Flow Boiling Heat Transfer; Experimental Study of Hydrocarbon Based Nanorefrigerant in a Vertical Tube

Flow boiling is a complex process but very efficient for thermal management in different sectors; enhancing flow boiling heat transfer properties is a research field of great interest. This study proposes the use of various nanomaterials, carbon-based materials, and metal oxides; in n-pentane as a hydrocarbon-based refrigerant to enhance the flow boiling heat transfer coefficient. This thermal property has been experimentally evaluated using a vertical evaporation device of glass with an internal diameter of 20 mm. The results have shown that proposed nanomaterials dispersion in n-pentane has a limited effect on the thermophysical properties and is conditioned by their dispersibility but promotes a significant increment of pentane heat transfer coefficient (h), increasing the overall heat transfer coefficient (U) of the evaporator. The enhanced heat transfer performance is attributed to the behavior of nanoparticles under working conditions and their interaction with the working surface, promoting a higher generation of nucleation sites. The observed behavior suggests a heat transfer mechanism transition from forced convection to nucleate heat transfer, supported by visual observations

Designing multifunctional pigments for an improved energy efficiency in buildings

Materials science offers solutions that when are combined can offer important energy savings in the building sector. In this study, high reflectance coating and thermal storage capacity are combined with the aim of improving energy efficiency in buildings. For this issue a multifunctional pigment having a phase change material adsorbed on its surface and a high total solar reflectance has been manufactured. The total solar reflectance of the pigment will make the paint to reflect the sunlight radiation in the infrared part of the spectrum reducing the amount of absorbed radiation. This high reflection provides a surface level effect as is a passive stimulus-responsive solution that acts with sunlight radiation. On the other hand, the thermal storage capability provides a bulk level effect as is passive stimulus-responsive solution acting by temperature changes, making it possible to use constructive materials as a thermal energy storage media. The preparation process is described and the pigment is characterized conveniently. The thermal performance of corresponding pigmented coatings was evaluated by an experiment simulation in which different boxes were covered with the coating containing the multifunctional pigment and traditional pigmented coating on their tops. The indoor air temperature and the interior temperature of the substrate were measured obtaining differences of 4–5°C.European Union Seventh Framework Programme, FP7-NMP-2010-Small-5 (under grant agreement no 280393) Dpto. Educación, Política Lingüística y Cultura of the Basque Goverment, IT-630-13 Ministerio de Ciencia e Innovación, MAT2013-42092-R Engineering and Physical Sciences Research Council, EP/I00393

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

Effects of Graphene Oxide and Chemically-Reduced Graphene Oxide on the Dynamic Mechanical Properties of Epoxy Amine Composites

Composites based on epoxy/graphene oxide (GO) and epoxy/reduced graphene oxide (rGO) were investigated for thermal-mechanical performance focusing on the effects of the chemical groups present on nanoadditive-enhanced surfaces. GO and rGO obtained in the present study have been characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and X-ray powder diffraction (XRD) demonstrating that materials with different oxidation degrees have been obtained. Thereafter, GO/epoxy and rGO/epoxy nanocomposites were successfully prepared and thoroughly characterized by dynamic mechanical thermal analysis (DMTA) and transmission electron microscopy (TEM). A significant increase in the glass transition temperature was found in comparison with the neat epoxy. The presence of functional groups on the graphene surface leads to chemical interactions between these functional groups on GO and rGO surfaces with the epoxy, contributing to the possible formation of covalent bonds between GO and rGO with the matrix. The presence of oxidation groups on GO also contributes to an improved exfoliation, intercalation, and distribution of the GO sheets in the composites with respect to the rGO based composites.Authors would like to acknowledge the Basque Government funding within the ELKARTEK 2015-2016 (KK-2015/00094) and 2016-2017 (KK-2016/00097) Programme, "ACTIMAT", ETORGAI 2014, Graphnology (ER-2014/00014) and Ayudas para apoyar las actividades de los grupos de investigacion del sistema universitario vasco (IT718-13)

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

Systematic Approach to the Synthesis of Cobalt-Containing Polyoxometalates for Their Application as Energy Storage Materials

New energy storage materials are an object of study within the framework of the global energy transition. The development of renewable sources is being boosted thanks to stationary energy storage systems such as redox flow batteries (RFBs). This work reports the synthesis of the cobalt-containing Keggin-type polyoxometalates [CoW12O40]6− (CoW12) and [Co(H2O)SiW11O39]6− (CoSiW11), which have previously been shown to have applicability in RFBs. These procedures were reassessed to meet the strict requirements associated with the further implementation of RFBs, including fast and affordable synthetic procedures with high reaction yields. In contrast to the lengthy and complicated synthetic approaches published to date, the optimized synthesis reported in this work enables the isolation of the pure crystalline salt of the CoW12 anion with a 75% reduction of the time of the whole reaction procedure, eliminating tedious steps such as the recrystallization and including a 20% increased yield. The control of the stoichiometry, fine-tuning of reaction conditions, and the identification of intermediate species, as well as the acidic equilibria taking place during the process, were monitored via thermal, spectroscopic, and structural analyses. In the case of the CoSiW11 anion, its preparation was based on a simple and highly efficient procedure. Moreover, promising electrochemical properties were observed with the use of the one-pot synthetic approach, in which the stoichiometric amounts of the starting reagents are dissolved in the supporting electrolyte to be directly implemented as the electrolyte for a RFB.This work was developed within the framework of the Almagrid project, CER-20191006 funded by Centro para el Desarrollo Tecnológico y la innovación (CDTI). Call for proposals: Accreditation and granting of aid for technological centers of excellence “Cervera”. In addition, this research was funded by the Basque Government within the framework of ‘Research on complementary energy storage technologies, and its combination in efficient and competitive systems for its stationary application in the grid’ project, grant number KK-2022/00043.B.A. and J.G.Z. thank Eusko Jaurlaritza/Gobierno Vasco for funding (grant IT1722-22)

A Review on Sustainable Inks for Printed Electronics: Materials for Conductive, Dielectric and Piezoelectric Sustainable Inks

In the last decades, the demand for electronics and, therefore, electronic waste, has increased. To reduce this electronic waste and the impact of this sector on the environment, it is necessary to develop biodegradable systems using naturally produced materials with low impact on the environment or systems that can degrade in a certain period. One way to manufacture these types of systems is by using printed electronics because the inks and the substrates used are sustainable. Printed electronics involve different methods of deposition, such as screen printing or inkjet printing. Depending on the method of deposition selected, the developed inks should have different properties, such as viscosity or solid content. To produce sustainable inks, it is necessary to ensure that most of the materials used in the formulation are biobased, biodegradable, or not considered critical raw materials. In this review, different inks for inkjet printing or screen printing that are considered sustainable, and the materials that can be used to formulate them, are collected. Printed electronics need inks with different functionalities, which can be mainly classified into three groups: conductive, dielectric, or piezoelectric inks. Materials need to be selected depending on the ink’s final purpose. For example, functional materials such as carbon or biobased silver should be used to secure the conductivity of an ink, a material with dielectric properties could be used to develop a dielectric ink, or materials that present piezoelectric properties could be mixed with different binders to develop a piezoelectric ink. A good combination of all the components selected must be achieved to ensure the proper features of each ink.This publication is supported by the SUINK project funded by the European Union’s Horizon Europe research and innovation programme under Grant Agreement No. 101070112. Funded by the Basque Government ELKARTEK2021 (KK-2021/00040) and ELKARTEK2023 KK-2023/0005

Slot-Die Process of a Sol–Gel Photocatalytic Porous Coating for Large-Area Fabrication of Functional Architectural Glass

The slot-die process is an appealing technology for the fabrication of coatings on large-area substrates. However, its application on the production of photocatalytic coatings based on sol–gel formulations remains virtually unexplored. Thus, assessing the suitable formulation of the sol and operational parameters that allow one to yield high-efficacy photocatalyst coatings is a current challenge. This work aims to analyze the transferability of titania sol formulation optimized for dip-coating processes to slot-die technology. In this sense, firstly, the sol formulation is optimized by analyzing the influence of several types of surfactants on the microstructural features and photoactivity of TiO2 coatings’ growth on glass substrates. All formulations rendered a meaningful porosity and nanoscopic anatase crystallites (11–15 nm) with optical band gap values close to the expectation (3.25–3.31 eV). Accordingly, the performance of the photocatalytic dye degradation was closely related to the porosity and crystallite size led by each titania sol, and no meaningful differences were found between the results provided by the coatings developed by dip-coating and the slot-die method, which demonstrates the capability of the latter for its application on a large-scale fabrication of photocatalytic coatings.This research was funded by the Basque Government (IT1291-19), the Spanish Ministry of Science and Innovation (MICINN project: PID2019-108028GB-C21), and the European Union’s Horizon 2020 research and innovation program (grant agreement N° 792103 SOLWARIS)

Understanding informal jewellery apprenticeship in Ghana: Nature, processes and challanges

Context: The processes of acquiring education in jewellery in Ghana has been dominated by the informal apprenticeship system and it forms the backbone of the workforce of the jewellery industry in Ghana. However, the patronage of informal jewellery apprenticeship in Ghana in recent times has been on decline even though it has the potential of training human resources to transform Ghana’s precious mineral resources sector.This is based on the belief that jewellery trade and its training are shrouded in secrecy, in other words, the jewellery trade is considered to be a sacred profession where information on its operating systems are not allowed to be shared easily. It is believed to be associated with cult and magic, hence the reluctant to admit people who are from outside the family of particular jewellery enterprise. This study is sought to bring to fore the understanding nature, processes and challenges of the informal jewellery apprenticeship in Ghana. Approach: The study adopted the descriptive and phenomenology research designs (qualitative research methods). Jewellers who own a jewellery business and who are training other people through apprenticeships as well as people who are trained are observed and interviewed. A sample size was selected through purposive and convenience sampling techniques from four jewellery enterprises in Accra, Ghana. A thematic analysis plan was adopted to generate fndings of the study. Findings: The results show that for a person to train as a jeweller, s/he has to enrol by going through induction, futhremore fees (money and perishable items) are to be paid. The training content is driven by orders received by the master jeweller, thereby making it unstructured and lacking criteria for assessing the performance and progress of apprentice jewellers. Teaching and learning methods are usually on-the-job training that rely on demonstrations and observation. Conclusion: Informal jewellery apprenticeship in Ghana uses a fexible, cost-efective approach for transferring jewellery making skills from masters to apprentice jewellers, and it has substantial potential for improving skills training in the country. Sometimes the reluctant of some jeweller to train others is to keep the trade to family members only

Metal-organic aerogels based on titanium(IV) for visible-light conducted CO2 photoreduction to alcohols

Metal-organic frameworks (MOFs) imply an appealing source of photocatalysts as they combine porosity with tailorable electronic properties and surface chemistry. Herein, we report a series of unprecedented metal-organic aerogels (MOAs) comprised by Ti(IV) oxo-clusters and aromatic dicarboxylic linkers as an alternative to microporous MIL-125 and MIL-125-NH2 MOFs. Discrete titanium oxo-clusters polymerized upon the addition of the dicarboxylic linkers to give rise to a metal-organic gel. Their supercritical drying led to aerogels comprised by nanoscopic particles (ca. 5-10 nm) cross-linked into a meso/macroporous microstructure with surface area ranging from 453 to 617 m2·g-1, which are comparatively lower than the surface area of the microporous counterparts (1336 and 1145 m2·g-1, respectively). However, the meso/macroporous microstructure of MOAs can provide a more fluent diffusion of reagents and products than the intrinsic porosity of MOFs, whose narrower channels are expected to imply a more sluggish mass transport. In fact, the assessment of the continuous visible-light-driven photocatalytic CO2 reduction into methanol shows that MOAs (221-786 [M] mol·g-1·h-1) far exceed not only the performance of their microporous counterparts (49-65 [M]mol·g-1·h-1) but also surpass the production rates provided by up-to-date reported photocatalysts.The authors gratefully acknowledge the financial support from the European Union's Horizon 2020 research and innovation program (grant agreement No.101037428), the Basque Government (KK-2016/ 00095-LISOL IT1291-19 and IT1722-22) and the Spanish Ministry of Science and Innovation (TED2021-129810B-C21 and TED2021- 129810B-C22 funded by MCIN/AEI/10.13039/501100011033 and Next Generation EU/PRTR, PID2019-108028GB-C21 and PID2019- 104050RA-I00 funded by MCIN/AEI/10.13039/501100011033). Technical and human support provided by SGIker (UPV/EHU, MICINN, GV/ EJ, and ESF) is also acknowledged