Search results for "Energy engineering"
showing 10 items of 1099 documents
Relaxation of remnant magnetisation in YBa2Cu3O7−δ films
2007
Abstract The relaxation of the remnant magnetisation in optimally doped disk-shaped YBa2Cu3O7−δ films with the initially applied magnetic field H oriented along the c axis was measured using dc SQUID magnetometry. The temperature (T) dependence of the experimentally observed normalised magnetisation relaxation rate S exhibits three distinct regions. At high T, S(T) increases with increasing T, which can be explained in terms of plastic vortex creep. The well known plateau in the S(T) variation at intermediate T appears to be caused by collective (elastic) creep in a dynamically ordered vortex system. At low T, where S increases again with increasing T, the magnetisation relaxation is not in…
Fluxon dynamics in Li–Al codoped by microwave surface resistance measurements
2010
Abstract The magnetic-field-induced variations of the microwave surface resistance, R s , have been investigated in ceramic Mg1−x(LiAl)xB2, with x in the range 0.1 – 0.4 . The measurements have been performed on increasing and decreasing the DC magnetic field, H 0 , at fixed temperatures. At low temperatures, we have observed a magnetic hysteresis in the R s ( H 0 ) curves in all the investigated samples. On increasing the temperature, the range of H 0 in which the hysteretic behavior is visible shrinks; however, in the sample with x = 0.1 it is present up to temperatures close to T c . We show that the field dependence of R s can be quantitatively justified taking into account the critical…
N‑Oxide Polyethers as Kinetic Hydrate Inhibitors: Side Chain Ring Size Makes the Difference
2021
The formation of gas hydrates in flow lines is one of the most severe problems for flow assurance in the gas and oil industry. Developing effective kinetic hydrate inhibitors (KHIs) to avoid the problem of gas hydrate formation has attracted widespread attention. In this study, a series of poly(glycidyl amine N-oxide)s (PGAOs) with 5–7-membered rings as side chains, poly(pyrrolidine glycidyl amine N-oxide)s (PPyrGAOs), poly(piperidine glycidyl amine N-oxide)s (PPiGAOs), and poly(azepane glycidyl amine N-oxide)s (PAzGAOs), with varying molecular weights, have been synthesized. The KHI performance of these glycidyl amine N-oxide polyethers has been evaluated in high-pressure rocking cells wit…
Methyl-3-Hexenoate Combustion Chemistry: Experimental Study and Numerical Kinetic Simulation
2020
International audience; This work represents a detailed investigation of combustion and oxidation of methyl-3-hexenoate (CAS Number 2396-78-3), including experimental studies of combustion and oxidation characteristics, quantum chemistry calculations and kinetic model refinement. Following experiments have been carried out: Speciation measurements during oxidation in a jet-stirred reactor at 1 atm; chemical speciation measurements in a stoichiometric premixed flame at 1 atm using molecular-beam mass-spectrometry; ignition delay times measurements in a shock tube at 20 and 40 bar; and laminar burning velocity measurements at 1 atm using a heat-flux burner over a range of equivalence ratios. …
Combustion of activated aluminum
2006
Abstract Combustion of activated aluminum was studied by four different methods: microscopic imaging of the preignition process, digital imaging of the combustion process at pressures up to 64 bar in air, nitrogen, and carbon dioxide, TGA, and DSC. Activation by three fundamentally different methods was found effective in enhancing both the ignitability and the burn rate. The complex fluoride coating prevented agglomeration completely in all stages of combustion, while the nickel and cobalt coatings promoted agglomeration of aluminum oxide at combustion, but prevented the agglomeration of the aluminum metal before combustion. Nickel coating catalyzed aluminum nitride formation, accelerating…
An ultrasonic-assisted process for copper recovery in a des solvent: Leaching and re-deposition
2017
Abstract The continuous growth of the electronic equipment market has led to an increased amount of scraping that it becomes necessary to recover. A hydrometallurgical method for copper and precious metal recovery from e-waste must consist of a number of steps: leaching, ion separation and subsequent electrochemical re-deposition of the target metal. Although this task is achievable in aqueous solutions, it requires strong acid or cyanide solutions. The aim of the study is to develop a new environmentally benign process by using a Deep Eutectic Solvent (DES), a form of cheap and safe ionic liquid, as an electrolyte for both leaching and electrodeposition. The experiments were conducted in a…
Phosphomolybdic acid and mixed phosphotungstic/phosphomolybdic acid chitosan membranes as polymer electrolyte for H2/O2 fuel cells
2017
Abstract Flat, free-standing phosphomolybdic acid and mixed phosphotungstic/phosphomolybdic acid chitosan membranes were prepared by in-situ ionotropic gelation process at room temperature on porous alumina support firstly impregnated by heteropolyacid. Scanning electron microscopy revealed the formation of compact and homogenous polymeric membranes, whose thickness resulted to be dependent on reticulation time, and almost independent on the employed heteropolyacid nature and concentration. X-ray diffraction and Fourier transform infrared spectroscopy evidenced the formation of crystalline membranes without appreciable concentration of unprotonated NH 2 groups and heteropolyacid ions with p…
Design and experimental validation of a high voltage ratio DC/DC converter for proton exchange membrane electrolyzer applications
2019
Abstract This paper deals with hydrogen production via water electrolysis, which is considered the most attractive and promising solution. Specifically, the use of renewable energy sources, such as wind electric power generators, is hypothesized for supplying the electrolyzer, aiming to strongly reduce the environmental impact. In particular, micro-wind energy conversion systems (μWECSs) are attractive for their low cost and easy installation. In order to interface the μWECS and the electrolyzer, suitable power conditioning systems such as step-down DC-DC converters are mandatory. However, due to the requested high conversion ratio between the DC bus grid, i.e. the output of a three-phase d…
Harmonic emission at microwave frequencies in YBa2Cu3O7 single crystals near Tc
1998
Abstract Nonlinear microwave emission by YBa 2 Cu 3 O 7 single crystals is investigated at temperatures close to T c . Second- and third-harmonic signals are studied as a function of the temperature and input power, for different values of the external magnetic field. The results are discussed in the framework of a phenomenological theory based on the two-fluid model which assumes that both the microwave and static fields perturb the partial concentrations of the normal and condensate fluids. It is suggested that, at temperatures very close to T c , this mechanism is the only one responsible for the harmonic emission by YBa 2 Cu 3 O 7 single crystals in the Meissner state. It is also effect…
Evaluation of a new Cr-free alloy as interconnect material for hydrogen production by high temperature water vapour electrolysis: Study in cathode at…
2012
International audience; For economic and ecological reasons, hydrogen is considered as a major energetic vector for the future. Hydrogen production via high temperature water vapour electrolysis (HTE) is a promising technology. A major technical difficulty related to high temperature water vapour electrolysis is the development of interconnects working efficiently for a long period. Working temperature of 800 degrees C enables the use of metallic materials as interconnects. High temperature corrosion behaviour and electrical conductivity of a new Cr-free Fe-Ni-Co alloy were tested in cathode atmosphere (H-2/H2O) at 800 degrees C. The alloy exhibits a poor oxidation resistance but an excelle…