Silica/mullite fiber composite membrane with double-layer structure for efficient sub-micrometer dust removal

Here, we developed silica/mullite fiber composite membranes with double-layer structure by a simple vacuum procedure for the removal of sub-micrometer dust. The support with three-dimensional skeleton structure exhibited high porosity (higher than 90%), low density (lower than 0.25?g/cm³) and high compressive strength (higher than 0.55?MPa) at 1000?°C. By controlling the mass ratio of silica sol to mullite fiber, we can obtain uniform and complete filtering layers with different thicknesses. The composite membranes exhibited high PM filtration efficiency with 99% for 1–10?µm, 97% for 0.5?µm and 90% for 0.3?µm. These samples had high air flow with very low pressure drop (lower than 600?Pa when airflow velocity reached 1?m/s). These results indicated that the silica/mullite fiber composite membranes were very promising for PM pollution control in the field of hot gas filtration.     

基于划刻实验的单晶锗材料去除机理研究

采用Cube压头对单晶锗进行变载与恒载纳米划刻实验, 利用扫描电子显微镜和原子力显微镜对已加工表面进行观测, 根据表面形貌将划刻过程分为延性域、脆塑转变域及脆性域三种, 对各个阶段的表面成型及材料去除方式进行了研究。使用最小二乘法对不同阶段划刻力进行非线性拟合, 并利用相关系数检验拟合函数可靠性, 结果表明划刻力与划刻深度存在强相关性。同时分析了单晶锗的弹性回复率随划刻距离的变化趋势, 结果表明工件的弹性回复率将从纯弹性阶段的1逐步回落至0.76左右。基于脆塑转变临界载荷, 以裂纹萌生位置作为脆塑转变标志, 首次结合工件已加工表面弹性回复, 提出一种适用于计算单晶锗的脆塑转变临界深度模型, 其脆塑转变临界深度为489 nm。     

Optimized techniques for driving and control of the switched reluctance motor to improve efficiency

This work presents modeling, driving and classical speed control techniques for the switched reluctance motor. The aim is to improve the computational model, the control response and the machine efficiency. A parametric regression model was used to find the inductance profile of the switched reluctance motor and from the new inductance profile model. The drive and control techniques are shown: (i) with speed control acting on the excitation voltage and fixed switching angles, (ii) with speed control acting on the switching angles and fixed excitation voltage and (iii) with speed control acting on the excitation voltage, in this case, with dynamic switching angles and controller parameters. The inductance profile is represented by expression and inserted into the machine computer model, allowing greater precision and low computational cost. The speed control acting on the excitation voltage with dynamic controller parameters and dynamic switching angles allowed: (i) shorter response time for a wide range of control, (ii) higher efficiency, (iii) low computational cost and (iv) simplified implementation and maintenance. The techniques proposed in this work obtained precision of the computational model with respect to the system (in workbench) and optimized parameters in a wide range of the speed control, allowing an improvement of switched reluctance motor efficiency.     

基于正交试验的含氮硼酸酯铝材轧制润滑油摩擦学性能研究

合成一种新型含氮硼酸酯铝材轧制润滑油添加剂,利用四球试验机考察添加含氮硼酸酯的铝材轧制润滑油的油膜强度、摩擦因数,通过显微镜观察磨斑形貌并测量磨斑直径。利用正交试验法评估极压剂含量、基础油种类、四球试验机载荷和转速对含氮硼酸酯润滑油摩擦学性能的影响,并通过多目标优化设计,对4种参数对铝材轧制润滑油摩擦学性能的强化效果进行综合研究。结果表明:各工艺参数对油样的摩擦学性能影响显著性由大到小依次为极压剂添加量、基础油种类、转速和载荷;经过多目标优化设计,得到的含氮硼酸酯铝材轧制润滑油强化工艺参数的最佳组合:极压剂质量分数为1.0%,基础油种类为D100,载荷为294 N,转速为1 200 r/min;通过极差、方差等分析,发现极压剂添加量和基础油种类对油样的摩擦学性能有显著影响。     

Introducing the energy efficiency map of lithium‐ion batteries

The charge, discharge, and total energy efficiencies of lithium‐ion batteries (LIBs) are formulated based on the irreversible heat generated in LIBs, and the basics of the energy efficiency map of these batteries are established. This map consists of several constant energy efficiency curves in a graph, where the x‐axis is the battery capacity and the y‐axis is the battery charge/discharge rate (C‐rate). In order to introduce the energy efficiency map, the efficiency maps of typical LIB families with graphite/LiCoO₂, graphite/LiFePO₄, and graphite/LiMn₂O₄ anode/cathode are generated and illustrated in this paper. The methods of usage and applications of the developed efficiency map are also described. To show the application of the efficiency map, the effects of fast charging, nominal capacity, and chemistry of typical LIB families on their energy efficiency are studied using the generated maps. It is shown how energy saving can be achieved via energy efficiency maps. Overall, the energy efficiency map is introduced as a useful tool for engineers and researchers to choose LIBs with higher energy efficiency for any targeted applications. The developed map can be also used by energy systems designers to obtain accurate efficiency of LIBs when they incorporate these batteries into their energy systems.     

Comparative study to use nanofluid ZnO and CuO with phase change material in photovoltaic thermal system

In this study, the simultaneous use of nanofluid and phase changing material as a coolant for photovoltaic fluid collector system and its effects are investigated experimentally. Two types of nanofluid are taken for the consideration, that is, ZnO and CuO, which are water‐based fluid. The experiments are performed in five different types of photovoltaic thermal system conventional: PT, PVT (ZnO), PVT (CuO), PCM medium (PVT/PCM/ZnO), and PCM medium (PVT/PCM/CuO). The results are obtained for surface temperature, energy, and thermal efficiency, and it is compared with each other. Further, the effect of the nanofluid as the effective alternative for pure deionized water is measured. From the results, it is evident that the PVT/PCM/CuO system minted 15% high electric output compared with convention module. Furthermore, the addition of the CuO nanofluid increases the thermal output significantly up to 8% for PVT and 12% for PCM without energy consumption. It also found that the nanofluid increases the overall energy efficiency of the system compared with convention PV.     

Nitrogen‐doped self‐shrinking porous 3D graphene capacitor deionization electrode

Traditional three‐dimensional (3D) graphene has a large pore structure, which makes the graphene structure not well interact with the anion and cation during the desalination process, thereby restricting the capacitive deionization (CDI) ability of the 3D graphene. In this work, we prepared a nitrogen‐doped self‐shrinking porous 3D graphene electrode by adding a pyrrole monomer to a graphene oxide solution, which was then applied to a CDI electrode. The results show that the electrochemical performance of the as‐prepared nitrogen‐doped self‐shrinking porous 3D graphene (NSPG) is significantly improved. Compared with traditional 3D graphene, NSPG has a denser pore structure with a larger specific surface area, thus exhibiting a good CDI performance: The NSPG electrode has an electroadsorption capacity of 13.16 mg/g.     

Improving the performances of earth air heat exchangers through Constructal design

Earth to air heat exchanger (EAHE) is a well‐known technique used to preheat or precool outdoor air before blowing it into a building. However, its geometry is often very simple as it consists in one or multiple straight pipes, while more complex arrangements can be found in heat exchangers design. In this paper, we explore the advantage of designing an EAHE as a network through the Constructal law point of view. A methodology is first proposed to design a single pipe EAHE when the need is defined in terms of cooling power, overall efficiency and enthalpy difference between the inlet air and the ground. Next, the single pipe EAHE is used as a reference for designing a tree‐shaped network under the constraint of identical fluid volume and cooling power. The geometrical features are allowed to change for the different branches of the network. The network coefficient of performance is found to increase significantly with the bifurcation level, illustrating the superior performances of the network. This approach was found to be robust as the improvements were not depending on the cooling demand or the environmental conditions. However, further work is needed to move from this theoretical result to practical considerations.