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A contact line force model for the simulation of drop impacts on solid surfaces using volume of fluid methods
(Elsevier, 2023-09-15) Esteban Paz, Adolfo; Gómez del Pino, Pablo Joaquín; Zanzi, Claudio; López, Joaquín; Bussmann, Markus; Hernández Rodríguez, Julio
Characterizing the contact line dynamics on solid walls is often a crucial problem encountered in the simulation of complex interfacial unsteady flows, such as drop impacts on solid surfaces. In this work, a new model is proposed to reproduce the contact line dynamics in a simple but effective way, based on introducing in the momentum equation a force term proportional to the deviation of the calculated contact angle from the value predicted by a dynamic model that takes into account wettability hysteresis. The model has been implemented in a volume of fluid (VOF) method and is applied to the simulation of drop impacts leading to deposition outcomes, although it could be extended to other interface tracking methods and is also applicable to more complex drop impacts involving fingering and splashing. Numerous tests have been performed to evaluate the accuracy and robustness of the proposed model over a wide range of Reynolds and Weber numbers. The results substantially improve those obtained by imposing only the contact angle as a boundary condition at the contact line, and satisfactorily predict a variety of experimental results from the literature for very different impact and wettability conditions.
A Multi-Response Optimization of Thrust Forces, Torques, and the Power of Tapping Operations by Cooling Air in Reinforced and Unreinforced Polyamide PA66
(MDPI, 2018-03-20) Domingo Navas, María Rosario; Agustina Tejerizo, Beatriz De; Marín Martín, Marta María
The use of cooling air during machining is an environmentally conscious procedure, and its applicability to different processes is a research priority. We studied tapping operations, an important operation in the assembly process, using cooling air with unreinforced polyamide (PA66) and polyamide reinforced with glass fiber (PA66-GF30). These materials are widely used in industry, but their behavior with respect to tapping has not been studied. We analyze the outcomes regarding the thrust force, torque, and power at cutting speeds between 15 and 60 m/min. The experimental tests were executed using cooling air at 22 °C, 2 °C, and −18 °C in dry conditions. The M12 × 1.75 mm taps were high-speed steel, with cobalt as the base material and coatings of TiN and AlCrN. To identify the more influential factors, an analysis of variance was performed, along with multi-response optimization to identify the desirability values. This optimization shows that the optimum for PA66can be found in environments close to 3 °C, while the optimum for PA66-GF30 is found at the minimal temperature studied (−18 °C). Thus, cooling air can be considered an adequate procedure for tapping operations, to increase the sustainability of the manufacturing processes.
A new design of multi-tube receiver for Fresnel technology to increase the thermal performance
(Elsevier, 2022-03-05) Abbas, Rubén; Montes Pita, María José; Barbero Fresno, Rubén; Rovira de Antonio, Antonio José
Solar heat for industrial processes is a promising way to meet the high thermal demand required by the industry, while this application becomes an important niche market for solar technology. In this research line, it is proposed a novelty concept based on a rotary Fresnel solar collector to supply heat above 150 °C. This work is focused on the multi-tube receiver for this Fresnel collector, proposing a thermal design based on three criteria that can be generalized for any multi-tube receiver: the fluid flow layout is arranged to meet the symmetry of the solar flux map; the fluid circulates from the lower to the higher flux density zone; and the fluid velocity is modified by modifying the tube diameter, to optimize the heat transfer. Following these criteria, the final configuration of the receiver is chosen based on an exergy optimization, in which both heat loss and pressure drop must be quantified. It has been also accomplished a generalization of the optimization methodology for Fresnel collectors providing heat at different temperatures, showing that, in these cases, the configuration that maximizes the exergy efficiency does not correspond to the one with the highest energy efficiency. This thermal design method can be applied to multi-tube receivers working at higher temperatures in longer Fresnel loops, in which case the optimization will result in more marked differences between the optimal values and the standard ones.
A new method for calculating conduction response factors for multilayer constructions based on frequency–Domain spline interpolation (FDSI) and asymptotic analysis
(Elsevier, 2017-08-01) Sanza Pérez, Javier; Chicote, Manuel Andrés; Velasco Gómez, Eloy; Varela Díez, Fernando
Conduction heat transfer through building construction elements is one of the main components of space heating and cooling loads, and, thus, one of the key aspects when planning sustainable energy designs in the building sector. The Response Factors (RF) method sets the base for related dynamic calculations implemented by most well-known Building Energy Simulation (BES) software, and it represents a research topic of present interest. In this regard, this work introduces a new method for calculating conduction Response Factors in building multilayer constructions, based on the definition of an approximated wall model through Frequency–Domain Spline Interpolation (FDSI) and asymptotic analysis. Its conceptual development as well as first validations comparing with existing methods from previous literature are presented. Finally, as a result of applying a table-lookup approach and the possibility of pre-calculating most of the involved operations, an accurate, fast and easy-to-code algorithm is obtained, which constitutes a promising alternative to improve the current state-of-art calculation procedures.
A New Thermodynamic Model to Approximate Properties of Subcritical Liquids
(MDPI, 2023-06-29) Sánchez Orgaz, Susana; González Fernández, M. Celina; Varela Díez, Fernando; Rodríguez Laguna, Javier
In order to obtain the thermodynamic properties of compressed liquids, it is usual to consider them as incompressible systems, since liquids and solids are well represented by this thermodynamic model. Within this model, there are two usual hypotheses that can be derived in two different submodels: the strictly incompressible (SI) model, which supposes a constant specific volume 𝑣=𝑣0, and a more general model, called temperature-dependent incompressible (TDI) model, which relates a specific volume to temperature, 𝑣=𝑣(𝑇). But, usually, this difference ends here in the thermal equation of state, and only the SI model was developed for caloric and entropic equations. The aim of this work is to provide a complete formulation for the TDI model and show where it can be advantageously used rather than the SI model. The study concludes that the proposed model outperforms the traditional model in the study of subcritical liquid. One conceivable utilization of this model is its integration into certain thermodynamic calculation software packages (e.g., EES), which integrate the more elementary SI model into its code for certain incompressible substances.
A novel energy conversion system based on supercritical CO2 recompression Brayton power cycle for power tower concentrating solar plants
(Elsevier, 2020-02-09) Linares Hurtado, José Ignacio; Cantizano, Alexis; Sánchez, Consuelo; Montes Pita, María José
Power tower concentrating solar plants with thermal energy storage will play a key role in the transition to a low carbon scenario, thanks to be a dispatchable renewable energy system. The ternary MgCl2/KCl/NaCl salt appears as one of the most promising due to its lower melting point, higher heat capacity, lower cost and stability up to 800 °C. A cavity-type receiver has been selected because minimizes radiation heat loss at high working temperatures, compared to an external-type receiver, since all commercial selective coatings degrade in air. Supercritical Brayton power cycle is chosen for the power block because it can surpass 50% efficiency, even when working in dry cooling conditions, and printed circuit heat exchangers are usually recommended due to its ability to support the high pressures. However, plugging/clogging issues arise in their small channels when using molten salts. This paper proposes a novel supercritical CO2 Bayton power cycle whose heat power is supplied through the low pressure side (over 85 bar) allowing the use of shell and tube heat exchangers, achieving a higher compactness and a lower investment. Thus, different options based on the recompression layout with intercooling and reheating have been investigated in both dry and wet cooling scenarios. Reheating is recommended for wet cooling, reaching 54.6% efficiency and an investment of 8662 $/kWe; intercooling with reheating is the best option for dry cooling, reaching 52.6% efficiency and an investment of 8742 $/kWe.
A novel method for the determination of fatty acid esters in aqueous emulsion on Ti6Al4V surface with IRRAS and carbon quantification
(Elsevier, 2018-12-01) Benedicto Bardolet, Elisabet; Carou Porto, Diego; Batlle, L.; Rubio Alvir, Eva María
A novel direct method based on infrared reflection absorption spectroscopy (IRRAS) and carbon elemental analysis has been developed for the quantitative determination of fatty acid ester on Ti6Al4V surface. The new approach involves the IR spectra and carbon analysis of a Ti6Al4V strip treated with a surfactant and ester emulsion adjusted to pH 9.2 with 2-aminoethanol. The results are dependent on the ester and surfactant concentration. The analytical signals are the integral value of the CH2 and CO signals of the IR spectra and the carbon content. The main advantage of the proposed method is that the analysis made directly on the metal surface allows knowing the film forming ability of the emulsion. The method may be useful for research and development of more environmentally friendly water-based metalworking fluids for the metal industry.
A solar air-cooled high efficiency absorption system in dry hot climates: Reduction of water consumption and environmental impact
(VINČA Institute of Nuclear Sciences, 2018) Lizarte, Raquel; Palacios Lorenzo, María Esther; Blanco Marigorta, Ana María; Marcos del Cano, José Daniel; Varela Díez, Fernando
A solar cooling system with an optimized air-cooled double-effect water/LiBr absorption machine is proposed as a sustainable alternative to meet cooling demands in dry hot climates. This system allows eliminating the cooling towers in those regions of the planet where water is scarce. This work analyses the environmental benefits of this air-cooled system, as well as its environmental foot-prints, compared to a solar water-cooled single effect. In this regard, a methodology has been applied to calculate the annual saving in water consumption produced in a case study: a hospital located in Almería, in South of Spain. Further-more, the reduction in energy consumption and CO2 emissions is also quantified since this machine can be driven by solar energy and with higher efficiency than those of single effect.
A spatio-temporal fully meshless method for hyperbolic PDEs
(ELSEVIER, 2023) Flores, Jesús; García, Ángel; Negreanu, M.; Salete Casino, Eduardo; Ureña, Francisco; A.M. Vargas; https://orcid.org/0000-0003-0533-3464
We introduce a meshless method derived by considering the time variable as a spatial variable without the need to extend further conditions to the solution of linear and non-linear hyperbolic PDEs. The method is based on the moving least squares method, more precisely in the Generalized Finite Difference Method which allows us to select well-conditioned stars. Several 2D and 3D examples including the time variable are shown for both regular and irregular node distributions. The results are compared with explicit GFDM both in terms of errors and execution time.
A unified concept of approximate and quasi efficient solutions and associated subdifferentials in multiobjective optimization
(Springer Nature, 2020-11-18) Jiménez, B.; Luc, D. T.; Novo, V.; Huerga Pastor, Lidia
In this paper, we introduce some new notions of quasi efficiency and quasi proper efficiency for multiobjective optimization problems that reduce to the most important concepts of approximate and quasi efficient solutions given up to now. We establish main properties and provide characterizations for these solutions by linear and nonlinear scalarizations. With the help of quasi efficient solutions, a generalized subdifferential of a vector mapping is introduced, which generates a number of approximate subdifferentials frequently used in optimization in a unifying way. The generalized subdifferential is related to the classical subdifferential of real functions by the method of scalarization. An application of generalized subdifferential to express optimality conditions for quasi efficient solutions is also given.
ACABLoop simulation tool: Improving the activation prediction of flowing PbLi alloy in support of DEMO fusion reactor design
(ELSEVIER, 2024) García Camacho, Mauricio; Catalán Pérez, Juan Pablo; Sanz Gozalo, Javier
PbLi alloy as breeder material is considered within the EUROfusion Programme in the Water-Cooled Lithium-Lead blanket concept of DEMO fusion reactor. The PbLi travels along loops entering and leaving the Breeding Blanket for recovering the produced tritium, removing generated impurities and activated corrosion products, etc. Prediction of activation-related responses in the flowing PbLi is a key safety issue in support of DEMO design. Traditionally, the activation inventory generated in the flowing PbLi has been calculated considering a simplistic approach, valid only for a pre-conceptual analysis. Additionally, the simulation of some phenomena is not possible when using that simple methodology. ACABLoop has been conceived as a tool to overcome such limitations predicting more realistically the activation of the PbLi alloy, providing all the information related to the generated isotopic inventory in the fluid. Status of ACABLoop development is presented as well as some applications for PbLi activation in DEMO loops, proving its suitability for fusion activation calculations. Additionally, a promising first validation of ACABLoop using a water loop and a D-T fusion neutron spectrum is shown. Last improvements of ACABLoop are devoted to allowing incorporation of CFD information as a tool for increasing the reliability in some specific situations.
Acetylene absorption by ionic liquids: A multiscale analysis based on molecular and process simulation
(Elsevier, 2018-10-02) Bedia, Jorge; Moreno, D.; Moya, C.; Riva Silva, Juan de; Larriba, M.; Palomar Herrero, José Francisco; Santiago Lorenzo, Rubén
A COSMO-based/Aspen Plus multiscale simulation methodology was used to evaluate a wide variety of ionic liquids (ILs), more than 300, as potential acetylene absorbents. First, by means of Conductor-like-Screening Model for Real Solvents (COSMO-RS) method, molecular simulations were conducted to select ILs with adequate thermodynamic (Henry’s law constants) and kinetic (diffusion coefficients) properties as acetylene absorbents, using N,N-dimethylformamide (DMF) as benchmark industrial solvent for such solute absorption. Then, the operating units of acetylene absorption of an acetylene and argon mixture, and exhausted solvent regeneration were modeled in Aspen Plus. Simulations of absorption column using equilibrium based design model demonstrated that at least two ILs (1-butyl-3-methylimidazolium cation and acetate and sulfonate anions) present competitive solvent performance in acetylene absorption respect to DMF. In contrast, process analyses with a more realistic rate-based column model revealed that the mass transfer rate clearly controls the acetylene absorption with ILs compared to DMF, due to their viscosity differences. Finally, modeling solvent regeneration stage showed clear advantages of using ILs as acetylene absorbents since efficient acetylene recovery is achieved by flash distillation (vacuum pressure and temperature increase), operation hindered in the case of DMF due to is high volatility, requiring the solvent regeneration by a distillation equipment with higher operating and investment costs. Current COSMO-based/Aspen Plus approach has been demonstrated useful to perform preliminary analyses of the potential application of ILs in new separation processes, before starting with experimental essays, highly demanding in cost and time.
Adaptive Control of the Oxidation Ditch Reactors in a Wastewater Treatment Plant
(Wiley, 2012-10) Kandare, Gregor; Viúdez Moreiras, Daniel; Hernández del Olmo, Félix
This paper describes the application of adaptive predictive expert (ADEX) control methodology to the oxidation ditch reactor in the wastewater treatment plant of Ceutí (Murcia, Spain) and evaluates the performance of the ADEX control system against that of the previous control system operating the plant. After a basic description of ADEX control methodology, the ditch reactor is described, as well as the control objectives and the control strategy, which focused on energy consumption reduction. The results of the application of the ADEX control system show significant improvement compared with the previous control system in terms of higher stability and precision of controlled variables, reduction of energy consumption of the plant, and better quality of the effluent water.
Adaptive model predictive control for electricity management in the household sector
(Elsevier, 2022-05) Muñoz Gómez, Antonio Miguel; Rosales Asensio, Enrique; Fernández Aznar, Gregorio; Galán Hernández, Noemi; Colmenar Santos, Antonio
This paper focuses on the optimisation of electricity consumption in residential buildings. To deal with the increase in electricity consumption, the intermittency of renewable energy generation and grid contingencies, a greater effort is required towards residential management optimisation. A novel adaptive model predictive control algorithm is proposed to achieve this objective. The challenges for this research included recognising and modelling the economic and technical constraints of the sources and appliances and addressing the uncertainties concerning the weather and user behaviour. Data-driven models are developed and trained to predict the user behaviour and buildings. Artificial neural networks and statistical models based on the weighted moving average are proposed to capture the patterns of deferrable and non-deferrable appliances, battery storage, electric vehicles, photovoltaic modules, buildings and grid connections. A dual optimisation method is devised to minimise the electricity bill and achieve thermal comfort. The proposed optimisation solver is a two-step optimisation method based on genetic algorithm and mixed integer linear programming. A comprehensive simulation study was carried out to reveal the effectiveness of the proposed method through a set of simulation scenarios. The results of the quantitative analysis undertaken as part of this study show the effectiveness of the proposed algorithm towards reducing electricity charges and improving grid elasticity.
Adaptive Self-Tuning Flight Control System for ATLANTE UAS.
(American Society of Civil Engineers (ASCE), 2016-09) Viúdez Moreiras. Daniel; Martín Sánchez, Juan
This paper presents an adaptive self-tuning flight control system (AST-FCS) for a fixed-wing aircraft, applied to a high-fidelity dynamic model of the ATLANTE unmanned aircraft system (UAS). This new adaptive control system is based on adaptive predictive (AP) control methodology and a new guidance system. AP control has been implemented in many complex industrial applications with excellent results, but it has not been applied in the aerospace sector yet. Experimental results obtained in simulation by flying a high-fidelity model of the ATLANTE UAS illustrate excellent control system performance and show the robustness of the AST-FCS, which has been designed without using accurate knowledge of the aircraft dynamics embedded within the model. It is expected that the application of AP control in this field could introduce significant advantages in aircraft control, improving performance in a wide variety of flight conditions and reducing design costs.
Advanced thermodynamic cycles for finite heat sources: proposals for closed and open heat sources applications
(Elsevier, 2020) Sánchez, Consuelo; Rovira de Antonio, Antonio José; Muñoz Domínguez, Marta; Barbero Fresno, Rubén
This paper analyses two non-conventional thermodynamic cycles designed to work with finite heat sources, which are suitable for maximum temperatures of about 400 °C. The Hybrid Rankine-Brayton (HRB) cycle fits well to closed heat sources and, in the paper, it is analysed considering its exergy efficiency and some requirements for the maximum and minimum temperature of the heat transfer fluid that feeds the cycle, obtaining promising results. The other one is a new proposal called Recuperated and Double Expanded (RDE) cycle, aimed to translate the good features of HRB from closed heat sources to open ones, where the performance of HRB is limited. Both cycles are compared to some reference ones. Results show that the HRB cycle is a good candidate for finite closed heat sources, particularly with maximum temperature around 400 °C and with temperature changes of the heat transfer fluid from 100 °C to 150 °C. The RDE cycle exhibits good performance for finite open heat sources with maximum temperatures between 200 °C and 400 °C, and it behaves similarly to tri-lateral cycles.
Advances in solar thermal power plants based on pressurised central receivers and supercritical power cycles
(Elsevier, 2023-07-28) Guedez Mata, Rafael; Linares Hurtado, José Ignacio; Reyes Belmonte, Miguel Ángel; Montes Pita, María José
This work addresses the comparative thermo-economic study of different configurations of solar thermal power plants, based on supercritical power cycles and pressurised central receiver systems. For all the cases examined, two innovations are introduced in the solar subsystem, compared to other similar studies. Firstly, the heat transfer fluid in the receiver is either a pressurised gas or a supercritical fluid. Secondly, the receiver is composed of compact structures performing as absorber panels, arranged in a radial configuration. The investigation considers different supercritical CO2 recompression cycles of 50 MWe, including a novel proposal of a directly coupled cycle with heat input downstream of the turbine. Furthermore, the study evaluates different heat transfer fluids in the receiver, specifically CO2, N2, and He, concluding that the former is preferred due to its better thermal performance. The main results show that an increase in the receiver inlet pressure yields to a reduction in its size, favouring the thermal efficiency but penalising the optical efficiency of the solar field. Therefore, optimal working pressures may exist for each configuration, depending on the operating temperature. When comparing the optimal configurations, it is observed that the plant based on the intercooling cycle demonstrates the highest overall efficiency, reaching 32.05%. At last, an economic analysis is conducted to assess the viability of the identified optimal configurations. In this regard, the plant based on the partial-cooling cycle exhibits the lowest levelised cost of electricity at 0.15 $/kWh. This is primarily due to its lower investment cost. The innovative directly coupled cycle follows closely with a cost of 0.17 $/kWh, driven by its high electricity production resulting from its low self-consumption.
An Experimental and Numerical Analysis of the Compression of Bimetallic Cylinders
(MDPI, 2019-12-07) Herrero, José Manuel; Aragón, Ana María; Lorenzo Martín, Cinta; Yanguas Gil, Ángel; Martins, Paulo A. F.; Camacho López, Ana María; Rodríguez Prieto, Álvaro; Bernal Guerrero, Claudio
This paper investigates the upsetting of bimetallic cylinders with an aluminum alloy center and a brass ring. The influence of the center-ring shape factor and type of assembly fit (interference and clearance), and the effect of friction on the compression force and ductile damage are comprehensively analyzed by means of a combined numerical-experimental approach. Results showed that the higher the shape factor, the lower the forces required, whereas the effect of friction is especially important for cylinders with the lowest shape factors. The type of assembly fit does not influence the compression force. The accumulated ductile damage in the compression of bimetallic cylinders is higher than in single-material cylinders, and the higher the shape factor, the lower the damage for the same amount of stroke. The highest values of damaged were found to occur at the middle plane, and typically in the ring. Results also showed that an interference fit was more favorable for preventing fracture of the ring than a clearance fit. Microstructural analysis by scanning electron microscopy revealed a good agreement with the finite element predicted distribution of ductile damage.
Análisis comparativo de modelos de bloques rígidos triangulares en el estudio mecánico de procesos de estirado por límite superior.
(CSIC, 2004-02-28) Rubio Alvir, Eva María; Domingo Navas, María Rosario; González, C.; Sanz, A.; CSIC
El objetivo principal de este trabajo es estudiar la configuración geométrica optimizada para llevar a cabo el embutido mecánico de placas. Para ello, se ha realizado un análisis comparativo de algunas configuraciones geométricas y cinemáticas adecuadas del material situado en la zona de deformación. En concreto, se han elegido varios modelos de zona rígida triangular, para cada uno de ellos se ha calculado la energía global implicada en el proceso y se ha realizado una estimación de sus diferentes componentes. El cálculo de la energía se ha realizado aplicando el Teorema de la Cota Superior en condiciones de deformación plana y fricción parcial. Además, se ha establecido el rango de utilización de las configuraciones seleccionadas.
Analysis and comparison of Integrated Solar Combined Cycles using parabolic troughs and linear Fresnel reflectors as concentrating systems
(Elsevier, 2015-11-12) Abbas, Rubén; Rovira de Antonio, Antonio José; Barbero Fresno, Rubén; Montes Pita, María José; Varela Díez, Fernando
This paper compares the annual performance and economic feasibility of Integrated Solar Combined Cycles (ISCC) using two solar concentration technologies: parabolic trough collectors (PTC) and linear Fresnel reflectors (LFR). Integration of solar energy to the steam turbine of a combined cycle gives some advantages: the first one is the fuel saving due to the solar contribution and, additionally, the second one is that this contribution takes place especially in highly insolated periods with high ambient temperatures, when conventional combined cycles decrease their power rate and work with decreased efficiency. Previous works showed the convenience of ISCC using PTC and direct steam generation in locations with severe climatology. Besides, LFR technology is currently considered as a good option for reducing the cost of concentrating solar power. Thus, in the present work both concentrating technologies are studied and compared. Solar contribution is only used for evaporating water, increasing the production of the high pressure level of the steam generator. Two locations, Almeria and Las Vegas, are selected for the annual analyses. Results show that the proposed evaporative configurations increase the annual performance. Also, the thermal contribution is higher with PTC, but LFR may improve the economic feasibility of the plant.

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