Adsorber heat exchanger using Al-fumarate beads for heat-pump application – a transport study
Metal-Organic Frameworks (MOFs) thanks to their Type V water adsorption isotherm (“S-Shape”) and large water capacity are considered as potential breakthourgh adsorbents for heat-pump applications. In particular Al(OH)-fumarate could enable efficient regeneration at lower temperature than silica-gel which would allow to adress the conversion of waste heat at low temperature such as found in data centers. Despite greater adsorption capacity features, heat and mass transport limitations could jeopardize potential performances of Al(OH)-fumarate. Such heat and mass transports depend on the size of bodies (mm range), their packing and on the pore structures, i.e. macro-mesopore volume and sizes. This paper describes cost-efficient and scalable synthesis and shaping processes of Al(OH)-fumarate beads of various sizes appropriate for use in water Adsorption Heat Pumps (AHP). The objective was to study transport limitations (ie. mass and heat) in practical e beads which meet mechanical stability requirements. Dynamic data at grain scale has been obtained by Large Temperature Jump method while dynamic data at adsorber scale was obtained on a heat exchanger filled with more than 1kg of Al(OH)-fumarate beads. Whereas the binder content has little impact of mass nor heat transfer in this study, we found that Knudsen diffusion in mesopores of the grain may be the main limiting factor at grain scale. At adsorber scale, heat-transfer within the bed packing as well as to the heat exchanger is likely responsible for slow adsorption and desorption kinetics which have been observed for very low temperature of desorption.
- This article is part of the themed collection: Cooperative phenomena in framework materials