Applied Mechanics and Materials Vol. 598

Abstract: The manned spacecraft is a typically confined space in microgravity and it suffers severe fire risks. This paper studies on the distribution of the fire parameters in space-confined microgravity to find a more rational way to install the fire detectors. The experiments are carried out in the ground simulation experiment platform for fire based on the International Space Station. Based on the functional simulation principle, this paper maintains Gr (Grashof number) and increases Re (Reynolds number) to simulate microgravity environment in such a full-scale platform. The results show that Fire Detector 5 on the center of the side wall and Fire Detector 7 on the corner of the ceiling are the best installing locations for smoke detection. And, temperature detection is not appropriate in manned spacecraft. Namely, the way to install the fire detectors in manned spacecraft should be different from that in normal gravity.

Abstract: Subjected to fixed total heat transfer surface area, the distribution of surface in multiple-effect evaporator affects the performance of the evaporator. Previous studies have been concerned with optimization of surface distribution with the assumption that no fouling occurs. The present study considers a more realistic case when the last-effect vessel is subjected to fouling. It is shown that, in order to consume the minimum steam exergy to produce a given amount of evaporation, the area of the last-effect vessel must be increased as the rate of fouling increases.

Abstract: This paper proposes an epoxy-based anti-reflective micron structure layer for solar cell modules. A Solidworks software is used to design the micro-structure layers with different size and shapes (inverted pyramid and micro-lens). Then, An optical simulation software, Tracepro, is used to simulate the anti-reflection efficiency under the standard lighting source of AM1.5G. The difference between the flat layer and micro-structured layer has been analyzed to obtain the best micro-structure layer for solar cell modules. From the simulated results, the inverted pyramid textured layer that each pyramid’s width is 10μm and height is 5μm can improve the flux increment rate up to 13% compared with the flat layer at normal incidence. However, the best efficiency for micro-lens structure layer increases about 10% with radius of 25μm and height of 18.75μm and 25μm at 15o incidence. In addition, the thinner the Epoxy layer is, the better the anti-reflection efficiency is. Therefore, the proposed Epoxy-based micro-structure can improve the solar module for obtaining higher efficiency and best qualities.

Abstract: Harvesting ambient wasted energy has been in recent years a prominent research endeavor, aimed at providing alternative energy sources for low-power electronic mobile devices. Among various solutions, piezoelectric energy harvesters have attracted major attention due to the scalability, high-efficiency and the universal presence of vibration sources. In this paper, we studied the charge redistribution phenomenon in piezoelectric energy harvesters employing flextensional structures numerically and experimentally. A finite element model was developed firstly to study the mechanical and electrical response of flextensional transducers. The simulation results were then validated by a corresponding experiment. The research reveals that energy is dissipated in the process that charge flows from the high potential region to the low potential region. The electrode shape has a significant effect on the efficiency, and therefore should be considered fully when designing new energy harvesters. This study also assists in the design of flextensional sensors and actuators.

Abstract: We fabricated silver nanoprisms (AgNPs) on ITO by immersing ITO substrates in AgNPs solution for a series of immersion times. The amount of adsorbed AgNPs increased with immersion time. The AgNPs showed plasmonic absorption in the range of 400 – 600 nm and were used in organic solar cells (OSCs). The device performance was the best when the immersion time was 30 min, corresponding to AgNPs coverage of 68%. Under this condition, the device showed short-circuit current density (J_SC) of 10.10 mA cm^-2 (18% improved), and power conversion efficiency (PCE) of 3.88% (23% improved).

Abstract: A new type of hollow cathode using a radioisotope heat source instead of a conventional sheathed heater was introduced and it achieved thermionic emission performances similar to the ones of conventional hollow cathodes. Strontium-90, Plutonium-238 and Curium-244 were chosen as radioisotope heat sources and a thermal reductive layer was also used to obtain precise thermionic emissions. A new system design methodology called the Self-Sufficiency Principle was introduced and was applied by powering the keeper electrode with the radioisotope decay heat using a radioisotope thermoelectric generator (RTG). The heater supply of the hollow cathode power configuration was replaced with a RTG supply and the mode of operation of the device was modified because radioisotope heat sources cannot be switched off. This hollow cathode was then benchmarked against two ion thruster configurations and a maximal overall power saving of 3% was achieved. Its advantages are its power saving capability and scalability but it can however be voluminous, heavy and potentially hazardous. Further research in this field ought to explore the range of applications of this new power-free electron emission technology.

Abstract: With the advantage of high energy density, long cycle life and environmental friendliness, Lithium-ion battery has become a promising power source for hybrid and electric vehicles, which are liable to two kinds of failure, overcharge and overdischarge. Because of the capability of detecting multiple faults, Multiple Model Adaptive Estimation (MMAE) method was applied to a model-based fault detection of a lithium-ion battery with a two-order linear electrical model. Parameters that represent normal-mode and faulty-mode of the battery were obtained by a series of experiments, and three Kalman filters were designed thereafter. Finally, simulation verified the performance of the MMAE algorithm on fault detection of these two kinds of fault and it is shown that this technique is able to discern these faults rapidly and accurately.

Abstract: This article describes the Parabolic trough solar collector design of single-axis tracking system based on PLC, Siemens S7-300 as a controller, using a complex mathematical model, based on the special climate of Western Region, select the single-axis design process, greatly reduced cost, collectors need only be completed that automatically tracks the sun azimuth. Feedback device selection angle sensor, light intensity sensor and sun sensor, strain two conditions that cloudy and sunny, which greatly improves the efficiency of the collector, the better to achieve real-time tracking grasp the situation.

Abstract: The effects of electrode length on the characteristics of flow induced by an electrohydrodynamic (EHD) gas pump in circular pipe have been experimentally examined in this study. The gas pump has a diameter of 61.8 mm and uses eight evenly spaced emitting electrodes which are flush mounted on the tube inner wall. The gap distance between emitting and ground electrodes is fixed at 25 mm and two emitting electrode lengths (15 mm and 40 mm) are considered. Experiments are conducted using positive corona discharge with voltage varying from 17.5 kV to 23 kV. Several important implications from the present results for practical engineering applications are presented.

Abstract: The capacitance-voltage (C–V) characteristics of inverted staggered amorphous indium–gallium–zinc-oxide thin film transistors (α-IGZO TFTs) with various dimensions are investigated by physics-based technology computer aided design (TCAD) simulation. For gate bias lower than the threshold voltage of the TFT, the electrons in the channel region are nearly fully depleted. It causes that the total gate capacitance is determined by the overlap region of gate, α-IGZO, and source/drain metals. When the applied gate bias is higher than the threshold voltage, the high electron density channel with density of ~6 × 10¹⁷ cm^-3 and thickness of ~3-4 nm is observed near the interface of α-IGZO and gate dielectric. It results that the total gate capacitance is dominated by the gate to channel overlap. Quantitative analysis of the carrier distribution and energy band structures are utilized to study the physical mechanism underlying the C–V characteristics of the α-IGZO TFTs.