Numerical study of the pressure drop phenomena in wound woven wire matrix of a Stirling regenerator

Friction pressure drop correlation equations are derived from a numerical study by characterizing the pressure drop phenomena through porous medium of both types namely stacked and wound woven wire matrices of a Stirling engine regenerator over a specified range of Reynolds number, diameter and porosity. First, a finite volume method (FVM) based numerical approach is used and validated against well known experimentally obtained empirical correlations for a misaligned stacked woven wire matrix, the most widely used due to fabrication issues, for Reynolds number up to 400. The friction pressure drop correlation equation derived from the numerical results corresponds well with the experimentally obtained correlations with less than 5% deviation. Once the numerical approach is validated, the study is further extended to characterize the pressure drop phenomena in a wound woven wire matrix model of a Stirling engine regenerator for a diameter range from 0.080 to 0.110 mm and a porosity range from 0.472 to 0.638 within the same Reynolds number range. Thus, the new correlation equations are derived from this numerical study for different flow configurations of the Stirling engine regenerator. The results indicate flow nature and complex geometry dependent friction pressure drop characteristics within the present Stirling engine regenerator system. It is believed that the developed correlations can be applied with confidence as a cost effective solution to characterize and hence to optimize stacked and woven Stirling engine efficiency in the above specified ranges

Numerical study of the heat transfer in wound woven wire matrix of a Stirling regenerator

Nusselt number correlation equations are numerically derived by characterizing the heat transfer phenomena through porous medium of both stacked and wound woven wire matrices of a Stirling engine regenerator over a specified range of Reynolds number, diameter and porosity. A finite volume method (FVM) based numerical approach is proposed and validated against well known experimentally obtained empirical correlations for a random stacking woven wire matrix, the most widely used due to fabrication issues, for Reynolds number up to 400. The results show that the numerically derived correlation equation corresponds well with the experimentally obtained correlations with less than 6% deviation with the exception of low Reynolds numbers. Once the numerical approach is validated, the study is further extended to characterize the heat transfer in a wound woven wire matrix model for a diameter range from 0.08 to 0.11 mm and a porosity range from 0.60 to 0.68 within the same Reynolds number range. Thus, the new correlation equations are numerically derived for different flow configurations of the Stirling engine regenerator. It is believed that the developed correlations can be applied with confidence as a cost effective solution to characterize and hence to optimize stacked and wound woven wire Stirling regenerator in the above specified ranges

Energetic study of ultrasonic wettability enhancement

[EN]Many industrial and biological interfacial processes, such as welding and breathing depend directly on wettability and surface tension phenomena. The most common methods to control the wettability are based on modifying the properties of the fluid or the substrate. The present work focuses on the use of high-frequency acoustic waves (ultrasound) for the same purpose. It is well known that ultrasound can effectively clean a surface by acoustic cavitation, hence ultrasonic cleaning technology. Besides the cleaning process itself, many authors have observed an important wettability enhancement when liquids are exposed to low and high (ultrasonic) frequency vibration. Ultrasound goes one step further as it can instantly adjust the contact angle by tuning the vibration amplitude, but there is still a lack of comprehension about the physical principles that explain this phenomenon. To shed light on it, a thermodynamic model describing how ultrasound decreases the contact angle in a three-phase wetting system has been developed. Moreover, an analytical and experimental research has been carried out in order to demonstrate that ultrasound is an important competitor to surfactants in terms of energy efficiency and environmental friendliness.The projects leading to this research have received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement N° 654479 WASCOP and N°792103 SOLWARIS

Ultrasound and Eco-Detergents for Sustainable Cleaning

Green chemistry faces a major challenge imposed by the Sustainable Development Goals (6, 14 and 15) defined in the 2030 Agenda. In the case of cleaning products (detergents), the challenges often become a paradox: even if it is biodegradable, no surfactant is harmless to aquatic life. Compared to other studies in the field, this paper covers ultrasound–detergent interactions beyond the cavitation removal process. It also considers synergistic effects with regard to the initial wetting phase and final rinsing. It concludes that the best detergent–ultrasound combination is that which minimises receding and critical sliding angles. At the same time, detergent concentration should be reduced so as to just to capture grease in micelles and avoid reattachment during rinsing. In combination with ultrasound, the concentration of eco-detergents can thus be reduced by up to 10% of their nominal value while attaining the same results.The projects leading to this research have received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreements No. 654479 WASCOP and No. 792103 SOLWARIS

Non-Immersion Ultrasonic Cleaning: An Efficient Green Process for Large Surfaces with Low Water Consumption

Ultrasonic cleaning is a developed and widespread technology used in the cleaning industry. The key to its success over other cleaning methods lies in its capacity to penetrate seemingly inaccessible, hard-to-reach corners, cleaning them successfully. However, its major drawback is the need to immerse the product into a tank, making it impossible to work with large or anchored elements. With the aim of revealing the scope of the technology, this paper will attempt to describe a more innovative approach to cleaning large area surfaces (walls, floors, façades, etc.) which involves applying ultrasonic cavitation onto a thin film of water, which is then deposited onto a dirty surface. Ultrasonic cleaning is an example of the proliferation of green technology, requiring 15 times less water and 115 times less power than conventional high-pressurized waterjet cleaning mechanisms. This paper will account for the physical phenomena that govern this new cleaning mechanism and the competition it poses towards more conventional pressurized waterjet technology. Being easy to use as a measure of success, specular surface cleaning has been selected to measure the degree of cleanliness (reflectance) as a function of the process’s parameters. A design of experiments has been developed in line with the main process parameters: amplitude, gap, and sweeping speed. Regression models have also been used to interpret the results for different degrees of soiling. The work concludes with the finding that the proposed new cleaning technology and process can reach up to 98% total cleanliness, without the use of any chemical product and with very low water and power consumption.This research was funded by European Union’s Horizon 2020 research and innovation programme under grant agreement Nº 654479 WASCOP and Nº 792103 SOLWAR

On modelling of laser assisted machining: forward and inverse problems for heat placement control

Laser assisted machining (LAM) is one of the most efficient ways to improve the machinability of difficult-to-cut materials (e.g. Nickel-based superalloys). In the conventional LAM process, the laser beam is focused ahead of the cutting area at a fixed location, which leads to a series of restrictions, e.g. small heating area and non-uniform heat distribution due to the limitation of beam size and energy distribution. In this paper, a novel spatially and temporally (S&T) controlled laser heating method was proposed, in which a large area can be heated up with a small laser spot by controlling the beam scanning, i.e., laser power, path and speed of scanning. The laser configuration for the prescribed HAZ (heat affected zone) was achieved by solving the inverse heat conduction problem where the laser power together with either laser path or laser speed were optimised to achieve a particular temperature distribution in the chip to be removed by the following milling cutter. The proposed S&T laser heating method was thoroughly validated both for the direct and, the more important, inverse heating models by performing extensive temperature experiments by both infrared thermal camera and thermocouple array and further verified by laser assisted milling (LAMill) tests of Inconel 718 for large widths of cuts. The results showed that by applying path-optimised LAMill based on the inverse solution of the thermal problem, the peak and mean principal cutting forces were reduced by 55% and 47.8% respectively compared with the conventional dry milling process while the surface roughness improved by at least 14%. Moreover, after controlling the HAZ using the inverse thermal problem, a microstructure analysis of the machined surface showed that the proposed laser heating method avoids overheating of the workpiece below the planned depth of cut for the milling operation

Scrapping of PEKK-based thermoplastic composites retaining long fibers and their use for compression molded recycled parts

In this work, a novel method for a more sustainable recycling and cost-efficient manufacturing technique of polyether ketone ketone (PEKK) based thermoplastic composite materials is proposed to recover and reprocess waste and end-of-life materials in the aerospace industry. For the recycling of carbon fiber reinforced thermoplastics (CFrTP), an innovative scrapping process based on mechanical cutting was developed and the properties of the obtained scrap and the recycled panel were analyzed. Thus, a cutting tool was developed for the delamination of the input material so that long fibers can be retained in the resulting scrap. Different processing approaches of material scrapping were evaluated, aiming to obtain manageable scrap that can be subsequently used for a compression molding process. Additionally, an automatic process was evaluated to manage the scrap and perform the corresponding lay-up to manufacture high-quality thermoplastic composite products with recycled materials

A review of conventional and innovative-sustainable methods for cleaning reflectors in concentrating solar power plants

The severe soiling of reflectors deployed in arid and semi arid locations decreases their reflectance and drives down the yield of the concentrating solar power (CSP) plants. To alleviate this issue, various sets of methods are available. The operation and maintenance (O&M) staff should opt for sustainable cleaning methods that are safe and environmentally friendly. To restore high reflectance, the cleaning vehicles of CSP plants must adapt to the constraints of each technology and to the layout of reflectors in the solar field. Water based methods are currently the most commonly used in CSP plants but they are not sustainable due to water scarcity and high soiling rates. The recovery and reuse of washing water can compensate for these methods and make them a more reasonable option for mediterranean and desert environments. Dry methods, on the other hand, are gaining more attraction as they are more suitable for desert regions. Some of these methods rely on ultrasonic wave or vibration for detaching the dust bonding from the reflectors surface, while other methods, known as preventive methods, focus on reducing the soiling by modifying the reflectors surface and incorporating self cleaning features using special coatings. Since the CSP plants operators aim to achieve the highest profit by minimizing the cost of cleaning while maintaining a high reflectance, optimizing the cleaning parameters and strategies is of great interest. This work presents the conventional water-based methods that are currently used in CSP plants in addition to sustainable alternative methods for dust removal and soiling prevention. Also, the cleaning effectiveness, the environmental impacts and the economic aspects of each technology are discussed

Influence of surface integrity induced by multiple machining processes upon the fatigue performance of a nickel based superalloy

Machining operations are of key importance to the fatigue performance of nickel based superalloys due to the high thermal/mechanical loadings yielded on the machined workpiece which can significantly alter the surface integrity of the components. Therefore, understanding the influence mechanisms of machining induced surface integrity upon fatigue response is vital to determine their manufacturing processes and applications. In this respect, this paper investigates the surface integrity of nickel based superalloy subject to different mechanical and thermal loadings induced by various machining processes including conventional machining (e.g. finish and rough milling) and nonconventional machining (e.g. laser assisted milling and abrasive waterjet cutting) methods, as well as their influences upon fatigue performance and failure mechanisms. In-depth surface metallurgical and crystallographic analysis has been conducted to reveal the surface damage mechanisms, which allows the description of the machining induced mechanical and thermal alterations on the machined workpiece. Furthermore, the examination of the fractography from the fatigue specimen has been conducted, which enables the understanding of the influence mechanism of the corresponding surface defects on the fatigue crack initiation and propagation, subject to a four points bending fatigue test. While the resulted S-N curves indicate that the high cycle fatigue of machined nickel based superalloy is mainly dominated by the machining induced residual stress conditions, the surface defects from different machining processes can particularly influence fatigue crack initiation and propagation mechanisms in both the low and high cycle regimes

Fisicoquímica de la limpieza por ultrasonidos sin inmersión

170 p.La presente tesis se centra en el estudio y escalado de una tecnología disruptiva denominada "limpieza por ultrasonidos sin inmersión". La limpieza ultrasónica convencional se basa en la introducción de componentes sucios en un baño líquido, al cual, se le aplica ultrasonido de alta intensidad que desprende las partículas. La necesidad de sumergir el componente en un recipiente supone una desventaja diferencial frente a otros procedimientos como el cepillado y los chorros de agua a presión. El estudio parte de la hipótesis de poder aplicar los mismos principios de limpieza sin necesidad de sumergir el objeto en cuestión. Para ello, se plantea y se demuestra el concepto aplicar el ultrasonido a través de un puente capilar sustentado entre el emisor de ultrasonido (sonotrodo) y la superficie a limpiar. El puente capilar se barre a lo largo de la superficie, dando lugar a un novedoso proceso de limpieza. De ahí la motivación y principal objetivo del trabajo realizado: estudiar y comprender los fenómenos fisicoquímicos que intervienen durante la limpieza por ultrasonidos sin inmersión. Para ello, se han combinado modelos analíticos, experimentación a escala de laboratorio y escalado de la tecnología para la limpieza de componentes de concentración solar, donde el grado de limpieza impacta directamente sobre la producción energética. El principal resultado del estudio teórico es el planteamiento, modelizado termodinámico y validación de un mecanismo de no-retorno por el cual, los sistemas de tres fases aumentan su mojabilidad mecánicamente al inducirles vibración de alta frecuencia. Dicho aumento de mojabilidad es la clave a la hora de generar un puente capilar estable entre el sonotrodo y el sustrato. Tanto analíticamente como experimentalmente, se ha podido concluir que la eficiencia energética del sonido a la hora de aumentar la mojabilidad entre fases es similar a la del SDBS, siendo a su vez 8 órdenes de magnitud superior al calor. A su vez, se ha estudiado la sinergia de la tecnología con detergentes de carácter ecológico.De cara al proceso de arranque de partículas, se ha concluido que, el efecto de la cavitación acústica es 4 veces superior al aumento de mojabilidad. Las variables críticas de proceso son la potencia del sonido, la altura del puente y la velocidad de barrido. La combinación de las tres variables puede optimizarse, dando lugar a un equilibrio entre consumo, productividad y grado de limpieza. Además, se ha estudiado la sinergia de la tecnología con detergentes de carácter ecológico.Finalmente se ha escalado el sistema de limpieza para poder trabajar en una planta energética del sector termo-solar. Para ello, se ha desarrollado e integrado un equipo capaz de limpiar una faceta completa de un heliostato. Se ha comparado la tecnología frente a la limpieza por chorros de agua a presión, concluyendo que el ultrasonido requiere de 6.4 veces menor cantidad de agua y 2.7 veces menos energía eléctrica. La tecnología tiene por lo tanto el potencial de impactar favorablemente en los tres pilares de la sostenibilidad: economía, sociedad y medioambiente