Experimental Investigation of silica-gel based composite adsorbent for adsorption refrigeration system

Abstract

Two novel composite adsorbents have been developed with porous home silica-gel to enhance the performance of the adsorption refrigeration system. The two types of thermal conductivity enhancers (TCEs) namely graphite and copper powder with a polymeric binder polyvinyl alcohol (PVA) are used to develop the high-performance composite adsorbents. The thermal stability, crystallinity and morphology of prepared composite adsorbents are analyzed. The porous properties such as specific surface area, pore volume and pore size distribution, and the thermophysical properties such as specific heat, thermal conductivity and thermal diffusivity are also investigated. A maximum specific surface area of 417 m2/g and pore volume of 0.3648 cm3/g is observed for a composite of 80% silica-gel + 10% graphite + 10% PVA. The copper-based composite adsorbents show lower specific heat values as compared to the graphite-based composite adsorbents. The thermal conductivity and diffusivity of composite adsorbents are significantly increased with the increased percentage of TCEs. A maximum thermal conductivity of 0.5 W/m K and diffusivity of 0.34 × 10-6 m2/s is observed for graphite-based composite adsorbent with a composition of 50% silica-gel + 40% graphite powder + 10% PVA. This is 4.23 times and 2.12 times greater than the thermal conductivity and thermal diffusivity of the silica-gel respectively. Similarly, a maximum thermal conductivity of 0.433 W/m K and diffusivity of 0.214 × 10-6 m2/s are observed for copper-based composite adsorbent with the same composition of TCE. This is 3.66 times and 33% greater than the thermal conductivity and diffusivity of the silica-gel respectively. The developed composite adsorbents show improved thermal and physical properties as compared to the conventional silica-gel.