autores: Ruiz de Galarreta Moriones, Sergio; Cazón Martín, Aitor; Antón Remírez, Raúl; et al.
Revista: JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME
ISSN 0148-0731  Vol. 136  Nº 1  2013  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.
Autores: Goikoetxea, E., ; Rivas Nieto, Alejandro; Antón Remírez, Raúl; et al.
Revista: EUROPEAN RESPIRATORY JOURNAL
ISSN 0903-1936  Vol. 42  Nº 57  2013  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.
Autores: Altimira Ferrer, Mireia; Rivas Nieto, Alejandro; Ramos González, Juan Carlos; et al.
Revista: ATOMIZATION AND SPRAYS
ISSN 1044-5110  Vol. 22  Nº 9  2012  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.
Autores: Antón Remírez, Raúl; Bengoechea García, Asier; Rivas Nieto, Alejandro; et al.
Revista: JOURNAL OF ELECTRONIC PACKAGING
ISSN 1043-7398  Vol. 134  Nº 1  2012  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]
Autores: Masip Macia, Yunesky; Rivas Nieto, Alejandro; Sánchez Larraona, Gorka; et al.
Revista: INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
ISSN 0142-727X  Vol. 38  2012  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.
Autores: Antón Remírez, Raúl; Gastelurrutia Roteta, Jon; Ramos González, Juan Carlos; et al.
Revista: INTERNATIONAL JOURNAL OF ENGINEERING EDUCATION
ISSN 0949-149X  Vol. 27  Nº 4  2011  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.
Autores: Martínez Galván, Eduardo; Ramos González, Juan Carlos; Antón Remírez, Raúl; et al.
Revista: JOURNAL OF ELECTRONIC PACKAGING
ISSN 1043-7398  Vol. 133  Nº 1  2011  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]
Autores: Antón Remírez, Raúl; Aramburu Ibarlucea, Amaya; Rubio Díaz-Cordovés, Ángel
Revista: BMC BIOINFORMATICS
ISSN 1471-2105  Vol. 11  2010 
Background: Exon arrays provide a way to measure the expression of different isoforms of genes in an organism. Most of the procedures to deal with these arrays are focused on gene expression or on exon expression. Although the only biological analytes that can be properly assigned a concentration are transcripts, there are very few algorithms that focus on them. The reason is that previously developed summarization methods do not work well if applied to transcripts. In addition, gene structure prediction, i.e., the correspondence between probes and novel isoforms, is a field which is still unexplored. Results: We have modified and adapted a previous algorithm to take advantage of the special characteristics of the Affymetrix exon arrays. The structure and concentration of transcripts -some of them possibly unknown-in microarray experiments were predicted using this algorithm. Simulations showed that the suggested modifications improved both specificity (SP) and sensitivity (ST) of the predictions. The algorithm was also applied to different real datasets showing its effectiveness and the concordance with PCR validated results. Conclusions: The proposed algorithm shows a substantial improvement in the performance over the previous version. This improvement is mainly due to the exploitation of the redundancy of the Affymetrix exon arrays. An R-Package of SPACE with the updated algorithms have been developed and is freely available.
Autores: Altimira Ferrer, Mireia; Rivas Nieto, Alejandro; Ramos González, Juan Carlos; et al.
Revista: PHYSICS OF FLUIDS
ISSN 1070-6631  Vol. 22  Nº 7  2010  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]
Autores: Pio Osés, Rubén; Blanco Barrenechea, David; Pajares Villandiego, María Josefa; et al.
Revista: BMC GENOMICS
ISSN 1471-2164  Vol. 11  2010  págs. 352
Background: Microarrays strategies, which allow for the characterization of thousands of alternative splice forms in a single test, can be applied to identify differential alternative splicing events. In this study, a novel splice array approach was developed, including the design of a high-density oligonucleotide array, a labeling procedure, and an algorithm to identify splice events. Results: The array consisted of exon probes and thermodynamically balanced junction probes. Suboptimal probes were tagged and considered in the final analysis. An unbiased labeling protocol was developed using random primers. The algorithm used to distinguish changes in expression from changes in splicing was calibrated using internal non-spliced control sequences. The performance of this splice array was validated with artificial constructs for CDC6, VEGF, and PCBP4 isoforms. The platform was then applied to the analysis of differential splice forms in lung cancer samples compared to matched normal lung tissue. Overexpression of splice isoforms was identified for genes encoding CEACAM1, FHL-1, MLPH, and SUSD2. None of these splicing isoforms had been previously associated with lung cancer. Conclusions: This methodology enables the detection of alternative splicing events in complex biological samples, providing a powerful tool to identify novel diagnostic and prognostic biomarkers for cancer and other pathologies.
Autores: Masip Macia, Yunesky; Rivas Nieto, Alejandro; Bengoechea García, Asier; et al.
Libro:  Advances in Fluid Mechanics VIII
2010  págs. 569 - 584