| 1. |
- Altimira, Mireia, 1981-, et al.
(author)
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Characterization of fan spray atomizers through numerical simulation
- 2009
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In: International Journal of Heat and Fluid Flow. - : Elsevier. - 0142-727X .- 1879-2278. ; 30:2, s. 339-355
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Journal article (peer-reviewed)abstract
- The present paper focuses on the mathematical modeling of industrial fan spray atomizers. The two-phase flow taking place inside the nozzle's tip and the exterior region near the outlet of three different industrial nozzle designs has been modeled and simulated. As a result, valuable information has been obtained regarding the influence of the inner geometry on the flow and also the formation and development of the liquid sheet. Characteristic magnitudes such as the discharge coefficient and the liquid sheet thickness factor have been obtained and validated through experimental measurements. The accumulation of liquid at the border of fan-shaped liquid sheets, also known as rim, has been studied in the analyzed designs, revealing the presence of a tangential velocity component in the liquid sheet and a relationship between the incoming flow rate of the rim and the angle of the liquid sheet. The dependence of the results on turbulence modeling has also been analyzed, drawing interesting conclusions regarding their influence on the liquid sheet mean flow characteristics and on the surrounding gas. Thus, the mathematical model developed has been proved to be a useful tool for nozzle manufacturers; it provides the most important characteristic parameters of the liquid sheet formed given certain nozzle geometry and, additionally, those data necessary to carry out studies of instability, breakup and atomization of the liquid sheet.
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| 2. |
- Altimira, Mireia, 1981-, et al.
(author)
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Fan-Spray Atomizers Analysis through Mathematical Modeling
- 2007
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In: Proceedings of the 21st ILASS - Europe Meeting 2007.
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Conference paper (peer-reviewed)abstract
- The main objective of this work is to determine the most important design parameters in fan spray atomizers and their effect in the atomization features in order to provide a design tool for nozzle manufacturers. A mathematical model relating the geometry and operating conditions to the characteristics of the spray has been obtained and validated. Three different sub-models have been used in series, so that the results of one model become inputs of the next one, namely multiphase flow simulation, instability and break-up model and maximum entropy model. These have been joined achieving a global model of the whole primary atomization process.
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| 3. |
- Anton Remirez, Raul, et al.
(author)
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Compact CFD modeling of EMC screen for radio base stations : A porous media approach and a correlation for the directional loss coefficients
- 2007
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In: IEEE transactions on components and packaging technologies (Print). - : IEEE Press. - 1521-3331 .- 1557-9972. ; 30:4, s. 875-885
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Journal article (peer-reviewed)abstract
- A methodology to obtain the directional pressure loss coefficients in a porous media model of an electromagnetically compatible screen of a radio base station model is presented. The directional loss coefficients of this compact model are validated against a detailed computational fluid dynamics model not only by comparing the total pressure drop, but also by evaluating the flow pattern after the screen. The detailed model was validated in an earlier article by the authors. A parametric study is conducted for 174 cases. Seven parameters were investigated: velocity, inlet height, screen porosity, printed circuit board (PCB) thickness, inlet-screen gap, distance between two PCBs and screen thickness. Based on the compact model parametric study, two correlations for the directional loss coefficients are developed as a function of the Reynolds number and the above geometrical parameters. The average disagreement between the compact model that uses the directional loss coefficients from the correlations and the detailed model was of 3% for the prediction of the total pressure drop and less than 6.5% and 9.5% for two coefficients that accurately characterize the flow pattern. © 2007 IEEE.
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| 4. |
- Anton Remirez, Raul, et al.
(author)
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Detailed CFD Modelling of EMC Screen for Radio Base Stations : A Conjugate Heat Transfer Problem
- 2007
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In: International Journal of Heat Exchangers. - : R.T Edwards Inc.. - 1524-5608. ; 8:1, s. 95-116
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Journal article (peer-reviewed)abstract
- The objective of this paper is to perform an experimental as well as CFD investigations of the conjugate heat transfer problem in a sub-rack slot model. A steady-state three-dimensional detailed model, which serves as the most accurate representation of the model, was used in order to evaluate the details of the airflow paths and temperature field. A general model that covers a considerable range of velocities, screen porosities and heat fluxes was validated experimentally by wind tunnel measurements. The result shows that the RNG k-ε model used with correct y+ and mesh strategy accurately predicts the temperature field. The average temperature deviation at several locations is less than 4% compared to experimental data. The influence of the velocity, screen porosity, heat flux and presence of the EMC screen on the PCB temperature field is commented.
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| 5. |
- Anton Remirez, Raul, et al.
(author)
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Detailed CFD modelling of EMC screen for radio base stations : a parametric study
- 2009
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In: IEEE transactions on components and packaging technologies (Print). - 1521-3331 .- 1557-9972. ; 32:1, s. 145-155
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Journal article (peer-reviewed)abstract
- The objective of this paper is to make a parametric study of the hydraulic resistance and flow pattern of the flow after an electromagnetic compatibility screen and between two printed circuit boards (PCBs) in a model of a 90° subrack cooling architecture. The parametric study is carried out using a detailed 3-D model of a PCB slot. The detailed model was experimentally validated in a previous paper by the authors. Seven parameters were investigated: velocity, inlet height, screen porosity, PCB thickness, distance between two PCBs, inlet-screen gap and screen thickness. A correlation for the static anddynamic pressure drop, the percentage of dimensionless wetted area, Aw*, and the RMS* factor (a function of the flow uniformity along the PCB) after the screen is reported as a function of six geometrical dimensionless parameters and the Reynolds number. The correlations, that are based on 174 three dimensional simulations, yield good results for the total pressure drop, in which the values are predicted within the interval of ±15%. For the, Aw* all the predicted values are within the interval of ±22% of the observed values. Finally, for the RMS* factor, the majority of the values also have a disagreement of less than 20% of the observed values. These last two parameters are believed to provide a correct insight about the flow pattern after the screen.
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| 6. |
- Anton Remirez, Raul, et al.
(author)
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Detailed CFD modelling of EMC screen for radio base stations : a benchmark study
- 2007
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In: IEEE transactions on components and packaging technologies (Print). - 1521-3331 .- 1557-9972. ; 30:4, s. 754-763
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Journal article (peer-reviewed)abstract
- The objective of this paper is to investigate the performance of five well-known turbulence models, in order to find a model that predicts the details of the flow patterns through an electromagnetic compatibility (EMC) screen. The turbulence models investigated in the present study are five different eddy-viscosity models; the standard k-ε model, the renormalization group (RNG) k-ε model, the realizable k-ε model, the standard k-ω model, as well as the shear stress transport k-ω model. A steady-state 3-D detailed model, which serves as the most accurate representation of the model, was used in order to evaluate the details of the airflow paths and pressure field. The flow was assumed to be isothermal, turbulent and incompressible. A general model that covers a considerable range of velocities and geometries was validated experimentally by wind tunnel measurements. The result shows that for most of the k-ε models used with correct y+ and mesh strategy, the pressure drop and the velocity field deviation is small compared to experimental data. The k-ω models overpredict the overall pressure drop. When using the RNG k-ε model, the total static pressure drop predicted differs around 5%-10% and the average velocity deviation at several locations before and after the screen is around 5%.
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| 7. |
- Antón Remírez, Raúl, 1977-
(author)
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Experimental and numerical study of the thermal and hydraulic effect of EMC screens in radio base stations : detailed and compact models
- 2006
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Doctoral thesis (other academic/artistic)abstract
- Today’s telecommunication cabinets use Electro Magnetic Compliance (EMC) screens in order to reduce electromagnetic noise that can cause some miss functions in electronic equipment. Many radio base stations (RBSs) use a 90-degree building architecture: the flow inlet is perpendicular to the EMC screen, which creates a complex flow, with a 90-degree air turn, expansions, compressions, perforated plates and PCBs. It is of great interest to study how the EMC screen interacts with the rest of components and analyze the total pressure drop and how much the flow pattern changes due to the placement of the screen. Velocity, pressure and temperature measurements as well as flow pattern visualizations have been carried out to gain good insight into the flow and heat transfer characteristics in a subrack model of an RBS. Furthermore, these measurements have been very useful for validating detailed CFD models and evaluating several turbulence models. Nowadays, industrial competition has caused a substantial decrease in the time-to-market of products. This fact makes the use of compact models in the first stages of the design process of vital importance. Accurate and fast compact models can to a great extent decrease the time for design, and thus for production. Hence, to determine the correlations between the pressure drop and flow pattern on the PCBs as a function of the geometry and the Reynolds number, based on a detailed CFD parametric study, was one objective. Furthermore, the development of a compact model using a porous media approach (using two directional-loss coefficients) has been accomplished. Two correlations of these directional loss coefficients were found as a function of the geometry and Reynolds number.
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| 8. |
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| 9. |
- Martínez-Galván, Eduardo, et al.
(author)
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Heat transfer and film thickness measurements in a closed loop spray cooling system with R134a
- 2009
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In: 15th International Workshop on Thermal Investigations of ICs and Systems, THERMINIC 2009. - : Academic Conferences Publishing. - 9782355000102 ; , s. 180-185
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Conference paper (peer-reviewed)abstract
- Experimental measurements in a spray cooling test rig have been carried out for different heat fluxes in the heater and different volumetric spray fluxes of the refrigerant. Results of the thermal parameters and the sprayed refrigerant liquid film thickness over the heater 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 of the heat transfer coefficient and the film thickness along the spray boiling curve.
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