Thermophysical, rheological and dielectric behaviour of stable carbon black dispersions in PEG200

Phase change materials can store or release large amounts of energy during phase change. An increasing number of authors are studying the influence of the dispersion of nanometric particles on these materials. This article presents the design and experimental characterization of temporal stability, thermal conductivity, isobaric heat capacity, phase change transitions, rheological behaviour, and dielectric properties of nano-enhanced phase change materials based on carbon black (CB) dispersions in polyethylene glycol (PEG200) by using polyvinylpyrrolidone (PVP) as surfactant. We studied the temporal stability of carbon black nanoparticles dispersed in PEG200 using dynamic light scattering and spectrophotometry techniques. All the samples showed good temporal stability, since the measurements of the hydrodynamic size of the nanoparticles are practically constant over time and the wavelength observed by UV–vis shows a small variation of around 4% for static conditions. We observed small changes in thermal conductivity and isobaric heat capacity. Nevertheless, the thermograms evidence how the latent heat clearly increases with the load of carbon black nanoparticles up to four times that of the PEG200. The viscosity studies do not show variation with shear rate, indicating a Newtonian behaviour, excluding the 2.0 wt% CB/PVP + PEG200 nanofluid. Additionally, we noticed frequency dependent and independent regions for permittivityAgencia Estatal de Investigación | Ref. PID2020-112846RB-C21Agencia Estatal de Investigación | Ref. PDC2021-121225-C21Ministerio de Universidades | Ref. 33.50.460A.752European Cooperation in Science and Technology | Ref. IG15119Universidade de Vigo/CISU

The strategies to support the COVID-19 vaccination with evidence-based communication and tackling misinformation

COVID-19 vaccinations are about to begin in various countries or are already ongoing. This is an unprecedented operation that is also met with a loud response from anti-vaccine communities—currently using all available channels to manipulate public opinion. At the same time, the strategy to educate on vaccinations, explain their mechanism of action, and build trust in science is subdued in different world parts. Such actions should go much beyond campaigns promoting the COVID-19 vaccines solely on the information provided by the health institutions and national authorities. In this paper, actions provided by independent expert groups needed to counteract the anti-vaccine propaganda and provide scientific-based information to the general public are offered. These actions encompass organizing groups continuously communicating science on COVID-19 vaccines to the general public; tracking and tackling emerging and circulating fake news; and equipping celebrities and politicians with scientific information to ensure the quality of messages they communicate, as well as public letters, and statements of support for vaccination by healthcare workers, recognized scientists, VIPs, and scientific societies; and no tolerance to false and manipulated claims on vaccination spread via traditional and social media as well as by health professionals, scientists, and academics. These activities should be promptly implemented worldwide, regardless of the current status and availability of the COVID-19 vaccine in a particular region. If we are about to control the pandemic for the sake of public benefit, it is high time to collectively speak out as academic and medical societies with support from decision-makers. Otherwise, the battle will be lost to those who stand against scientific evidence while offering no feasible solution to the problem

The influence of ash content on thermophysical properties of ethylene glycol based graphite/diamonds mixture nanofluids

Authors wish to thank Dr. Magdalena Gizowska from Department of Nanotechnology, Institute of Ceramics and Building Materials, Warsaw, Poland for measurements of density of nanopowders. The authors acknowledge also Loïc Joanny from CMEBA, Université Rennes 1 and Mathieu Pasturel from the Institut des Sciences Chimiques de Rennes, Université Rennes 1 for performing respectively SEM and XRD characterization.International audienceSince the second half of the twentieth century, nanofluids are very promising engineering materials that can find numerous applications in the processes of heat exchange. Scientist and engineers are developing new and more advanced nanosuspensions which may differ from their physical properties, production costs and practical use. The aim of this paper is to study the differences between two nanofluids containing a mixture of graphite and nanodiamonds with various ash content. Here, ethylene glycol was used as a base fluid. Rheological properties, thermal and electrical conductivities at a constant temperature 298.15K were investigated for nanoparticle volume content ranging from 0.004 to 0.023. It was presented that ash content in nanofluids changes significantly rheological properties of nanofluids containing graphite/nanodiamonds mixture nanoparticles. While the variation in ash content does not affect thermal conductivity of nanofluids, a big impact on electrical conductivity is reported

Nanofluids in the Service of High Voltage Transformers: Breakdown Properties of Transformer Oils with Nanoparticles, a Review

The continuous development of electrical systems and high voltage transformers builds the need for looking for new insulating media or to improve the insulating properties of commercially available transformer oils (TO) by various modification techniques. One of these techniques is the modification of existing mineral oils by the addition of different types of nanoparticles in various concentrations. These types of materials, suspensions of nanoparticles called nanofluids, have found numerous applications in the energy industry, especially in heat exchanger systems and solar cells. Much research has been done on attempts to replace mineral oils (MO), which are harmful for the environment, with natural ester oils (NE), but to make this possible, it is necessary to improve the insulating properties of these oils, for example by adding nanoparticles. This paper presents an extensive overview of the insulating properties; including for AC, DC and the lightning impulse breakdown voltage; for both mineral and natural ester oils containing various type of nanoparticles (NP). It is presented that the use of nanofluids could improve the efficiency of existing high voltage infrastructures with a low financial cost

Experimental study on rheological properties, thermal conductivity and dielectric properties of TiN-EG nanofuids

International audienc

Thermal and physical characterization of PEG phase change materials enhanced by carbon-based nanoparticles

This paper presents the preparation and thermal/physical characterization of phase change materials (PCMs) based on poly(ethylene glycol) 400 g·mol−1 and nano-enhanced by either carbon black (CB), a raw graphite/diamond nanomixture (G/D-r), a purified graphite/diamond nanomixture (G/D-p) or nano-Diamond nanopowders with purity grades of 87% or 97% (nD87 and nD97, respectively). Differential scanning calorimetry and oscillatory rheology experiments were used to provide an insight into the thermal and mechanical changes taking place during solid-liquid phase transitions of the carbon-based suspensions. PEG400-based samples loaded with 1.0 wt.% of raw graphite/diamond nanomixture (G/D-r) exhibited the lowest sub-cooling effect (with a reduction of ~2 K regarding neat PEG400). The influences that the type of carbon-based nanoadditive and nanoparticle loading (0.50 and 1.0 wt.%) have on dynamic viscosity, thermal conductivity, density and surface tension were also investigated in the temperature range from 288 to 318 K. Non-linear rheological experiments showed that all dispersions exhibited a non-Newtonian pseudo-plastic behavior, which was more noticeable in the case of carbon black nanofluids at low shear rates. The highest enhancements in thermal conductivity were observed for graphite/diamond nanomixtures (3.3–3.6%), while nano-diamond suspensions showed the largest modifications in density (0.64–0.66%). Reductions in surface tension were measured for the two nano-diamond nanopowders (nD87 and nD97), while slight increases (within experimental uncertainties) were observed for dispersions prepared using the other three carbon-based nanopowders. Finally, a good agreement was observed between the experimental surface tension measurements performed using a Du Noüy ring tensiometer and a drop-shape analyzer.EU COST | Ref. COST-STSM-CA15119-42918EU COST | Ref. COST-STSM-CA15119-45590EU COST | Ref. COST-STSM-CA15119-45123Ministerio de Economía y Competitividad | Ref. ENE2017-86425-C2-1-R

Complex dielectric response and EDL characteristics of different types of ionic liquid iron oxide nanofluids (ionanofluids)

Ionic liquid based magnetic nanofuids (ILMFs), an important subclass of ‘IoNanofuids’, have promising prospectus in numerous technological fields. Herein, we have investigated on the dielectric response and ac conductance behaviour of 1 wt% iron oxide-based ILMFs synthesized using pyridinium-based ILs viz., 1-Butyl-4-methylpyridinium tetrafuoroborate (A), 1-Butyl-4-methylpyridinium chloride (B), 1-Butyl-4-methylpyridinium bromide (C) and 1-Butylpyridinium bromide (D), and having variable stability. The dielectric permittivity exhibited a strong correlation with temperature and frequency, especially at low frequency ranges. Havriliak-Negami (H-N) function was plotted for all the four ILMFs which demonstrated a complex dielectric behaviour. The complex dielectric responses (in the range between 10−1–107 Hz) of these ILMFs at various frequencies and temperatures showed two relaxation processes following either Debye or non-Debye nature. The ILMF synthesized in B and D were the stablest. In B, two relaxation processes at 104 Hz and 6 × 102 Hz were observed (at 373.15 K), the temperature dependence being much stronger for the second process. Cole-Cole processes are observable in both relaxations. α parameters varied in the range 0.8 – 1.0 and 0.62 – 0.9 for first and second relaxation process respectively and β parameter equal to 1 at all temperature range for both relaxation processes. In ILMF synthesized using D, Debye relaxation with two relaxation processes were observed closer at 9.1 × 103 Hz and 1.1 × 103 Hz. All the α and β parameters were 1 or 0.99 indicating same relaxation time for all molecules. With D having higher anion-cation interaction energy, Debye process could be observed. The alternating current (AC) conductance of these ILMFs tends to increase with increase in temperature as well as frequency of applied field till 105 Hz after which it decreases

Electrical Conductivity and Dielectric Properties of Ethylene Glycol-Based Nanofluids Containing Silicon Oxide–Lignin Hybrid Particles

This paper presents results of experimental investigation into dielectric properties of silicon oxide lignin (SiO2-L) particles dispersed with various mass fractions in ethylene glycol (EG). Measurements were conducted at a controlled temperature, which was changed from 298.15 to 333.15 K with an accuracy of 0.5 and 0.2 K for dielectric properties and direct current (DC) electrical conductivity, respectively. Dielectric properties were measured with a broadband dielectric spectroscopy device in a frequency range from 0.1 to 1 MHz, while DC conductivity was investigated using a conductivity meter MultiLine 3410 working with LR925/01 conductivity probe. Obtained results indicate that addition of even a small amount of SiO2-L nanoparticles to ethylene glycol cause a significant increase in permittivity and alternating current (AC) conductivity as well as DC conductivity, while relaxation time decrease. Additionally, both measurement methods of electrical conductivity are in good agreement

Electrical conductivity of titanium dioxide ethylene glycol-based nanofluids: Impact of nanoparticles phase and concentration

International audienceNanofluids containing titanium oxide nanoparticles are one of the most often investigated by researchers and their properties such as viscosity or thermal conductivity were largely reported. On the other hand, electrical conductivity of this type of nanofluids are often omitted. Therefore, this paper reports experimental data on the electrical conductivity of ethylene glycol based nanofluids with three types of titanium dioxide nanoparticles dispersed in it. Samples of all nanofluids were prepared in mass fraction between 0.01 and 0.20, and for this purpose well known two-step method was used. The electrical conductivity was measured in temperature range from 10 to 45°C. The results show effect of TiO2 nanoparticles content on electrical conductivity of ethylene glycol as well as the influence of nanoparticles phase. The highest enhancement has been noted for anatase at lowest tested temperature. Finally the experimental data were compared to available models and a new theoretical correlation was proposed