Search

We develop a Stockmayer fluid model that accounts for the dielectric responses of polar solvents (water, MeOH, EtOH, acetone, 1-propanol, DMSO, and DMF) and NaCl solutions. These solvent molecules are represented by Lennard-Jones (LJ) spheres with permanent dipole moments and the ions by charged LJ spheres. The simulated dielectric constants of these liquids are comparable to experimental values, including the substantial decrease in the dielectric constant of water upon the addition of NaCl. Moreover, the simulations predict an increase in the dielectric constant when considering the influence of ion translations in addition to the orientation of permanent dipoles. [ABSTRACT FROM AUTHOR]

By means of massive (more than 1.2 · 106 molecules) molecular dynamics simulations at 300 K we have disentangled self- and cross-dipolar contributions to the dielectric relaxation of liquid water that cannot be experimentally resolved. We have demonstrated that cross dipolar correlations are of paramount importance. They amount for almost a 60% of the total dielectric amplitude. The corresponding relaxation function is a one-step Debye-like function with a characteristic time, τcross, of the order of the phenomenological Debye time, τD. In contrast, the relaxation function corresponding to the self-contribution is rather complex and contains a fast decay related to dipolar librations and a second relaxation step that can be well described by two exponentials: a low-amplitude fast process (τ0 = 0.31 ps) and a main slow process (τself = 5.4 ps) that fully randomizes the dipolar orientation. In addition to dipolar relaxation functions, we have also calculated scattering-like magnitudes characterizing translation and rotation of water molecules. Although these processes can be considered as "jump" processes in the short time range, at the time scale of about τD–τcross, at which the cross-dipolar correlations decay to zero, the observed behavior cannot be distinguished from that corresponding to uncoupled Brownian translational and rotational diffusion. We propose that this is the reason why the Debye model, which does not consider intermolecular dipolar interactions, seems to work at time t ≳ τD. [ABSTRACT FROM AUTHOR]

A new design of a flexible and compact electrostatic generator with dielectric fluid is presented in this work. The generator utilizes the flow of dielectric fluid between two dielectric films to change the capacitance and converts mechanical energy into electrical energy. We fabricate a dielectric fluid generator (DFG) and build up an experimental setup to investigate the performance of energy harvesting. We use an optimal triangular electromechanical cycle and achieve a maximum energy harvesting power of 1.83 mW with a device that the length of the longest side is 15 cm. The power density is 35.2 μW g−1, and the conversion efficiency is 17.8%. The parameters of the DFG, including the initial voltage, the applied force, and the mechanical loading time, are studied. As a demonstration, we use the DFG to harvest electrical energy from hand tapping to power LEDs. The DFG is flexible and compact, which is promising for harvesting energy from human movements. [ABSTRACT FROM AUTHOR]

Organic compounds pose significant environmental concerns, including groundwater contamination. Clays are commonly used as liners to prevent contaminant permeation into the groundwater tables, necessitating an understanding of clay's behavior in the presence of organic compounds. The presence of organic contaminants results in changes in the dielectric constant of pore fluid, which influences the interparticle energies and double layer thickness in the soil-pore fluid system. This study aims to elucidate the mechanisms of these changes by examining the response of smectite and kaolinite to variations in the dielectric constant. Experimental tests, including Atterberg limits, unconfined compression strength, water adsorption, sedimentation, pH, and XRD, were performed on clay samples at different concentrations of water-isopropyl alcohol mixtures. Results indicate that smectite exhibits higher Atterberg limits and water adsorption capacity compared to kaolinite. Smectite also shows more pronounced changes in response to decreasing dielectric constant. Conversely, changes in kaolinite's behavior were attributed to variations in pore fluid viscosity and dipole moment. These findings emphasize the importance of considering viscosity and dipole moment alongside dielectric constant in predicting kaolinite behavior. Overall, this study enhances the understanding of how variations in pore fluid dielectric constant affect the geotechnical and geo-environmental behavior of smectite and kaolinite. [ABSTRACT FROM AUTHOR]

Introduction. Spark-erosion processing of metals and alloys granules in working liquids is the basis of a several technological processes. Efficiency of energy use in them and parameters of the resulting product largely depend on the accuracy of stabilization and regulation of pulse power in each plasma channel between the granules. To achieve this, until now only the voltage and current of the discharge pulses in the entire layer of granules have been controlled. Problem. The measurement methods, which are used, are not effective enough for monitoring the parameters of individual plasma channels and predicting the size distribution of eroded metals particles at the stage of their formation. The aim of the work is to develop a method for determining the volumes of components of plasma channels in layers of metals granules during their spark-erosion treatment to predict the size distribution of eroded metal particles at the stage of their formation, as well as to simplify the method of spectrometric analysis of the elemental composition of substances surrounding plasma channels for the operational prediction of the chemical composition of resulting products. Methodology. A series of experiments were carried out on spark-erosion processing of Al and Ag granules layers in distilled water. Using a digital camera, images of the plasma channels in them were obtained. Based on the theory of pulsed electrical breakdown of liquid dielectrics, an analysis of the components of plasma channels was carried out. Using the specialized ToupView program, the volumes of equivalent ellipsoids of rotation were determined, approximating the halos of colored radiation likely arising from streamers, as well as the spark cores of plasma channels emitting white light. The shades of the resulting radiation were studied for several metals and working liquids. The obtained data were compared with the known results of spectrometric studies for the same elements excited by similar mechanisms. Results. The theory of discharge-pulse systems for sparkerosion processing of granular conductive media has been developed in the direction of new methods for monitoring the parameters of discharge pulses and predicting the chemical composition and size distribution parameters of eroded metal particles at the stage of their production. An optic-metric method has been developed for determining the volumes of halos and cores of plasma channels. A simplified spectral method for determining the chemical composition of erosion particles based on the shade of the resulting radiation was proposed. Originality. The developed new optic-metric method makes it possible to obtain information about almost every plasma channel, which refines predictions of the size distribution of erosion particles. To implement the method, generalpurpose hardware and specialized software that is freely available are used. The developed method of simplified spectral analysis of excited atoms makes it possible to make preliminary predictions of the chemical composition of the obtained erosion particles already at the stage of their formation without the use of expensive specialized equipment. Practical significance. The ratio of the volumes of halos and cores of plasma channels between Al and Ag granules in distilled water was measured. An analysis of the emission spectra of plasma channel halos between Al, Ag and Cu granules in distilled water, Fe in ethyl alcohol, Ni-Mn-Ga and Ti- Zr-Ni alloys in liquid nitrogen, and Ti-Zr-Ni in liquid argon was carried out. Based on spectrometry data, the resulting shades of these radiations were substantiated and their description in the RGB system is given. [ABSTRACT FROM AUTHOR]

Hydraulic electrostatic actuators have become a research hotspot for their inherent flexibility and safety of human-machine interaction. This paper aims to combine the characteristics of dielectric elastomers and fluid actuators, enhancing the dielectric constant and breakdown field strength by modifying Al2O3 on the surface of nanostructured BaTiO3 and in order to develop a hydraulic electrostatic actuator with silicone rubber as the matrix material. Single-factor experiments were firstly conducted to confirm the range of three factors affecting the actuation strain of the actuator: BaTiO3@Al2O3 content, thickness of the silicone rubber elastomer film, and pre-stretching ratio coefficient. The response surface methodology was used to study the interactive influence of the above three influencing factors on the actuation strain. It was obtained that A has an insignificant influence on the actuation strain, AB has a significant influence on the actuation strain, and B, C, AC, and BC have a highly influence on the actuation strain. Maximizing actuation strain as the optimization objective yielded the combination results of each factor: BaTiO3@Al2O3 content of 2.57%, thickness of 0.60 mm, and pre-stretching ratio coefficient of 2.50. Actuation strain tests were conducted with optimized parameters under no-load. The experimental results of the actuation strain test show that the relative error between the test value and the model prediction value of 16.47% is less than 5%, and the optimization model results are reliable. The optimized hydraulic electrostatic actuator was tested for actuation strain and electrical performance under different loads. The experiment showed that the maximum actuation strain of the hydraulic electrostatic actuator was 17.20% under a load of 100 g. The critical breakdown current of the actuator ranged from 115 μA to 130 μA, and the maximum electromechanical conversion efficiency of the actuator under different loads was 67.93%. Finally, a joint actuating device was developed based on the structure of the actuator, amplifying the output displacement of the actuator to 30 mm, and the linear displacement of the soft electro-fluid actuator can be converted into a 20° rotation angle through the gear steering mechanism, thus validating the effectiveness of the hydraulic electrostatic actuator. [ABSTRACT FROM AUTHOR]

In the present global scenario, manufacturing industries are trying to make the process more sustainable by improving economic feasibility, machining efficiency, environment, and operator's safety as prescribed by ISO-14000 standards. The present study investigates the machining efficiency and sustainability analysis of the single wall carbon nano tube (SWCNT) mixed rotary electric discharge machining (EDM) process by utilizing waste vegetable oil (WVO) as a dielectric medium. Peak current, pulse on time, pulse off time, powder concentration, and tool rotation are taken as an input variable. The result reveals that SWCNT mixed rotary EDM utilizing WVO as a dielectric fluid exhibit 119.91% higher material removal rate (MRR) and 61.23% lower surface roughness (SR) as compared to the EDM process using EDM oil as a dielectric medium. Further, due to the superior thermo-physical properties of WVO, the proposed dielectric shows better surface morphology, lower recast layer thickness, better wear resistance, and low micro-hardness of machined surface as compared to EDM oil. Finally, the sustainability index analysis result concludes that WVO could be a better replacement of hydrocarbon-based oils in the EDM industry to make the process more sustainable in terms of cost, performance, ecological balance, and operator's safety. [ABSTRACT FROM AUTHOR]

A novel concentrating photovoltaic-thermal solar collector was designed, fabricated and experimentally investigated at the University of Lleida, in Spain. Two designs based on two dielectric liquids, isopropyl alcohol (IPA) and deionised water (DIW), were developed. In both cases, the solar cells were directly liquid-immersed. The study includes experiments and numerical simulations. The proposed concentrator was incorporated into a testing unit to examine its potential as a façade by controlling light and thermal flux transmitted into a building. The results show promising electrical performance and acceptable thermal performance, with thermal losses ranging from 14 to 20 W °C−1m−2. The optical efficiency was around 73% in the case of the concentrator with DIW and about 76% for the one with IPA. Regarding electrical performance, the fill factors for IPA and DIW configurations are as follows: 62.8% and 61.7%, respectively. The comparison results reveal striking differences between the testing unit with and without solar concentrators, with the concentrator-equipped unit showing around four times lower illuminance and a 50% reduction in maximum heat fluxes and interior temperature. Generally speaking, it can be said that these energy-generating façades show satisfactory behaviour and offer interesting possibilities for building-integrated applications. [ABSTRACT FROM AUTHOR]

Shape-morphing displays alter their surface geometry to convey information through three-dimensional shapes. However, rapid transformation into seamless shapes with multimodal tactile sensations poses challenges. Here, we introduce a versatile soft shape-morphing and tactile display, using a novel actuator that combines a PVC gel composite, dielectric liquid, and an electrode array. Proposed device facilitates on-demand liquid flow control through electrohydraulic actuation. Liquid channels within the device can be dynamically reconfigured using localized electrostatic zipping, enabling swift shape morphing and reconfiguration into diverse seamless 3D shapes. Our device achieves a large deformation and high output force, in a slim and lightweight framework. It also offers various haptic feedback, including dynamic tactile patterns and vibrations for localizable surface textures on the morphed shape. Additionally, its potential in robotics was demonstrated through high-speed object manipulation, leveraging liquid flow-induced inertia. In summary, our innovative soft shape-morphing tactile display could open new ways that we interact with technology, offering a more immersive and intuitive experience. [ABSTRACT FROM AUTHOR]

One potential eco-friendly variant of electro-discharge machining is dry electro-discharge machining (EDM), in which the liquid hydrocarbon–based dielectric is substituted with a gaseous medium. The primary challenge associated with dry EDM is the excessive dissipation of heat within the machining gap, which restricts its utilisation only to a microscale machining. Consequently, further modifications to the underlying mechanism of the process are being undertaken with the aim of efficient industrialising it on a larger scale. In the present study, a novel approach is proposed to enhance the efficiency of dry-EDM process while using carbon dioxide as a gaseous medium together with introducing additional external workpiece cooling with deionised water. A series of experiments were conducted to determinate the impact of external workpiece cooling with deionised water and the main machining parameters, namely pulse-on time and current intensity gas pressure, on the material removal rate, working electrode wear, and surface integrity of Inconel 625 during EDM in milling kinematics. The results demonstrated that, under the same machining parameters, the wear of the working electrode, the surface roughness, and the thickness of the recast layer were significantly reduced in the EDM with external workpiece cooling in comparison to the dry-EDM process without water cooling. Furthermore, the EDM with coolant exhibited superior performance in comparison to the dry-EDM process due to the fact that there were fewer changes in the surface morphology and chemical composition of the machined material. [ABSTRACT FROM AUTHOR]

The demand for high‐performance flexible electronic devices has propelled research toward dielectric elastomer composites that exhibit excellent stretchability, high dielectric constant, exceptional transparency, and enduring stability. Compositing with soft fillers is an emerging method that can increase the dielectric constant of the materials while retaining good flexibility. However, liquid metals inclusion results in opaque composites while liquid electrolytes inclusion brings issues with long‐term stability. In this study, compositing polymeric ionic liquids with elastomeric matrix is proposed to address these requisites. Benefiting from adjustable refractive index, high ionic conductivity, softness, and excellent stability, the prepared dielectric elastomer composites exhibit remarkable transparency, excellent elasticity, and increased dielectric constants. Notably, the composites demonstrate resilience to high temperatures up to 250 °C without compromising dielectric or mechanical properties. Furthermore, the composites retain all properties after prolonged exposure at 80 °C for 6 months, highlighting the potential for sustained performance in real‐world applications. Utilizing the exceptional characteristics of polymeric ionic liquid including dielectric elastomers, strain sensors, and alternating current electroluminescence devices are demonstrated, which also presents excellent stability over prolonged use, emphasizing the reliability and long‐term stability of the composites, and showcasing potentials for multifaceted applications in flexible electronics. [ABSTRACT FROM AUTHOR]

Heat exchange on a heat-stressed surface and the critical heat flow from it in the process of cooling this surface by a system of distributed impact submerged microjets of a dielectric liquid, depending on the velocity of these jets, were investigated experimentally for the case where the initial subcooling of the liquid in the jets to the saturation temperature comprises 40 ± 2°C. The experiments were conducted for 36 jets of the HFE-7100 dielectric liquid with an initial diameter of 174 μm, outflowing from the nozzles positioned at a distance of 1 mm from a cooling surface. It was established that the heat transfer coefficients of this surface and the critical heat flow from it are determined by the velocity of the jets, acting on the surface, and the initial subcooling of the cooling liquid, and that they are much larger than those in the case of pool boiling of the cooling liquid on the surface and in the case of its cooling by a single jet of a liquid with a small subcooling to the saturation temperature. [ABSTRACT FROM AUTHOR]

It is proved analytically that the complex growth rate n = nr + ini (nr and ni are the real and imaginary parts of n , respectively) of an arbitrary neutral or unstable oscillatory disturbance of growing amplitude in rotatory electrothermoconvection in a dielectric fluid layer saturating a sparsely distributed porous medium heated from below, for the case of free boundaries, is located inside a semicircle in the right half of the nrni − plane, whose centre is at the origin and radius = max T a P r 2 , R ea P r A , where Ta is the modified Taylor's number, Pr is the modified Prandtl number, Rea is electric Rayleigh number and A is the ratio of heat capacities. The upper limits for the case of rigid boundaries are derived separately. Furthermore, similar results are also derived for the same configuration when heated from above. [ABSTRACT FROM AUTHOR]

The authors propose a novel yet simple way of passive beamforming using a liquid antenna. A hemispherical dielectric resonator antenna filled with a dielectric liquid is considered to realise the fundamental TE111 mode, and a small, weighted metal ball is dropped inside the hemispherical container. This metal ball functions as a movable director and passively steers the realised fundamental mode of the DRA always towards the ground. The proposed design finds its applications in static‐subject‐based applications such as indoor base stations, and beam‐stabilisation/pattern‐correction works in case of dynamic‐subject‐based applications. The overall profile of the antenna is 0.60λ0 × 0.60λ0 × 0.19λ0 targeting the ISM band at 2.4 GHz with decent efficiency and far‐field characteristics. The working prototype is developed and experimentally verified. [ABSTRACT FROM AUTHOR]

The light pressure of an evanescent electromagnetic wave formed by total internal reflection near the flat interface of a dielectric and a liquid on a dielectric spherical nanoparticle located in a liquid medium is considered. Phase portraits of a two-dimensional system of equations that is equivalent to the equation of nanoparticle transportation under the influence of the force gradient of the light pressure of the evanescent field taking into account the medium resistance force are plotted. Various phase portraits can be realized both without equilibrium points and with one equilibrium point (stable focus, stable node or saddle) on the phase plane, depending on the parameters of the laser radiation and the material of the nanoparticle suspended in the water. [ABSTRACT FROM AUTHOR]

A technique for solving the one-port closed coaxial transmission line sample holder scattering equation for complex permittivity inversion for lossy materials is presented. A non-linear least-squares procedure is used for the determination of parameters for the specification of the spectral functional form of the complex permittivity. The method allows for accurate retrieval of many low- and high-permittivity dielectric materials in the frequency range of 1 GHz to 3 GHz inserted into the coaxial cell. Using this method, the complex permittivity of a number of liquids and a Maltese soil known as Bajjad soil have been extracted by measurements using a short terminated coaxial transmission line sample holder. The proposed novel inversion method is mainly based on the reflection coefficient of the test material. The measured results of the complex permittivity of liquid dielectrics such as ethanol, methanol, and TX100 are validated and compared with previously published data obtained from measurements made by the National Physical Laboratory (NPL) using a two-port measurement setup made with the same commercial coaxial transmission line sample holder used in the one-port setup. Since the technique allows broadband measurements, it has been used to characterise the soil dielectric spectrum in the frequency range of 1–3 GHz, which is also compared with results from a two-port setup of the same coaxial line. The experimental results are a validation of the proposed approach for different types of materials. [ABSTRACT FROM AUTHOR]

When using transformer insulation oil as a liquid dielectric, the oil is easily polluted by the solid particles generated in the operation of the transformer, and these metallic impurity particles have a significant impact on the insulation performance inside the power transformer. The force of the metal particles suspended in the flow insulation oil is multidimensional, which will lead to a change in the movement characteristics of the metal particles. Based on this, this study explored the motion rules of suspended metallic impurity particles in mobile insulating oil in different electric field environments and the influencing factors. A multiphysical field model of the solid–liquid two-phase flow of single-particle metallic impurity particles in mobile insulating oil was constructed using the dynamic analysis method, and the particles' motion characteristics in the oil in different electric field environments were simulated. The motion characteristics of metallic impurity particles under conditions of different particle sizes, oil flow velocities, and insulation oil qualities and influencing factors were analyzed to provide theoretical support for the detection of impurity particles in transformer insulation oil and enable accurate estimations of the location of equipment faults. Our results show that there are obvious differences in the trajectory of metallic impurity particles under different electric field distributions. The particles will move towards the region of high field intensity under an electric field, and the metallic impurity particles will not collide with the electrode under an AC field. When the electric field intensity and particle size increase, the trajectory of the metallic impurity particles between electrodes becomes denser, and the number of collisions between particles and electrodes and the motion speed both increase. Under the condition of a higher oil flow velocity, the number of collisions between metal particles and electrodes is reduced, which reduces the possibility of particle agglomeration. When the temperature of the insulation oil changes and the quality deteriorates, its dynamic viscosity changes. With a decrease in the dynamic viscosity of the insulation oil, the movement of the metallic impurity particles between the electrodes becomes denser, the collision times between the particles and electrodes increase, and the maximum motion speed of the particles increases. [ABSTRACT FROM AUTHOR]

This article investigates the behavior of two parallel layers of different miscible dielectric liquids enclosed and sandwiched between two electrodes. By applying an electric potential to one electrode while grounding the other, electro-convection occurs when the electric Rayleigh number exceeds a critical value, setting the fluid into motion and resulting in rapid mixing between the two liquids. A numerical model is developed to account for the varying ionic mobility and permittivity of the two liquids, considering their evolution based on the relative concentration field. The simulations confirm that electro-convection significantly enhances the mixing between the two liquids, as expected. Additionally, intriguing ripples are observed near the initial interface during the early stages of electro-convection instability growth. To explain and describe the flow dynamics in terms of stability analysis, a semi-analytical model is presented. This study provides insights into the mixing behavior and flow dynamics of miscible dielectric liquids under the influence of electro-convection. The findings contribute to a better understanding of the underlying mechanisms and can be valuable for applications such as microfluidics, energy conversion, and mixing processes. Further research is encouraged to explore additional parameters and optimize the control of electro-convection for practical applications. [ABSTRACT FROM AUTHOR]

Microstrip fed complementary spiral sensor (MFCSS) for dielectric characterization of liquid samples is proposed in this paper. The samples chosen are coconut oil, sunflower oil, palm oil, castor oil and paraffin. The sensor comprises a complementary spiral resonator embedded in a microstrip fed patch antenna. The resonant frequency of the sensor is 2.4GHz. The sensor is fabricated on FR4 substrate with dielectric constant 4.4, loss tangent 0.02 and thickness 1.6mm. The overall dimension of the sensor is 12.5mmx15mmx1.6mm. The compact size of the sensor is attributed to the complementary spiral resonator. The resonant frequency of the sensor shifts to a lower frequency when immersed in liquid samples. The shift in resonant frequency and reflection coefficient are used to determine the relative permittivity (εr) and loss tangent (tan δ) of liquid samples. The sensor exhibits capabilities in detecting trans fat content in coconut oil. Adulteration of oil samples can also be detected using this procedure as detailed in the paper. The MFCSS exhibits high near field, resulting in improved sensitivity (5.8%). The MFCSS offers precise measurement, the ability to detect minor variations in the dielectric properties of liquid samples, compact size and ease of fabrication. Microstrip feed provides good impedance matching to the sensor. [ABSTRACT FROM AUTHOR]

Owing to sensitivity to external perturbations such as temperature, electric field, and magnetic field, the dielectric and electro-optical properties of liquid crystals (LCs) can be easily tuned. In recent years, the dispersion of nanomaterials into LCs has proven to be an important tool for the fabrication of various devices with improved characteristics. In the present study, we have synthesized a nanocomposite of vanadium-doped titanium oxide (VTO) with the integration of molybdenum diselenide (MoSe2) and molybdenum trioxide (MoO3), designated as VTO-MSE (V-TiO2/MoSe2/MoO3), through a hydrothermal procedure and measured the dielectric features of 4′-octyl-4-biphenylcarbonitrile (also known as 8CB) LC material doped with the VTO-MSE nanocomposite at different concentrations (0.1 wt.%, 0.25 wt.%, 0.5 wt.% and 1 wt.%) in smectic A (SmA) and nematic (N) phases of 8CB at 28 °C and 36 °C, respectively. The uniform dispersion of VTO-MSE in 8CB was confirmed using polarizing optical microscopy, and the dielectric measurements were performed using frequency-dependent dielectric spectroscopy in the frequency range of 20 Hz–2 MHz. The dielectric parameters (ɛ′ and ɛ″) decreased on the dispersion of the nanocomposite in 8CB LC in the low-frequency region due to the reduction of mobile ions. The peak of the dielectric loss factor (tan δ) also shifted towards the low-frequency side because of the decrease in the mobile ion density. The threshold voltage was found to decrease for the VTO-MSE-mixed 8CB samples and dielectric anisotropy was also obtained, which shows an increase in its value for the nanocomposite dispersed systems. These results can be beneficial for the manufacture of display devices. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Liquid Crystal & Displays is the property of Chinese Journal of Liquid Crystal & Displays and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To tackle the challenges of environmentally friendly dielectric fluid, the current research focuses on the diverse biodegradable oils that are utilised as dielectric fluids in electro-discharge machining (EDM) processes. When it comes to machining extremely hard materials, EDM is a cutting-edge, non-traditional technology. As part of this research, Ti-6Al-4 V material has been machined in two phases: the first phase, using conventional EDM oil, and the second phase, utilising four distinct bio-dielectric fluids. Comparisons have been made between EDM oil and other bio-dielectric fluids in terms of machining performance measures such as material removal rates (MRR), tool wear rate (TWR), and surface roughness (SR). The primary goal of this research is to identify an appropriate bio-dielectric fluid that will be environmentally acceptable, cost-effective, and provide better machining performance when compared to other dielectric fluids on the market. When the MRR, TWR, and SR are taken into account, mixed vegetable oil is found to be the best bio-dielectric fluid, and in cases where only the MRR is considered, sunflower oil is the best dielectric. It was discovered that the surface obtained with sunflower oil is the best in terms of crack size and number of cracks when compared to other dielectric fluids. [ABSTRACT FROM AUTHOR]

The physical aging of supercooled glycerol induced by upward temperature steps of amplitude reaching 45 K was studied by a new method consisting in heating a micrometer-thick liquid film at a rate of up to 60 000 K/s, holding it at a constant high temperature for a controlled duration before letting it quickly cool down to the initial temperature. By monitoring the final slow relaxation of the dielectric loss, we were able to obtain quantitative information on the liquid response to the initial upward step. The so-called TNM (Tool–Narayanaswamy–Moynihan) formalism provided a good description of our observations despite the large distance from equilibrium, provided that different values of the nonlinearity parameter were used for the cooling phase and for the (much further from equilibrium) heating phase. In this form, it allowed to precisely quantify how to design an ideal temperature step, i.e., where no relaxation occurs during the heating phase. It helped bringing a clear physical understanding of how the (kilosecond long) final relaxation is related to the (millisecond long) liquid response to the upward step. Finally, it made possible the reconstruction of the fictive temperature evolution immediately following a step, evidencing the highly non-linear character of the liquid response to such large amplitude temperature steps. This work illustrates both the strengths and limitations of the TNM approach. This new experimental device offers a promising tool to study far-from-equilibrium supercooled liquids through their dielectric response. [ABSTRACT FROM AUTHOR]

The transformer mineral oil is generally hydrocarbon-based and is not environmentally friendly, so it holds a significant share in environmental pollution. As an alternative to conventional transformer oil, plant-based insulation oil has been investigated globally in the past few decades. Even though vegetable oils are considered an environmentally viable alternative to mineral oil, the extensive utilization of vegetable oils could create a threat to Indian food security. The present work focuses on using Pongamia Pinnata oil (PPO) as a significant alternative to conventional transformer oil (CTO) in distribution transformers. The effectiveness of the proposed PPO is experimentally verified using thermal studies and electrical studies through a low-level distribution transformer of 1 kVA. A comparative analysis was carried out between the proposed and conventional oil regarding physical, chemical, and thermal properties. Also, scanning electron microscopy (SEM) and Energy Dispersive X-ray spectroscopy analysis have been carried out for fibreglass cloth insulation material with PPO and CTO to ensure the intrinsic structural strength of the insulation material. The structural strength ensures the bonding and life span of the insulation in the transformer. The cost–benefit analysis is also favourable for the proposed oil as a better green liquid dielectric for transformers. [ABSTRACT FROM AUTHOR]

We present the design, fabrication, and characterization of an innovative silicon-based micropump with high potential for portable lab-on-chip (LoC) as well as point-of-care (PoC) applications. The actuators of the pump are electrostatic driven in-plane bending devices, which were presented earlier (Borcia et al. in Phys Rev Fluids 3(8): 084202, 2018. 10.1103/PhysRevFluids.3.084202; Uhlig et al. in Micromachines, 9(4), 2018. 10.3390/mi9040190). This paper presents the characterization results achieved with the micropump. The dielectric non-polar liquid Novec7100™ was used as a test liquid due to its adequate physical properties. When applying a periodic voltage of 130 V, a flow rate of up to 80 µL/min was detected. The counter pressure amounts up to 30 kPa and the correspondent fluidic power (volumetric flow rate times the counter pressure) was calculated to 10 µW. The pump contains passive flap valves at the inlet and outlet, which are based on a bending cantilever design. Depending on the application requirements, the micropump can be designed modularly to adjust the specific parameters by an adequate arrangement of pump base units. In this paper, the proof of principle is shown using a single base unit with different number of stacked NED-actuator beams, as well as the serial arrangement of base units. Both modular concepts target the increase of backpressure of the NED-micropump in an inherently different way compared to conventional membrane micropumps. [ABSTRACT FROM AUTHOR]

Bentonite-sand mixture is considered to be a potential liner material for landfill facilities owing to its excellent sorption potential and swelling characteristics. Such liner materials are expected to perform satisfactorily if the hydraulic conductivity is maintained less than 10−7 cm/s and thereby inhibiting the migration of the generated leachate. However, the performance assessment of these liners in the presence of highly concentrated organic fluids and under the overburden stresses that is usually expected in landfill conditions is scarce. Therefore, in the present work, the hydraulic performance of the bentonite-sand mixtures in the presence of the organic compounds commonly encountered in the landfill leachate is studied, which is a need of the hour. Flow tests were performed to evaluate the hydraulic conductivity of different bentonite-sand mixtures in unhydrated conditions and permeated with varied proportions of methanol-water and ethanol-water mixtures. The study reveals that the proportions of the organic pore fluids significantly influence the hydraulic conductivity of the bentonite-sand mixtures. A very good linear relationship was observed between the pore fluids' dielectric constants and the hydraulic conductivity of the bentonite-sand mixtures. The chemo-mechanical behavior suggests that the conventional bentonite-sand mixtures perform poorly in terms of the hydraulic and swelling characteristics with the change in the dielectric constant of the organic fluids. The microstructural analysis also supports the experimental findings that as the dielectric constant of the fluid are reduced, the effective flow path through the soil increases considerably resulting in higher hydraulic conductivity. [ABSTRACT FROM AUTHOR]

The possible mechanisms of electrical breakdown of transformer oil at low voltage values at alternating voltage were investigated. The formation of streamers from the surface of bubbles into a liquid dielectric after partial discharge in a bubble was detected. This phenomenon has been observed for bubbles in pure transformer oil, in transformer oil with the addition of carbon nano-tubes, in oil after operation. At very low voltages, streamers in transformer oil were registered if a partial discharge in the bubble was stimulated by X-rays. Three possible mechanisms of electric breakdown of a gap filled with transformer oil were revealed at low values of electric field strength in the range from 13 to 51 kV/cm. The appearance of streamers from bubbles was preceded by deformation of the bubble due to one or more partial discharges in it. Streamers always appeared in pairs from the poles of the bubble except for the case of the transformer oil with carbon nanotubes. The results obtained are important for understanding the mechanisms of breakdown of transformer oil at very low voltage and can explain the causes of a number of accidents in high-voltage installations. [ABSTRACT FROM AUTHOR]

The study examined the chemical structure of azo-based liquid crystalline compounds that were altered to form a branch of cyclotriphosphazene. Moreover, the research explored the interplay between their mesomorphic and dielectric properties. The structures of the compounds were defined by Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, and CHN elemental analysis. Only intermediates 2a–e and cyclotriphosphazene compounds 4d–e were mesogenic with smectic A (SmA) and smectic C (SmC) phases, respectively. Intermediate 2d and compound 4d were used as representative samples to determine the type of liquid crystal, which was confirmed through X-ray diffraction (XRD). The calculated d/L ratios for both compounds were 1.69 and 0.76, respectively, indicating that d was approximately equal to L (d ≈ L ≈ 1). This finding suggests that the SmA and SmC phases observed under polarized optical microscope (POM) are arranged in a monolayer. For the dielectric study, only compounds 2d–e and 4d–e were proceeded and compared for dielectric characteristics testing. The dielectric constants and dielectric loss factors of these four compounds were measured over the frequency range of 100 Hz to 0.1 MHz at room temperature. The dielectric constant trend decreased with the increasing frequency. Meanwhile, the dielectric loss showed two types of trends. The first trend was identical to the dielectric constant trend, in which the dielectric loss decreased as the frequency increased. However, in the second trend, the dielectric loss began to rise with the increase in frequency and then began to fall gradually after reaching a certain peak. Meanwhile, compounds 4d and 4e had low dielectric constants and losses due to the effect of hexasubstituted cyclotriphosphazene that had been attached as a core. [ABSTRACT FROM AUTHOR]

This study aims to assess the compatibility of various e-thermal fluids for immersion cooling in battery electric vehicles through a copper wire resistance corrosion test. The tested fluids include a polyalphaolefin, diester, mineral oil API G-III, transformer oil, and a fully formulated dielectric coolant. The test was conducted at 130 °C for 336 h, and the resistance of the copper wires was monitored in vapor and oil phases. By comparing the resistance variation and analyzing portions of the wires through scanning electron microscopy, it was found that the vapor phase of PAO and diester in one of the tests exhibited significant corrosion, while the dielectric coolant showed minimal corrosive effects, implying better compatibility. These results provide insights into the corrosion behavior and compatibility of the fluids with copper, which are essential for selecting suitable dielectric fluids for immersion cooling applications in electric vehicles. [ABSTRACT FROM AUTHOR]

In the current research work, in-house developed and fabricated multi-axis near-dry Electrical Discharge Machine (near-dry EDM) has been used having different tool positions, i.e. tool electrodes in horizontal position (Case-I) and vertical positions (Case-II) as a novel machining techniques in hard-to-reach places and also to improve the process performance. Design of Experiment tool has been used with three process parameters: voltage, discharge current, and pulse-on-time for experimentation purposes. In order to maximize Material Removal Rate (MRR), it was necessary to compare and enhance these parameters in both cases, i.e. Case-I, and Case-II. The machining process is significantly influenced by the vertical tool positions, as indicated by the largest percentage contribution in the Analysis of Variance results. The voltage has the least influence, while the pulse-on time is relatively less. In contrast, for the horizontal tool position, the voltage proved the most prominent factor in terms of influence, while the current ranked second in significance. Conversely, the pulse-on time exhibited the least impact among the three factors. The highest MRR 2.45 mm3/min was achieved in the vertical tool position while in horizontal machining, the highest MRR 0.144 mm3/min was observed. These findings provide valuable insights into the multi-axis near-dry EDM with proposed methodology. [ABSTRACT FROM AUTHOR]

Water can cause damage to power transformers by accelerating aging processes, reducing the dielectric margin, decreasing the partial-discharge inception voltage, and increasing the risk of unexpected failures. Modern electrical companies utilize a variety of drying techniques but sometimes do not comprehend them, making drying less effective. To address these challenges, this study proposes the application of synthetic ester to dry distribution transformers because water dissolves better in the ester than other dielectric liquids. An improved laboratory model of transformer insulation was used for the investigation. This model dried the ester using a molecular filter and carefully selected adsorbed weight. Pressboard strip water content before and after drying was analyzed to determine the drying efficacy of the cellulose insulation. The water content was measured using the Karl-Fischer titration method. The investigation proved that the drying procedure worked. At an ester moisture level of 105-120 ppm and an insulation system temperature of 70°C, samples dried for 5 days showed above 1% water loss. The experimental investigation demonstrated the high efficiency of the proposed drying method for distribution transformers. [ABSTRACT FROM AUTHOR]

We propose a bandpass/bandstop-switchable frequency-selective metasurface (FSM) designed for high-speed vehicles that generate high temperatures during flight, based on a high-temperature-resistant dielectric substrate and liquid metal (LM). We fabricated a cavity structure by utilizing a high-temperature-resistant dielectric substrate to form a metal FSM element by introducing LM, enabling specific electromagnetic functions. The flow state of the LM can be controlled to achieve the switching of the FSM's bandpass/bandstop performance. The bandstop characteristic has a resonance frequency of 6.1 GHz and the bandpass interval is 5.53–6.51 GHz. The bandpass characteristic has a resonance frequency of 5.41 GHz and the bandstop interval is 5.30–5.76 GHz, achieving a bandpass/bandstop switching range of 5.53–5.76 GHz. LM fluidity can aid in high-temperature heat dissipation. When the LM reaches a certain flow rate, the FSM structure's average temperature can be reduced by an order of magnitude from a thousand to less than a hundred degrees. The FSM exhibits low RCS, with 22.35 dB and 36.79 dB reductions in bandstop and bandpass properties, respectively, compared with that of sheet metal. A prototype was developed and tested, validating the design of the FSM structure with high-temperature resistance, bandpass/bandstop switchability, and low RCS characteristics, and is expected to be applied in high-speed aircraft. [ABSTRACT FROM AUTHOR]

Flow boiling with dielectric coolant is not only a highly desirable approach for effective electronic cooling but is also notorious for its poor scalability. Most current flow boiling enhancement strategies are based on silicon substrates with footprint areas less than 1 cm2, which greatly limits their applications to large-size electronics. This study developed a scalable channel configuration to facilitate efficient flow boiling on large copper substrates (∼10 cm2), in which the channel walls are formed by porous pin-fin arrays. This type of hybrid capillary wall makes up for the limitation of conventional machining in creating intricate features, making it scalable and feasible for developing large-size, two-phase cold plates. Moreover, effective two-phase separation and sustainable film evaporation have been realized in the current work. As a result, the proposed structure achieved a 512% increase in heat dissipation when the heating area scales up 480% from the silicon microchannels with micro-pin-fin arrays. Experiments showed a base heat flux of 106.1 W/cm2 was dissipated over a heating area of 9.6 cm2 using the dielectric fluid HFE-7100 at a mass flux of 247 kg/m2 s. It outperformed most existing metallic flow boiling heat sinks using the same coolant at a similarly high coefficient of performance as small-size enhanced silicon microchannels. [ABSTRACT FROM AUTHOR]

Microscale-oscillating heat pipes (micro-OHPs) have recently drawn interest for electronic cooling applications due to their compact size and passive operating mechanism. The occurrence of dryout in OHPs, however, at which the working liquid no longer wets the evaporator, limits the maximum operating cooling power, preventing their integration for direct cooling of high heat flux semiconductor chips. Here, we report on high power and high flux operation of silicon-based OHPs by using microchannels with hydraulic diameters of ∼200 μm. Particularly, a micro-OHP with 100 μm channel height is shown to effectively operate at 210 W using a dielectric working fluid, corresponding to an unprecedented cooling power density of 145 W/cm2, without dryout. A distinctive oscillating mode with highly periodic bulk circulations occurs at high heating power and can provide efficient heat dissipation. The flow speed of the liquid under this bulk circulation mode can be as high as 10 m/s. The empirical relationships between the heat transfer rate, oscillating frequency, and device temperatures are studied. [ABSTRACT FROM AUTHOR]

The electrothermoconvection in a rotating dielectric fluid layer heated from below (or above) is studied analytically using linear stability theory. First, we derive the necessary conditions for oscillatory motion when the fluid layer is heated from below and from above. Then as a consequence, sufficient conditions for the validity of the exchange principle are derived for the two configurations in terms of the parameters of the systems alone. The results hold for free boundaries for all wave numbers and for rigid boundaries with some restrictions. Further, the results for electrothermoconvection without rotation, rotatory Rayleigh–Bénard convection and Rayleigh–Bénard convection are also obtained as special cases which validate the existing results. To the best of author's knowledge such results are not reported in the literature as far as the domain of electrothermoconvection studies is concerned. [ABSTRACT FROM AUTHOR]

Since it is difficult to obtain 3D micro-electrodes, simple micro-electrodes with round or rectangular cross-sections are used when performing layer-by-layer scanning EDM to machine 3D micro-structures. This process can process 3D micro-structure, which has deficiencies of complicated technical process and low processing efficiency. In the study, copper was used to fabricate 3D micro-electrodes by micro-milling. Using a reciprocating processing method, micro-EDM was conducted with the 3D micro-electrodes to obtain 3D micro-structures. This method had the advantages of high processing efficiency and a simple technical process. The above work is the main content and novelty of this paper. The paper detailedly studied the effects of the stand-off distance and flushing quantity of dielectric fluid on the machining quality of 3D micro-structure. Furthermore, the effects of rough machining and finish machining on the machined surface were also analyzed. Finally, with flushing quantity of 0.3 L/min, stand-off distance of 300 μm, the 3D micro-structures with 5 μm dimensional error were machined in 304# stainless steel by applying 3D micro-electrodes in micro-EDM, which had good processing efficiency and processing accuracy. [ABSTRACT FROM AUTHOR]

Mineral oils and synthetic and natural esters are the predominant insulating liquids in electrical equipment. Structure–activity relationship models to predict the key properties of pure insulating liquids, including pulse breakdown strengths, AC breakdown voltages, dielectric constants, flash points, and kinematic viscosities, have been proposed for the first time. Dependence of the specific properties on the molecular structures has been illustrated quantitatively in terms of surface area, statistical total variance, and average deviation of positive and negative electrostatic potentials, as augmented by molecular weight, volume, and ovality. Moreover, the individual contribution of the functional groups to viscosity has been revealed by an additive approach. The predicted properties are in good agreement with the experimental data. The present theoretical work provides new insights on the development of novel dielectric fluids. [ABSTRACT FROM AUTHOR]

In this study, a near-dry electrical discharge machining (NDEDM) process has been conducted using compressed air mixed with a low quantity of biodegradable refined sunflower oil (called oil-mist) to investigate the machining characteristics. The Box-Behnken method looks at how oil flow rate (OR), air pressure (AR), spark current (SC), and pulse width (PW) affect gas emission concentration (GEC), material removal rate (MRR), and surface roughness (SR). The TOPSIS (The Technique for Order of Preference by Similarity to the Ideal Solution) technique estimates the parameter optimal set for the best machining characteristics. The optimal machining parameters have been used to examine the microstructure of the machined surfaces using a scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS) analysis. The 0.981 mg/min of GEC, 55.145 mg/min of MRR, and 2.43 µm of surface roughness have been attained by the 14 ml/min flow rate, 7 bar of air pressure, 10 A spark current, and 48 µs pulse duration of the sun-flower oil-mist NDEDM process. [ABSTRACT FROM AUTHOR]

Copyright of Mugla Journal of Science & Technology is the property of Mugla Journal of Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In Electric Discharge Machining (EDM), the material is eroded due to the generation of spark. It is mainly used for machining the materials which conduct the electric current. In this article, a thorough literature review is carried out to study the effect of control factors on response parameters such as cylindricity, circularity, surface roughness, material elimination rate and tool erosion rate in the profile created. Control factors which can be varied are tool material, voltage, current, Ton and Toff. In this review, a proper study has been done to find the process controlling parameters and the relationship between process parameter variables and optimisation of rate of material removal, rate of tool erosion and surface finish. The working principle, ionisation of dielectric fluid, removal of material, tool wear and overcut have also been considered. A detailed analysis has also been done on the basis of previously published research work linking with variants of EDM, limitations of EDM, work material, tool material, process parameters and optimisation methods used. [ABSTRACT FROM AUTHOR]

Powder-Mixed Electrical Discharge Machining (PM-EDM) is one of the latest advancements in EDM process capability augmentation. This procedure involves effectively mixing a suitable material in fine powder form with the dielectric fluid. The dielectric fluid's breakdown properties are enhanced by the additional powder. The objective of the present research is to machine the Ti-35Nb-7Zr-5Ta alloy prepared by powder metallurgy and study the influence of process parameters, such as peak current, pulse-on time, pulse-off time, powder type (Ag, Si, Ag+Si), and powder concentration. The metal removal rate and SR represent the response parameters. The Taguchi approach was followed to design the experiments. The five-factor three-level design was chosen to use the Taguchi L27 orthogonal array. It was found that the addition of Ag, Si, or Ag+Si powders to the dielectric fluid enhanced the metal removal rate and the surface finish for this alloy. The addition of Ag powder to the dielectric fluid gave a higher Material Removal Rate (MRR) and a lower SR compared to Si or Ag+Si powders. Powder concentration and pulse current are the most effective parameters on MRR and SR followed by powder type, pulse-on, and pulse-off. The maximum Grey Relational Grade (GRG) exists at (I=5 A, Ton=9 µs, Toff=37 µs, PT=Ag, PC=20 g/L). These are the optimal conditions for PM-EDM of the Ti-35Nb-7Zr-5Ta alloy that give maximum MRR with minimum SR. [ABSTRACT FROM AUTHOR]

We develop the positive dielectric liquid crystals for flicker free that saves the power consumption and improves the image quality. The dielectric constant was optimized for a low flexoelectric effect and flicker is advanced by adding the LC component which reduces the luminance difference between frames. We confirmed that the a‐Si TFT LCD Panel incorporating the developed LC operates without flicker at the driving frequency of 40Hz. [ABSTRACT FROM AUTHOR]

Electrowetting has the potential to realize stand-alone point-of-care devices. Here, we report droplet-migration characteristics on oil-infused electrowetting-on-dielectric substrates. We prepare sparse micropillars to retain the oil layer in order to exploit the layer as a lubricating film. A physical model of the droplet velocity is developed, and the effects of the lubrication, the oil viscosity, the droplet volume, and the thickness of solid and liquid dielectric layers are discussed. It is found that the droplet velocity is scaled as U ≈ E 2 , which differs from a relationship of U ≈ E 3 , which is predicted from the dominant drag force for droplets sliding down on liquid-infused surfaces by gravity. Furthermore, our device achieves droplet velocity (19 μ l) of ∼ 1 mm s − 1 at the applied voltage of 15 V. The velocity is approximately tenfold as high as the same condition (applied voltage and oil viscosity) on porous-structure-based liquid-infused surfaces. The achieved high velocity is explained by a lubrication-flow effect. [ABSTRACT FROM AUTHOR]

Optimization of electrical discharge machining (EDM) processes is a critical issue due to complex material removal mechanism, presence of multiple input parameters and responses (outputs) and interactions among them and varying interest of different stakeholders with respect to relative importance assigned to the considered responses. Multi-criteria decision making (MCDM) techniques have become potent tools in solving parametric optimization problems of the EDM processes. In this paper, more than 130 research articles from SCOPUS database published during 2013-22 are reviewed extracting information with respect to experimental design plans employed, materials machined, dielectrics used, process parameters and responses considered and MCDM tools applied along with their integration with other mathematical techniques. A detailed analysis of those reviewed articles reveals that the past researchers have mostly preferred Taguchi's L9 orthogonal array as the experimental design plan; EDM oil as the dielectric fluid; medium and high carbon steels as the work materials; peak current and pulse-on time as the input parameters; material removal rate, tool wear rate and surface roughness as the responses; and grey relational analysis as the MCDM tool during conducting and optimizing EDM operations. This review paper would act as a data repository to the future researchers in understanding the stochastic behaviour of EDM processes and providing guidance in setting the tentative operating levels of varying input parameters along with achievable response values. The extracted dataset can be treated as an input to any of the machine learning algorithms for subsequent development of appropriate prediction models. This review also outlines potential future research avenues, emphasizing advancements in EDM technology and the integration of innovative multi-criteria decisionmaking tools. [ABSTRACT FROM AUTHOR]

This paper presents an extended work on the Finite Element Method (FEM) simulation of Love Wave (LW) sensors in a liquid medium. Two models are proposed to simulate the multiphysical response of the sensor. Both are extensively described in terms of principle, composition and behavior, making their applications easily reproducible by the sensor community. The first model is a Representative Volume Element (RVE) simulating the transducer and the second focuses on the sensor's longitudinal (OXZ) cut which simulates the multiphysical responses of the device. Sensitivity of the LW device to variations in the rheological and dielectric properties of liquids is estimated and then compared to a large set of measurements issued from LW sensors presenting different technological characteristics. This integral approach allows for a deeper insight into the multiphysical behavior of the LW sensor. This article also explores the advantages and drawbacks of each model. Both are in good accordance with the measurements and could be used for various applications, for which a non-exhaustive list is proposed in the conclusion. [ABSTRACT FROM AUTHOR]