Power generation characteristics of a sandwich‐type self‐heating thermoelectric generator with spatially varying embedded heat source

Power generation characteristics of a sandwich‐type thermoelectric generator in which the heat source is embedded into thermoelectric elements are investigated. Our previous work on a similar concept only considered a uniform heat source distribution inside thermoelectric elements. In this work, the effect of the spatial distribution of a heat source is examined. In particular, the effect of the concentration of heat source near the one end, that is, the hot end, is intensively studied as a potential means of improving the efficiency of the device. Although the effects of heat source concentration in impractical cases without heat transfer limitations on the cold side remain ambiguous, it become clear that heat source concentration indeed has positive effects in more realistic cases with finite heat transfer coefficients imposed on the cold side. Because of the relatively low efficiency of typical thermoelectric generation, a significant amount of heat must be dissipated from the cold end of the thermoelectric element. Greater heat source concentration near the hot end leads to more effective utilization of available heat source, reduces the amount of heat rejected at the cold end, and lowers the hot end temperature of the thermoelectric element. Overall, it is suggested that heat source concentration can be used as a method to achieve more efficient operation and better structural integrity of the system. Copyright © 2015 John Wiley & Sons, Ltd.     

Modeling,simulation, and optimization of a microalgae biomass drying process

The aim of the present work was to develop a transient mathematical model focused on microalgae biomass drying, considering two phases: solid (wet biomass) and gas (drying air). Mass and thermal energy balances were written for each phase producing a system of ordinary differential equations (ODE). The solution of the ODE set delivers the temperature and air humidity ratio and biomass profiles with respect to time. The numerical results were directly compared with temperature experimental measurements—for both phases—and with the biomass humidity content. Data from experiment 1 were used to carry out the mathematical model adjustment, whereas data from experiment 2 were used for the experimental validation of the model. The model was adjusted by proposing a new correlation for the mass transfer coefficient and by calibrating the heat transfer coefficient. The transient numerical results were in good quantitative and qualitative agreement with the experimental results, ie, within the experimental error bars. Then the experimentally validated mathematical model was utilized to optimize the following parameters: (i) the electric heater power ( ) and the dry air mass flow rate ( ) and (ii) the convection oven length to width ratio (L/W). The goal was to minimize system energy consumption (objective function). The optimization procedure was subject to the following physical constraints: (i) fixed convection oven total volume and (ii) fixed biomass and drying air contact surface area. For the oven original geometry,  = 3.0 kW and  = 9 g s^?1 were numerically found for minimum energy consumption, so that 36.9% and 43.5% energy consumption decreases were obtained, respectively, in comparison with the measurements of experiment 1. Next, the numerical geometric optimization found (L/W)_opt = 9, with and , which was capable to reach a 51.6% energy consumption reduction in comparison with the original system tested in experiment 1. The novelty of this work consists of the development and experimental validation of a physically based microalgae biomass drying mathematical model, ie, instead of using empirical correlations to predict the drying time and temperature profiles and then minimize system energy consumption. Therefore, the results show that it is reasonable to state that the model could be used to design, control, and optimize drying systems with configurations similar to the one analyzed in this study.     

Formation of quasi-single crystalline porous ZnO nanostructures with a single large cavity

We report a method for synthesizing quasi-single crystalline porous ZnO nanostructures containing a single large cavity. The microwave-assisted route consists of a short (about 2 min) temperature ramping stage (from room temperature to 120 °C) and a stage in which the temperature is maintained at 120 °C for 2 h. The structures produced by this route were 200-480 nm in diameter. The morphological yields of this method were very high. The temperature- and time-dependent evolution of the synthesized powders and the effects of an additive, vitamin C, were studied. Spherical amorphous/polycrystalline structures (70-170 nm in diameter), which appeared transitorily, may play a key role in the formation of the single crystalline porous hollow ZnO nanostructures. Studies and characterization of the nanostructures suggested a possible mechanism for formation of the quasi-single crystalline porous ZnO nanostructures with an interior space.     

Bacterial cellulose nanocrystals-embedded silk nanofibers

Nanofibrous Bacterial cellulose nanocrystals (BCNs)-embedded silk fibroin were successfully fabricated using electrospinning. The morphology, structure and mechanical properties of the silk fibroin nanofibers were investigated at various BCNs concentrations from 0 to 7 wt%. SEM, TEM and XRD analyses were conducted to confirm the incorporation of the BCNs in the electrospun silk fibroin nanofibers. The average diameter of the silk fibroin/BCNs nanofibers increased from 230 to 430 nm according to the increasing of the BCNs ratio due to the rising solute content. The FT-IR spectra confirmed the conformational transition of the silk fibroin, from a random coil to a beta-sheet structure, which shows the enhanced mechanical properties of silk fibroin based nanofibers even with small amounts of the BCNs. Moreover, it was observed that the Young's modulus of the silk fibroin/BCNs nanofibers unexpectedly increased with the formation of BCNs with a percolation structure at a concentration between 3 and 5 wt%.     

Integrated waste-to-energy conversion and waste transportation within island communities

Usually in islands both primary energy sources and drinking water are missing. Additionally, municipal solid waste (MSW) must be managed avoiding exclusive use of landfills, which limits sustainable development. Power generation from MSW incineration contributes significantly to replacing energy produced from fossil fuels and to reduce overall emissions. A solution based on thermodynamics, environmental and economic analyses and 3D-GIS modelling for the afore-mentioned problems for Cape Verde is proposed. This model integrates waste transportation optimisation and incineration with energy recovery combining production of heat and power (CHP), the heat being used for drinking water production. The results show that extraction condensing steam turbines are more suitable when power production is a priority (5.0 MW with 4000 m³/d of drinking water), whereas back-pressure turbines yield 5540–6650 m³/d of drinking water with an additional power production of 3.3–4.7 MW. The environmental and economic assessment performed shows the feasibility of the proposed CHP solution, which brings a considerable reduction in net air emissions (1.6 kt), including a significant decrease in the greenhouse gas emissions (131 ktCO₂), and that the revenue from energy sales (€15 million) has potential to balance the incineration cost. Moreover, when terrain relief is accounted for in the route optimisation for minimum fuel consumption, savings up to 11% are obtained.     

Process Variations-Aware Statistical Analysis Framework for Aging Sensors Insertion

As process technology continues to shrink, Process Variations and Aging effects have an increasing impact on the reliability and performance of manufactured circuits. Aging effects, namely due to Negative Bias Temperature Instability (NBTI) produce performance degradation as time progresses. This degradation rate depends on a) Operational conditions (e.g., V_DD, Temperature and time of electrical stress on MOS transistors) and b) Static technological parameters defined in the fabrication process. Moreover, performance of electronic systems for safety-critical applications which operate for many years in harsh environments are more prompt to be impacted by aging. In order to guarantee a safe operation in advanced technologies, aging monitoring should be performed on chip using built-in aging sensors. The purpose of this work is to present a methodology to determine the correct location for aging sensor insertion, considering the combined impact of process variations (PV) and aging effects (namely due to NBTI). In order to implement the methodology, a path-based statistical timing analysis framework and tools have been developed. It is shown that delay path reordering, associated with PV and aging, may justify the insertion of a few additional sensors, to cover abnormal delays of signal paths that become critical, under long system operation (e.g., 10 years).     

Three-dimensional swimming tadpole mini-robot using three-axis Helmholtz coils

Electromagnetic-actuated robotic systems have been studied recently for special purposes. Because these systems use external magnetic fields to control their robots, the robots can have simple structures and move with much freedom. In particular, these electromagnetic actuation (EMA) systems are being widely adopted for the actuation of biomedical mini-robots and microrobots for minimally invasive surgery (MIS) and diagnosis. We previously reported, as a feasible biomedical robot, the biomimetic swimming tadpole mini-robot, which can only swim above water. Indeed, the two-dimensional (D) plane swimming tadpole mini-robot is limited in its use because of its motility in the 2D plane. Therefore, this paper proposes a 3D swimming tadpole mini-robot that can move freely in water. First, in the proposed 3D swimming tadpole mini-robot, the buoyancy force was regulated for subaqueous swimming, and the permanent magnet was rearranged for precise movement. Second, to attain a 3D swimming motion, the actuation mechanism of the robot was developed using an EMA system. Finally, various experiments verified that the proposed 3D swimming tadpole mini-robot can swim freely in a 3D water environment.     

Controlling microstructure of three-dimensional scaffolds from regenerated silk fibroin by adjusting pH

For tissue engineering, it is very important to design and control the pore architecture of three-dimensional (3D) polymeric scaffolds, which plays an important role in directing tissue formation and function. In this study, 3D porous silk fibroin scaffolds produced using a freeze drying technique were prepared at pHs ranging from 5 to 9. The effects of pH on the pore microstructure of the silk fibroin scaffold were examined by rheometry, FESEM and FTIR. Different pore structures were formed according to the pH of silk fibroin because silk fibroin exhibits water-like behavior under basic conditions and gel-like behavior under acidic conditions.     

神经形态芯片:仿生学的驱动力

《麻省理工科技评论》(MIT Technology Review)刊出了"2014十大突破性科学技术"的文章,神经形态芯片(Neuromorphic Chips)名列其中。本文就这一技术进行简要分析。模仿人类大脑的理解、行动和认知能力,成为重要的仿生研究目标。     

Effect of superplastic forming exposure on tensile and S-N fatigue behavior of Ti64 alloy

The effect of superplastic forming (SPF) on tensile and S (stress)-N (number of cycles to failure) fatigue properties of Ti64 alloy was examined at 298 and 473 K. For simulating the superplastic forming exposure, millannealed Ti64 alloy sheet was heated in a vacuum chamber with a pre-determined temperature profile. For some as-exposed specimens, the α-case formed on the surface during expousre was mechanically removed to understand the effect of α-case on the mechanical properties of Ti64 alloy. It was found that the presence of α-case significantly affected the tensile and the fatigue properties of Ti64 alloy at 298 and 473 K by providing an easy initiation site for both tensile and fatigue fracture. The microstructural change during the SPF exposure was marginal in affecting the S-N fatigue properties of Ti64 alloy. Different testing temperature of 298 and 473 K affected the S-N fatigue behavior of as-received and as-exposed (α-case removed) Ti64 specimens, but not that of as-exposed specimen.