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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 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.

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.

Swirl combustors have proven as effective flame stabilisers over a wide range of operation conditions thanks to the formation of well-known swirl coherent structures. However, employment of swirl combustors to work on lean premixed combustion modes while introducing alternative fuels such as high hydrogen blends result in many combustion instabilities. Under these conditions, flame flashback has been considered as one of the major instability problems that have the potential of causing considerable damages of the combustion systems hardware in addition to the significant increase in pollutant levels. Combustion Induced Vortex Breakdown (CIVB) is considered a very particular mode of flashback mechanism in swirling flows as this type of flashback occurs even when the fresh mixture’s velocity is higher than the flame speed, consequence of the interaction between swirl structures and swirl burner geometries. Improvements of burner geometries and manipulation of swirl flows can produce good resistance against this type of flashback. However, increase flame flashback resistance against CIVB can lead to an increase in the propensity of another flashback mechanism, Boundary Layer Flashback (BLF). Thus this paper presents an experimental and numerical approach that allows the increase in CIVB resistance by using diffusive air injection and simultaneously avoid BLF by changing the wall boundary layer characteristics using microsurface grids as a liner for the nozzle wall. Results show that using those two techniques together has promising potentials regarding wider stable operation for swirl combustors, enabling them to burn a great variety of fuel blends safely.

In this article, a compound unit of swirl and impingement cooling techniques is designed to study the performance of flow and heat transfer using multi-conical nozzles in a leading-edge of a gas turbine blade. Reynolds Averaged Navier-Stokes equations and the Shear Stress Transport model are numerically solved under different nozzle Reynolds numbers and temperature ratios. Results indicated that the compound cooling unit could achieve a 99.7% increase in heat transfer enhancement by increasing the nozzle Reynolds number from 10,000 to 25,000 at a constant temperature ratio. Also, there is an 11% increase in the overall Nusselt number when the temperature ratio increases from 0.65 to 0.95 at identical nozzle Reynolds number. At 10,000 and 15,000 of nozzle Reynolds numbers, the compound cooling unit achieves 47.9% and 39.8% increases and 63.5% and 66.3% increases in the overall Nusselt number comparing with the available experimental swirl and impingement models, respectively. A correlation for the overall Nusselt number is derived as a function of nozzle Reynolds number and temperature ratio to optimize the results. The current study concluded that the extremely high zones and uniform distribution of heat transfer are perfectly achieved with regard to the characteristics of heat transfer of the compound cooling unit.

The influence of electromagnetic induction coil launcher (EICL) system parameters on the launch performance was analyzed, and a method for measuring the launch performance of an EICL system with a muzzle velocity and energy conversion efficiency was proposed. The EICL system mainly includes a pulse power supply and launcher. The parameters of the pulse power supply mainly include the discharge voltage and the capacitance value of the capacitor bank. The structural parameters of the launcher mainly include the bore size of the launcher, the air gap length between the armature and the drive coil, the length and width of the drive coil, and the trigger position of the armature. Change in single or multiple parameters in the launch system will influence the launch performance. The influence of single or multiple parameters on the launch performance was summarized, and the physical law as analyzed. The influence law of the EICL system parameters on the launch performance was obtained, which lays a theoretical foundation for the optimization design of EICL. Finally, experimental verification was carried out by a single-stage test platform.

Abstract High-performance multicrystalline silicon (HPMC-Si) wafers were produced using upgraded metallurgical-grade silicon (UMG-Si) materials in the seed-assisted growth system at the industrial scale. The HPMC-Si wafers yielded low dislocation density and fine and uniform grain size. We observed that fine grain size suppressed the segregation effect of metal impurities. The effective segregation coefficients of Fe, Al, and total metal impurities approximated 0.265, 0.492, and 0.386, respectively. The concentration of impurities within 10–90% of the solidified fraction in the ingot was relatively uniform based on the improved crystal structure control. The heterogeneous nucleation mechanism of concave and planocera nucleation was discussed intensively. HPMC-Si wafers were obtained under the crystal structure control coupled with behavior regulation of impurity segregation in the seed-assisted growth system. The average conversion efficiency of Al-BSF processed solar cells reached 18.65%.