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Les machines a absorption liquide eau-bromure de Lithium representent une gamme majeure de groupes refroidisseurs de liquide fournissant de l’eau glacee a 7 °C a partir d’une source chaude thermique (eau chaude, vapeur, gaz naturel ou fuel, etc.) et en rejetant de la chaleur a la temperature ambiante. Plusieurs types d’unites fonctionnant avec des cycles thermodynamiques differents, dont le lecteur peut simuler les performances grâce a une feuille de calcul, sont proposes par les constructeurs. Les COP de ces unites commencent a 0,7-0,8 pour les unites a simple effet alimentees avec de la chaleur a 95 °C, pour atteindre 1,3 pour des unites a double effet alimentees par de la chaleur a 175 °C et meme culminer a 1,7-1,8 pour les cycles a triple effet utilisant de la chaleur a 200 °C.

Western France is at the crossroads of the migratory routes of two subspecies of black-tailed godwit, Limosa limosa. After leaving Iceland, the godwit L.l. islandica Icelandic black-tailed godwit (IBTG) winters on the coast of western Europe, while the continental black-tailed godwit (CBTG) L.l. limosa can stop in France when migrating between Iberia or Africa and their main breeding grounds in the Netherlands. In this study, we analysed δ15N and δ13C from flight feathers and whole blood throughout the non-breeding period to trace variations in habitat use for both subspecies on the western French coast. Adults and juveniles of IBTG adopt the same feeding habitats as soon as they arrive in the study area, progressively losing the Icelandic freshwater habitat signal, and becoming clearly restricted to marine habitats in winter. Some individuals begin to move locally to freshwater habitats, joining CBTG in a stopover at the end of the wintering period in preparation for northward migration.

Metal-Organic Frameworks (MOFs), thanks to their type V water adsorption isotherms ("S-Shape") and large water capacities, are considered as potential breakthrough adsorbents for heat-pump applications. In particular, Al(OH)-fumarate could enable efficient regeneration at a lower temperature than silica-gel which would allow us to address the conversion of waste heat at low temperature such as found in data centers. Despite its greater adsorption capacity features, heat and mass transport limitations could jeopardize the potential performance of Al(OH)-fumarate. Heat and mass transport depend on the size of the bodies (mm range), their packing and on the pore structures, i.e. macro-mesopore volumes and sizes. This paper describes the cost-efficient and scalable synthesis and shaping processes of Al(OH)-fumarate beads of various sizes appropriate for use in water Adsorption Heat-Pumps (AHPs). The objective was to study transport limitations (i.e. mass and heat) in practical e beads which meet mechanical stability requirements. Dynamic data at the grain scale was obtained by the Large Temperature Jump method while dynamic data at the adsorber scale was obtained on a heat exchanger filled with more than 1 kg of Al(OH)-fumarate beads. Whereas the binder content had little impact on mass and heat transfer in this study, we found that Knudsen diffusion in mesopores of the grain may be the main limiting factor at the grain scale. At the adsorber scale, heat-transfer within the bed packing as well as to the heat exchanger is likely responsible for the slow adsorption and desorption kinetics which have been observed for very low desorption temperature. Finally, the dynamic aspects of the observed water adsorption isotherm shift with temperature are discussed in light of reported reversible structure modification upon temperature triggered water adsorption-desorption.

This study investigates the performance of an adsorption chiller driven by thermal heat collected from solar collectors’ panels with heat storage. The heat is reserved in a storage tank and the reserved heat is used to drive the adsorption chiller. The investigation was carried on the climatic conditions of Dhaka, Bangladesh. Heat transfer fluid goes from the collectors to the adsorption cooling unit, then from the adsorption cooling unit to the storage tank. It is seen that heat storage is more effective than direct solar coupling; however, it requires more collectors, depending on the size of the storage tank. The analysis shows that cycle time is one of the most influential parameters for the solar-driven adsorption cooling system. It is seen that the size of the collector can be reduced if the proper cycle time is adjusted. The analysis also revealed that the system with 22 collectors (each of 2.415 m2) along with 1000 s cycle time provides better performance for the base run conditions. It is also se...

Kim et al . (Reports, 28 April 2017, p. 430) describe a method for harvesting water from air, using a metal-organic framework (MOF) as the adsorbent. The process as described in the paper is, however, inadequate, and the system cannot deliver the claimed amount of liquid water in an arid climate. A modification of the process design and the use of more suitable MOFs may be more likely to achieve the goals targeted by Kim et al .

Summary. Coastal shorebird species overlap at many wintering sites or migratory stopovers. However, each species is morphologically and physiologically specialised for reducing competition for space, time or habitat. A species can encompass several populations, sometimes designated as subspecies. Differences between populations, ages and sexes within the same species can also lead to segregation between individuals in a foraging area. In this study, we explored the non-breeding spatial and temporal overlap between two subspecies of the black-tailed godwit Limosa limosa on the central Atlantic coast of France (the Pertuis Charentais). The proportions of individuals of each sex and each age within the populations were assessed to explore differences in the wintering distribution. The subspecies L.l. islandica winters in the area from July to March whereas the subspecies L.l. limosa may stopover in the area during south- and northward migration. The two subspecies occasionally overlap at some sites just afte...

A review of the state of the art of adsorption heat powered heat pumps is presented. Interesting results on solar cooling, advanced cycles and consolidated materials were obtained in early developments until 1995 but, at that time, commercialization was not successful. Recently, breakthroughs were achieved on materials (including composite ones) and on coated surfaces but no obvious progresses have been obtained on advanced cycles and this is a gap to be completed. In parallel, commercialization has improved with the perspectives of the boiler new market. A promising future for those components exists if the recent and ongoing innovation yields more efficient commercialized products.

In expanding populations, individuals may increasingly be forced to use sites of relatively low quality. This process, named the "buffer effect," was previously described for the Black-tailed Godwit (Limosa limosa islandica) in its use of nonbreeding sites in Great Britain and of breeding areas in Iceland. On the basis of diet analyses from droppings and stable isotopes, we describe a new case for the expanding French wintering population of the Black-tailed Godwit, an expansion accompanied by a drastic change in feeding strategy. In the 1990s, Black-tailed Godwits started using intertidal mudflats at Ile de Re, where they eat the rhizomes of seagrass (Zostera noltii) rather than the customary shellfish (Macoma balthica) eaten at both the preferred (initial) site (Aiguillon Bay) and the area occupied last (Yves to Marennes-Oleron bays). Individually color-marked godwits appeared faithful to both diet type and site, suggesting a cost of a change of strategy. This represents a first case of rhizome-feeding in shorebirds, and it exemplifies a case of carnivorous birds occupying a new site shifting to herbivory.

L’adsorption est une technique de separation de molecules d’un gaz ou d’un liquide par attraction sur un solide poreux. C’est un phenomene de surface qui fait intervenir des interactions physiques et chimiques. La retention des molecules a lieu essentiellement sur la surface interne de l’adsorbant. Cette technique est utilisee pour la separation et la purification de molecules dans des domaines tres varies : la petrochimie, l’agroalimentaire, le traitement des effluents … Cet article presente les bases theoriques de l’adsorption pour le Genie des Procedes : les materiaux utilises, les equilibres en jeu, les mecanismes de transferts et les comportements dynamiques d’un lit fixe d’adsorbant.

Les systemes thermiques a sorption solide representent une gamme de composants majeurs pour l’utilisation rationnelle de l’energie. Ils ont d’ores et deja trouve plusieurs niches ou ils sont bien developpes: des roues dessicantes aux groupes refroidisseurs de liquide a sorption a faible temperature de regeneration (adaptes notamment pour la climatisation solaire et les rejets thermiques).De plus, des produits innovants et tres prometteurs emergent: stockage du froid dans le transport de produits thermosensibles ainsi que des pompes a chaleur integrees dans des chaudieres a gaz. Enfin, l’emergence de materiaux adsorbants ainsi que d’echangeurs, a surface enduite, innovants ouvre de nouvelles perspectives pour reduire le poids et le volume de ces systemes et etendre ainsi leur marche.

Numerous animals move vast distances through media with stochastic dynamic properties. Avian migrants must cope with variable wind speeds and directions en route , which potentially jeopardize fine-tuned migration routes and itineraries. We show how unpredictable winds affect flight times and the use of an intermediate staging site by red knots ( Calidris canutus canutus ) migrating from west Africa to the central north Siberian breeding areas via the German Wadden Sea. A dynamic migration model incorporating wind conditions during flight shows that flight durations between Mauritania and the Wadden Sea vary between 2 and 8 days. The number of birds counted at the only known intermediate staging site on the French Atlantic coast was strongly positively correlated with simulated flight times. In addition, particularly light-weight birds occurred at this location. These independent results support the idea that stochastic wind conditions are the main driver of the use of this intermediate stopover site as an emergency staging area. Because of the ubiquity of stochastically varying media, we expect such emergency habitats to exist in many other migratory systems, both airborne and oceanic. Our model provides a tool to quantify the effect of winds and currents en route .

Electric generation by wind turbine is growing very strongly. However, the environmental impact of wind energy is still a matter of controversy. This paper uses Life Cycle Assessment, comparing two systems: a 4.5 MW and a 250 W wind turbines, to evaluate their environmental impact. All stages of life cycle (manufacturing, transports, installation, maintenance, disassembly and disposal) have been analysed and sensitivity tests have been performed. According to the indexes (PEPBT (primary energy pay back time), CO2 emissions, etc.), the results show that wind energy is an excellent environmental solution provided first, the turbines are high efficiency ones and implemented on sites where the wind resource is good, second, components transportation should not spend too much energy and, third, recycling during decommissioning should be performed correctly. This study proves that wind energy should become one of the best ways to mitigate climate change and to provide electricity in rural zones not connected to the grid.

This work explores the possibility to perform heating and air-conditioning of state of the art building located near Paris in France. For air-conditioning, enhanced compound parabolic solar collectors are used as a heat source of an adsorption system (methanol/activated carbon), while during winter direct coupling with the building is performed. A model describing the adsorption unit, the solar collectors and the house was used to simulate the performances of such an installation. For air-conditioning, thermal comfort is achieved as indoor temperature is kept below 25 °C during five consecutive hot days (heat wave effect), contrarily to the case for which only free-cooling during nighttime is used. For heating, the indoor temperature remains below the comfort temperature value by 2 K. Nevertheless, the auxiliary heating need will remain limited so that savings on electricity or fossil fuel consumption will be possible.

Experimental results of CO2 post-combustion capture for a TSA process including an internal heat-exchanger (indirect heating/cooling) are presented. The comparative experimental study is carried out on 13X and 5A zeolites, with a mixture 90% N2−10% CO2 modeling the flue gas. With 5A zeolite having given the best performances, we tested it with various operating conditions including one with nitrogen purge during desorption. This one showed a good compromise between CO2 capture rate, purity of the desorbate, volumetric productivity, and specific-heat consumption. We obtained a volumetric productivity of 37 kgCO2/m3ads·h and a specific-heat consumption of 6 MJ/kgCO2 at our laboratory scale and 4.5 MJ/kgCO2 for the adiabatic estimate (in the same order of magnitude as those obtained industrially with the reference MEA amine process). These results are promising because our process is not optimized yet and the scale-up on an industrial version involves a reduction in specific-heat consumption.

This paper analyzes and presents the thermodynamic cycles and the experimental performance parameters of a solar adsorptive icemaker that uses activated-carbon methanol pair. The solar energy technology employed is far less sophisticated than that of collectors using selective surface or evacuated tubes. The collector-adsorber is multi-tubular with an opaque black radiation-absorbing surface, and thermal insulated by means of transparent covers, the so-called transparent insulation material (TIM). The solar radiation hits on both faces of the tubes by means of semi-cylindrical reflectors. It is shown the results of tests carried out in a region of Brazil close to the Equator, on days characterized by the predominant cloud cover degree. Three cycles have been analyzed: one with clear sky, another with partially cloudy sky, and a third under entirely cloudy sky. The maximum regenerating temperatures were 100.1, 87.3 and 92.7 °C, with an ice production of 6.05, 2.10 and 0 kg by square meter of projected area, for cycles of clear sky, partially cloudy and overcast nights, respectively.

Climate change induced by global warming is a result of an excess of energy at the earth’s surface due to the greenhouse effect. But a new energy management can reverse the situation taking advantage of the greenhouse effect to produce renewable energy. In fact, both the renewable energy and the energy consumed which are not dissipated into heat are subtracted from the excess of energy produced by the greenhouse effect and contribute to mitigate climate change. This opens perspectives to harness the greenhouse effect [F. Meunier, Domestiquer l’effet de serre, Dunod, 2005]. Should all the primary energy be renewable energy and should part of the energy production not dissipated into heat, the present earth’s energy imbalance should be beneficial and should serve to produce renewable energy.

The aim of this article is to investigate the performances of an indirect temperature swing adsorption process for CO2 removal from nitrogen using 13X zeolite. Breakthrough experiment, with a 10% CO2–N2 mixture, were performed showing that thanks to the cooling, the adsorbent capacity is preserved and close to that of an isothermal adsorption. For the desorption step, CO2 at a concentration of nearly 100% is recovered thanks to the indirect heating and the non-use of purge gas. During the cycle experiments, we obtained 7.9 MJ/kg for the specific heat consumption. This value is slightly higher than amine absorption ones, which is the reference process for CO2 capture. However, it has to be taken into account that there is a good potential of energy saving because our process configuration (adsorbent choice, number of beds, step duration, etc.) has not been optimized yet. Moreover, in scaled-up process, the heat losses are of less importance, which will decrease the specific heat consumption. This is confirmed by a first estimation, which gives a value of 5.9 MJ/kg. © 2006 American Institute of Chemical Engineers Environ Prog, 25: 327–333, 2006

A refrigeration Carnot-type cycle based on isothermal compression and two reversible expansions is proposed. Although ideal, this cycle is close to a realistic one which could be designed with existing hardware.

A life cycle analysis performed on biogas co- or tri-generation units shows that the environmental impact depends on the fraction of heat (or cold) used, the distance for crops collection, the efficiencies of the unit and on the NO x emissions. A high efficiency unit ( η el = 0.4 and η g = 0.8) and low NO x content (80 mg/N m 3 ) based on 20 km crops collection will save CO 2 emissions and act in a CO 2 sink resulting in one of the very few technologies capable of reducing atmospheric CO 2 concentration.

The performances of a recently developed TSA process for gaseous pollutant treatment, based on indirect heating and cooling by means of an internal heat-exchanger, have been investigated both numerically and experimentally. Heating is carried out by condensing steam, and cooling by water circulation. The cycle performances are usually better than those of competing processes, but with increased heat consumption. The sensitivity of the performances to the regeneration temperature and purge flow rates is discussed. Lastly, it is shown that in the conditions of an adsorber scaled-up to a typical practical size including a mass of adsorbent 1000 times higher than in the laboratory column, the specific heat consumption is in the same range as conventional TSA processes.

It is the purpose of this work to present an experimental analysis of the thermodynamic cycles in a multi-tubular adsorber of a solar-powered icemaker that uses activated carbon-methanol pair. The experimental cycles were obtained from tests made under different meteorological conditions—mainly the conditions pertaining to cloud cover degree. The system was tested in a Brazilian region close to the Equator (7∘8′S, 34∘50′WG) during the period October-December 2003. On a typical clear sky day, the regenerating temperature reached 94∘C, the condensed methanol mass amounted to 3 kg, and the machine produced 6 kg of ice/m2 day at −3.3∘C, with a net solar coefficient of performance (COPs) of 0.085. These results were compared to those obtained from a similar prototype that utilizes the same adsorptive pair and an usual flat adsorber, tested in Tunisia (35∘45′N, 10∘45′WG).

The aim of this article is to highlight the behavior differences between an indirectly cooled temperature swing adsorption (TSA) adsorber and other adsorbers classically studied in TSA systems (adiabatic, near-adiabatic and isothermal) during adsorption of a mixture of gases. For this purpose, a numerical model is presented and validated from experimental results. By means of this model, the temperature, gas molar fractions and adsorbed concentration profiles are drawn at different times. The various zones of the adsorption patterns are identified and compared. The influence of the feed and initial bed temperatures is discussed too. From these results, the advantages of indirectly cooled adsorbers are pointed out. A new criterion for the possibility of omitting the cooling step in TSA cycles, based on the bed cooling efficiency, is then proposed for the indirectly cooled adsorbers.

In this paper, the impact of the oil presence on the performances of a refrigerating machine is investigated both experimentally and numerically. To highlight the effect of oil, particularly on the evaporator behaviour, a theoretical model of enthalpy calculation for a refrigerant/oil mixture has been previously developed [Int J Refrigeration, 26(2003), 284]. In order to validate this model, tests were carried out on an industrial refrigerating machine working with R-407C. The lubricant is a polyol-ester oil whose solubility curves are given by the oil manufacturer. The oil circulating mass fraction is measured by a sampling technique and by an on-line density measurement method, whose advantages and drawbacks are presented. Both the model and the experiments show that the ratio of enthalpy change through the evaporator with to without the oil presence increases when the apparent superheat at the evaporator outlet increases. This is due to the presence of a non-evaporated amount of liquid refrigerant dissolved in the oil at this location, which is confirmed by visual observations. The numerical and experimental results are found to be in a good agreement as the maximum deviation is about 2.2%.

This paper documents the fundamental relation between the maximization of global performance and the maleable (morphing) architecture of a flow system with global constraints. The example is the coaxial two-stream heat exchanger with flow through a porous bed in the annular space. It is shown that the constraints force the design toward heat exchangers with finite axial length, where additional improvements are derived from installing high-conductivity fins across the porous bed. The maximization of global performance is achieved through the optimization of the configuration of plate fins. Configurations with radial fins are optimized analytically and numerically. Configurations with branched fins are optimized numerically. It is shown that the best configuration (radial vs. branched) depends on the size of the heat exchanger cross-section. When the size is small, the best is the radial pattern. When the size exceeds a certain threshold, the best configuration is the optimized branched tree of fins.

We propose in this study a simplified model of enthalpy calculation for a refrigerant–oil mixture, as well as a new presentation of the pressure–enthalpy–vapour quality diagram which is applied to refrigerant–oil mixtures with different oil circulating mass fractions. This presentation allows the calculation of the enthalpy change through an evaporator, with and without taking into account the effect of oil, and the prediction of the non evaporated quantity of refrigerant at the compressor suction. The results of the model for two pairs of R407C/POE oil of different solubilities show that under the same working conditions, the solubility of the refrigerant in oil can have a considerable effect on the evaporator performances. Indeed, for two oils presenting the same viscosity grade, the evaporator performances decrease when the refrigerant–oil solubility increases.

In expanding populations, individuals may gradually be constrained to use new sites with non-optimal quality habitats. On the coast of Western Europe, the Black-tailed Godwit Limosa limosa islandica, breeding in Iceland, is one of the rare shorebird species with an increasing population trend. The coast of France hosts 28 % of this population in mid-winter, with the remainder of the population wintering in the British Isles or in the Iberian Peninsula. Unlike godwits in Britain and Ireland, they are distributed among a small number of sites across France and are concentrated in high numbers at each. The Pertuis Charentais hosts up to 65 % of the Black-tailed Godwits recorded nationally (ca 18 000 individuals). In this study, we describe how prey selection and feeding strategies in intertidal areas are linked to site selection at the local scale and could explain the distribution of birds during the non-breeding period. The selection of site and prey species by godwits was studied by describing the diet and food supply of the species in six feeding areas at four local wintering sites. In the Pertuis, it has been confirmed that they have expanded into a herbivorous niche at newly established wintering sites on Ré Island where they feed on the seagrass Zostera noltii. The species remains strictly carnivorous at continental sites, where it forages actively on the bivalve Macoma balthica. Within sites, godwits target the most profitable preys. With the exception of human disturbances, the distribution of individuals within the Pertuis seems to be determined by the distribution, abundance and accessibility of only two prey species among a large array of macrofaunal species., Sélection des sites et des proies par les Barges à queue noire Limosa limosa islandica s’alimentant sur les herbiers de zoostères et les vasières du centre de la côte atlantique française. Dans une population en expansion, certains individus sont voués à explorer et exploiter de nouveaux habitats de moindre qualité. Sur la façade ouest européenne, la Barge à queue noire Limosa limosa islandica, qui se reproduit exclusivement en Islande, est l’une des rares espèces de limicoles avec une tendance démographique positive. Les côtes françaises accueillent 28 % de la population au milieu de l’hiver, le reste se distribuant sur les îles britanniques et la péninsule ibérique. Contrairement à la Grande Bretagne et l’Irlande, la population française se concentre sur un nombre restreint de sites mais avec de fortes concentrations. Les Pertuis Charentais accueillent plus de 65 % de la population nationale (ca 18 000 individus). Dans cette étude, nous décrivons comment la sélection des proies et les stratégies d’alimentation en milieux intertidaux sont liées à la sélection des sites à l’échelle locale and peuvent expliquer la distribution des oiseaux en période de non reproduction. La sélection des sites et des espèces-proies par les barges a été étudiée par la description du régime alimentaire et de la ressource trophique sur six zones d’alimentation sur les quatre principaux sites hivernages. Dans les Pertuis Charentais, il a été confirmé que ces barges occupent une niche écologique herbivore sur le nouveau site d’hivernage de l’île de Ré, où elles s’alimentent de Zostères naines Zostera noltii. La barge garde un régime carnivore sur les sites continentaux, où elle s’alimente principalement du bivalve Macoma balthica. Sur ces sites, les barges ciblent la proie la plus rentable. À l’exception du dérangement humain, la distribution des individus dans les Pertuis Charentais semble être déterminée par la distribution, l’abondance et l’accessibilité de seulement deux espèces-proies parmi un large éventail d’espèces benthiques., Robin Frédéric,Meunier Francis,Corre Frédéric,Joyeux Emmanuel,Cayatte Marie-Laure,Delaporte Philippe,Lemesle Jean-Christophe,Pineau Philippe,Bocher Pierrick. Site and prey selection by wintering Black-tailed Godwit Limosa limosa islandica feeding on seagrass beds and bare mudflats on the central Atlantic coast of France. In: Revue d'Écologie (La Terre et La Vie), tome 70, n°2, 2015. pp. 134-147.

The conditions for co- and tri-generation to reduce CO2 emissions are discussed as well as the global impact of these techniques if they were extensively used. CO2 emissions saving will depend on several factors. First, on the efficiency of the co- and tri-generation unit, second on the CO2 emissions of the electric network. CO2 emissions savings will range from 10% to 50% or even more depending on the conditions. The best solutions correspond to the use of non-fossil fuel and total energy systems.

A solar adsorptive ice maker model is presented and experimentally validated. In order to determine the model parameters, the identification procedure is carried out employing an experimental data base obtained from tests carried out on two adsorptive solar-powered ice-makers using a methanol/carbon pair. The packaged component, the collector–condenser, represents the main new feature of these units. The prediction is compared with results of correlations. This allows a comparison of the collector–condenser behavior in the two units since the collector–condenser of one of these units is equipped with a radiation shield. The model is then used to study daily ice production sensitivity vis-a-vis critical physical parameters of the unit and to estimate the limits of the collector–condenser technology with flat plate collectors.

An adsorption air conditioning unit has been built operating with a heat nd mass recovery cycle and a zeolite-water pair. A new consolidated adsorbent composite with good heat transfer properties has been developed and implemented in the adsorber. At an evaporating temperature of 4 C, the experimental specific cooling power (SCP) of 97 W/kg achieved represents a real improvement in comparison with those measured with a packed bed technology. At this evaporating pressure, the mass transfer resistance controls the process. Therefore, at higher evaporating temperature a COP of 0.68 and a SCP of 135 W/kg were experimentally achieved. A new model has been developed to take into account the mass transfer limitations. The model has been validated and can predict the average pressure inside the adsorber and the components temperature of the unit. A new high conductive material with enhanced mass transfer properties has been developed. The predictive model shows that a SCP of 600 W/kg and a COP of 0.74 could be achieved with this new material.

Heat powered solid sorption is a feasible alternative to electrical vapour compression. However, the emergence of that technology takes time. In this review, the possibilities and limits of this technology are analysed. The performances are shown to be very interesting and in progress, and right now applications are foreseen. The use of waste heat for solid sorption air-conditioning may be an attractive application, but, for a large dissemination, higher efficiencies as well as cost reduction are required. With respect to primary energy and global warming, sorption cooling and heat pumping is coherent, except for waste heat or solar applications, only if the cooling COP is larger than about 1 or 1.2 depending on operating conditions. Technical results are close to that point which provide a wider perspective.

Temperature–entropy diagrams are usually used to describe heat-driven engines as well as vapour compressor refrigerators, but they have not yet been used for sorption refrigeration. Such Carnot cycles are introduced here to describe three sorption refrigeration technologies (liquid absorption, solid adsorption, chemical reaction). This is performed for basic cycles (without heat recovery) and for simple advanced cycles. Equivalent four-temperature Carnot cycles are obtained for basic cycles, whereas equivalent six-temperature Carnot cycles are obtained for advanced cycles. This approach shows that the quantity ΔH-TΔS (where ΔH and ΔS are the enthalpy and entropy variations associated with mass transfer during a cycle in/out of the sorbers) plays the same role as the mechanical energy in vapour compression cycles.

The reason why the performance of adsorptive refrigeration cycles is always less than that of the Carnot cycle corresponding to the same heat reservoir temperatures is analysed. This analysis is performed using the entropy production concept and introducing numbers of entropy production which are a direct measure for the efficiency degradation. The thermal entropy production due to the external thermal coupling of the isothermal heat reservoirs to the temperature varying adsorbers is important in all cases considered. It prevails for the basic uniform temperature cycle (about 95% of the total entropy production). For n-adsorber uniform temperature cycles, internal thermal entropy production (due to heat recovery between adsorbers) may reach 50% of the external thermal entropy production. The entropy production due to the refrigerant flow inside the unit does not depend on the process and is small (less than about 10%) in all cases. For thermal wave cycles, the origin of the entropy production depends highly on the cycle time. For very short cycle times, the external thermal entropy production is very small but an important internal thermal entropy production is observed in the adsorbers. For long cycle times, it is the opposite, the external thermal entropy production becomes very large while the internal thermal entropy production in the adsorbers does not increase.

As a consequence of the phasing out of CFCs, sorption systems appear to be potential candidates to replace vapour compression systems. Amongst sorption systems there exists a choice between several systems, such as liquid absorption, solid adsorption and chemical reaction heat pumps. Nevertheless, few comparative studies between these systems have been undertaken so far. It is the aim of this paper to present such a study based on combined first and second law thermodynamical analysis of the different cycles. Simple entropy generation processes explain why the basic cycles for these systems yield performances much lower than the Carnot efficiency. The possibility of operating regenerative cycles with internal heat recovery and higher efficiencies has also been considered for typical common base conditions. Different entropy generation considerations have been visualised, such as thermal coupling (external/internal), non-uniform temperature component entropy production and other irreversible processes for the COP degradation in these systems. It is found that thermal coupling irreversibilities in solid sorption systems and other internal irreversibilities in liquid sorption systems with solution heat exchanger are dominant in the actual COP degradation with respect to the reversible Carnot COP.

An adsorptive heat pump system with the temperature wave heat generation is numerically analysed, using a two-dimensional model which takes into account both heat and mass transfer processes inside the adsorber. In the model, the gaseous phase flow is described by Darcy's law. The adsorber is heated or cooled by an external thermal fluid which is considered as one-dimensional. The mathematical model is numerically solved using the ADI finite difference method. Numerical simulations are performed on two adsorption systems: zeolite NaX-water and activated carbon AX21-ammonia. The effects of the operating parameters, such as cycle time, permeability and heating temperature, on the cooling coefficient of performance and the power of cold production are discussed. Finally, the temperature wave regenerative heat pump system is compared to the basic adsorptive heat pump process.

Adsorptive heat pumps are promising for providing a safe alternative to CFC-based refrigeration devices. The temperature fronts process (also called thermal regeneration) has been claimed by several authors in recent years as a way for improving performance of adsorptive refrigerating devices. Cooling COPs of at least one are possible. However, up to now, almost no experimental results have been published. Efficient heat transfer is a key point for efficient thermal regeneration. Consolidated composite adsorbents (expanded natural graphite + zeolite) have much better heat transfer characteristics than granular packed beds: from 50 to 100 times larger, according to Guilleminot et al. [Proc. Int. Absorption Heat Pump Conf., ASME, AES 31, 401–406 (1993)]. Therefore, temperature fronts have been studied in an adsorber containing such composite adsorbents. The adsorber is 1 m long, 10 cm in diameter and it is built on the principle of a double pipe (adsorbent inside, heat transfer fluid outside). The heat transfer fluid flows in one direction during the hot front (heating period), and in the other direction during the cold front (cooling period). This experimental set-up permits simulating real refrigeration cycles. Performance analysis deduced from the experimental data (axial and radial temperature gradients in the adsorber, inlet and outlet temperatures and flow-rate of the heat transfer fluid) demonstrates the respective influences of heat transfer fluid mass flow-rate and cycle time. Experimental COPs of 0.9 were obtained.

This communication presents an entropic analysis based on combined first and second laws of thermodynamics for a vapour liquid absorption (VLAB) cooling system. The model provides an insight understanding of entropy production mechanisms of various irreversible processes inherent in absorption systems and also gives an explicit explanation of actual COP degradation with respect to the ideal reversible Coefficient of Performance (COP) in terms of entropy generation associated with irreversible processes. Numerical results for water-LiBr absorption system and given cold production, source and sink temperatures are presented for different effectiveness of solution heat exchanger and the components/parameters which affect most the system performance are visualised. It is ascertained that the solution circuit components are most sensitive and the individual entropy productions are inter-dependent on each other as well as on the solution recirculation ratio and the effectiveness of the solution heat ex...

There is a need for better understanding and correlation of water vapor adsorption on hydrophobic surfaces, especially on activated carbon. Water vapor is present in most air-pollution control problems, since it is one of the major impurities in atmospheric air. Treatment of polluted air streams with active carbon is gaining ever increasing importance as the only technology which can perform at a satisfactory level mandated by strict worldwide environmental regulations. A general theory for the adsorption of self-associating molecules in microporous structures is developed. The approach is similar to the chemical interpretation of nonideality of vapor and liquid phases. The theory displays Type 5 isotherm behavior and can explain Types 1 and 5 transition. Isothermal data are represented by only three parameters: Henry`s law constant, saturation capacity, and reaction constant for cluster formation in the micropores. When isotherms at different temperatures are available, the theory can be used with five temperature-independent parameters to describe the entire phase behavior including the heat of adsorption. Water adsorption on activated carbon, the most common display of Type 5 behavior, is used to test the theory. Analysis of several data sets indicates that the theory can closely correlate data, provide physically meaningful parameter valuesmore » in line with carbon properties, and it is highly effective in correlating temperature variation. The reaction enthalpy for water dimerization in the carbon micropores is lower than that in vapor phase. This preliminary conclusion with the theory needs to be supported with more accurate data when available.« less

This paper presents a numerical study of coupled heat and mass transfers in an adsorber with external fluid heating. A one-dimensional model incorporating both heat transfer and Ergun flow of the adsorbate inside the adsorber is developed. Numerical investigations are made for two adsorbent-adsorbate pairs: zeolite 13X-water and 13X-ammonia, whose operating pressures are considerably different. It is shown that, for the 13X-water pair which has a low operating pressure and therefore a low gas density, the dynamics of the adsorber can be significantly limited by the mass transfer inside the adsorbent bed, when its dimension is large. The poor mass transfer can lead to very large pressure variations and small adsorbed or desorbed quantities, making the heat pump process ineffective. Conversely, the zeolite-ammonia pair operates at much higher pressures (several bars) and the corresponding pressure variations in the bed are, in general, negligible. In this case, the limitation by mass transfer can be neglected and the uniform-pressure assumption is acceptable.

A consequence of urban heat islands in summer is an increase in the use of air conditioning in urbanized areas, which while cooling the insides of buildings, releases waste heat to the atmosphere. A coupled model consisting of a meso-scale meteorological model (MESO-NH) and an urban energy balance model (TEB) has been used to simulate and quantify the potential impacts on street temperature of four air conditioning scenarios at the scale of Paris. The first case consists of simulating the current types of systems in the city and was based on inventories of dry and evaporative cooling towers and free cooling systems with the river Seine. The other three scenarios were chosen to test the impacts of likely trends in air conditioning equipment in the city: one for which all evaporative and free cooling systems were replaced by dry systems, and the other two designed on a future doubling of the overall air conditioning power but with different technologies. The comparison between the scenarios with heat releases in the street and the baseline case without air conditioning showed a systematic increase in the street air temperature, and this increase was greater at nighttime than day time. It is counter-intuitive because the heat releases are higher during the day. This is due to the shallower atmospheric boundary layer during the night. The increase in temperature was 0.5 °C in the situation with current heat releases, 1 °C with current releases converted to only sensible heat, and 2 °C for the future doubling of air conditioning waste heat released to air. These results demonstrated to what extent the use of air conditioning could enhance street air temperatures at the scale of a city like Paris, and the importance of a spatialized approach for a reasoned planning for future deployment of air conditioning in the city.

International audience; Post-combustion CO2 capture remains one of the most-challenging issue to lower CO2 emissions of existing power plants or heavy industry installations because of strong economy and energy efficiency aspects. The major issue comes from CO2 dilution (4% for NGCC and 14% for PC) and the high flow rates to be treated. Furthermore, CO2 purity has to be higher than 95% with recovery at 90%, to match the transportation/injection requirements. The MEA absorption process remains the reference today but its energy consumption (about 3 MJ/kgCO2) and the amine consumption are still challenging drawbacks. The interest of CO2 capture by indirect TSA (Temperature Swing Adsorption) was demonstrated experimentally in a previous work. The aim of this paper is to present the results of a numerical parametric study. Two main parameters are explored: the desorption temperature (100 to 200 °C) and the purge flow rate (0.1 to 0.5 Ndm 3 .min-1). Four performance indicators are evaluated: CO2 purity, recovery, productivity and specific energy consumption. Results show that purity above 95% can be achieved. Keeping the 95% target, it is possible to achieve recovery at 81% with productivity at 57.7 gCO2/kgads.h and a specific 2 energy consumption of 3.23 MJ/kgCO2, which is about the same level than for up to date MEA processes. Comparison with other adsorption processes exhibits that this process has good potential especially since some improvements are still expected from further research.