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F. Meunier
The activities in adsorption have been dedicated to three main fields:
- characterisation of consolidated materials
- kinetics of adsorption
- adsorptive refrigeration processes.
Studies on adsorptive refrigeration processes are strongly supported by institutions: CEC Joule program, french ADEME , french gas utility GDF and a european EUREKA program.
TOPIC 1 : CHARACTERIZATION OF CONSOLIDATED MATERIALS
(J.J. Guilleminot)
The efforts devoted during the last five years, in collaboration with B. Spinner from IMP Perpignan and with the company LCL, have been successfull since the thermal conductivity of consolidated beds has been improved by a factor of 50 to 100 as compared to the unconsolidated granular bed. However, with the consolidated beds, limitations to mass transfer have now been observed. Systematic permeability measurements have, therefore, been performed. A technical solution which has been found, to get reasonably high permeabilities, is to introduce artificial arteries in the consolidated blocs. The major consequence of the good results obtained by those studies, is that the specific cooling rate of the adsorbers should be improved by a factor of 5 to 10 with respect to unconsolidated adsorbers. New applications like vehicle air conditioning should become possible with this new technology. To validate this technology, a 3 kW pilot for building air conditioning, funded by GDF, has been designed and built.
TOPIC 2 : KINETICS OF ADSORPTION (Ph. Grenier, L.M. Sun)
The original technique developed at LIMSI by Ph. Grenier has been used to study ageing of 5A zeolite. A rigorous protocol has been developed which enables to extract not only intercrystalline and intracrystalline coefficients of diffusion but also to detect the existence of surface barriers. Results are very useful to analyse the location of coke formation. This work is a result of a collaboration with a laboratory in Poitiers (P. Magnoux and Guisnet) and with IFP (S. Jullian).
TOPIC 3 : ADSORPTIVE PROCESSES (J.J. Guilleminot, M. Pons)
Adsorptive refrigeration regenerative cycles are currently under study in several laboratories. Two strategies of regenerative cycles are tested:
- uniform temperature adsorbers regenerative cycles
- thermal wave regenerative cycles.
The first class of regenerative cycles (uniform temperature adsorbers regenerative cycles) corresponds to the strategy developed for several years at LIMSI. The novelties introduced on the pilot under construction are two fold:
- consolidated adsorbers with high thermal conductivity are used
- a cycle with a heat recovery associated to a mass recovery (pressurisation and depressurisateps steps) is being used.
The second class of regenerative cycles has been first studied in US. Thermal waves are generated in adsorbers. Recently, studies on this subject have started at LIMSI. Our objective is to validate this concept with the consolidated materials and to study the possibilities of innovation through process modifications.
The Adsorption group is integrated into several research networks:
- the Stelf Club (Stelf is a consortium animated by Elf and LCL to promote solid gas refrigeration using consolidated materials besed on the use of expanded graphite). The main objective of this consortium is to disseminate research results obtained on consolidated materials at IMP Perpignan (on ammonia salts like calcium chloride) and at LIMSI (on adsorbents) for refrigeration or heat pump applications,
- three european networks funded by the European Community: two Joule programs (the first one on Adsorption Gas Separation and the second one on Solid Gas Refrigeration) and a Human Capital Mobility network coordinated by LIMSI on Sorption Refrigeration.
- several scientific societies in which the group holds some responsabilities:
- International Adsorption Society
- Absorption Heat Pump
- International Institute of Refrigeration.
The group has participated in the most important international conferences in the field (AIChE meeting in San Francisco, IAS meeting "Fundamentals of Adsorption" in Asilomar).
Scientific activities of LTF are dedicated to two main directions:
- Heat and mass transfer in cryogenic two-phase fluid
- Thermo-acoustic refrigeration.
Diphasic studies concern experimental measurements of boiling effects around a heated wire in a liquid nitrogen reservoir.
With respect to thermo acoustic refrigeration, an experimental test rig to study the regenerator of the system has been built. In this rig, the acoustic impedance is measured as a function of the design of the regenerator. It is also possible to measure the temperature gradients induced by the acoustic field.
Experimental results have also been obtained on the Kapitza thermal resistance at the interface between Niobium and superfluid Helium.