Green synthesis of copper ferrite-based nanofluids using Chlorella vulgaris for heat transfer enhancement

• Copper ferrite nanoparticles were synthesized using Chlorella vulgaris. • Green synthesis proved to be an eco-friendly alternative to conventional methods. • Enhanced thermal conductivity was observed with higher nanoparticle concentrations. This study investigates the green synthesis of copper ferrite nanoparticles (CuFe 2 O 4 NPs) using an aqueous extract of Chlorella vulgaris as a reducing agent and their application in enhancing heat transfer through nanofluids. The successful formation of CuFe 2 O 4 NPs was confirmed through UV–vis spectroscopy, revealing a progressive blue shift in absorption peaks from 380 nm to 350 nm over 4 h, accompanied by a reduction in band gap energy from 2 eV to 1.83 eV, indicating increased particle size and crystallinity. Scanning electron microscopy demonstrated relatively uniform morphology with an average particle size of 130 nm. The EDS analysis revealed strong Cu, Fe, and O peaks, consistent with the expected spinel ferrite composition. Water-based nanofluids containing 0.1 wt%, 0.5 wt%, and 1 wt% CuFe 2 O 4 NPs were prepared and characterized. The 1 wt% nanofluid showed a 4.8 % improvement in thermal conductivity compared to water, while viscosity remained within a manageable range (∼1.1 mPa·s), ensuring low pumping power requirements. In heat transfer experiments using a serpentine heat exchanger, the CuFe 2 O 4 1 wt% nanofluids achieved a significant increase in heat absorption capacity, increasing the outlet temperature by at least 0.5 °C at all volumetric flow rates tested and with a significant improvement in heat storage capacity at the highest flow rate. These results highlight the efficacy of green-synthesized CuFe 2 O 4 -based nanofluids in significantly improving heat transfer performance while maintaining practical fluid properties, making them ideal for sustainable and efficient thermal management applications, and suitable for monophasic and biphasic applications.