Enhancing the Heat and Interparticle Mass Transfer of Adsorption Cooling and Desalination Systems

Abstract

Adsorption systems which utilise low-temperature renewable and waste heat sources, have emerged as a feasible alternative to conventional water desalination and cooling systems, despite their poor heat and mass transfer performance. This PHD project experimentally and computationally studies the utilisation of graphene oxide (GO) of a few atomic layers as a parent adsorbent material owing to its reported high thermal performance potential, the development and investigation of new composites employing few-layered graphene platelets GNP and ionic liquids (IL), namely ethyl-methylimidazolium methane sulfonate (EMIMCH3SO3) and Ethyl-methylimidazolium-chloride (EMIM Cl) and new consolidated composite synthesised from GNP, (EMIMCl) / (EMIMCH3SO3) and binder Polyvinyl alcohol (PVA). The impact of the Graphene oxide, few-layered graphene platelets, and the developed composites thermal properties (thermal diffusivity) and water adsorption properties of were experimentally investigated. Benchmarking them against the widely investigated silica gel (SG) adsorbent, emphasising adsorption cooling cum desalination application. Besides, the overall cyclic performance was studied experimentally at the material level. A 2D computational dynamic model was developed and employed to envisage the dynamic heat and mass transfer of a packed bed (component level) configuration. The thermal diffusivities and adsorption characterisation of the adsorbents were experimentally investigated and empirically modelled. The results showed that GO enhances thermal performance by 44% compared to silica gel and adsorption uptake by up to 57%. Furthermore, GO compared to silica gel, enhanced the system’s SDWP by 44.4%, SCP by 29.5%, COP by 17.2% and exergy efficiency by 15.8%. The GP/IL composites showed higher thermal diffusivities and the highest thermal diffusivity was 11.84 mm2/s for GP-CH3SO3-10, 394 times higher than silica gel. The cumulative advanced adsorption and thermal characteristics of the developed composites resulted in higher cyclic performance by up to 82% and 85% than silica gel. At system level the SDWP, SCP, COP and exergy efficiency for the GP-CL-30 based system was 60%, 70.5 %, 38.5% and 30% higher than the SG-based system. The consolidated composite GP-CL-30-CP7 showed the highest thermal diffusivity of 4.652 mm2/s which was 12.7 times higher than SG. System level performance of the highest performing consolidated composite GP-CL-30-CP1 based system for SDWP, SCP, COP, and exergy efficiency was 95%, 75%, 76% and 68% higher than the SG-based system.