Revistas
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.
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:
JOURNAL OF WATER PROCESS ENGINEERING
ISSN:
2214-7144
Año:
2022
Vol.:
46
Págs.:
102624
This paper presents a Computational Fluid Dynamics (CFD) model of a pilot scale dissolved air flotation (DAF) tank. A Multiphase Mixture model was used to analyse the influence of bubble sizes on the formation of a stratified flow structure. Critical bubble diameter is defined as the size of the bubble that implies the equality of the bubble rising velocity and flow downward velocity in the separation zone (SZ). The fact as to whether using air bubble sizes which are greater or less than the critical diameter value significantly affects the air content, flow structure and the limit of the whitewater blanket inside the SZ is assessed. The study was carried out using two approaches, namely, mono-and multi-diameter. The results obtained via the mono-diameter approach proved to be closely in line with experimental data when air concentration in the SZ had almost, but not quite, a constant value. However, it failed to predict the case of the progressive decrease in air below half of SZ height. A combined effect of bubbles with different rising speed was required to reproduce a smooth air profile curve, as measured experimentally. In this context, a multi-diameter approach is deemed to be a suitable method for reproducing the stratified structure. In addition, this approach offers the chance to study bubble size distribution inside the SZ domain.
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:
DYNA
ISSN:
0012-7361
Año:
2020
Vol.:
95
N°:
6
Págs.:
570 - 571
Autores:
Arregi, B. (Autor de correspondencia); Garay-Martínez, R.; Astudillo, J.; et al.
Revista:
ENERGY AND BUILDINGS
ISSN:
0378-7788
Año:
2020
Vol.:
214
Págs.:
UNSP 109846
Building envelope systems are rapidly evolving, driven by increasingly stringent requirements for limiting energy consumption. Current trends favour lightweight, prefabricated wall assemblies with high levels of insulation, which have been shown to be particularly sensitive to thermal bridging through anchoring and framing elements. This paper presents a self-supporting multi-layer wall component made from bio-based materials, where novel biocomposite profiles are used instead of conventional metallic frames. The thermal performance of the proposed solution is calculated from numerical modelling and characterised through in-situ measurement of a full-scale prototype. For the plane areas of the wall with continuous insulation, theoretical calculations are broadly in line with results from experimental monitoring (7-15% deviation). Additionally, an area along a framing profile was specifically monitored, and it was found that the numerical model overestimated thermal resistance with a deviation of 121%. The presence of air gaps between the rigid insulation and framing elements, linked to the fabrication process of the prototype, was identified as a plausible cause. A subsequent explanatory numerical assessment, considering the effect of such cavities in the numerical model, provided results that are consistent with measurements from the experiment and previous literature. The study aims at demonstrating the insulation levels achievable with the use of novel bio-based materials of low thermal conductivity, and more generally, contributing to a better understanding of the thermal performance of framed lightweight insulated assemblies in service conditions, by monitoring and modelling the impact of thermal bridges and workmanship at framing elements. (C) 2020 Elsevier B.V. All rights reserved.
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:
ENERGY
ISSN:
0360-5442
Conventional cooling systems in large office buildings typically incorporate evaporative cooling towers, despite the drawbacks of direct evaporation. An alternative approach is based on highly selective innovative surfaces capable of daytime radiant cooling, however, prototypes of these cooling radiators have not yet demonstrated a system capable of cooling an actual building. This paper presents a third approach: A hybrid cooling system designed to partly or completely replace a cooling tower using dry heat dissipation panels. Unlike nocturnal cooling radiators, these panels may be integrated into a facade in a vertical position. The hybrid system is described firstly, where two configurations of the system are considered. Then, an evaluation of the hybrid system in comparison to a conventional system is performed by means of a simulation-based study, resulting that the replacement of a cooling tower by cooling panels increases the annual energy consumption by 3.6% compared to a conventional open circuit cooling tower system. However, the decrease in maintenance costs may reduce the annual operational expenses by over 50%. (C) 2020 Published by Elsevier Ltd.
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.
Revista:
IOP CONFERENCE SERIES. EARTH AND ENVIRONMENTAL SCIENCE
ISSN:
1755-1307
Año:
2018
N°:
154
Págs.:
1 - 8
Revista:
INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING
ISSN:
2040-7939
Año:
2018
Vol.:
34
N°:
7
Págs.:
e2983
Revista:
APPLIED THERMAL ENGINEERING
ISSN:
1359-4311
Año:
2018
Vol.:
129
Págs.:
93 - 105
A computational fluid dynamics (CFD) model representing the effect of wafters in a totally enclosed electric machine is presented, introducing the most relevant theoretical assumptions and simplifications. The validation of the model is conducted through experimental measurements. From the CFD simulation data, a second-order response surface is developed using statistical tools, from which the wafters' influence on the convective heat transfer from the stator end windings is predicted. Wafter design criteria are obtained from the response surface information. Finally, a specific case is analysed, showing through CFD simulations that temperatures in the machine are reduced by including wafters in the design.
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:
APPLIED THERMAL ENGINEERING
ISSN:
1359-4311
Año:
2017
Vol.:
114
Págs.:
1018 - 1028
An analytical thermal model of an IC71W Induction Machine (IM) is presented, introducing the most relevant theoretical assumptions and equations. The validation of this model is conducted through experimental measurements. Some criteria for design of the most critical parts of the cooling system are provided using both a model based on Computational Fluid Dynamics (CFD) techniques and the analytical thermal model. First, the design of the water jacket and its main parameters are broadly analysed and some correlations for the design of the cooling ducts are presented. The influence of wafters on this cooling arrangement is also discussed.
Revista:
ENERGY AND BUILDINGS
ISSN:
0378-7788
Año:
2017
Vol.:
142
Págs.:
158 - 166
The energy used for cooling has increased in recent decades and the predicted future rise in consumption is driving a pressing need for more efficient technologies. Some technologies use environmental sinks as heat dissipation alternatives. This paper presents a model validation with experimental data from a passive vertical cooling panel. The novelty of the solution lies in two main characteristics. The first is that the panel is in a vertical position, and thus the heat sink is the ambient temperature and surrounding instead of the sky temperature. The second is that the panel is north-oriented. Avoiding the sun lengthens the operating time to the entire day, while most studies explore options that are limited to night radiation. The aim is to include this element as a heat exchanger before water moves into the cooling tower from the condenser stage in cooling systems. The results have shown that the model approaches significantly the experimental data with an average error of 1.5% in the dissipated heat. Besides, the cooling capacity of the panel varies from 107 to 230 W/m2 depending on the inlet temperature and fluid flow conditions, confirming the viability of the integration in buildings.
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:
RENEWABLE AND SUSTAINABLE ENERGY REVIEWS
ISSN:
1364-0321
Año:
2017
Vol.:
72
Págs.:
73 - 82
The amount of energy consumed for cooling purposes is increasing and expected to rise in the following years. The active cooling mechanisms used to meet these requirements can be partially replaced by harnessing environmental conditions and developing passive solutions. Through the multidisciplinary knowledge offered by biomimicry, a bio-inspired solution was developed with the aim of reducing the drawbacks of cooling towers. This experimental study shows the development of a passive cooling panel prototype and attempts to analyse tests carried out in the north of Spain. The results show that with three different inlet temperatures (35, 45 and 55 °C) and a fluid flow rate of 0.5 l/min, the average heat dissipation power per unit area of the panel is 140.4, 284.8 and 309.7 W/m2, respectively. By increasing the flow rate to 1.5 l/min, the heat rejection rate rises to 250.8, 397.5 and 479.6 W/m2, respectively. These outcomes confirm the cooling potential of the passive panel and open the possibility to the development of numerous applications. Further development of this solution would seek the decrease of the peak demand and the reduction of the energy consumption of cooling towers in tertiary buildings or small industry.
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:
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:
APPLIED THERMAL ENGINEERING
ISSN:
1359-4311
Año:
2016
Vol.:
102
Págs.:
1081 - 1094
Environmental sustainability, more efficient use of energy, and active safety concepts are becoming important requirements for the actual elevation sector. In this context IK4-IKERLAN and ORONA have designed an auxiliary energy storage system (ESS) for a residential elevation application based on lithium-ion cells. Safety and specially lifetime are two of the main concerns surrounding this new technology, which is closely related to the cells operating behavior and temperature asymmetries in the complete ESS. Therefore, the temperature of the cells in battery packs (BPs) needs to be controlled in an efficient way. This paper describes the development of the thermal management system (TMS) designed for this application based on various Computational Fluid Dynamics (CFD) mathematical models. The accuracy of Transient model is validated by using a single module to compare the simulation temperature results with experimental measurements, with a maximum time-averaged temperature prediction error of 1.5 degrees C. The proposed design is validated as it fulfills the requirements for a wide operating window, with a maximum cell temperature of 39 degrees C and a thermal dispersion at system level below 3 degrees C for the worst tested case. A more realistic current profile is checked numerically in the worst ambient and operative conditions for different virtual design variants to propose improvements. (C) 2016 Elsevier Ltd. All rights reserved.
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:
BUILDING SERVICES ENGINEERING RESEARCH AND TECHNOLOGY
ISSN:
0143-6244
Año:
2016
Vol.:
37
N°:
4
Págs.:
431 - 449
The article describes from an architectonical point of view the design, assembly, and energy behavior of a prototype for air-conditioning in residential buildings using Peltier cells, which means the application in the field of construction of a technology used in very specific areas. The new system has been designed as an independent, prefabricated, modular construction element that must fit perfectly between the structural floors and is easily adapted to the demands of different buildings. The thermoelectric cooling heating unit is designed to offer a high level of comfort to those living in the building. The only mechanical elements are the dissipation heat fans placed on the outside of the prototype, and heat sinks to transfer the heat from the power elements, reducing the possibilities of failure. The result of all these ideas is the construction of a prefabricated module, consisting of a simplified inhabited housing unit with a thermoelectric installation serving the module, which has obtained a national patent. The results of the thermal and electric behavior demonstrate that the system does not work as well as had been expected; nevertheless, the system has a high potential for its use in buildings associated with photovoltaic.
Revista:
APPLIED THERMAL ENGINEERING
ISSN:
1359-4311
Año:
2015
Vol.:
75
Págs.:
277 - 288
Prediction of the thermal behavior of electric motors in the early design stage is crucial in any design process. The most popular prediction methods are analytical, and based on the lumped parameter model approach. These methods require experimental data in order to obtain accurate results, but this data is often not available. This paper deals with the problem of the lack of experimental data for an Open Self-Ventilated (OSV) Induction motor and reviews some of the most controversial parameters in thermal modeling, such as the bearings model and the axial conductivity of the lamination stack. Due to the nature of the OSV machine, through ventilation is also investigated, and a hydraulic model with improvements focused on rotational effects observation is presented. Moreover, the heat transfer in end spaces and ducts is studied, using dimensionless analysis correlations, along with focusing on new hydraulic phenomena, such as the development of the flow and the roughness effect. An implementation of a thermal circuit for an OSV machine that has good agreement with reference results is used to compare heat transfer coefficients used regularly for Totally Enclosed Fan Cooled (TEFC) enclosures. Finally, a sensitivity analysis is carried out on some parameters to determine their importance.
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:
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:
JOURNAL OF POWER SOURCES
ISSN:
0378-7753
Año:
2014
Vol.:
272
Págs.:
291 - 302
Battery packs conformed by large format lithium-ion cells are increasingly being adopted in hybrid and pure electric vehicles in order to use the energy more efficiently and for a better environmental performance. Safety and cycle life are two of the main concerns regarding this technology, which are closely related to the cell's operating behavior and temperature asymmetries in the system. Therefore, the temperature of the cells in battery packs needs to be controlled by thermal management systems (TMSs). In the present paper an improved design methodology for developing TMSs is proposed. This methodology involves the development of different mathematical models for heat generation, transmission, and dissipation and their coupling and integration in the battery pack product design methodology in order to improve the overall safety and performance. The methodology is validated by comparing simulation results with laboratory measurements on a single module of the battery pack designed at IK4-IKERLAN for a traction application. The maximum difference between model predictions and experimental temperature data is 2 degrees C. The models developed have shown potential for use in battery thermal management studies for EV/HEV applications since they allow for scalability with accuracy and reasonable simulation time. (C) 2014 Elsevier B.V. All rights reserved.
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.
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:
INTERNATIONAL REVIEW ON MODELLING AND SIMULATIONS
ISSN:
1974-9821
Año:
2013
Vol.:
6
N°:
5
Págs.:
1446 - 1451
This paper describes an algebraic model for predicting the air flow-rate in the cooling system of an open self-ventilated machine. The method is easily applicable to any type of air-cooled electrical machine. The air flow-rates in different areas of the machine as well as the head losses of the hydraulic system were obtained, and the results were compared with a more detailed model developed with Computational Fluid Dynamic (CFD) techniques. Moreover, a sensitivity analysis was carried out in order to compare the different topologies of the machine studied
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:
INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER
ISSN:
0017-9310
Año:
2013
Vol.:
58
N°:
1-2
Págs.:
568 - 577
The flow and heat transfer characteristics are investigated in micro and mini communicating channel pressure driven flows by 2D numerical simulations using a computational method. The continuum based Navier-Stokes and continuity equations are solved by the Spectral Element Method (SEM). Flow and heat transfer characteristics are determined for 10 < Re < 227. The 2D communicating channel physical domain contains many blocks within the parallel,.upper and lower walls. A periodic computational domain of length 2 (L) over cap and an aspect ratio of r = (a) over cap/(2 (L) over cap) is used, where a is the height of block within the channel and (L) over cap is the periodic length. For low Reynolds number, viscous forces dominate and two stationary symmetric vortices are generated between blocks with very laminar parallel viscous flow in the upper and lower communicating channel. For moderate Reynolds numbers, numerical results show a transition scenario with two Hopf flow bifurcations, as the flow evolves from a laminar to a time-dependent flow regime. The first Hopf bifurcation B-1 occurs at a critical Reynolds number (Re-c1) leading to a periodic flow characterized by a frequency omega(1). A quasi periodic flow sets in for higher Reynolds numbers through a second Hopf flow bifurcation B-2 occurring at a critical Reynolds number (Re-c2 < Re-c1) with two frequencies omega(1) and omega(2), and a linear combinations of omega(1) and omega(2). The existence of either regime will depend on the previous flow regime, the process of furthering the Reynolds number from one condition to another, and the aspect ratio r. Numerical results show that Nusselt numbers are at least 50% larger in quasi periodic than in periodic and laminar flow regimes. The existence of periodic and quasi periodic flows leads to a heat transfer enhancement at the same Reynolds number. (C) 2012 Elsevier Ltd. All rights reserved.
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:
JOURNAL OF THE ELECTROCHEMICAL SOCIETY
ISSN:
0013-4651
Año:
2013
Vol.:
160
N°:
2
Págs.:
A212 - A217
This paper describes a thermal model that represents the heat generation behavior of a large format (10.5 Ah) Li-ion pouch cell. The thermal model is based on the calculation of the heat generation from experimental measurements of internal resistance and the entropic heat coefficient. Predictions from the thermal model are compared with experimental adiabatic calorimetry data. Higher discharge rates and larger temperature operation ranges than the ones reported in prior studies are considered. Results from the thermal model simulations have a prediction error of 21% in comparison with the experimental ones for discharge processes carried out at moderate rates. For discharge processes carried out at high discharge rates a maximum prediction error of 15% has been determined. The advantages and disadvantages of the model are further discussed, taking into account aspects such as accuracy, model development and implementation in different thermal management system designs. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.042302jes] 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:
APPLIED THERMAL ENGINEERING
ISSN:
1359-4311
Año:
2011
Vol.:
31
N°:
4
Págs.:
493 - 505
The thermal behaviour of several ONAN (Oil Natural Air Natural) distribution transformers has been numerically modelled. A simplified differential model has been developed with the aim of reducing the computational cost that would require a model with the complete geometrical description. This model has been capable of reproducing the expected oil flow and the thermal distribution inside the transformer. The influence of turbulence modelling in the obtained results has been evaluated and the model has been verified in terms of discretization errors. The thermal boundary conditions have been thoroughly analysed searching for the most appropriate expressions for this particular case instead of using inadequate mean values obtained from bibliography. The devised model has been validated by comparing the numerical results with the experimental ones obtained for different transformers and power losses. This mathematical tool can be used to study the natural convection of the oil inside the transformers and allows the manufacturers to optimise their designs from a thermal point of view. (C) 2010 Elsevier Ltd. All rights reserved.
Revista:
APPLIED THERMAL ENGINEERING
ISSN:
1359-4311
Año:
2011
Vol.:
31
N°:
17-18
Págs.:
4024 - 4035
The present paper proposes an algebraic zonal model describing the cooling process, via internal oil and external air natural convection, of distribution transformers during a standardised heating test. The conception and adjustment of the presented algebraic zonal model rely on the oil flow and thermal results obtained by a more complex numerical differential model that has been verified and validated by the authors. The domain of the original differential model is divided into several interrelated control volumes or zones where mass and energy conservation laws are applied in conjunction with the necessary boundary conditions. The generated nonlinear algebraic equation system is solved, obtaining in the process the top oil temperature, the internal and external surface temperatures and the heat dissipation distribution. The results of the zonal model have been validated using the previous results from the differential model as well as experimental measurements from heating tests with three different transformers under various power loads. The model developed has proven to be an efficient tool in improving and optimising the thermal design of these devices. (C) 2011 Elsevier Ltd. All rights reserved.
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]
