• Energy Research
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Characteristics of Tm:YAG ceramic for high efficient 2-μm lasers are analyzed. Efficient diode end-pumped continuous-wave and Q-switched Tm:YAG ceramic lasers are demonstrated. At the absorbed pump power of 53.2W, the maximum continuous wave (cw) output power of 17.2 W around 2016 nm was obtained with the output transmission of 5%. The optical conversion efficiency is 32.3%, corresponding to a slope efficiency of 36.5%. For Q-switched operation, the shortest width of 69 ns was achieved with the pulse repetition frequency of 500 Hz and single pulse energy of 20.4 mJ, which indicates excellent energy storage capability of the Tm:YAG ceramic.

Abstract The molten droplet fragmentation dominated by hydrodynamic mechanisms is the key process at the stage of pressure propagation in the process of the fuel–coolant interaction (FCI) which may occur during the course of a severe accident in a light water reactor (LWR). However, due to complication of the process, hydrodynamic fragmentation cannot be described by a particular mechanism, and there is no sufficient experimental studies under high pressure shock condition for this kind of fragmentation evaluation. In this paper, a multi-phase thermal hydraulic code with the Volume of Fluid Method (VOF) is developed, Continuum surface force (CSF) model is employed to compute the surface tension. The breakup process of a molten droplet under sudden accelerations is numerically analyzed to investigate the mechanism of fragmentation in vapor explosion. The results show that the breakup process experiences two stages: deformation and disintegration, which agrees with the simulation by Duan et al. (2003) using Moving Particle Semi-implicit (MPS) method. It is found that an increase in intensity of pressure pulse will accelerate the completion of breakup process and the dimensionless breakup time from the simulation is not strongly affected by Bond number ( Bo ). The simulation results suggest that the deformation imposed by the external hydrodynamic pressure distribution should be the dominant factor in breakup process for molten droplets in liquid–liquid system simulated in this paper.

Safety and Security Science

Abstract In this work, we propose an acoustic energy harvesting metamaterial consisting of an array of silicone rubber pillars and a PZT patch deposited on an ultrathin aluminum plate with several holes based on locally resonant mechanism. The resonance is formed by removing four pillars, drilling a few of holes and attaching the PZT patch on the aluminum plate. The strain energy originating from an incident acoustic wave is centralized in the resonant region, and the PZT patch is used to convert the elastic strain energy into electrical power. Numerical analysis and experimental results show that the proposed millimeter-scale harvester with holes obviously improves the effect of acoustic energy harvesting while performing at the subwavelength scale for sonic low-frequency environment (less than 1150 Hz). In addition, the experimental results demonstrate that the maximum output voltage and power of the proposed acoustic energy harvesting system with 16 holes of 2 mm radius are 3 and 10 times higher than those without holes at the resonant mode for 2 Pa of incident acoustic pressure. Both the number and size of holes have a significant effect on the performance of acoustic energy harvesting. The advantages of the proposed structure are easy-to-machine and full of practicality, and it can be used in broad applications for low-frequency acoustic energy harvesting.

AbstractNiNb2O6‐BaTiO3 ceramics were prepared using a solid‐state reaction method, and the effects of the addition of NiNb2O6 on the dielectric properties and energy‐storage characteristics of BaTiO3 were investigated systematically. We used XRD to show that the obtained NiNb2O6‐BaTiO3 ceramics possess a single perovskite structure. The addition of NiNb2O6 improves the energy density efficiency and leads to a decrease of the dielectric loss to less than 1 %. Moreover, optimum performances of the BaTiO3 ceramics can be achieved by the addition of 1.0 mol % NiNb2O6, at which content the obtained ceramic satisfies the X7R specification. The addition of NiNb2O6 stabilizes the crystalline lattice, which enhances the temperature stability of the dielectric properties accordingly.

Abstract As promising candidates for thermophotovoltaic energy conversion systems, epitaxial thin film III–V cells have gained increasing attention due to their potential for reduced weight. However, few studies have been done to date to enhance the performance of epitaxial single crystal GaSb thin film cells. In this work, the internal quantum efficiencies of epitaxial single crystal GaSb thin film cells with Zn-diffused and epitaxial p–n junctions were predicted with models verified using the corresponding experimental results. The results are the first to indicate that, for the former, when the base region thickness is approximately equal to minority carrier diffusion length, the maximal IQE can be obtained and it is notably higher than the IQE of GaSb bulk cell at wavelengths from 800 to 1700 nm. Reducing bottom surface recombination velocity and increasing hole Shockley–Read–Hall lifetime could also increase the IQE. While for the latter, the results demonstrated that the optimal base region thickness is also approximately equal to minority diffusion length, and reducing emitter region thickness will increase the IQE when the base region is optimized. The comparison of the two optimized GaSb thin film cells showed that the GaSb thin film cell with epitaxial p–n junction has a higher IQE.

A new approach for the electromagnetic control and propulsion of a current carrying electric arc plasma ring is described. The essence of the approach is to form and manipulate the arc plasma outside rather than inside a magnetic field producing coil so that pulsed plasma thrusts can be produced in a choice of different directions. The interaction of the electric arc, formed in atmospheric pressure air, with such a magnetic field has been investigated. It has been shown that a stable azimuthal plasma ring can be rapidly produced by the simple process of separating two annular contacts. Pulsed plasma propulsion is obtained when the arc plasma and B-field sustaining current is reduced to zero whereby the constraining electromagnetic forces are removed and, as a consequence, the resulting plasma ring expands radially outwards. Several different measurement techniques have been deployed for investigating the behavior of the plasma ring. These include electrical probing, B-field probing and high-speed plus video photography. The results suggest that the plasma control and propulsion is governed by a combination of effects including ablation of the material around which the plasma ring is formed and self-pressurization related to the device geometry, as well as the electromagnetic forces. Preliminary results indicate that through the use of appropriate device geometries, the arc plasma may be propelled in axially opposite directions as well as radially.