Multi-objective optimization of split and recombine micromixer using grey relational analysis method

PurposeThe effective, efficient and optimal design of micromixer is the need in the field of biochemical and biomedical diagnostic systems.Design/methodology/approachIn this paper, multi-objective optimization of split and recombine micromixer (SRM) with different geometrical configurations is carried out. The finite element method-based three-dimensional models are prepared and analyzed using COMSOL Multiphysics 5.0 Software. Taguchi’s design of experiment (DoE), main effect plot analysis, ANOVA and grey relational analysis (GRA) method are used to find out optimum condition. The five geometrical parameters with three levels, namely, angle between inlets, pillar size, pillar shape, aspect ratio and constriction height of SRM are considered as design variables. The mixing index (MXI) and pressure drop (∆P) are considered objective functions.FindingsThe MXI is significantly influenced by pillar shape and aspect ratio, whereas the pressure drop (∆P) by constriction height. Maximum MXI (0.97) with minimum pressure drop (64,587 Pa) is the optimal conditions and obtained at 180 deg angle between inlets, 50 µm of pillar size, 1.5 of aspect ratio, 100 µm of constriction height and ellipse shape pillar cross-section, respectively.Research limitations/implicationsThis optimized SRM can be combined with lab-on-a-chip for biochemical and biomedical analysis.Originality/valueThis work is useful to obtain optimal geometry of SRM for getting efficient performance of micromixer.

Research on the Redistribution Law of Lateral Mining Stress and the Bearing Characteristics of Section Coal Pillar in Extra-Thick Fully Mechanized Top-Coal Caving Mining

Due to the change of ground stress environment caused by underground coal mining, the intense lateral mining stress concentration is formed around the stope; so section coal pillar is generally set up to bear the mining pressure, but the different sizes of coal pillars have obvious influence on the bearing capacity of those pillars and the characteristics of mining pressure. Mastering the mechanism characteristics by which coal pillars bearing capacity and mining stress distribution is crucial to identify the reasonable coal pillar size and give full play to the bearing role of section coal pillar, given their importance for the safety and bearing stability of engineering rock mass in underground coal mining. Therefore, the bearing characteristics of section coal pillar and the redistribution of mining stress are achieved with a mechanical model analysis on the basis of the analysis of coal pillar bearing and mining influence characteristics. Moreover, applying the elastic-plastic mechanics theory revealed the mechanical equations of the effective bearing size of coal pillar and redistribution of mining stress in longwall face. Combined with the analysis of a specific engineering example, the research results are as follows. During a roadway excavation, the continuous mining stress transfer occurs “stress redistribution” and the mechanical failure of bearing coal pillar consists of lateral mining and roadway side failures. The bearing coal pillar has two critical dimensions (i.e., the critical dimension W e of the self-bearing stability coal pillar and the critical dimension W p of failure through the coal pillar). The mechanical state of the lateral mining stress redistribution and bearing coal pillar is divided into the three situations: ① when the width of coal pillar W < W p , only one stress concentration area exists, the bearing capacity of the coal pillar is invalid at this stage, and the lateral mining stress concentration transfers to the roadway solid coal side; ② when the width of the coal pillar W e ≥ W ≥ W p , two stress concentration areas appear at this stage, and the coal pillar is in the critical state of self-bearing stability; ③ when the width of the coal pillar W > W e , three stress concentration areas are present, and the coal pillar at this stage is in a self-bearing stable state. Among all these factors, only the size of coal pillar is completely controllable, so the aspects of safe bearing and reserved size design of coal pillar, after estimating the critical size of coal pillar, the coal pillar size design is carried out according to the mine pressure control needs of mining engineering, and the cohesion, internal friction angle, interlayer friction coefficient, and coal seam mining height are improved by artificial technology, so as to realize the resource safe and efficient mining of all kinds of coal seam mining conditions; in the calculation of wide coal pillar size, the advance mining stress concentration at the end of the self-working face should be taken as the mining load condition, and the reserved size meets the condition of W > W e , thereby ensuring the stable bearing of the wide coal pillar despite the advanced mining stress concentration during the self-working face mining; in the calculation of narrow coal pillar size, the lateral mining stress concentration before mining should be taken as the mining load condition and the reserved size meets the condition W < W p , thereby realizing the effective transfer of mining stress concentration to the roadway solid coal side.

Study on Stress Relief of Hard Roof Based on Presplitting and Deep Hole Blasting

For the problem that the hard roof causes wider end-mining coal pillar, and the roadway is greatly affected by mining, this paper took Shanxi Luning Coal Mine as the engineering background; based on the stress distribution characteristics of the coal pillar, the calculation method of the limit end-mining coal pillar size was given; considering the formation conditions and transmission forms of the advanced abutment stress, a method combining presplitting and deep hole blasting was proposed to weaken the advanced abutment stress. The numerical simulation was used to analyze the stress distribution of coal pillars, which was verified by on-site industrial tests. The results showed that the presplitting can achieve the blocking of stress. The closer it is to the peak of the abutment stress, the better the blocking effect. Deep hole blasting can weaken the source of the advanced abutment stress and reduce the peak of abutment stress. With the combination of the two blasting methods, the end-mining coal pillar size of Luning Coal Mine can be reduced to 60 m. The method combining presplitting and deep hole blasting can effectively reduce the end-mining coal pillar size and reduce the impact of mining on the deformation of the dip roadway.

Effects of pillar size modulation on the magneto-structural coupling in self-assembled BiFeO3–CoFe2O4 heteroepitaxy

The magneto-structural coupling of BiFeO3 (BFO)–CoFe2O4 (CFO)/LaAlO3 (LAO) heteroepitaxy with various lateral sizes of CFO pillars embedded in a BFO matrix was investigated.

Effect of the Pillar Size on the Electrochemical Performance of Laser-Induced Silicon Micropillars as Anodes for Lithium-Ion Batteries

Silicon micropillars with tunable sizes are successfully fabricated on copper foils by using nanosecond-pulsed laser irradiation and then used as anodes for lithium-ion batteries. The size of the silicon micropillars is manipulated by using different slurry layer thicknesses ranging from a few microns to tens of microns. The effects of the pillar size on electrochemical properties are thoroughly investigated. The smaller the pillars, the better the electrochemical performance. A capacity of 1647 mAh g−1 at 0.1 C current rate is achieved in the anode with the smallest pillars, with 1215, 892, and 582 mAh g−1 at 0.2, 0.5, and 1.0 C, respectively. Although a significant difference in discharge capacity is observed in the early period of cycling among micropillars of different sizes, this discrepancy becomes smaller as a function of the cycle number. Morphological studies reveal that the expansion of micropillars occurred during long-term cycling, which finally led to the formation of island-like structures. Also, the formation of a solid electrolyte interphase film obstructs Li+ diffusion into Si for lithiation, resulting in capacity decay. This study demonstrates the importance of minimizing the pillar size and optimizing the pillar density during anode fabrication.

Study on Efficient Utilization Technology of Coal Pillar Based on Gob-Side Entry Driving in a Coal Mine with Great Depth and High Production

Improving the utilization of non-renewable resources takes a crucial position in circular economy. Gob-side entry driving technology has been widely applied in coal mines in China, such as in the Shilawusu mine (Ordos City, Inner Mongolia), here considered as a case study due to its high safety and resource-recovery rate. However, at present the complexity of coal pillar utilization makes it hard to fully master the key technology for coal pillar size design, which leads to huge waste of coal resources. Based on theoretical calculation and numerical simulation, this study analyzed the basic mechanical structure of coal pillar and the characteristics of its weakening failure, providing theoretical reference for efficient recovery of coal resources. In general, results of this study can be helpful in pursuing the efficient, hence sustainable, development of mines with Gob-side entry driving technology.