The present investigation addressed the entropy generation, fluid flow, and heat transfer regarding Cu-Al 2 O 3 -water hybrid nanofluids into a complex shape enclosure containing a hot-half partition were addressed. The sidewalls of the enclosure are made of wavy walls including cold isothermal temperature while the upper and lower surfaces remain insulated. The governing equations toward conservation of mass, momentum, and energy were introduced into the form of partial differential equations. The second law of thermodynamic was written for the friction and thermal entropy productions as a function of velocity and temperatures. The governing equations occurred molded into a non-dimensional pattern and explained through the finite element method. Outcomes were investigated for Cu-water, Al 2 O 3 -water, and Cu-Al 2 O 3 -water nanofluids to address the effect of using composite nanoparticles toward the flow and temperature patterns and entropy g... [more]

Forest and agricultural biomass are important sources of renewable and sustainable fuel for energy production. Their increasing consumption is mainly related to the increase in global energy demand and fossil fuel prices but also to the limited availability of petroleum and the lower environmental impact of these biomass compared with other non-renewable fuels. In particular, the pellet sector has seen important developments in terms of both production and the number of installed transformation plants. In addition, pellet production from non-woody biomass is increasing in importance. One of the fundamental aspects for the correct and sustainable use of a biofuel is evaluation of its quality. This is even more important when dealing with pellet production, considering the broad spectrum of possible raw materials for pelletizing. Considering the significant number of papers dealing with pellet quality evaluation and improvement in the last decade, this review aims to give the reader an o... [more]

Installation costs of ground heat exchangers (GHEs) make the technology based on ground-coupled heat pumps (GCHPs) less competitive than air source heat pumps for space heating and cooling in mild climates. A smart solution is the dual source heat pump (DSHP) which switches between the air and ground to reduce frosting issues and save the system against extreme temperatures affecting air-mode. This work analyses the coupling of DSHP with a flat-panel (FP) horizontal GHE (HGHE) and a mixture of sand and phase change materials (PCMs). From numerical simulations and considering the energy demand of a real building in Northern Italy, different combinations of heat pumps (HPs) and trench backfill material were compared. The results show that PCMs always improve the performance of the systems, allowing a further reduction of the size of the geothermal facility. Annual average heat flux at FP is four times higher when coupled with the DSHP system, due to the lower exploitation. Furthermore, t... [more]

Adding nanoparticles to fluid has led to a new class of fluids named as nanofluids. Different concentrations and its effective cooling have attracted many engineering applications to test this new fluid. Lately, important heat enhancement has been observed by dispersing two distinct nanoparticles in the regular fluid. This type of hybrid nanofluid has led researchers to study its effectiveness in the cooling process. Here, we experimentally studied the forced convection of Al2O3−Cu hybrid nanofluid in porous media at a constant flow rate and heating condition. The numerical code after being calibrated with the experimental results is used to predict the effectiveness in cooling by using a set of hybrid fluid of TiO2−SiO2, MWCNT−Fe3O4, and ND−Fe3O4 at different concentrations. In the experiment, we used water and a water−ethylene glycol mixture as base fluids. The results revealed that the hybrid fluid contributed to heat enhancement levied increased pumping power. However, the index of... [more]

In perovskite photovoltaics (PSCs), the role of the hole transporting material (HTM) is highly important as it significantly influents to the global device’s performance and stability. Hole transporter ensures the extraction of hole at the perovskite/HTM interface and transport it towards the cathode. Thus, accurate molecular design affording to efficient and cost-effective HTM is of major interest. Small molecules having glass forming property is an attractive class as it can form morphologically stable thin film. Herein, a carbazole molecular glass bearing a polymerizable function was designed and synthetized. Its characteristics are suitable for application as HTM in PSCs. The preliminary photovoltaic application lead to device efficiency of 14−15% depending on the chemical composition of the perovskite employed. These promising results open the way to design new alternative molecular and polymeric HTMs suitable for solution processed hybrid solar cells.

Ferroelectret-based piezoelectric transducers are, nowadays, commonly used in energy harvesting applications due to their high piezoelectric activity. Unfortunately, the processing properties of such materials are limited, and new solutions are sought. This paper presents a new solution of a piezoelectric transducer containing electret bubbles immersed in an elastomer matrix. Application of a gas-filled dielectric bubble as the fundamental cell of the piezo-active structure is discussed. A simplified model of the structure, containing electret thin-wall bubbles and elastomer dielectric filling, was applied to determine the value of the piezoelectric coefficient, d33. An exemplary structure containing piezo-active bubbles, made of an electret material, immersed in an elastomer filling is presented. The influence of the mechanical and electrical properties of particular components on the structure piezoelectric properties are experimentally examined and confirmed. The quasi-static method... [more]

The influence of hydrothermal pretreatment temperature on the hydration products and carbonation efficiency of Al-rich LF slag was investigated. The results showed that the carbonation efficiency was strongly dependent on the morphology of hydration products and the hydration extent of the raw slag. Hydrothermal pretreatment at 20 °C or 80 °C favored the formation of flake-shaped products with a higher specific surface area and therefore resulted in a higher CO2 uptake of 20 °C and 80 °C-pretreated slags (13.66 wt% and 10.82 wt%, respectively). However, hydrothermal pretreatment at 40 °C, 60 °C or 100 °C led to the rhombohedral-shaped calcite layer surrounding the unreacted core of the raw slag and the formation of fewer flake-shaped products, resulting in a lower CO2 uptake of 40 °C, 60 °C and 100 °C-pretreated slags (9.21 wt%, 9.83 wt%, and 6.84 wt%, respectively).

Mutual diffusion coefficients of chloroquine diphosphate (CDP) in aqueous solutions both without and with β-cyclodextrin (β-CD) were measured at concentrations from (0.0000 to 0.0100) mol dm−3 and 298.15 K, using the Taylor dispersion technique. Ternary mutual diffusion coefficients (Dik) measured by the same technique are reported for aqueous CDP + β-CD solutions at 298.15 K. The presence of β CD led to relevant changes in the diffusion process, as showed by nonzero values of the cross-diffusion coefficients, D12 and D21. β-CD concentration gradients produced significant co-current coupled flows of CDP. In addition, the effects of β-CD on the transport of CDP are assessed by comparing the binary diffusion coefficient of aqueous CDP solutions with the main diffusion coefficient (D11) measured for ternary {CDP(1) + β-CD(2)} solutions. These observations are supported by viscosity analysis. All data allow to have a better interpretation on the effect of cyclodextrin on the transport beha... [more]

The conformation of a ceramic piece follows the steps of preparing the raw material, molding, lamination, drying, and firing. Drying is a thermodynamic process of heat and mass transfer, with dimensional variations of the product that requires a large amount of energy. Ceramic materials when exposed to non-uniform drying may suffer cracks and deformations, reducing their post-drying quality. Thus, this work aimed to study the drying of industrial ceramic blocks in an oven with forced air circulation. Experiments were carried out to characterize the clay and drying of the ceramic block at temperatures ranging from 50 °C to 100 °C. Results of the chemical, mineralogical, granulometric, differential thermal, and thermogravimetric analysis of the clay, and heating kinetics, mass loss, and dimensional variation of the industrial ceramic block are presented and analyzed in detail. It was found that the clay is basically composed of silica and alumina (≈ 80.96%), with an average particle diam... [more]

This paper presents the results of studies on the possibility of using lignite to produce blast furnace coke. The aim of the investigation was to evaluate the influence of lignite addition (direct addition or incorporated into briquettes) on the textural, structural and quality parameters (NSC-CRI and CSR) of blast furnace coke. It was found that the introduction of lignite in briquettes (4.5% addition) allows coke to be produced that is characterized by equally high NSC parameters as for coke obtained without lignite addition for standard top-charged operation.

Recently, eco-friendly energy conversion policies have been being promoted through de-nuclearization and de-coal. For this purpose, a super grid should be built to optimize sustainable renewable energy resources such as solar and wind power. Accordingly, considering the various problems such as technology and cost, a system for efficient energy transmission is required. Hence, research is being actively conducted to apply it, owing to the development of the high voltage direct current (HVDC) system. Among HVDC systems, the cable system is extremely important, in addition to the measurement of the dielectric breakdown strength, space charge, and volume resistivity of insulating materials. The existing resistivity measurement method measures both the volume and surface resistivity using a three-terminal electrode that is used in the international standards of American Society for Testing and Materials (ASTM) D 257 and International Electrotechnical Commission (IEC) 60093. However, the ci... [more]

The present investigation aimed to study the physicochemical characteristics of supported catalysts comprising various percentages of zinc dispersed over SiO2. The physiochemical properties of these catalysts were surveyed by N2 physisorption (BET), thermogravimetry analysis (TGA), H2 temperature-programmed reduction, field-emission scanning electron microscopy (FESEM), inductively coupled plasma-optical emission spectrometry (ICP-OES), and NH3 temperature-programmed desorption (NH3-TPD). In addition, to examine the activity and performance of the catalysts for the hydrodeoxygenation (HDO) of the bio-oil oxygenated compounds, the experimental reaction runs, as well as stability and durability tests, were performed using 3% Zn/SiO2 as the catalyst. Characterization of silica-supported zinc catalysts revealed an even dispersion of the active site over the support in the various dopings of the zinc. The acidity of the calcinated catalysts elevated clearly up to 0.481 mmol/g. Moreover, cha... [more]

Substation connectors, like many other high-voltage products, are tested once manufactured. However, the corona behavior of aged specimens can differ from that exhibited by newer ones, thus generating detrimental technical and environmental effects. Manufacturers need to know the long-term corona behavior of substation connectors to offer their customers maximum safety and transparency about such critical products. This paper analyzes the ageing effect on the surface roughness and the visual corona extinction voltage of sand-cast aluminum connectors, which were artificially aged in a salt spray chamber for different periods. The experimental results show an important variability of the surface roughness and corona extinction voltage (CEV) among connectors with the same ageing level due to the sand-casting manufacturing process. The results in this paper also show a slight increase in the surface roughness with the ageing period, although there is not a clear pattern between the applied... [more]

This paper presents an energetically autonomous IoT sensor powered via thermoelectric harvesting. The operation of thermal harvesting is based on maintaining a temperature gradient of at least 26.31 K between the thermoelectric-generator sides. While the hot side employs a metal plate, the cold side is attached with a phase-change material acting as an effective passive dissipative material. The desired temperature gradient allows claiming power conversion efficiencies of about 26.43%, without efficiency reductions associated with heating and soiling. This work presents the characterization of a low-cost off-the-shelf thermoelectric generator that allows estimating the production of at least 407.3 mW corresponding to 2.44 Wh of available energy considering specific operation hours—determined statistically for a given geographic location. Then, the energy production is experimentally verified with the construction of an outdoor IoT sensor powered by a passively-cooled thermoelectric gen... [more]

The high throughput and rapid flame-assisted spray pyrolysis method has been adapted to synthesize cathode materials LiNi0.apCo0.15Al0.035O2 (NCA). This method is considered low cost and simple. By varying the precursor solution concentration and sintering temperature, the optimal condition was established at temperature sintering of 800 °C and precursor solution concentration of 1 M. X-ray diffraction patterns showed the as-prepared NCA particles exhibit a pure well-ordered hexagonal layer structure with high crystallinity. Polyhedral shaped micro-sized particles are confirmed by SEM images. Galvanostic charge−discharge tests were conducted using cylindrical full-cell utilizing artificial graphite as the anode. The highest specific initial discharge capacity measured between 2.7 and 4.3 V is 155 mAh g−1 with capacity retention of 92% after cycled at 0.2 C for 50 cycles. Thus, this method is considered as a satisfying approach for NCA mass production.

Latent heat thermal energy storage (LHTES) systems allow us to effectively store and release the collected thermal energy from solar thermodynamic plants; however, room for improvements exists to increase their efficiency when in operation. For this reason, in this work, a smart management strategy of an innovative LHTES in a micro-scale concentrated solar combined heat and power plant is proposed and numerically investigated. The novel thermal storage system, as designed and built by the partners within the EU funded Innova MicroSolar project, is subdivided into six modules and consists of 3.8 tons of nitrate solar salt kNO3/NaNO3, whose melting temperature is in the range 216 ÷ 223 °C. In this study, the partitioning of the storage system on the performance of the integrated plant is evaluated by applying a smart energy management strategy based on a fuzzy logic approach. Compared to the single thermal energy storage (TES) configuration, the proposed strategy allows a reduction in st... [more]

Nanogenerators (NGs) based on Ni-doped ZnO (NZO) nanorod (NR) arrays were fabricated and explored in this study. The ZnO films were grown on indium tin oxide (ITO) glass substrates, and the NZO NRs were prepared by the chemical bath deposition (CBD) method. The samples were investigated via field-emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) spectral analysis. The results showed that the growth of NRs presented high-density single crystalline structures and were preferentially oriented in the c-axis direction. The optical characteristics of the NZO NRs were also measured by photoluminescence (PL) spectra. All samples exhibited two different emissions, including ultraviolet (UV) and green emissions. ITO etching paste was used to define patterns, and an electrode of Au film was evaporated onto the ITO glass substrates by the electron beam evaporation technique to assemble the NG device. In summary, ZnO NRs with Ni dopant (5 mM) showed significantly excellent... [more]

Electrochemical CO2 reduction reaction (CO2RR) to fuels and chemicals represents nowadays one of the most challenging solutions for renewable energy storage and utilization. Among the possible reaction pathways, CO2-to-CO conversion is the first (2e−) reduction step towards the production of a key-feedstock that holds great relevance for chemical industry. In this report we describe the electrocatalytic CO2-to-CO reduction by a series of tailored N-decorated carbon nanotubes to be employed as chemoselective metal-free electrocatalysts. The choice of an exohedral functionalization tool for the introduction of defined N-groups at the outer surface of carbon nanomaterials warrants a unique control on N-configuration and electronic charge density distribution at the dangling heterocycles. A comparative electrochemical screening of variably N-substituted carbon nanomaterials in CO2RR together with an analysis of the electronic charge density distribution at each heterocycle have suggested t... [more]

This paper describes a correlation of partial discharge phase-resolved patterns with an optical imaging performed in a non-uniform electric field configuration. The influence of different dielectric barrier materials, placed on the plane electrode, on the discharge propagation and surface landing was investigated. The investigations were focused on the corona at positive polarity of AC high voltage. It was found that the initial positive corona stage is similar for all cases whereas the discharge propagation and surface landing strongly depends on the barrier material properties. The observed streamer discharge modes have been described by the geometrical measures such as stem length, stretch of a discharge profile on the dielectric barrier surface and an hemispherical envelope of discharge filaments. Since various dielectrics reveal different properties of charge accumulation and surface neutralization, the charge memory effect may be visible and can be related to the ability to creat... [more]

The following work presents a numerical evaluation of the use of TiO2 and Al2O3 nanofluids operating with ethylene glycol and water as base fluids—as well as an experimental evaluation of Al2O3-water nanofluid. Both numerical and experimental systems were tested and operated under various flow and heat transfer conditions, including four flow rates and three heat fluxes. When compared, the numerical schemes and experimental results showed deviation of under two degrees Celsius. This led the authors to conclude that the numerical scheme accurately reflected the experimental conditions. When all combinations of mixtures were compared numerically, it was found that ethylene glycol provided the highest average Nusselt number, while water offered significantly lower pumping requirements. When comparing nanoparticles, it was found that, in a carrying-fluid of water, TiO2 had superior performance by approximately one percent.

The solar photovoltaic (PV) cell is a prominent energy harvesting device that reduces the strain in the conventional energy generation approach and endorses the prospectiveness of renewable energy. Thus, the exploration in this ever-green field is worth the effort. From the power conversion efficiency standpoint of view, PVs are consistently improving, and when analyzing the potential areas that can be advanced, more and more exciting challenges are encountered. One such crucial challenge is to increase the photon availability for PV conversion. This challenge is solved using two ways. First, by suppressing the reflection at the interface of the solar cell, and the other way is to enhance the optical pathlength inside the cell for adequate absorption of the photons. Our review addresses this challenge by emphasizing the various strategies that aid in trapping the light in the solar cells. These strategies include the usage of antireflection coatings (ARCs) and light-trapping structures... [more]

Geopolymers are less energy-demanding alternatives to Portland cement binders. The subject of geopolymer rheology has not yet been fully explored, and the available literature is limited to a narrow range of material compositions. This paper presents the rheological and mechanical response of fly-ash based geopolymer mortars. Investigations were made of the effect of different levels of ground granulated blast furnace slag (GGBFS) addition levels on the rheological properties of fresh geopolymers as well as their mechanical performances at 2, 14 and 28 days. The aim of the study was to obtain flow curves and to establish the correlation between shear stress and shear rate. The results have shown that geopolymer mortar is a pseudoplastic liquid presenting shear thinning behavior, moreover, with the increase of GGBFS content, higher material strengths were obtained and the total porosity was reduced.

Lithium-ion batteries are actively used for many applications due to many advantages. Although electrodes are important during laser cutting, most laser cutting studies use commercially available electrodes. Thus, effects of electrodes characteristics on laser cutting have not been effectively studied. Since the electrodes’ characteristics can be manipulated in the laboratory, this study uses an uncompressed anode on laser cutting for the first time. Using the lab-made anode, this study identifies laser cutting characteristics of the uncompressed anode. First, the absorption coefficients of graphite and copper in the ultraviolet, visible, and infrared range are measured. The measured absorptivity of the graphite and copper at the wavelength of 1070 nm is 88.25% and 1.92%, respectively. In addition, cutting phenomena can be categorized in five regions: excessive cutting, proper cutting, defective cutting, excessive ablation, and proper ablation. The five regions are composed of a combin... [more]

We present a detailed study of dynamic switching instability and static reliability of a Gallium Nitride (GaN) Metal-Insulator-Semiconductor High-Electron-Mobility-Transistor (MIS-HEMT) based cascode switch under off-state (negative bias) Gate bias stress (VGS, OFF). We have investigated drain channel current (IDS, Max) collapse/degradation and turn-on and rise-time (tR) delay, on-state resistance (RDS-ON) and maximum transconductance (Gm, max) degradation and threshold voltage (VTH) shift for pulsed and prolonged off-state gate bias stress VGS, OFF. We have found that as stress voltage magnitude and stress duration increases, similarly IDS, Max and RDS-ON degradation, VTH shift and turn-on/rise time (tR) delay, and Gm, max degradation increases. In a pulsed off-state VGS, OFF stress experiment, the device instabilities and degradation with electron trapping effects are studied through two regimes of stress voltages. Under low stress, VTH shift, IDS collapse, RDS-ON degradation has ver... [more]

In view of the problem that ZnO varistors are often subjected to thermal breakdown and deterioration due to lightning strikes in low-voltage power distribution systems, this article used a 8/20 µs multi-pulse surge current with a pulse time interval of 50 ms to perform shock experiments on ZnO varistors. SEM scanning electron microscope and an XRD diffractometer were used to analyze the structure of the grain boundary layer and the change of the crystalline phase material of ZnO varistor under the action of a multi-pulse current. The damage mechanism of ZnO varistor under the multi-pulse current was studied at the micro level. The results show that the average impact life of different types of ZnO varistor is significantly different. It was found that the types of trace elements and grain size in the grain boundary layer will affect the ability of ZnO varistor to withstand multi-pulse current. As the number of impulses increases, the grain structure of the ZnO varistor continues to deg... [more]