The micro-explosion phenomenon is involved in emulsified fuel droplets placed in a hot atmosphere, such as spray combustion. Droplets of water-in-sunflower oil emulsion are used, since they are ...representative of a class of emulsions used in practical applications of biofuels. Once the micro-explosion is triggered after a short delay, the rapid (⩽1ms) vaporization of the inside water droplets and the subsequent disintegration of the emulsion droplet blow the fragmented droplets away. These fragmented droplets are called “child-droplets”, and they are too small and fast for an on-the-fly infra-red imaging thermal characterization. The present study focuses on the thermal reaction of a thin plate when impacted by them. Thorough and detailed tests are carried out, to make sure that the plate and the acquisition system are collecting a data that is actually representative of the child-droplets thermal energy. A quantitative post-processing is applied to the transient temperature field on the plate. It leads to the thermal energy of the whole plate, and of representative samples of individual child-droplets. The results show that their thermal energy is governed by a log-normal distribution.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The heating of two-component droplets and the following explosive breakup of those droplets have been extensively studied over the most recent years. These processes are of high interest, since they ...can significantly improve the performance of many technologies in fuel ignition, thermal and flame liquid treatment, heat carriers based on flue gases, vapors and water droplets, etc. Research throughout the world involves various schemes of droplet heating and supply (or, less frequently, injection) to heating chambers. The most popular scheme features the introduction of a two-component or multi-component droplet onto a holder into the heating chamber. In this research, we study how holder materials affect the conditions and integral characteristics of droplet heating and explosive breakup: heating time until boiling temperature; minimum temperature sufficient for droplet breakup; number and size of fragments in the resulting droplet aerosol, etc. Experiments involve droplets that are produced from flammable (oil) and non-flammable (water) components with significantly different thermophysical and optical properties, as well as boiling temperature and heat of vaporization. The most popular elements with the scientific community, such as ceramic, steel, aluminum, copper, and phosphorus rods, as well as a nichrome wire, serve as holders. We establish the roles of energy inflow from a holder to a droplet, and energy outflow in the opposite direction. We compare the holder results with a supporting thermocouple, recording the drop temperature under a heat transfer provided at 350°C. Finally, we forecast the conditions that are required for a significant improvement in the performance of thermal and flame water treatment through the explosive breakup of two-component droplets.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Compressed-Air energy storage (CAES) is a well-established technology for storing the excess of electricity produced by and available on the power grid during off-peak hours. A drawback of the ...existing technique relates to the need to burn some fuel in the discharge phase. Sometimes, the design parameters used for the simulation of the new technique are randomly chosen, making their actual construction difficult or impossible. That is why, in this paper, a small-scale CAES without fossil fuel is proposed, analyzed, and optimized to identify the set of its optimal design parameters maximizing its performances. The performance of the system is investigated by global exergy efficiency obtained from energy and exergy analyses methods and used as an objective function for the optimization process. A modified Real Coded Genetic Algorithm (RCGA) is used to maximize the global exergy efficiency depending on thirteen design parameters. The results of the optimization indicate that corresponding to the optimum operating point, the consumed compressor electric energy is 103 . 83 k W h and the electric energy output is 25 . 82 k W h for the system charging and discharging times of about 8.7 and 2 h, respectively. To this same optimum operating point, a global exergy efficiency of 24.87% is achieved. Moreover, if the heat removed during the compression phase is accounted for in system efficiency evaluation based on the First Law of Thermodynamics, an optimal round-trip efficiency of 79.07% can be achieved. By systematically analyzing the variation of all design parameters during evolution in the optimization process, we conclude that the pneumatic motor mass flow rate can be set as constant and equal to its smallest possible value. Finally, a sensitivity analysis performed with the remaining parameters for the change in the global exergy efficiency shows the impact of each of these parameters.
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The present article describes experimental results of liquid injection in a thermal plasma jet by particle-tracking velocimetry (PTV). This technique delivers an in-situ real-time analysis of the ...liquid breakup and measures the velocities and the trajectories of the particles. The observations were done within the 10 mm surrounding the injection location where the plasma brightness is considerable. First, a validation of the proposed investigation method was carried out in a slower plasma jet. Subsequently, PTV measurements within faster plasma jets, resulting in a set of trajectories, were compared with trajectories achieved through optical diagnostics based on a simple shadow-graph technique proposed by Damiani et al. Injection d’un liquide au sein d’un jet plasma thermique: optimisation de la trajectoire des particules, Proceedings of Congrès Francophone de Techniques Laser, CFTL 2010, Vandoeuvre lès nancy, France,
2010
(in French). These trajectories indicated that a higher plasma flow rate was required to spray all droplet sizes in the axis of the flow, thereby enabling an optimal spraying (then coating) application for producing nanostructured thin layers. This study showed that the liquid injection parameters are of main importance to obtain optimal injection and plasma parameters to achieve the required coating properties.
Carbon capture, utilization, and storage (CCUS) is a crucial strategy for achieving CO2 emission reduction targets and mitigating the impacts of global warming and climate change. Among various CCUS ...technologies, chemical absorption of CO2 has proven to be a mature and widely-used technique in various industrial sectors. However, the current CO2 chemical absorption process involves large-scale equipment with low efficiencies, making it difficult to control. To address these issues, microfluidic devices have emerged as a promising technology to intensify the CO2 absorption process by providing a smaller required volume, enhanced mass transfer, cleaner and safer operations, higher productivity, and more efficient energy use.
This paper aims at presenting a comprehensive literature review on research advances of the microfluidic technology for CO2 chemical absorption. The review covers various aspects, including microchannel geometries, two-phase flow patterns, mass transfer models, effects of operating factors, and measures to intensify the CO2 absorption process. In addition, the paper discusses the measurement of interfacial and local parameters, such as liquid film thickness, velocity field, and local CO2 concentration, which are primordial for understanding the transport phenomena and for optimizing the CO2 absorbers. This paper may serve as an essential reference that contributes to the development and exploitation of highly-efficient microfluidic-based CO2 chemical absorption technology for future large-scale industrial applications.
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•Recent researches on microfluidic-based CO2 chemical absorption are reviewed.•Absorption performance is determined by the mass transfer between CO2 and absorbent.•Effects of influencing operational factors are discussed.•Optical techniques are frequently used to measure local & interfacial parameters.•Different techniques used to intensify the CO2 absorption process are surveyed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
When a water-in-oil (W/O) emulsion droplet is heated, a phenomenon called micro-explosion (μ-exp) may occur. Micro-explosion can be defined as the burst of the continuous phase (i.e. oil) by the ...energy of evaporation of dispersed droplets (i.e. water) and the volume expansion that goes with it. In the paper are presented results that show a strong correlation between size average value (and distribution size) of water droplets and micro-explosion occurrence rate. Emulsion dispersed phase size, when using micro-channel techniques, depends highly on the emulsion composition and the energy provided to the system (Oil flow rate). A (3–18) μm diameter range was measured in the tests discussed in the paper. Micro-explosion occurrence can reach 70% for larger droplet sizes (about 20 μm). It declines to less than 20% for small sizes (between 5 and 10 μm). Influence of other parameters on micro-explosion occurrence like temperature heating or physical properties is also studied. Ohnesorge number seems to be an adequate parameter to study micro-explosion occurrence because of its direct relation with the relevant emulsion properties: droplet size, oil viscosity and interface tension. Micro-explosion rate achieves its maximum rate (60%) for Oh = 0.12, in other words, for emulsion where dispersed droplets move easily (low viscosity) with a great ability to coalesce (larger droplets and no surfactant).
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•Micro-explosion is the atomization of emulsion drops. Puffing breaks up a part of it.•Micro-explosion is not guaranteed every time, as puffing can happen.•Novel study of the Oh number shows a link between micro-explosion and coalescence.•Micro-explosion is prevalent for less viscous oils, where coalescence is enhanced.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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•CO2 capture realized by chemical absorption in microchannel using MEA solvent.•Spiral baffle structure embedded in the microchannel to enhance the mass transfer.•Better CO2 ...absorption achieved at low Re numbers with small pressure drop increase.•New correlations proposed considering both structure and chemical reaction factors.
This paper presents an experimental study on CO2 chemical absorption by Monoethanolamine (MEA) solution in microchannel. In particular, a novel spirally distributed baffle structure is proposed to be embedded into the microchannel so as to generate the swirling flow pattern and to enhance the mass transfer. The effect of spiral baffle structure on the two phase flow pattern transition, the CO2 gas void fraction, the pressure drop, and the mass transfer performance are characterized and discussed, under varied gas and liquid flow rates, and MEA concentrations. Results demonstrate that the spiral baffle structure could significantly enhance the gas–liquid mass transfer, with overall liquid side volumetric mass transfer rate (kLa) up to 2.35 s−1 and enhancement number E up to 1.387 at small gas and liquid Reynolds numbers (ReG < 5.5; ReL < 14). New predictive correlations have also been proposed by considering both the structure enhancement factor and the chemical reaction factor.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•The atomization trigger of emulsified fuel drops is investigated.•Temperature measurements using LIF2C are carried out.•The trigger drop’s temperature, size and position affect the atomization ...occurrence.
Biofuels in the form of water-in-oil (W/O) emulsions are a promising substitution for hydrocarbon fuels, mainly thanks to the micro-explosion phenomenon that occurs under strong heating. Micro-explosion is the atomization of a W/O emulsion drop into daughter droplets because of the water embedded droplets phase change. This atomization leads to the reduction of pollutants and unburnt hydrocarbons emissions. However, micro-explosion is not a systematic phenomenon: indeed, for some cases the water phase change is weak and leads to a partial atomization, called “Puffing”. This paper relates a novel approach to better understand the occurrence of micro-explosion. It consists on the identification of the drop triggering the atomization, called the trigger drop, and measure its properties (temperature, size and position within the emulsion drop) thanks to non-intrusive optical diagnostics. Two colors laser induced fluorescence (LIF2C) is the main method used in this work for temperatures. These temperature measurements showed promising results of both quantitative and qualitative aspects. After the calibration steps and the method validation, it is applied for the temperature measurements of water droplets embedded in oil with the maximum temperature recorded around 130 °C. Using these measurements methods, a correlation is found between quality of atomization (either micro-explosion or puffing) and the properties of the trigger drop (temperature, size and position). When one of these parameters is not optimal, it can indeed be compensated by the others.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•CO2 chemical absorption by MEA aqueous solution in minichannel investigated.•Taylor bubble generation, moving and shrinkage monitored, visualized and analyzed.•Inhabitation effect of ...chemical reaction-enhanced mass transfer on bubble generation.•New Da number-based correlation proposed to predict the initial bubble length.•A simple model developed to determine the channel effective length for CO2 absorption.
Taylor bubble dynamic characteristics of CO2 chemical absorption into MEA aqueous solution in a vertical minichannel were systematically investigated in this study. The generation, movement, and shrinkage of bubbles in the minichannel were visualized and monitored using a high-speed camera, and their dynamic behaviors were characterized by image analysis method. The effects of gas and liquid Re numbers and absorbent concentration on two-phase flow patterns, bubble generation frequency, initial bubble length, bubble length decrease rate, and bubble velocity were examined and analyzed. Results showed that chemical reaction-enhanced mass transfer hindered the bubble cap penetration into the main channel, and alleviated the bubble neck thinning, both effects inhibiting the bubble generation. A new Damköhler number (Da)-based correlation has been proposed to predict the initial Taylor bubble length, showing good prediction accuracy for experimental data in the literature using different absorbents. Results also showed that before the formation of sphere bubble at the end of absorption, an approximate linear relationship exists between bubble length decrease rate and bubble velocity, with the slop decided by chemical reaction rate that could be characterized by the Da number. Finally, a simple model has been developed to determine the effective channel length at a given operating condition, providing design guidelines for microchannel-based miniaturized CO2 absorbers.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•A new milli-channel mixer is proposed and tested for well-controlled mixing.•The design is based on the split-intersect-recombine principle with nature-inspired geometries.•An optical, ...easy-to-implement measurement of the tracer's local concentration profiles is carried out.•Fluid collision at the numerous intersections of the meshed circuit enhances the mixing.•A critical value of shear rate that favors the flow deviation is figured out.
This study proposes a new design of milli- or micro-mixers based on the split-intersect-recombine principle. The vascular flow topology mimics the respiratory or circulatory architectures existing in nature, including tree-like bifurcated networks and meshed flow circuit. Special focus is given to the enhancement of mixing performance by fluid collisions and flow deviations at the intersections of the meshed circuit. To do that, an optical tracer is added in one of the fluids to be mixed and its progression is monitored and recorded by a high-definition CCD camera. The mixing efficiency of the meshed circuit is then characterized by the evolution of the tracer's local concentration profiles based on the Beer-Lambert absorption. Experimental results obtained show that compared to straight channels, the mixing performance can be improved by about 20% owing to the numerous flow intersections in the meshed circuit. Moreover, the viscosity difference between two fluids to be mixed has a positive effect on the mixing performance by augmenting the chance of flow deviation from one stream into another at the crossroads. An optimum performance can be noticed in the form of a plateau of the estimated shear stress.
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GEOZS, IJS, IMTLJ, IZUM, KILJ, KISLJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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