Adsorption of difluoromethane onto activated carbon based composites: Thermophysical properties and adsorption characterization

In an attempt to promote research on adsorption cooling systems, novel activated carbon-based composite adsorbents have been studied for thermophysical properties and adsorption characterization with difluoromethane (HFC 32) refrigerant. High surface area activated carbon of type Maxsorb III has been selected as the primary constituent of adsorbent composites, with H25 graphene nanoplatelets (GNPs), 1-Hexyl-3-methylimidazolium bis(trifluormethylsulfonyl)imide ([HMIM][Tf2N]) ionic liquid, and Polyvinyl alcohol (PVA) binder in varying fractions. The various thermophysical properties such as surface area and porosity, specific heat capacity, and thermal conductivity have been experimentally evaluated. The thermal diffusivities have been measured in two different planes of the composites: parallel and perpendicular to the direction of the compression. It has been observed that the perpendicular plane has significantly higher thermal diffusivities (up to 2.32 times) over the parallel plane of the composites. Besides, a considerable improvement in thermal conductivity of up to 65.6 times is observed over powdered activated carbon. Adsorption uptake characteristics are studied gravimetrically for the composite samples in the temperature range of 30-70 degrees C. Dubinin-Astakhov (D-A) and Toth models are fitted successfully for the adsorption isotherms, with the D-A model seen to offer better fits. Further, the specific and volumetric cooling energies are estimated for the consolidated carbon composites based on the respective D-A adsorption equilibrium parameters and thermophysical properties of the working pairs. Significant enhancements in volumetric cooling energy up to 78% over that of powdered activated carbon are seen for the consolidated composites. (C) 2021 Elsevier Ltd. All rights reserved.