Enhanced solar absorption and steam generation in lithium bromide-based modified copper oxide nanofluids under simulated solar flux

Multiphase flow and heat transfer processes are involved in various applications, such as water desalination, sterilisation, and power generation. Environmentally friendly and sustainable system operation can be ensured through the utilisation of renewable energy resources. Furthermore, the thermal efficiency of these systems can be enhanced by using nanofluids. This study reports an experimental investigation of the photothermal conversion properties of polyethylenimine (PEI) functionalised Copper oxide (CuO) nano particles used in Lithium Bromide (LiBr) salt solutions. The nano particles were characterised by the dynamic light scattering (DLS), transmission electron microscope (TEM), ultraviolet visible (UV–Vis) spectrophotometer. The long-term stability of the prepared nanofluid was evaluated using a high-speed centrifuge analyser. The instability index of 0.071 ± 0.002 indicated low agglomeration and sedimentation tendencies. Photothermal conversion efficiency for different concentrations of CuO was experimentally investigated under a solar simulator. The experiments were conducted with nanofluids containing 55 wt% of LiBr and PEI functionalised nanoparticles, with loading ranging from 0.05 to 0.15 wt%. The addition of nanoparticles resulted in an increase in surface temperature, up to 90.69 ± 2.7 % higher than the base case tested with deionised water (DIW). Experimental results further confirms that the nanofluid tested in this study has the potential to significantly increase solar energy trapping efficiency and evaporation rate due to a localised solar energy harvesting by the surface of nanofluid. It was found that a 0.1 wt% CuO NP concentration is the optimum nanofluid concentration in terms of stability for enhanced sensible and latent heat efficiencies. • A highly stable functionalised CuO nanofluid in 55 wt% LiBr for solar absorption refrigeration has been developed. • Increased bulk temperature and evaporation rates under solar radiation were demonstrated. • Notable boost in the latent and sensible heat has been observed which enhanced steam evaporation efficiency. • CuO nanofluid's potential for eco-friendly, energy-efficient solar refrigeration has been showcased.