Stability and photo-thermal conversion performance of binary nanofluids for solar absorption refrigeration systems

The photo-thermal conversion characteristics of a long-term stable binary nanofluid (i.e., nanoparticles in 50 wt% lithium bromide-50 wt% water) were investigated in this work. The stability of the binary nanofluid against the agglomeration and sedimentation process was evaluated by a high-speed centrifuge analyzer and transmission electron microscopy. The photo-thermal conversion efficiency of the nanofluid was also studied using a solar simulator. Experimental results indicated that the use of binary nanofluid could significantly increase the light trapping efficiency and, therefore, the bulk temperature, which in turn could increase the evaporation rate due to surface localized heat generation. The experimental results showed the increase of 4.2 and 4.9% solar radiative energy in the form of sensible heat after the addition of 64 and 321 mg/L iron oxide NPs to the pure water, respectively. The enhancement percent was 4.9% and 11.9% for latent heat efficiency in the presence of 64 and 321 mg/L iron oxide NPs, respectively. Possessing both high stability and excellent photo-thermal conversion rate, rod shape iron oxide nanoparticle is suggested to be a potential candidate used for the solar absorption refrigeration systems.