Aqueous lithium bromide nanosolution for solar absorption refrigeration systems

Abstract

Solar-driven absorption refrigeration technology has the potential to reduce the peak electricity demand and the greenhouse gas emission. The optimisation of the generator and the absorber performance is crucial to develop this technology. Recently, seeding refrigeration working fluids with nanoparticles has attracted intense interest of research groups to develop existing technologies. In this study, the proposal of seeding aqueous lithium bromide (LiBr) solutions with nanoparticles was investigated. Well-controlled experiments were performed to assess the effect of adding nanoparticles, i.e. carbon black (CB) and multiwall carbon nanotubes (MWCNTs), on the optical properties, viscosity, thermal conductivity, steam absorption and photo-thermal conversion of aqueous LiBr solutions. Contrary to previously reported, the steam absorption rate was not enhanced by adding nanoparticles to the aqueous LiBr solution, which revealed that grazing and Brownian motion have negligible effects on the mass transfer. A negligible nanoparticle effect on the effective thermal conductivity was also observed. However, a low nanoparticle concentration of 0.005 wt.% decreased the aqueous LiBr solution transparency to 0%, which significantly increased the photo-thermal conversion of the samples. Contrary to CB, MWCNTs increase the viscosity significantly. Therefore, seeding cheap commercial CB in aqueous LiBr solution has the potential to contribute into the development of solar-driven refrigeration technology.