Catalytic effect of ZrCrNi alloy on hydriding properties of MgH2

MgH₂ nanocomposites with ZrCrNi alloy obtained by high energy ball-milling were studied as-milled and after several hydriding-deydriding cycles. The microstructure and morphology of the samples was characterized by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD patterns show that no phase formation between MgH₂ and elements of the alloys takes place during milling and after cycling. Different morphology of the powders as-milled and after cycling was observed by SEM. Pressure-composition isotherms of these composites were obtained in the pressure and temperature range of 0.1–15 bar and 200–300 °C respectively. The maximum reversible storage capacity was found to be 6.2 wt% at 300 °C. Absorption/desorption kinetics data at pressures of 0.1–5.0 bar and temperatures of 275 °C and 300 °C show that an activation process of about 20 cycles at 300 °C is necessary for stabilization of the kinetics and for achievement of the full hydrogen capacity. The thermodynamic parameters, i.e. enthalpy of formation and dissociation calculated using Van't Hoff plots, were found to be 73.53 kJ mol^?1 and 87.63 kJ mol^?1 respectively, in agreement with MgH₂ data reported in literature.     

Triple-Networked Hybrid Hydrogels Reinforced with Montmorillonite Clay and Graphene Nanoplatelets for Soft and Hard Tissue Regeneration

Hydrogel is a three-dimensional (3D) soft and highly hydrophilic, polymeric network that can swell in water and imbibe a high amount of water or biological fluids. Hydrogels have been used widely in various biomedical applications. Hydrogel may provide a fluidic tissue-like 3D microenvironment by maintaining the original network for tissue engineering. However, their low mechanical performances limit their broad applicability in various functional tissues. This property causes substantial challenges in designing and preparing strong hydrogel networks. Therefore, we report the triple-networked hybrid hydrogel network with enhanced mechanical properties by incorporating dual-crosslinking and nanofillers (e.g., montmorillonite (MMT), graphene nanoplatelets (GNPs)). In this study, we prepared hybrid hydrogels composed of polyacrylamide, poly (vinyl alcohol), sodium alginate, MMT, and MMT/GNPs through dynamic crosslinking. The freeze-dried hybrid hydrogels showed good 3D porous architecture. The results exhibited a magnificent porous structure, interconnected pore-network surface morphology, enhanced mechanical properties, and cellular activity of hybrid hydrogels.     

Photovoltaic effect in arylenevinylene-co-pyrrolenevinylene (AVPV)

Arylenevinylene-co-pyrrolenevinylene (AVPV) is a promising candidate amongst the group of new photovoltaic materials. It is a low band gap organic material with a band gap of 1.84 eV and absorbs sunlight in 300-700 nm range. In this paper, we demonstrate the photovoltaic effect in an organic bulk heterojunction photovoltaic device based on the blend of AVPV as an electron donor and [6,6]-phenyl-C₆₁ butyric acid methyl ester (PCBM) as the acceptor. The short-circuit current density of the device was of the order of 0.55 μA cm⁻² with an open-circuit voltage of 0.7 V, measured under 1 sun illumination of AM 1.5 through a calibrated solar simulator. Fill factor was estimated to be 12%. Further, the tests conducted after 2 weeks showed that short-circuit current was 0.21 μA cm⁻² and open-circuit voltage was 0.5 V with a fill factor of 9.8%, suggesting the possibility of stable AVPV-based organic solar cell (OSC).     

Study of cyclic performance of V-Ti-Cr alloys employed for hydrogen compressor

The development of a suitable hydrogen compressor plays one of the key roles to realize the fuel cell vehicle as well as for many other stationary and mobile applications of hydrogen. V-Ti-Cr BCC alloys are considered as promising candidates for effective hydrogen storage. The cyclic durability of hydrogen absorption and desorption is very important for these alloys to be realized as practical options. In connection to this, two alloys of V-Ti-Cr, (1) V₄₀Ti_21.5Cr_38.5 and (2) V₂₀Ti₃₂Cr₄₈, were selected and their cyclic hydrogen absorption-desorption performance was evaluated up to 100 cycles for temperature and pressure ranges of 20–300 °C and 5–20 MPa, respectively. It has been found that the cyclic hydrogen storage capacity continuously decreased for one composition while it was stable after 10 cycles for another composition. This performance difference of the alloys was studied in terms of their structural and microscopic properties and the results are presented in this paper.     

Synthesis of nano-crystalline Zr-M (M=Ni,Co, Fe,Cu) bilayer films and their thermodynamics of hydrogen uptake by resistance measurement

Nano-crystalline thin metal films for hydride formation for small amount of hydrogen storage is an emerging field of research for portable applications e.g. thin film fuel cells. Nano-crystalline films of Zr/ M (M = Ni, Co, Fe, Cu) bilayer systems were synthesized using ion beam sputtering technique in argon atmosphere which were characterized using GIXRD and AFM techniques. In thin film metal hydride it is difficult to measure P-C-T isotherm because of the small amount of hydrogen present and the same difficulty is to study thermodynamics of such systems. Hence in the present work change in electrical resistance with hydrogen pressure in temperatures range 298 to 573 K has been used to investigate thermodynamic properties and found that resistance of film increases with the absorption of hydrogen and decreases due to hydrogen desorption.     

Experimental exergy and entransy analyses on designed and fabricated crossflow heat exchanger

A crossflow heat exchanger (CFHEx) is designed and fabricated in a workshop. For designing this heat exchanger (HEx), the number of passes, frontal areas, HEx volumes, heat transfer areas, free-flow areas, ratios of minimum free-flow area to frontal area, densities, mass flow rates of flowing fluids, maximum/minimum heat capacities, heat capacity ratio, outlet temperatures of hot/cold fluids, average temperatures, mass velocities, Reynolds numbers, and convective heat transfer coefficients are evaluated by considering Colburn/friction factors. After fabrication of the HEx, effectiveness, exergy destruction, entransy dissipation, entransy dissipation-based thermal resistance, entransy dissipation number, and entransy effectiveness for hot/cold fluids sides are found at different flow rates and inlet temperatures of fluids. By experimental results, optimum operating conditions are found, which gives maximum effectiveness and entransy effectiveness but minimum rates of exergy destruction, entransy dissipation, entransy dissipation-based thermal resistance, and entransy dissipation number for the fabricated CFHEx. This study is concluded as follows: minimum exergy destruction and entransy dissipation rates (ie, 3.061 kJ/s·K and 1125.44 kJ·K/s, respectively) are found during experiment 2. Maximum entransy effectiveness of hot/cold fluids (ie, 0.689/0.21) is achieved in experiment 1. Moderate values of entransy dissipation number (ie, 4.689), entransy dissipation-based thermal resistance (ie, 0.04 s·K/J), exergy destruction (ie, 3.845 kJ/s·K), and entransy dissipation (ie, 1374.04 kJ·K/s) rates are found during experiment 1. Maximum effectiveness (ie, 0.4) for the fabricated HEx is also obtained through experiment 1. After comparative analyses, it is found that experiment 1 provides optimum results, which shows the best performance of the fabricated HEx.     

Effect of La-content on the hydrogenation properties of the Ce1−xLaxNi3Cr2 (x=0.2, 0.4, 0.6, 0.8, 1) alloys

The effect of partial substitution of Ce by La in CeNi₃Cr₂ hydrogen storage alloy has been systematically investigated. All intermetallic compounds Ce_1-xLa_xNi₃Cr₂ (x = 0.2, 0.4, 0.6, 0.8, 1) synthesized by arc melting method are well characterized by the means of XRD and SEM. XRD results show that all the alloys are crystallized as a single-phase compound in the hexagonal CaCu₅ type structure. The substitution of Ce by La leads to increase the unit cell volume of the alloy. Hydrogen storage capacity has been investigated in the temperature and pressure range of 293 K ≤ T ≤ 323 K and 0.5 ≤ P ≤ 45 bar respectively using pressure-composition isotherm. The P-C isotherm curves show that the plateau pressure of the hydrogen absorption decreases and hydrogen storage capacity increases with increasing La content in the alloy. The enthalpy (?H) and entropy (?S) of dissolved hydrogen for all systems has been calculated using Van’t Hoff plot. The variation of ?H and ?S with hydrogen content has also been studied which confirm the phase boundaries.     

Experimental and numerical investigation of heat transfer in Li‐ion battery pack of a hoverboard

Li‐ion cells are used for energy storage and conversion in electric vehicles and a variety of consumer devices such as hoverboards. Performance and safety of such devices are severely affected by overheating of Li‐ion cells in aggressive operating conditions. Multiple recent fires and accidents in hoverboards are known to have originated in the battery pack of the hoverboard. While thermal analysis and measurements have been carried out extensively on large battery packs for electric vehicles, there is relatively lesser research on smaller devices such as hoverboards, where the extremely limited thermal management design space and the critical importance of user safety result in severe thermal management challenges. This paper presents experimental measurements and numerical analysis of a novel approach for thermal management of the battery pack of a hoverboard. Measurements indicate that temperature rise in cells in the pack can be as large as 30°C at 4C discharge rate, which, although unlikely to be a standard discharge rate, may result from a malfunction or accident. A novel thermal management approach is investigated, wherein careful utilization of air flow generated by hoverboard motion is shown to result in significant temperature reduction. Measurements also indicate the key role of the metal housing around the battery pack in thermal management. Measurements are found to be in good agreement with finite element simulations, which indicate that the battery pack can be cooled as effectively in presence of a perforated metal casing as without the casing at all. Experimental data and simulation model presented here offer critical insights into the design of hoverboard thermal management and may result in safer, high performance hoverboard battery packs.