New composite materials based on anodic alumina for adsorption heat transformers

At present, due to high energy saving potential adsorption heat transformers (AHTs) – chillers and heat pumps - are considered as promising alternative to compression systems. Development of new efficient adsorbents of water and methanol specialised for AHT can essentially advance this emerging low-carbon technology. This work addresses the synthesis and study of novel composite sorbents based on inorganic salts inside pores of an anodic aluminium oxide (AAO) consolidated with aluminium support. The AAO texture is modified by varying the electrolyte nature (H2SO4, H3PO4, H2C2O4) and the current-voltage characteristics during the synthesis, and its duration. The AAO layer thickness reaches intently varied from 30 to 70 nm, and the pore volume - between 50 and 170 cm3/m2 of the Al plate. CaCl2 and LiCl are confined into the AAO pores to increase the sorption capacity that rises up to 23 and 84 g/m2 of the plate for water and methanol, respectively. The amount of sorbates exchanged under the working conditions of a typical air conditioning cycle reaches 13 and 30 g/m2. The composites cooling capacity is estimated as 27-30 kJ/m2. Dynamics of water sorption was investigated by Large Temperature Jump method, imitating conditions of the isobaric stages of real AHT cycle. The desorption runs are found to be extremely fast and ensure the maximal power of 17 kW/m2. The results obtained have clearly demonstrated that a) these new materials can be interesting for making compact AHT units with short working cycles, and b) more R&D effort are necessary for further progress towards practical implementation.