An aerogel-based adsorption structure for a high-performance adsorption heat pump system

Abstract

Efforts to address global warming and fossil fuel depletion have driven the development of environmentally friendly and efficient energy systems. Adsorption heat pumps, which use thermal energy, are becoming popular since they can use renewable energy sources such as solar, geothermal, and waste heat. To effectively deliver thermal energy to the adsorbent medium in the heat pump systems, two methods are often utilized: packing the adsorbent between the fins or coating the adsorbent on the fin surfaces. The packing type exhibits a higher refrigerant adsorption capacity than the coating type. However, the heat transfer ability is low in the former, and the adsorbent quantity is limited in the latter. Therefore, we developed aerogel-based structures as an alternative to fin structures—a breakthrough that offers improved heat transfer capabilities compared to packing, and it overcomes the quantity limitations of coating representing a significant advancement beyond the existing literature. As a result, our innovation presents a promising avenue for enhancing thermal energy delivery in heat pump systems. In our study, we impregnated sodium bromide (NaBr) adsorbent into graphene aerogel (GA). The GA-based structure achieved a significantly improved specific cooling power of adsorption (SCPads) of 3.043 [kW/kg], compared to the conventional NaBr-packed finned flat plate structure with 0.065 [kW/kg]. We also conducted a numerical analysis to gain a deeper understanding of the experimental behavior. Additionally, we conducted a sensitivity analysis using the numerical model, revealing the pivotal role of adsorbent structure porosity in influencing SCPads. This research demonstrates the potential of using aerogels impregnated with adsorbent materials in adsorption reactors, leading to enhanced performance of heat pumps. The proposed adsorbent structure could be applied in future adsorption and desorption reactors.