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Thermal energy storage is of critical importance for the highly-efficient utilization of renewable energy sources. Over the past decades, the single-tank thermocline technology has attracted much attention owing to its high cost-effectiveness. In the present work, we investigate the influence of the filler porosity’s non-uniform distribution on the thermal performance of the packed-bed sensible heat thermocline storage tanks, using the analytical model obtained by the Laplace transform. Our analyses prove that the different porosity distributions can result in the significantly different behaviors of outlet temperature and thus the varied charging and discharging efficiencies, when the total amount of filler materials (i.e., the integration of porosity) is fixed. The results indicate that a non-uniform distribution of the fillers with the proper design can improve the heat storage performance without changing the total amount of the filling materials, which may provide a new way to optimize the thermocline storage tanks.

In recent years, energy and environmental issues have become more and more prominent, and electric vehicles powered by lithium-ion battery have shown great potential and advantages in alleviating these issues. Compared with other batteries, lithium-ion batteries have the advantages of high specific energy, high energy density, long endurance, low self-discharge and long shelf life. However, temperature of the battery has become one of the most important parameters to be handled properly for the development and propagation of lithium-ion battery electric vehicles. Both the higher and lower temperature environments will seriously affect the battery capacity and the service life. Under high temperature environment, lithium-ion batteries may produce thermal runaway, resulting in short circuit, combustion, explosion and other safety problems. Lithium dendrites may appear in lithium-ion batteries at low temperature, causing short circuit, failure to start and other operational faults. In this paper, the used thermal management methods of lithium-ion batteries are introduced and their advantages and disadvantages are discussed and compared. At the same time, the prospect of future development is put forward.

This paper presents an experimental study on the catalytic methane combustion (CMC) in plate-type microreactors with wall-coated Pt/γ-Al2O3 catalyst. Firstly, the influence of different operational conditions and coating properties on the CMC in the straight parallel-channel microreactor has been investigated. A specific catalyst loading of 57.6 g m−2 was found to yield the highest methane conversion over 3.5 wt% Pt/γ-Al2O3. A higher or lower loading tended to decrease the methane conversion due to either the limited internal diffusion through the thicker coating layer or insufficient active sites in the thinner coating layer. Then, the above microreactor was compared with other five different geometries, including cavity, double serpentine microchannels, obstacled microchannels, meshed circuit and vascular network. The double serpentine microchannel geometry presented the highest methane conversion (especially at a relatively low mixture flow rate) due to the appropriate control over the residence time and catalyst coating surface area.

International audience; Compressed air energy storage systems (CAES) have demonstrated the potential for the energy storage of power plants. One of the key factors to improve the efficiency of CAES is the efficient thermal management to achieve near isothermal air compression/expansion processes. This paper presents a review on the Liquid Piston (LP) technology for CAES as a timely documentary on this topic with rapidly growing interests. Various aspects are discussed including the state-of-the-art on LP projects all over the world and the trend of development, the coupled fluid flow and heat transfer during the compression/expansion operations, and different actions proposed and implemented to enhance the heat transfer inside the piston column.It has been found that LP is a promising concept for isothermal CAES. However, the complex and transient fluid flow and heat transfer behaviors inside the LP are difficult to characterize and master. To enhance the heat transfer and increase the efficiency of the compression/expansion processes many approaches have been tested including liquid spray, wire mesh, porous media, optimal trajectory, hollow spheres and optimal geometry of the piston column. Numerous empirical correlations of Nusselt number have also been proposed to estimate the heat transfer in different types of LP, as reviewed and summarized in this paper.

International audience; Concentrated Solar Power (CSP) technology captures solar radiation and converts it into heat for electricity production. It has received an increasing attention because integrated thermal energy storage (TES) systems can largely enhancing the reliability and the dispatchability. Over the last decade, low-cost single storage tank based on the thermocline technology becomes an alternative to commonly-used two-tank TES system. However, the improper inlet/outlet manifolds may cause the strong mixing of hot and cold fluids and disturb the temperature stratification, resulting in reduced thermal performances of the storage tank. This study aims at solving the flow maldistribution problem in the single-tank thermocline storage system by appropriately structuring the inlet/outlet manifolds. The technical solution is based on the insertion of optimized perforated baffles in the manifolds. 2D Computational fluid dynamics simulations were performed to calculate the transient flow and temperature profiles in the storage tank during the charging and discharging operations. The optimal size distribution of orifices on the upper baffle has been determined for homogenizing passage times of the thermal front, so as to enhance the temperature stratification. A novel intermediate evaluation indicator was introduced to characterize the real-time thermal behavior, which could reduce the computational cost of the optimization problem by a factor of 6 at least. Numerical results shown that the proposed optimization algorithm could significantly improve the thermal performances, indicated by the increased values of charging/discharging efficiency, the capacity ratio and the overall efficiency, ex., the fully charging efficiency be increased by 29% by comparing the unstructured manifold geometry and the one with optimized baffles. The parametric study on certain geometry and operating factors also demonstrated that the proposed method for flow distribution optimization was robust, effective and efficient.

International audience; 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.

This paper presents an original study on the heat transfer characteristics of a multi-scale structured fluidic network consisting of a number of minichannels in parallel. Two sets of application are tested, including a single plate heat sink being heated on its base surface and a two-stream plate-type heat exchanger when several such plates are stacked one above another. Computational Fluid Dynamics (CFD) simulations were performed to characterize local temperature profiles and thermal performances in such a complex geometry. In parallel, a prototype made of Aluminum was fabricated and tested, providing experimental results for comparison and validation of the obtained numerical results. Results indicate that when used as a heat sink for cooling purpose, the overall thermal resistances of the multi-scale structuration concept are remarkably smaller than some micro- or mini-channels heat sinks tested in the literature. When used as a novel two-fluid plate-type heat exchanger, the volumetric heat transfer power could reach about 25 MW m−3. This novel concept of multi-scale structured plate heat exchanger showcases how to design and develop globally macro-sized, locally micro (milli)-structured process equipment while keeping high performances, aiming at large-scale industrial applications.

International audience; Natural gas (with methane as its main component) provides an attractive energy source because of its large abundance and its high heat of combustion per mole of carbon dioxide generated. However, the emissions released from the conventional flame combustion (essentially NO x) have harmful impacts on the environment and the human health. Within the scope of rational and clean use of fossil energies, the catalytic combustion of natural gas appears as one of the most promising alternatives to flammable combustion. The presence of catalysts enables complete oxidation of methane at much lower temperatures (typically 500 � C), so that the formation of pollutants can be largely avoided. This work presents a literature review on the catalytic methane combustion. Various aspects are discussed including the catalyst types, the reaction mechanisms and kinetic characteristics, effects of various influencing operational factors and different reactor types proposed and tested. This paper may serve as an essential reference that contributes to the development of well-designed reactors, equipped with appropriate catalysts, and under well-handled operating conditions to realize the favorable (kinetic) performance, for their future applications and propagation in different industrial sectors.

International audience; Solar thermal energy, especially concentrated solar power (CSP), represents an increasingly attractive renewable energy source. However, one of the key factors that determine the development of this technology is the integration of efficient and cost effective thermal energy storage (TES) systems, so as to overcome CSP's intermittent character and to be more economically competitive. This paper presents a review on thermal energy storage systems installed in CSP plants. Various aspects are discussed including the state-of-the-art on CSP plants all over the world and the trend of development, different technologies of TES systems for high temperature applications (200 °C-1000 °C) with a focus on thermochemical heat storage, and storage concepts for their integration in CSP plants. TES systems are necessary options for more than 70% of new CSP plants. Sensible heat storage technology is the most used in CSP plants in operation, for their reliability, low cost, easy to implement and large experimental feedback available. Latent and thermochemical storage technologies have much higher energy density thus may have a bright foreground. New concepts for TES integration are also proposed, especially coupled technology for higher operating temperature and cascade TES of modularized storage units for intelligent temperature control. The key contributions of this review paper consist of a comprehensive survey of CSP plants, their TES systems, the ways to enhance the heat and/or mass transfers and different new concepts for the integration of TES systems.

International audience; This paper presents the development of a novel parallel minichannel contactor for monodisperse water-in-oil emulsification. The novel contactor having 16 Y-junctions in parallel equipped with multi-scale tree-like fluid distributor and collector was realized and experimentally tested. Oils with different physical properties and water were used as continuous phase and dispersed phase, respectively. Influences of different factors including the parallelization, the water/oil flow-rate ratio and two-phase physical properties on the two-phase flow characteristics and on the coefficient of variation were studied and discussed. Results showed that for water-pure oil flow, the novel parallel minichannel contactor is capable of producing monodisperse water-in-oil emulsions with high throughput and low energy consumption under our tested conditions. The Ohnesorge number (Oh) has a significant influence on the emulsion monodispersity and the capillary number (Ca) appears as a proper indicator for liquid-liquid break-up regimes. A predictive correlation for the Oh number was proposed by fitting the experimental data obtained in the study.

A catalyst preparation method, consisting of slurry washcoating with γ-Al2O3 followed by impregnating platinum on the microreactor walls, has been investigated. The effect of various factors in the preparation procedures on the adhesion of the washcoated γ-Al2O3 was studied, including the slurry property (i.e., the binder type, concentration and molecular weight, γ-Al2O3 concentration and particle size, pH), and the (micro)reactor substrate and channel shape. The results show that the adhesion of γ-Al2O3 washcoat strongly depended on the slurry rheological characteristics. A good adhesion on FeCrAlloy substrates was obtained using the slurry with polyvinyl alcohol as the binder (typical concentration at 3–5 wt% and molecular weight of 57,000–186,000), 20 wt% γ-Al2O3 (particle size being around 3 µm) and pH = 3.5. FeCrAlloy as the substrate exhibited an excellent coating adhesion in rectangular or round channels, primarily due to the formation of alumina film over the surface during thermal pretreatment. The aluminum-free stainless steel as the substrate only showed a good adhesion in a round channel. Well-adhered Pt/γ-Al2O3 catalysts were then applied in a microreactor comprising parallelized microchannels made of FeCrAlloy under the optimized coating procedures, and investigated in terms of its performance in the catalytic methane combustion. It is shown that the reaction temperature has a greater influence on the methane conversion than the flow rate, and a favorable coverage of methane and oxygen on the catalyst surface is essential to obtain a good catalytic performance. These reaction results are in line with the temperature behavior measured along the microreactor.

This paper presents an original life cycle assessment (LCA) of a concentrating solar power (CSP) plant with thermochemical energy storage (TCES). The studied CSP plant is a hypothetic solar tower plant with a Rankine power cycle, and the TCES material used is calcium hydroxide. Based on three proposed TCES integration concepts, detailed sizing and the associated emission inventory are performed for four main groups that constitute the CSP plant, including the solar field, the solar tower, the storage system and the power cycle. Various midpoint impact categories are evaluated using the IMPACT 2002+ method embedded in the SimaPro 7.3 software. A sensitivity analysis is performed to identify the most influencing elements of the CSP plant on the environmental impacts. LCA results show that the CSP plant with different TCES integration alternatives has comparable global warming potential (approximately 11 kg CO2.eq/MWh) and energy payback time (approximately 4 months). The additional environmental burden due to the addition of the TCES system is relatively small (about 30%). The use of calcium hydroxide for the TCES has noticeable midpoint impacts on the respiratory inorganics, the terrestrial ecotoxicity and the mineral extraction. Solar field group (heliostat mirrors) is generally the most sensitive and environmental impacting factor of the CSP installation. The Turbine integration concept has the smallest environmental impacts among the three concepts proposed.

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International audience; Fluid flow maldistribution is considered as one of the main causes of performance deterioration in various energy and process systems, especially when parallel micro-or mini-channel fluidic networks are involved. For a specific purpose, the optimal flow distribution is not necessarily uniform. However, specific non-uniform distributions are somewhat more difficult to achieve than uniform ones. The insertion of a geometrically optimized baffle has been numerically confirmed as an effective solution to this issue, but experimental validation is still lacking which is indispensable for bridging the gap between theory and practice. This paper presents a numerical and experimental investigation on the realization of target flow distribution among parallel mini-channels, using the optimized baffle insertion method. A 15-channel fluidic network integrated with the distributor and the collector is fabricated and tested. Various perforated baffles are optimized and fabricated corresponding to different target distributions (uniform, ascending and descending). PIV technique is used for the flow distribution measurement while CFD simulations are also performed for comparison. CFD results and PIV data show that different target distributions could be successfully achieved by the optimized baffle insertion method. The robustness of the optimized baffle for uniform distribution is also evaluated and discussed to provide some guidelines for future applications.

Fluid flow distribution among parallel channels usually plays an important role on the global performance improvement of tubular process equipment, but remains difficult to be properly measured by experimental methods. This paper presents a systematic study on the measurement of flow distribution in a multi-channel fluidic network using Particle Image Velocimetry (PIV) technique. For the precise measurement of flow-rate in each individual channel, standard 2 dimensions, 2 components PIV technique is used to obtain velocity vectors on multiple sampling planes parallel to the flow direction, so as to reconstruct accurate velocity profiles on the cross-sectional surface. Such procedure is repeated for every micro- (mini-) channel to obtain the actual flow distribution properties in the fluidic network. Pre-test results on a double-channel device indicate that the maximum possible deviation of PIV measurements is 13.1% with respect to those of a flange flowmeter, implying that the PIV technique is relatively accurate and reliable. PIV results on the flow distribution in a 15-channel fluidic network are then compared with Computational Fluid Dynamics simulation results under the same working conditions. A quite good agreement could be observed. Moreover, the locations and sizes of vortices in the distributor have a significant influence on the flow distribution. © 2016 Curtin University of Technology and John Wiley & Sons, Ltd.

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 kWh and the electric energy output is 25.82 kWh 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.

International audience; This paper proposes and investigates novel concepts on the integration of a thermochemical energy storage (TCS) system in a concentrating solar power (CSP) plant. The TCS material used is calcium oxide reacting with water and the power cycle studied is a Rankine cycle driven by CSP. Firstly, three integration concepts on the coupling of the TCS system with the Rankine cycle are proposed, including the thermal integration concept, the mass integration concept and the double turbine concept. Then, an energy analysis is performed to determine and compare the theoretical overall energy efficiency of the proposed concepts. After that, an exergy analysis is also carried out for the selected integration concepts so as to evaluate and compare the overall exergy efficiency of the installation with TCS integration. The results show that the turbine integration concept has the highest overall energy efficiency (0.392), followed by the thermal integration concept (0.358) and the mass integration concept (0.349) under ideal conditions with 11 h of charging and 13 h of discharging. The energy storage density using calcium hydroxide as the storage media is estimated to be about 100 kWhel•t-1. Exergy analysis results also indicate that the turbine integration concept seems to be the best option under the tested conditions.

International audience; Residence Time Distribution (RTD) is a frequently used tool in conventional process equipment and it provides internal flow characterisation by simple tracer tests. In this paper, we explore the feasibility of using RTD to identify fluid distribution uniformity in millimetric multichannel devices. Both theoretical modelling and experimental implementation are conducted to 16-channel systems. Theoretical modelling confirms the effectiveness of non-intrusive RTD measurements in evaluating flowrate distribution uniformity. Different influencing factors, such as channel corrosion, blockage, distributor structure, channel length or width variation, etc., can be reflected by RTD response curve. The experimental setup consists of a lab-developed RTD test platform coupling a fast camera and two miniflowcells capable to quantify rapid tracer concentration evolution through carbon ink visualization. The platform is particularly powerful for very narrow RTD measurement with residence time down to 1 s. With the platform, we investigate the RTD characteristics of a multichannel device under several flow conditions. Model correlation of the experimental data gives valuable information such as fluid distribution, plug-flow ratio and perfectly mixed volume.

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This paper presents a numerical study on the water-in-oil emulsification process through the parallelization of micro/mini-channels. Firstly, the single-phase fluid flow distribution uniformity in the bifurcated tree-like fluidic network is discussed. Secondly, the separate roles of the oil viscosity and the interfacial tension on the plug details are clarified. Finally, the impact of flow distribution non-uniformity among the parallel mini-channels on polydispersity of the produced emulsion is evaluated by modelling. The obtained results show that for bifurcated tree-like fluidic network, the single phase flow distribution is the flow distribution non-uniformity increases linearly with the increasing mean Rech once a transitional Re is reached. The water plug length and volume increase with the increasing interfacial tension and the decreasing oil viscosity under our tested conditions. Correcting factors relevant to the modified liquid properties have to be added in the predictive correlations for plug length and volume. For water-in-oil emulsification in parallel channels, its polydispersity P w is affected by the single phase flow distribution uniformity, the total water/oil flow-rate ratio and most importantly by the flow-rate ratio distribution non-uniformity. An empirical correlation has been proposed to predict the emulsion P w based on these influencing factors.

International audience; In energy and process systems, the bad fluid flow distribution (flow maldistribution) is one of the main causes of performance deterioration, equipment dysfunction, safety defaults, product quality degradation, reduced lifetime and over-cost. Flow equidistribution among numerous parallel channels is a classical goal, but is not always the optimal option according to a given objective and constraints. Target flow distribution (uniform or non-uniform) is far more difficult to achieve because it requires the precise control of flow-rate in given time for every channel. There is no such attempt in the existing literature. In this study, a CFD-based evolutionary algorithm is developed to optimize the topology of an inserted perforated baffle, for the realization of target flow distribution among parallel channels. Several 2D numerical examples with different circuit geometries and different target curves are studied and compared. Results show that the optimized distribution curves obtained by performing the evolutionary algorithm are in good agreement with the target curves, with acceptable increase in pressure drop. This optimality algorithm may be easily applied to different working conditions. In this sense, the proposed algorithm is robust, effective, general and flexible, showing its promising application in various engineering fields dealing with fluid distribution problem.

International audience; This paper presents an original study on the fluid flow characteristics of a multi-scale fluidic network consisting of a number of elementary ladders. Computational Fluid Dynamics (CFD) simulations were performed to characterize local fluid flow patterns and flow distribution properties in such a complex geometry. In parallel, flow visualizations using fast camera and tracers were carried out in a transparent prototype. A special effort was made to improve the flow distribution uniformity among the 90 parallel mini-channels by inserting the geometrically optimized perforated baffles. The global pressure losses of the multi-scale network with or without baffles were also measured experimentally so as to be compared with the numerical results. For the multi-scale fluid network, non-uniform flow distribution was observed even under very low flow-rate conditions (e.g., mean Rech=10). For higher flow-rate conditions, significant flow nonuniformity seems inevitable. The insertion of optimized perforated baffles could provide a remarkable improvement on flow distribution uniformity, even under high flow-rate conditions (mean Rech up to 2000). Good agreements between numerical and experimental results are observed.

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International audience; In order to cut down the computing time, a simplified method for heat transfer analysis within a multi-tube and multi-plate latent heat storage exchanger is proposed. This method associates a 2D Finite Element method to solve energy equation within each plate and an analytical model to link the plates between them. Different formulations of the energy equation have been tested and compared with experimental results on a simple configuration. Enthalpy formulation, temperature dependent specific heat method, and source term of crystallization associated to kinetic equation method are the different options studied. The limitations of each methods is then exhibited.

This paper presents an original study on the design and optimization of baffled fluid distributor for the realization of optimal fluid flow distribution in a tubular solar receiver. The basic idea is to install a perforated baffle in the inlet fluid distributor and to optimize the configuration of orifices on the baffle so as to approach the target flow distribution among downstream parallel tubes. A pressurized-air solar receiver comprising of 45 parallel tubes is used for study, with copper or Inconel 600 used as the filling material. Results show that the final fluid flow distributions realized by the geometrically optimized baffles are in good agreement with the target curves. The peak temperature of the receiver wall can be minimized accordingly with moderate increase in total pressure drop of the receiver system. It is shown that the insertion of a geometrically optimized baffle is generally a practical solution with various features: capable of realizing non-uniform target distribution; small pressure drop increase; compact geometry; flexible and adaptive; easy fabrication with a reasonable cost, etc.

Convective heat transfer enhancement for solar receiver is considered as a variational problem in this paper. A predictive optimization method based on the minimum heat transfer entropy generation (MHEG) principle is developed for ideal gas in turbulent flow. A set of Euler–Lagrange equations is derived by the calculus of variations. By employing a porous media model and multiphase Volume of Fluid (VOF) model in the variational problem, the optimization constrained by the mechanical energy loss is performed to achieve a physically feasible geometry configuration to improve the performance of the convective heat transfer in a solar receiver. To validate and demonstrate the method, turbulent convection heat transfer process in a two-dimensional rectangular channel with fixed heat flux boundaries is optimized. The computation results show that higher air temperature at the outlet and lower wall temperature can be obtained, which may lead to the use of cheaper materials with lower heat-resistance for the exchanger. The present work shows that combining the calculus of variations with porous media and multiphase VOF model may be helpful for the design of efficient convective solar receiver.

This paper presents experimental results on the study of falling water film evaporation on a single vertical corrugated plate. The corrugated plate module, made of stainless steel having a total heat transfer area of 0.267 m 2 , was fabricated and tested in a pilot scale setup. The special geometry of the plate module allows the heat transfer between the liquid flowing in parallel channels inside de module and a film flowing on the two outer faces. Hydrodynamic and thermal tests were carried out. Results of heat transfer for evaporation from the surface of the water film are presented and compared to various correlations found in the literature. It is observed that when the surface is invaded by the film, decreasing film flow-rate provides higher ratio of wetted surface compared to increasing film flow-rate. The enhancement of heat transfer has been observed. Based on our own results, a new correlation has been proposed to predict the evaporative heat transfer by falling film.