Efficient Micro Research Articles

Flame characteristics depending on recirculating flows in a non-premixed micro combustor with varying baffles

For an efficient micro combustor, the introduction of a bluff body has been a major design factor due to favorable effects for flame holding. To investigate the relation between flame characteristics and recirculation patterns originated from bluff bodies, three kinds of the plate-type baffle and the multi-hole baffle are introduced for a micro combustor. In this regard, various simulations using the Reynolds Stress Model (RSM) and the Eddy Dissipation Concept (EDC) of GRI-Mech 3.0 are performed for such micro combustors. The pseudo flame extinction is proposed to determine the undesirable combustion condition and the global equivalence ratio which is one of the most important variables is changed to explore the reacting flows near the unstable combustion of the baffled micro combustors. From the results, it is ascertained that wall recirculation, center recirculation, and their mixed flows are variously formed depending on the baffle configuration inside the combustor due to the different baffle blockage. These features are largely connected to the extension of flammable range and the spatial development of flame zone which determines the efficient combustion or flame extinction. Under the same operating condition, combustion characteristics of flame length, maximum temperature, and combustion efficiency are comparatively discussed for plate-type baffles and multi-hole baffle. From the probability distributions of the local equivalence ratio, the plate-type baffle shows a unique role according to its location in the micro combustor like inducing the fuel-lean or fuel-rich mixture. And, it is found that the recirculating flows near the fuel stream produce a more effective combustion than those near the air streams. Also, the key features of flame shape and recirculating flows are examined at near the extinction condition and those are carefully compared for the premixed and non-premixed combustors. Finally, the baffle configuration giving the swirling flow structure is discussed and a flame stability diagram is obtained for the baffled micro combustor. So, the overall change of flame pattern and flammable range of the baffled micro combustor is identified depending on the baffle hole size.

A stable mesoporous metal-organic framework as highly efficient sorbent of dispersive micro solid-phase extraction for the determination of polycyclic aromatic hydrocarbons by HPLC.

Owing to the large molecular sizes of polycyclic aromatic hydrocarbons, their adsorption using microporous sorbents leads to a low adsorption capacity. Here, to increase the extraction capacity and detection sensitivity of polycyclic aromatic hydrocarbons, a highly efficient dispersive micro solid-phase extraction method was developed based on a stable mesoporous metal-organic framework named Jilin University China 48. Jilin University China 48 is a super hybrid with large one-dimensional hexagonal nanotube-like channels of 24.5×27.9Å, which exhibits high potential to be an efficient sorbent of dispersive micro solid-phase extraction to adsorb polycyclic aromatic hydrocarbons. By combining with high-performance liquid chromatography, a sensitive method was developed for the determination of seven polycyclic aromatic hydrocarbons. The synthesized Jilin University China 48 exhibited excellent characteristics of stability, good morphology, large surface area, and open adsorption sites. Under the optimized extraction conditions, better extraction results were obtained than that of other methods reported previously. The proposed method exhibited high sensitivity with the limit of detections in the range of 0.021-0.13ng/mL, good linearity in the range of 0.068-50ng/mL with related coefficients of >0.9988, satisfactory precision with relative standard deviation of <4.3%, and adequate recoveries between 85.8 to 109.55% for all the target compounds.

An efficient micro-mixer by elastic instabilities of viscoelastic fluids: Mixing performance and mechanistic analysis

Efficient mixing is one of the keen interest of many bioengineering and chemical engineering processes. In this work, we designed an efficient micro-mixer with viscoelastic fluid which can induce both strong shear and strong extension by being embedded several rhombic blocks to destabilize the viscoelastic fluid flow and can be also easily integrated. Experimental visualization and direct numerical simulation (DNS) of mixing process were conducted to evaluate the mixing performance. By adding green fluorescent particles into the fluids, apparent mixing enhancement was observed for viscoelastic fluid flow when the flow rate exceeded a threshold. The efficient micro mixing progress also shows great potential for bioengineering application with the biocompatible working fluids. Through DNS, we discussed the flow patterns and the role of polymers playing in viscoelastic fluid flow to respectively figure out the underlying mechanism of efficient mixing and the occurrence of unstable flow motions. The results show that when the elasticity is strong enough, the viscoelastic fluid flow is irregularly twisting and swinging in the channel, and as a result enhances the mixing by increasing the intersecting frequency of fluids of different concentrations. Moreover, owing to the special designed geometry, the polymers act as the energy supplier of unstable flow motions, which keeps the fluctuations from decaying towards the laminar regime.

Morphing and growing micro unmanned air vehicle: Sizing process and stability

An optimized and comprehensive method is proposed in order to design an efficient micro unmanned air vehicle with morphing and growing capabilities. In the sizing process, to select the optimum wing shape, three different shapes are compared based on an aerodynamic analysis, and a tapered wing is selected for the compressed mode. Then, since the wingspan, wing area, wing loading, and other parameters are changing as function of time, a transition analysis is carried-out during the sizing process. By using the calculated surface area and considered aspect ratio for compression and expansion modes, the wingspan is determined as function of time. Considering the estimated weight, the required lift coefficient is calculated and then two types of airfoils are selected. Finally, after completing the optimal geometric design, aerodynamic analyses are carried out to investigate the performance of the growing drone. The proposed strategy for designing efficient micro unmanned air vehicles for a well-defined mission can be utilized and extended to design other growing micro unmanned systems depending on the mission.

Novel rechargeable 3D-Microbatteries on 3D-printed-polymer substrates: Feasibility study

Miniature power sources are needed for a variety of applications, including implantable medical devices, remote microsensors and transmitters, “smart” cards, and Internet of things (IoT) systems. Today's rechargeable lithium-ion batteries - with the best performance on the subject of energy density and with a reasonably good power efficiency - dominate the consumer market. Insufficient areal energy density from thin-film planar microbatteries has inspired a search for three-dimensional microbatteries (3DMB) with the use of low cost and efficient micro- and nano-scale materials and techniques. The exclusive capabilities of the 3D-printing technology enable the design of different shapes and high-surface-area structures, which no other manufacturing method can easily do. We present a novel, quasi-solid rechargeable 3D microbattery assembled on a 3D-printed perforated polymer substrate (3DPS) with interconnected channels formed through XYZ planes. Simple and inexpensive electrophoretic-deposition routes are applied for the fabrication of all the thin-film active-material layers of the microbattery. With the advantage of thin films, which conformally follow all the contours of the 3D substrate and are composed of nanosize electrode materials, like modified Lithium Iron Phosphate (LFP, Lithium Titanate (LTO), and original polymer-in-ceramic electrolyte, our 3D microbatteries offer high reversible specific capacity and high pulse-power capability.

Combustion characteristics of premixed hydrogen/air flames in a geometrically modified micro combustor

Main challenges for a fuel efficient micro scale combustion are rooted from size restriction of micro combustors which results with inappropriate residence time of fuel/air mixture and intensified heat losses due to relatively high surface to volume ratio of such devices. One way of increasing energy output of micro combustors is to optimize its geometry by considering simplicity and easy manufacturability. In this study, effect of combustor geometric properties on combustion behavior of premixed hydrogen/air mixtures was numerically investigated. For this purpose, an experimentally tested micro combustor’s geometric properties were modified by establishing a backward facing step which is varying distance from combustor inlet and has varying step height, and adding opposing cavities which are varying distance from combustor inlet and have constant length to depth ratio into the flow area. Modeling and simulation studies were performed using ANSYS Design Modeler and Fluent programs, respectively. Combustion behavior was analyzed by means of centerline and outer wall temperature distributions, amount of heat transferred through combustor wall, conversion ratio of input chemical energy to utilizable heat, and species distributions. Turbulence model used in this study is Renormalization Group (RNG) k-ε. Multistep combustion reaction scheme with 9 species and 19 steps was simulated using Eddy Dissipation Concept model (EDC). Results showed that backward facing step in the flame region alters reaction zone distribution, flame length and shape, and consequently temperature value and distribution throughout the combustor. Lastly cavity was found to slightly increase peak temperature value.

Efficient micro processing with high power femtosecond lasers by beam engineering and modelling

Hybrid femtosecond lasers today deliver output powers of several hundred watts. Translating the available power into high-speed micromachining requires new approaches such as beam delivering tools with suitable synchronization of the laser pulses. We study the interest of rapid scanning systems or multi-beam shaping but also a rapid estimation of the ablation efficiency using a simple engineering model.

Development of an efficient Micro propagation based Agrobacterium-mediated Genetic Transformation Protocol in Commercial cultivar of Jute (Corchorus capsularis L.)

Development of an efficient Micro propagation based Agrobacterium-mediated Genetic Transformation Protocol in Commercial cultivar of Jute (<i>Corchorus capsularis</i> L.)

Improvement in capacitive performances of efficient micro electro mechanical system (MEMS) based power inverter

In this paper different electrostatic interdigitated comb designs for the new concept of MEMS based DC–AC capacitive power inverter for the solar photovoltaic applications has been compared and tes...

Non-premixed lean flame characteristics depending on air hole positions in a baffled micro combustor

Compared to a premixed micro combustor, non-premixed micro combustor has the advantage of being able to control more easily the fuel-air mixing with reducing flame flashback. To find an efficient micro combustor based on the non-premixed combustion, non-premixed flame characteristics of CH4-air in a baffled micro combustor are numerically studied. Among many factors of the combustor with a seven-hole baffle, the air hole position and air-fuel ratio are important parameters in understanding the combustion characteristics of non-premixed micro combustor. So, to investigate the relation of the combustion efficiency and flame characteristics under different geometrical conditions, six air hole positions of the baffle and five air-fuel ratios are selected. Various simulations based on the Reynolds Stress Model and detailed chemical mechanism of GRI 3.0 are performed. The results show combustion characteristics depending on recirculating flows and the relation between baffle configurations and flame structures for efficient combustion. The stoichiometric zone strongly depends on the relative positions of air and fuel holes. As the air holes of the baffle are away from the fuel hole, the center of dominant vortices is moved from near the inner combustor wall to the combustor center. So, the combustion efficiency can be maximized for the baffles of air hole positions having the center recirculation in addition to non-negligible wall recirculations. To examine this feature, turbulent flows for many combustors with different baffles are analyzed. Even though the air hole diameter changes, the efficient condition of air hole position is nearly fixed at two-thirds of the combustor radius. Another crucial factor in a non-premixed micro combustor is the equivalence ratio which can be linked to the operating condition. So, the geometrical effects are examined for different equivalence ratios. As the equivalence ratio decreases, the flame shape varies from the jet flame to the M−shape flame. As a result, the flame length decreases and the flame temperature increases. From such results, flame characteristics and various flame shapes are discussed with the global equivalence ratio and the effects of air hole position. So, the best baffle configuration is explored for the combustion efficiency. Also, the development of wall recirculations is analyzed with the wall heat transfer from the viewpoint of a heat emitter.

Measurement of degenerate two-photon absorption spectra of a series of developed two-photon initiators using a dispersive white light continuum Z-scan

To achieve efficient micro- and nanostructuring based on two-photon polymerization (2PP), the development and evaluation of specialized two-photon initiators (2PIs) are essential. Hence, a reliable method to determine the two-photon absorption (2PA) spectra of the synthesized 2PIs used for 2PP structuring is crucial. A technique by which absolute visible-to-near-infrared 2PA spectra of degenerate nature can be determined via performing a single dispersive white-light continuum (WLC) Z-scan has been realized. Using a dispersed white light beam containing 8 fs pulses at wavelengths ranging from 650 nm to 950 nm, the nonlinear transmittance as a function of the sample position can be measured for all spectral components by performing a single scan along the laser beam propagation direction. In this work, the 2PA spectrum of three different 2PIs was determined using this technique. 2PP structuring was also accomplished using the developed 2PIs at different wavelengths. Tuning the wavelength of the laser to match the peak of the 2PA spectra of the developed 2PIs resulted in lower intensity thresholds and facilitated higher structuring speeds. As an example, using M2CMK 2PI for 2PP, the scanning speed can be increased up to 5 folds when the laser wavelength is tuned to 760 nm (i.e., 2PA maximum) instead of the conventionally used 800 nm.

Solar Energy Fed to 3-Phase Induction Motor using Matlab Simulink and their analysis

This Paper emphasizes on proposing a cost effective photovoltaic (PV) fed 3 phase Induction motor drive which serves for rural pumping applications. Generally in a standalone system, the PV unit will charge the battery and the battery set up in turn will serve as a source for the inverter. A new single stage battery less power conversion is employed by designing a maximum power point tracker (MPPT) embedded boost converter which makes the overall cost of the setup to go down considerably. The realized as a prototype consisting PV array of 500watts, MPPT aided boost converter, three phase inverter and a three phase squirrel cage induction drive of 300 watts. An efficient and low cost micro controller dspic4011 is used a platform to code and implement the prominent perturb and observe MPPT technique. Sinusoidal pulse width modulation (SPWM) is the control technique employed for the three phase inverter. To validate the experimental results simulation of the whole set up is carried out in matlab /simulink environment. Simulation and hardware results reveal that the system is versatile.

Low Resistance Ohmic Contact for ZnSb Thin Film

To further improve the performance and power density of thermoelectric devices, the size of the device needs to be scaled down from macroscale to microscale. Different from the macroscale device, the specific contact resistivity ρc of the metal contact to the microscale device becomes a key point to the device's efficiency. In this study, a P type ZnSb thin film was deposited on glass substrate using a radio frequency magnetron sputtering system, followed by annealing at 325°C in an Ar atmosphere. X-ray diffraction, scanning electron microscopy, and the Hall measurement system were utilized for characterization of the ZnSb. The ohmic contact properties of metallic Co and Mo on the annealed ZnSb thin films were investigated, indicating that metallic Co has a lower specific contact resistivity ρc to ZnSb. The effect of a diluted HCl-etch prior to Co electrode deposition was also studied. The results show that a HCl-etch is effective for the reduction of the ρc. The dependence of ρc on the annealing temperature was also studied. Through HCl-etch and annealing at 200°C, specific contact resistivity ρc as low as 10−7 Ω cm2 is successfully obtained on the Co electrode, providing a good method to fabricate a highly efficient ZnSb-based micro device.

Solar cell as wings of different sizes for flapping-wing micro air vehicles

Currently, the biggest challenge for flapping-wing micro air vehicles is their very short flight duration due to limited on-board energy storage capacity. To overcome this challenge, a concept of solar-cell-flapping-wing micro air vehicle is herein proposed and studied. Thirty-three types of currently successful flapping-wing micro air vehicles (including insect-like, bird-like, and hummingbird-like flapping-wing micro air vehicles) are analyzed to explore scaling laws of flapping-wing micro air vehicles. The influences of wingspan, wing area, flapping frequency, and power on mass of flapping-wing micro air vehicles are studied. A dynamic energy harvesting model of solar-cell-flapping-wing is built up and utilized to formulate energy supply rate equations of three types of flapping-wing micro air vehicles. Considering the averaged ground solar spectral irradiance and today’s energy conversion efficiency of solar cells, the variation of energy supply rate by scales is analyzed. Several critical parameters to design an efficient long duration flapping-wing micro air vehicle are suggested.

Industry 4.0: A Cost and Energy efficient Micro PLC for Smart Manufacturing

“Smart Factory” is the future of industries. Industry 4.0 is the backbone in realizing this new concept. Industry 4.0 is based on the latest new technologies viz. Internet Of Things (IOT) and Cloud computing. IOT provides the devices which communicate between themselves and with the servers. Machine to machine communication is the base for IOT. Whereas the cloud computing provides us the space to store all the data and the facility to compute without the need of complex hardware thus reducing the cost of IOT devices. It is inventively challenging to construct devices and develop the services to realize the vision of the Fourth generation in Industrial Revolution. But it’s more challenging to get the existing Manufacturing setups and the Small scale industries in the realm of the Smart Factories. Thus a small cost effective MicroPLC is proposed which can be used in various configurations to enable the industrialist to enjoy the features of the Smart factories at optimal cost and energy.

Flame speed enhancement of a nitrocellulose monopropellant using graphene microstructures

The control and enhancement of the combustion wave propagation velocities of solid monopropellants are very important for the development of low cost and efficient micro power systems such as microthrusters and thermal-to-electrical energy conversion devices. In this work, the flame speed enhancement of a nitrocellulose (NC) solid monopropellant using highly conductive graphene structures was demonstrated. Two different graphene structures, namely, graphene foam (GF) and graphene nano-pellets (GNPs), were studied. For the GNP-doped NC films, fuel layers 500 ± 30 μm thick were deposited and the doping concentrations were varied from 1% to 5% by mass. For the GF, the fuel loading ratio (%) and the foam density were varied to study their effect on the flame speed propagation behavior. Self-propagating combustion waves were observed, with average flame speed enhancements up to 8 times the bulk value. The flame speed enhancement, for both the GNPs and the GF, showed a parabolic trend as a function of their concentrations, and an optimum value for each case was determined. However, the flame speed enhancement, as a function of the GF density (for a fixed fuel loading ratio), showed a monotonic decreasing trend. Moreover, the reusability of the GF structures was also tested by re-depositing them with fuel after combustion. Similar flame speed enhancement was obtained using the fresh and the re-used GF structures.

Development of a novel micro w-EDM power source with a multiple Resistor-Capacitor (mRC) relaxation circuit for machining high-melting point, -hardness and -resistance materials

This study presents the development of a novel micro-wire electric discharge machining (w-EDM) power source for machining high-melting point, -hardness and -resistance materials. The relaxation circuit power devised with a multiple Resistor-Capacitor (mRC) is triggered by a Programmable Logic Device (PLD) to generate a high-peak, short-pulse-time current train. The mRC relaxation circuit is characterized by high density discharge-spots per unit of time for swiftly removing material and creating fine discharge craters. Three microstructures made of tungsten carbide, WC-based cermet, and Boron-Doped Polycrystalline Composite Diamond (BD-PCD), respectively, are machined to validate the novel relaxation circuit. Experimental results demonstrate the 3RC relaxation circuit reduces machining times by 25%–35%, resulting in a more time efficient micro w-EDM process. Compared with a transistorized power source, the heat-affected zone is smaller and surface finish is better when using the 3RC relaxation circuit. A set of metrics for helping measure important electro-thermal machining related properties during micro w-EDM is proposed in this study. These are the ‘Spark Erosion Rate (SER)’, ‘Electro-Thermal Machinability (ETM)’, and ‘Cutting Performance (CP)’. An extensive examination of the quantitative and qualitative properties of material erosion mechanisms, material removal rates (MRR), and cobalt deposition for machining of difficult-to-machine materials is undertaken and the results discussed in detail.

Bi-decadal groundwater level trends in a semi-arid south indian region: Declines, causes and management

Study region Three districts in crystalline aquifer region of semi-arid south India. Study focus India, world’s largest groundwater user (250 billion m3 yr−1) has been reported to experience declining groundwater levels. However, the statistical significance of the decline has not been analyzed to separate human effects from natural variability. Trends in groundwater levels in three administrative districts of south India were analyzed and explained through changes in irrigation, rainfall, and agricultural power subsidy. New hydrological insights for the region Contrary to common perception of widespread groundwater declines only 22–36% of the wells showed statistically significant declines. The use of well depth during dry well periods may slightly underestimate the number of declining wells (by 1%) and rate of decline. Increase in groundwater irrigated area combined with rainfall and power subsidy policy, were the main causative factors for the decline. Groundwater decline after implementation of free-electricity policy in 2004 confirmed the nexus between power subsidy and groundwater. These declines are likely to worsen due to future well drillings. Trends in other regions with similar hydro-geologic conditions need to be analyzed to verify groundwater declines and its linkages with power subsidy. Once established, reforms in power subsidy and well permit policy along with conversion to efficient micro–irrigation may be needed to maintain or enhance groundwater availability in the crystalline aquifer region of India (240 million ha).

The effects of rectangular riblets on rectangular micro air vehicles for drag reduction

Reduced drag, increased lift and, consequently, increased vital ratio and lift-to-drag coefficients are crucial in almost all efficient micro air vehicles. Riblet geometries use a variety of air vehicles. Further investigation on micro air vehicles is, however, necessary for enhanced development. Rectangular riblets on a rectangular micro air vehicle are computationally investigated. In this study, the governing equation of fluid flow is solved numerically; the turbulent model around the NACA S5020 airfoil section is covered by riblets either on both sides or on the upper side of the wings. Results show a difference of behavior in drag reduction due to the angle of attack on the airfoil. When the lift-to-drag coefficient of an angle of attack is at its maximum, an improvement can be observed, where lift-to-drag ratio increases, and drag decreases. Results for the two-side riblets show an increase in the lift-to-drag ratio as well; although the lift-to-drag coefficient and the drag reduction of riblets on both sides were comparatively less than that for riblets on the upside.

Efficient and resilient micro air vehicle flapping wing gait evolution for hover and trajectory control

This paper deploys a recently proposed, biologically inspired, on-line, search-based optimization technique called Selective Evolutionary Generation Systems (SEGS) for control purposes; here, to evolve Micro Air Vehicle (MAV) flapping wing gaits in changing flight conditions to maintain hovering flight and track trajectories in unsteady airflow. The SEGS technique has several advantages, including: (1) search-efficiency, by optimally trading off prior search space information for search effort savings as quickly as possible in dynamic environments; (2) model-independence, as in biology, avoiding biases induced by built-in models rendered incorrect by environment changes; and (3) resilience, through sufficiency for stochastic behavior that is itself sufficient for responsiveness to search-objective variations caused by environment fluctuations. This work presents the first approach that can simultaneously evolve optimal MAV flapping wing gaits efficiently and resiliently, adapt on-line, and, via model-independence, allow feedback from either experimental sensors or alternate external models (affording control versatility for hover or forward flight, unsteady or quasi-steady aerodynamics, and any dynamics or wing kinematics). Performance benchmarks are also provided. Because the (1+1)-Evolution Strategy (ES) and the Canonical Genetic Algorithm with Fitness Proportional Selection (CGAFPS) are two SEGS special extreme cases, an additional comparison showcases SEGS possession of both (1+1)-ES computational speed and CGAFPS resilience.