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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.

International audience; Thermal energy storage (TES) system plays an essential role in the utilization and exploitation of renewable energy sources. Over the last two decades, single-tank thermocline technology has received much attention due to its high cost-effectiveness compared to the conventional two-tank storage systems. The present paper focuses on clarifying the performance indicators and the effects of different influencing factors for the thermocline TES systems. We collect the various performance indicators used in the existing literature, and classify them into three categories: (1) ones directly reflecting the quantity or quality of the stored thermal energy; (2) ones describing the thermal stratification level of the hot and cold regions; (3) ones characterizing the thermo-hydrodynamic features within the thermocline tanks. The detailed analyses on these three categories of indicators are conducted. Moreover, the relevant influencing factors, including injecting flow rate of heat transfer fluid, working temperature, flow distributor, and inlet/outlet location, are discussed systematically. The comprehensive summary, detailed analyses and comparison provided by this work will be an important reference for the future study of thermocline TES systems.

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.

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.

International audience

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.

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.

A heat storage process by absorption is studied in this paper. It is devoted to solar domestic systems. Energy and exergy studies are performed on the ideal cycle, and prove the contribution of the solution crystallisation to the system storage density, with an improvement of 22%, without degradation of the exergetic efficiency of the process. A prototype has been built and tested in conditions compatible with domestic solar thermal collectors. The process has been proved successful for heat storage. The heat charging was more efficient than the discharging phase, with respective heat transferred in the range of 1–2 kW and 0.3–0.5 kW, in typical solar domestic conditions. Crystallisation has been observed, and will increase the storage density but discrepancies were found between the ideal solution and the global prototype crystallisation behaviour, possibly due to some impurities presence, corrosion products and a slow dissolution kinetic.

This paper introduces an optimization method for improving thermoelectric heat pump performance by operating condition management of the thermoelectric modules (TEMs) and design optimization of the heat exchangers linked to the TEMs. The device studied, corresponding to an original configuration of the thermoelectric heat pump, comprises two commercial thermoelectric modules and two mini-channel heat sinks through which water flows, in contact with both sides of the TEMs. The objective function is the maximization of the device’s coefficient of performance (COP), including the electrical and mechanical consumption of the thermoelectric modules and the circulating auxiliaries. First, the optimization variables are the number and the diameter of mini-channels, and the mass flows for both heat sinks (hot and cold sides). The results show that similar results are obtained by minimization of the entropy generation in the device. Finally, the hot thermal power demand is included in the optimization variables for complete optimization of the device. The results of full optimization converge with those obtained with the previous partial optimization.

The general problem of describing the flow distribution in manifolds feeding parallel channels has been addressed in a number of earlier publications. Such systems are used for example as heat exchanger plates, as distributors for fuel cells, or as solar collectors. We address here the "inverse problem", i.e. of finding a design, which provides uniform flow distribution among the channels, for which much less literature is available. We approach that problem by considering the steady-state flow-rates in the branches of 2D rectangular lattice networks with a single inlet and a single outlet, of which the classical parallel channels (ladder) network can be viewed as a special case. The purpose of this paper is to show how to organize the flow resistances on the periphery of the lattice so as to achieve flow uniformity in all inside channels. This is done under the assumption of a resistive network, with linear flow/pressure behavior (pure viscous Stokes flow, neglecting the inertial terms, neglecting or linearizing the effect of branching singularities) allowing completely analytical solutions and comparison of different configurations. The compatibility of uniform flow distribution and uniform Residence-Time-Distribution is discussed. Examples of new conceptual designs of heat exchanger plates, of fluid distributors and of mixers are proposed, based on this possibility of uniform distribution.

International audience; This article proposes fully analytical solutions for a certain class of networks or circuits for fluid flow, called "ladders" by analogy with the designation used in electrical engineering. Fluidic ladders comprise a discrete number of parallel channels, the ends of which are connected to a straight distributor manifold and to a straight collector manifold. The hydrodynamics are assumed to be purely linear, i.e. viscous laminar flow is assumed everywhere, inertial effects and non-linear contributions of branching singularities are neglected. The known and relatively simple case of the classical electric ladders is taken as a starting point to formulate and solve Kirchhoff's equations together with Ohm's law. The solutions for the steady-state flow-rates in each branch of the ladder are in the form of polynomials of dimensionless resistance ratios. The polynomials and their coefficients are shown to obey simple and general recurrence relations, which allow any size of ladder to be solved. A number of special cases are investigated, from a unique resistance (homogeneous ladders) to two or three different resistances, or a resistance distribution allowing a homogeneous distribution of flow among the parallel channels.

International audience; This paper presents a heuristic optimality criterion algorithm for shape design of fluid flow. In this algorithm, the lattice Boltzmann method (LBM) is utilized to calculate the flow field of a fluid domain which is divided into elemental cells. A heuristic optimality criterion is applied for cells at the solid–fluid interface, i.e. the dynamic pressure for fluid cells and the viscous stress on their neighboring solid cells. An automatic program is processed step by step to exchange the positions of solid and fluid cells identified by the optimality criterion, with the objective of decreasing the flow resistance at the constraint of constant fluid volume. To illustrate the procedure of this algorithm for shape design of fluid flow, two simple examples are presented: one with fluid flowing through a right angle elbow and the other through a converging T-junction. Numerical results show that this algorithm can successfully reduce the total pressure drop of the system, demonstrating its potential applications in engineering optimal design.

Received 24 March 2009 Received in revised form 15 May 2009 Accepted 20 May 2009 Available online 17 June 2009; International audience; This article presents analytical resolutions of the problem of optimal channel size distribution for arborescent (ramified, branched, tree-like) networks used as flow distributors or collectors. The distributor network connects a single inlet port to an array of outlet ports distributed over a specified square or rectangular surface (point-to-surface problem), and the reverse for a collector. The optimization problem is formulated as follows: find the distribution of channel radii that minimizes total viscous dissipation (or entropy production, pumping power, pressure drop) under constraints of uniform irrigation and of total volume of channels (or of average residence time) and the assumption that the flow is split equally between branches at each junction. With respect to earlier work, the present approach does not assume Poiseuille flow, but accounts instead for singular pressure losses in T-type junctions. Different situations are investigated, with the pressure loss coefficient being either a constant for the whole structure, or depending on local flow conditions. The case where both Poiseuille and singular pressure losses are present is also addressed. Also two types of networks are taken as illustrations: a dichotomic tree (a branch divides into two sub-branches), and a tetratomic tree (a branch divides into four sub-branches). The analytical results are in the form of scaling relations between the different levels of the arborescence, and in the form of distributions for channel radii, dissipation, pressure drop, porous volumes. A so-called “constructal function” is introduced that depends on the network structure and on the pressure loss relation, and is calculable as the sum of a geometric series. All explicit relations for the above quantities may then be expressed in a compact fashion in terms of the constructal function. A remarkable property of the optimized structures concerns the distribution of dissipation density (i.e. dissipation divided by volume): when the singular pressure loss coefficient is independent of local flow conditions, this quantity is uniform over the whole structure, thus satisfying “equipartition of entropy production”. A weaker form of this property is found when the singular pressure drop coefficient depends on local conditions (parity dependence).

Thermoelectric (TE) modules are possible reversible pre-cooling and pre-heating devices for ventilation air in buildings. In this study, the opportunity of direct coupling of TE modules with photovoltaic (PV) cells is considered. This coupling is evaluated through a numerical simulation depending on the meteorological conditions of Chambery, Alpine region in France, and on the cooling or heating use of the TE modules, through annual energy and exergy efficiencies. For the considered conditions, TE module performances are of the same order as the ones of the vapour compression heat pumps, with a TE coefficient of performance higher than 2 for low values of input DC current. The PV–TE coupling efficiency varies between 0.096 and 0.23 over the year, with an average value of 0.157. Evolutions of the exergy effectiveness of PV and TE elements follow the same trends as the corresponding energy efficiencies but with steeper variations for the coupling exergy yield that varies between 0.004 and 0.014, with an annual average value of 0.010. The direct PV–TE coupling does not seem to be a sustainable option for the summer cooling purpose particularly. A case study with indirect coupling under a warm climate is considered and shows that the use of TE devices could be efficient in housing to ensure summer thermal comfort, but the corresponding necessary PV area would induce a high investment. Copyright © 2008 John Wiley & Sons, Ltd.

International audience; This article reports a numerical and experimental study on flow maldistribution and heat transfer intensification in a mini heat exchanger with constructal distributor/collector integrated. The flow distribution characteristics of the constructal component functioning as a fluid distributor or as a fluid collector have been investigated and compared using computational fluid dynamics simulations. An experimental setup is designed and constructed for thermal and hydraulic performances tests. The effects of various assembly configurations on heat transfer characteristics and pressure drops are discussed. The results indicate that the integration of one constructal collector at the outlet of the heat exchanger can achieve almost uniform flow distribution and consequently better intensify the heat transfer. It is also the most advantageous configuration based on a balanced consideration of heat transfer intensification and pump power consumption under the investigation conditions.

International audience; The flow distribution behavior of a plate-type constructal flow distributor, which has one inlet and 16 outlets and is designed according to constructal theory to achieve uniform flow distribution with smallest energy dissipation and shortest residence time, is investigated by experiments. When all the outlets are open, the standard flow rate deviation changes from 0.050 to 0.069 and the maximal flow rate ratio, i.e. the ratio of the highest flow rate to the lowest, changes from 1.170 to 1.252 when the averaged Re at the outlet increases from 1020 to 2247. Blocking one or two outlets of one branch will generally decrease the uniformity of the flow distribution, and it will have more influences on the rest outlets of the same branch than on the outlets of other branches.

International audience; This paper describes an experimental study and the numerical model of a system that cools or warms an airflow by means of thermoelectric modules (TE modules). The device consists of four TE modules in contact with fins within a circulating airflow. The opposite sides of TE modules are in contact with water box heat exchangers. The experimental results are in good agreement with the theoretical thermoelectricity equations, and confirm the feasibility of cooling or heating air through TE modules with a good COP. The numerical model presented afterward is based on an electric analogy and calculates temperatures along the flow. The results are very close to those obtained during the experiment, thereby reasonably validating this model.

International audience; Radial distribution profiles of ozone concentrations were measured along an 8.50 m high and 0.09 m inside diameter gas/solid co-current down-flow circulating fluidized bed (downer) to characterize the reactor performance. Tests were conducted under a series of operating conditions at room temperature and near atmospheric pressure, with FCC particles as the bed material. Results show that the concentration distribution of the ozone tracer gas correlates well with the flow structure of the downer. There is quite a uniform radial distribution of ozone concentrations in the core region of all tested axial sections in the fully developed region of the downer, except for the near-wall region where there is a sharp decrease in ozone concentration. And there exists a relatively significant non-uniform distribution in the entrance acceleration region of the downer.

International audience; In this paper, a literature review of the recent research advances and applications of microchannel (from 1 μm to 1 mm) heat exchangers (μHXs) is presented. After a brief introduction of basic definitions, the advantages and limitations of μHXs are summarized with examples. Recent applications of these exchangers are reported. Although much in-depth research work still needs to be done, great potential has already been shown for large-scale applications of μHXs in process intensification of various industrial areas. Moreover, in order to solve the key issue of the link between the micro-scale and the macro-scale, multi-scale methodology such as fractal and constructal approaches for the design optimization of μHXs are introduced. Finally, the concept of constructal heat exchanger is presented.

This paper addresses the thermal performances of a zeolite-based open sorption heat storage system to provide thermal energy for space heating needs. The study focuses on the experimentation of a significant scale prototype using zeolite 13X/H 2 O as the reactive pair, and on the development of a 1D mathematical model used to predict both the charging (desorption) and the discharging (adsorption) processes occurring inside the storage unit. The experimental campaigns and the numerical results lead to some promising conclusions on the thermal performances of such a storage unit. With 40 kg of zeolite, a temperature lift of 38 °C on average at the outlet of each zeolite’s vessel during 8 h was achieved during the discharging with an airflow inlet at 20 °C, 10 g/kg of dry air of specific humidity and a flow rate of 180 m 3 /h. Some discrepancies between the experimental and simulation results were observed during both the charging and discharging tests, and were explained.

International audience; In this paper, a review of the research state of art of the solar sorption (absorption and adsorption) refrigeration technologies is presented. After an introduction of basic principles, the development history and recent progress in solar sorption refrigeration technologies are reported. The application areas of these technologies are categorized by cooling temperature demand. It shows that solar-powered sorption refrigeration technologies are attractive alternatives that not only can serve the needs for air-conditioning, refrigeration, ice making and congelation purposes, but also can meet demand for energy conservation and environment protection. However, a lot of research work still needs to be done for large-scale applications in industry and for the replacement of conventional refrigeration machines.

International audience; The constructal approach, proposed by Bejan is an emergent notion which quickly develops at the international level and in a multidisciplinary frame. It is a method of optimization of the conception of objects and ‘‘components'' which allows finding the geometry of a multi-scale system in view of an optimal performance. The constructal concept, as the fractal concept, is a way of connecting the geometry of a microscopic world (the structures of an equipment or a material at the finest scales) with the macroscopic world in which it is immersed, through several intermediate scales. Essential differences with the fractal object are that the constructal object optimizes the passages from one scale to the other, that the geometry is not necessarily invariant from one scale to the other, and that there maybe some thermodynamic content to the optimization, such as minimizing entropy production. The present paper addresses these issues through several aspects: general introduction to the constructal approach; discussion of some examples of multi-scale components (heat exchanger, fluid distributor, coupling of fluid distributor to heat exchanger, mixer and its coupling to a micro reactor); manufacturing issues; perspectives for applications and for further scientific research.

International audience; In this paper a survey of solar-based driven thermoelectric technologies and their applications is presented. Initially, a brief analysis of the environmental problems related to the use of conventional technologies and energy sources is presented and the benefits offered by thermoelectric technologies and renewable energy systems are outlined. The development history of solar-based thermoelectric technologies is introduced together with the discussion of the existing drawbacks of current systems. Typical applications of the solar-driven thermoelectric refrigeration and the solar-driven thermoelectric power generation are presented in order to show to the reader the extent of their applicability. The application areas described in this paper show that solar-driven thermoelectric technologies could be used in a wide variety of fields. They are attractive technologies that not only can serve the needs for refrigeration, air-conditioning applications and power generation, but also can meet demand for energy conservation and environment protection.

International audience; Parallel micro or mini-channels are widely used in various devices of process and energy engineering including micro-reactors, compact heat exchangers and fuel cells. Nevertheless, the flow maldistribution due to the improper design of distributor/collector is usually observed, leading to globally poor performances of these devices. The objective of this study is to optimize the shape of the distributor/collector pipes so as to achieve a uniform flow distribution among an array of parallel minichannels. A Z-type ladder fluid network with 10 mini-channels in parallel having square section is introduced and investigated. Two methods are used to optimize the shape of distributor/collector pipes: an optimized discrete stairway shape and a continuous tapered shape with an inclined angle varying from 0° to 30°. 3D-CFD simulations are carried out using the ANSYS FLUENT code. Numerical results obtained show that a relatively uniform flow distribution may be reached by the discrete stairway shape or by the continuous tapered shape distributor/collector under very low flow-rate conditions. Larger inclined angle or fewer channels in parallel are favorable for more uniform flow distribution under higher flow-rate 2 conditions. Nevertheless the distributor and the collector pipes occupy a large volume so that the entire device is less compact.

International audience; Novel morphologies of activated carbons such as monolith, beads and fiber cloth can effectively capture organic vapors from industrial sources. These adsorbent materials are also unique because they can undergo direct electrothermal regeneration to recover the adsorbed organic vapors for potential re-use. This investigation compares and contrasts the properties of these adsorbents when using electrothermal–swing adsorption. The adsorption systems consisted of an organic vapor generation system, an electrothermal–swing adsorption vessel, a gas detection unit, and a data acquisition and control system. The activated carbon monolith (ACM) had the lowest pressure drop, highest permeability, highest electrical resistivity and lowest cost as compared to the activated carbon beads (ACB) and the activated carbon fiber cloth (ACFC). ACB had the largest throughput ratio and lowest length of unused bed as compared to the other adsorbents. However, ACFC had the largest adsorption capacity for toluene when compared to ACM and ACB. ACFC was also faster to regenerate and had a larger concentration factor than ACM and ACB. These results describe relevant physical, electrical, adsorption and cost properties for specific morphologies of the adsorbents to more effectively capture and recover organic vapors from gas streams.

International audience; The present work proposes an approach to building nonideal coadsorption models in a thermodynamically consistent fashion, including the effects of pressure and spreading pressure, from simple gravimetric measurements. This is an “inverse problem” of parameter determination from appropriate and limited experimental data.The approach relies on the nonideal adsorbed solution theory, which includes activity coefficients and their dependence on spreading pressure, and on an original form of the excess Gibbs energy of mixing. A fully analytical development leads to explicit relations between the infinite dilution activity coefficients and three sets of independent information: the parameters of this excess Gibbs function, the limiting slopes of measured binary gravimetric curves at two different total pressures, and the properties of the single-component isotherms. From there, the four parameters of the model may be determined quasi-analytically and uniquely. The method is exemplified with the coadsorption of CO2 and CH4 on activated carbon, and a heterogeneous set of data. On one hand, the total adsorbed mass of the two components is measured at 1 bar by “incremental gravimetry.” On the other hand, data obtained from independent batch-type equilibration measurements at 2 bar allow a comparison of calculated and measured data for the individual component concentrations. It is emphasized, however, that only total adsorbed mass data are needed for application of the method.

International audience; Constructal approach is a recent concept allowing to generate and optimize multi-scale structures, in particular, branching structures, connecting a microscopic world to a macroscopic one, from an engineer's point of view. Branching morphologies are found in many types of natural phenomena, and may be associated to some kind of optimization, expressing the evolutionary adaptation of natural systems to their environment. In a sense, the constructal approach tries to imitate this morphogenesis while short-cutting the trial-and-error of nature. The basic ideas underlying the constructal concept and methodology are illustrated here by the examples of fluid distribution to a multi-channel reactor, and of the design of a porous material and system for gas adsorption and storage. In usual constructal theory, a tree branching is postulated for the channels or flow-paths or conductors, usually a dichotomic tree (every branch is divided into two “daughters”). The objective function of the optimization is built from the resistances to mass or heat transport, expressed here as “characteristic transport times”, and the geometric result is expressed as a shape factor of a domain. The optimized shape expresses the compromise between the mass or heat transport characteristics at adjacent scales. Under suitable assumptions, simple analytical scaling laws are found, which relate the geometric and transport properties of different scales. Some challenging geometric problems may arise when applying the constructal approach to practical situations where strong geometric constraints exist. The search for analytical solutions imposes simplifying assumptions which may be at fault, calling for less constraining approaches, for example making only weak assumptions on the branching structure. Some of these challenges are brought forward along this text.

International audience; Gas phase propylene epoxidation on gold catalysts has attracted wide attention from industry and academia due to its high selectivity. However, it suffers from low propylene conversion and rapid catalyst deactivation. Experiments showed that propylene conversion could be increased by raising H2, O2, or C3H6 concentration in the feed, but the feed compositions were within the explosion limit. It was also shown that the activity of the used catalyst could be fully recovered, but the regeneration temperature was 280 °C, much higher than that for reaction. Therefore a microchannel reactor was devised to suppress explosion and was constructed with Fecralloy, to raise the temperature rapidly for catalyst regeneration by electric heating. In two minutes the temperature of the reactor could be raised from 50 to 300 °C. Catalysts were coated on the alloy belt by dip coating, and the performance of the reactor was evaluated under different operating conditions. Results showed that in the microreactor the overall reaction rate was controlled mainly by the intrinsic reaction rate, and also influenced by film diffusion to a certain extent. The deactivated catalyst was regenerated in the microchannel reactor and the activity was fully recovered.

International audience; This paper presents and develops a novel methodology to determine thermodynamic parameters of binary gas co-adsorption equilibria at given total pressure, based exclusively on binary gravimetric measurements at this same total pressure, together with single component isotherms. By “Incremental Gravimetry”, we designate a procedure in which the adsorbent sample is submitted to increments of composition of a flowing binary gas, and the corresponding increments of weight of the sample at equilibrium are measured. The experimental example is the co-adsorption of methane and carbon dioxide on Norit activated carbon near ambient temperature and pressure. The approach relies on the thermodynamics of non-ideal adsorbed solutions. The experimental methodology is described, the underlying theory is then presented. Compact analytical expressions are established that relate the measured limiting slopes of the incremental gravimetric curves (at infinite dilution of one component in the other) to quantities that derive only from the pure component isotherms, and to the infinite dilution activity coefficients. The latter are then uniquely determined. Classical two-parameter models for the composition dependence of activity coefficients are then implemented to reconstruct the complete binary isotherms and the incremental gravimetric curves. The comparison of the latter with the measured curves permits to test the different models

The long-term thermal storage by absorption process studied in this paper is devoted to building heating. A demonstrative prototype that can store 8 kWh of heat and produce a heating power of 1 kW has been designed and built. It has been tested in static and dynamic operating conditions, which are compatible with domestic solar thermal and heating plants. The process operating principle, the prototype design and first experimental results are presented and discussed in this contribution. The charging process has been proved successful. The observed power during the charging phases is satisfactory, according to the process design for a real plant (2–5 kW). Absorption during discharging phase is also verified. Discharging tests show that absorption operates in conditions that could allow house heating as the absorber outlet solution temperature can reach 40 °C. However, some problems related to the absorber design have not allowed observing the heat recovery by the heat transfer fluid as expected. Some avenues are explored prior to a new and more appropriate design and eventually a new operating mode. Various aspects such as the use of a heat and mass transfer enhancement additive and stratification in the solution storage tank have also been addressed.

In recent years, storage of thermal energy has become a very important topic in many engineering applications and has been the subject of a great deal of research activity. This paper reviews the thermal energy storage technologies suitable for building applications with a particular interest in heat storage materials. The paper provides an insight into recent developments on materials, their classification, their limitations and possible improvements for their use in buildings. Three major thermal energy storage modes (sensible heat, latent heat, thermochemical heat) are described emphasizing the main characteristics of the most suitable heat storage materials for each.

In this chapter, we will return to the local scale and present a fundamental approach for shape optimization. This numerical approach is based on the so-called cellular automaton (CA) algorithm, capable of treating a class of optimization problems that we encounter in heat and mass transfer. Two examples will be illustrated to demonstrate the procedure of CA approach: (1) how to organize a finite quantity of high conductivity material in order to efficiently drain heat from a heat generating surface to a sink and (2) how to optimize the shape of fluid path with a finite void volume that connects a source to one or several outlet ports, with the purpose of flow equidistribution and pressure drop minimization. The shape optimization by CA procedure generally leads to the creation of multi-scale arborescent geometries that commonly exist in nature, with consequently intensified heat and mass transfer.

With a view towards better efficiency in renewable energy utilisation, particularly solarenergy, the authors study along-termsolar thermal energystorage based on water absorption by alithiumbromide aqueous solution. After a description of the process, the systemdynamicsimulation model is detailed and used to investigate the influence of certain parameters (heat exchanger size, solution flow rate, absorption percentage) and operating conditions (heat supply temperature to the building, crystallisation ratio, heat need) on the system performance (storage density, thermal efficiency, etc.). The analysis of simulations made for a low-consumption building in Chambéry shows that the solution flow rate is a critical parameter in the process performance. It also appears that crystallisation in the solution storage tank increases the storage density more than three times. The simulation results are used in the design of a prototype that is under experimentation for validation of the model. With a view towards better efficiency in renewable energy utilisation, particularly solar energy, the authors study a long-term solar thermal energy storage based on water absorption by a lithium bromide aqueous solution. After a description of the process, the system dynamic simulation model is detailed and used to investigate the influence of certain parameters (heat exchanger size, solution flow rate, absorption percentage) and operating conditions (heat supply temperature to the building, crystallisation ratio, heat need) on the system performance (storage density, thermal efficiency, etc.). The analysis of simulations made for a low-consumption building in Chambéry shows that the solution flow rate is a critical parameter in the process performance. It also appears that crystallisation in the solution storage tank increases the storage density more than three times. The simulation results are used in the design of a prototype that is under experimentation for validation of the model.

International audience; The present paper investigates some families of simple 2D circuits or grids of intersecting tubes or channels (thus forming meshes) from the point of view of the fluid distribution and hydraulic characteristics in slow laminar flow. Square grids with a single inlet and a single outlet, and comprising from 4 to 100 meshes are considered, either with all channels identical, or with different channels along the borders of the circuit. Analytical resolution of the mesh and node relations to obtain the steady flow distributions are convenient up to 5x5 meshes, and formal computation furnishes numerical solutions for higher order circuits. This paper discusses some details of the flow and pressure distributions, in particular the symmetries, and also the behavior of some global properties such as overall or internal resistance and flow heterogeneity, as a function of the ratio of resistances of the two types of channels.

International audience; This paper presents the thermodynamic and hydrodynamic feasibility of the application of the ammonia-water absorption system for heat or cold transportation over long distance. A model of a long-distance heat energy transportation system is built and analyzed, and it shows satisfactory and attractive results. When a steam heat source at the temperature of 120°C is available, the user site can get hot water output at about 55°C with the thermal COP of about 0.6 and the electric COP of about 100 in winter, and cold water output at about 8°C with the thermal COP of about 0.5 and the electric COP of 50 in summer. A small-size prototype is built to verify the performance analysis. Basically the experimental data show good accordance with the analysis results. The ammonia-water absorption system is a potential prospective solution for the heat or cold transportation over long distance. Copyright © 2009 John Wiley & Sons, Ltd.

This study proposes a cellular automaton approach to deal with the typical “area-to-point” problem of how to effectively cool a heat generating surface by arranging the configuration of high conductivity material links which discharge the generated heat to a heat sink. To demonstrate the principle and the procedure of the cellular automaton approach, a simple case of square surface with single heat sink is treated: the approach starts with an initial shape of a certain quantity of high conductivity material. By shaping the initial conductive drain through the equipartition of thermal gradients, the high conductivity material evolves step-by-step and forms at convergence a final configuration, which turns out to be a multi-scale tree-like network. The effects of the conductivity ratio k ˆ , the fraction of high conductivity material ϕ0 as well as the influence of the initial shape are discussed. The cellular automaton approach, which allows increasing the effective overall thermal conductance of an area, is fast, easy to apply and nearly constraint-free. Finally, the present limitations of the cellular automaton are also exposed.