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

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

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

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