The potential use of graphene to intensify the heat transfer in adsorption beds

Adsorption system for cooling, heat pumps, heat storing and water desalination have gained increasing attention in the last few decades. Adsorption systems have the advantage of utilising low-grade heat (below 200 °C), available by solar energy, wasted from industrial processes or other potential domestic waste heat sources. Granular packed adsorbent bed is the most used design in the commercially available adsorption equipment because of its high permeability, but nonetheless it has poor heat transfer performance. Many approaches were investigated to enhance the heat transfer performance of the adsorbent bed; blending the adsorbent granules with metal additives to enhance the overall thermal conductivity of the adsorbent bed, coating the adsorbent bed surface with thin layers of adsorbent to reduce the contact thermal resistance, adsorbent deposition over metallic foam and other consolidation approaches. Blending the adsorbent granules with metal additives has shown great potential to improve the heat transfer performance without reducing the adsorbent bed permeability.
Graphene is a single layer of carbon atoms which are arranged in hexagonal shape. A single layer of graphene exhibits thermal conductivity of up to 5300 W/mK. However, the thermal conductivity of graphene-based materials can be reduced by increasing the number of carbon atomic layers. Reduced graphene platelets of 30-45 layers showed thermal conductivity close to the bulk thermal conductivity of graphite. Graphite is a 3D structured graphene of relatively high bulk thermal conductivity (1950 W/mK) and is commonly used in adsorption equipment. Given the outstanding thermal performance of graphene-based materials, the hypothesis of this research is to blend the adsorbent granules with graphene-based materials of just a few carbon atomic layers to enhance the heat transfer performance of granular packed adsorbent beds.