Etudes numériques et expérimentales des écoulements turbulents dans les échangeurs à chauffage asymétrique (application aux récepteurs solaires à haute température)

PERPIGNAN-BU Sciences (661362101) / SudocSudocFranceF

What is limiting MOF adsorption capacity in devices: Thermodynamics, kinetics or heat transport?

SSCI-VIDE+ING+DFA:CDAInternational audienceMetal-Organic Frameworks have been investigated as adsorbents for Heat-Pump applications, especially for chilling applications using water as working fluid. Today, Silica Gel bead is the current adsorbent technology which is used in adsorption chillers. While its water adsorption capacity is relatively limited, its very low manufacture cost made Silica Gel beads very competitive. Nevertheless, the performances of silica gel are still limited to address important application challenges. Technico-economical studies show that new very performing adsorbents shall be investigated for the conversion of low temperature heat produced by data center.Thanks to their very high adsorption capacity, type V isotherm and ease for regeneration thanks to their low heat of adsorption, MOFs are in principle ideal candidates for cycling adsorption and desorption of water. As consequence MOF could outperform silica gel based on technical criteria. Especially, Al-fumarate is regarded with promises as it is stable in hydrothermal conditions and can be produced without organic solvents. In addition, due to its framework flexibility upon adsorption Al-fumarate shows adsorption isotherm displacement as function of the temperature which shall enable a facilitated regeneration .However to date, technico-economical studies of Al-fumarate as adsorbent for adsorption chillers have not been published yet. To date, the promises rely mostly on water uptake at equilibrium conditions. In the frame of PRODIA, an European program, Al-fumarate beads have been developed to meet ambitious technical targets while being cost compatible.While the paper will not discuss the development of manufacture process, it is worth mentioning that the synthesis processes and shaping technics which have been developed meet industrialization criteria. The continuous mechano-chemical synthesis on Al-fumarate without solvent enables upscaling at high production rates whilst achieving high yields, adsorbent quality and higher operational safety. In addition, an original scalable shaping process was developed enabling continuous production of robust and size-controlled spheres from 0.3 to 2mm made of Al-fumarate.In the course of the development, we found that the cycling capacity on Al-fumarate beads were lower than the pristine powder at thermodynamic equilibrium. Three phenomena which could penalized adsorption capacities in were identified and investigated.1/ does the guest induced transformation of Al-fumarate occur in the time frame of the adsorption-desorption processes ?2/ are the uptake kinetics limited by a diffusion regime in the Al-fumarate porous beads ? due to the binders ? or due to the bead size ?3/ are the uptake kinetics limited by mass transport limitation in or between Al-fumarate beads ?In order to unravel the origin of kinetic limitations on Al-fumarate beads, series of beads of different diameter (0.4, 1.2, 1.6mm) and binder contents were synthesized. Mass ad heat transport were measured in a special device in adsorption and desorption modes. Kinetic results are compared with silica-gel beads. We will show that beads of 0,4 mm of diameter show fast uptake kinetics.Small spheres of 0.4 mm of Al- and Zr-MOF were produced at multi-kg scale. The performances of MOFs were evaluated in 3 liter adsorber demonstrator. We will show that MOFs outperform commercial Silica Gel under standard cycling conditions. Results in extremely low regeneration temperature will be presented and discussed in the frame application market requirements

Pilot scale production and demonstration of low cost MOFs for chilling applications

SSCI-VIDE+ING+DFA:CDAInternational audienceWe present here the results of a 3-year project aiming at the development of pilot scale production and shaping of MOFs and at their demonstration in Heat-Pump application at kilogram scale in relevant process conditions.Although MOFs outperform commercial adsorbents for heat-pump application in terms of higher water uptake and cyclability, their commercialisation was until now strongly penalized by their price due to high production process costs. The objective of this program was to develop low cost manufacture processes allowing the production of advanced and cost-competitive adsorbents. We have developed innovative and scalable MOF production processes including synthesis and shaping, for which (i) manufacturing equipment’s are readily available at industrial scale, and (ii) enable upscaling at high production rates whilst achieving high yields, product (sorbent) quality and higher operational safety. We will present three main technological innovations: (i) aqueous synthesis of UiO-66 without the use of corrosive acid modulator (ii) continuous mechano-chemical synthesis on Al-fumarate without solvent and (iii) original scalable shaping process enabling continuous production of robust and size-controlled spheres (beads). In contrast to other adsorbents, we discovered that performances of MOF were jeopardized due to severe mass transport limitations likely due to the organic binder. In order to overcome this limitation small spheres of 0.4 mm (0.3 mm – 0.7 mm) of Al- and Zr-MOF were produced at multi-kg scale. The performances of MOFs were evaluated in 3 liter adsorber demonstrator. We will show that MOFs outperform commercial Silica Gel under standard cycling conditions with stability over 10.000 cycles. Results in extremely low regeneration temperature will be presented and discussed in the frame application market requirements.This work has received funding from the EU under grant agreement No 685727

Adsorber heat exchanger using Al-fumarate beads for heat-pump application – a transport study

International audienceMetal–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

Pilot scale production and demonstration of low cost MOFs for chilling applications

SSCI-VIDE+ING+DFA:CDAInternational audienceWe present here the results of a 3-year project aiming at the development of pilot scale production and shaping of MOFs and at their demonstration in Heat-Pump application at kilogram scale in relevant process conditions.Although MOFs outperform commercial adsorbents for heat-pump application in terms of higher water uptake and cyclability, their commercialisation was until now strongly penalized by their price due to high production process costs. The objective of this program was to develop low cost manufacture processes allowing the production of advanced and cost-competitive adsorbents. We have developed innovative and scalable MOF production processes including synthesis and shaping, for which (i) manufacturing equipment’s are readily available at industrial scale, and (ii) enable upscaling at high production rates whilst achieving high yields, product (sorbent) quality and higher operational safety. We will present three main technological innovations: (i) aqueous synthesis of UiO-66 without the use of corrosive acid modulator (ii) continuous mechano-chemical synthesis on Al-fumarate without solvent and (iii) original scalable shaping process enabling continuous production of robust and size-controlled spheres (beads). In contrast to other adsorbents, we discovered that performances of MOF were jeopardized due to severe mass transport limitations likely due to the organic binder. In order to overcome this limitation small spheres of 0.4 mm (0.3 mm – 0.7 mm) of Al- and Zr-MOF were produced at multi-kg scale. The performances of MOFs were evaluated in 3 liter adsorber demonstrator. We will show that MOFs outperform commercial Silica Gel under standard cycling conditions with stability over 10.000 cycles. Results in extremely low regeneration temperature will be presented and discussed in the frame application market requirements.This work has received funding from the EU under grant agreement No 685727