Low-cost and high-throughput synthesis of copper nanopowder for nanofluid applications

Copper (Cu) is a low cost and efficient filler for nanofluids. However, commercially available copper nanopowders are as costly as silver. A few methods are available for synthesis of copper nanopowder in the lab, but the amount of powder produced per batch is very small, and it is impractical to produce a large volume of nanofluid using these methods. Solution based high concentration synthesis for production of copper nanopowder using batch reactor has been reported in this work. Cost of production is minimal in this method and nanoparticles are separated from the suspension by a controlled flocculation process. The proposed method relies on the higher solubility of cuprammonium complex in an aqueous medium and its chemical reduction using hydrazine hydrate. The colloid has been stabilised using sodium citrate and obtained as sub 50 nm powder re-dispersible in water and ethylene glycol (EG). Continuous synthesis of this product using a Continuous Stirred Tank Reactor (CSTR) has also been demonstrated. The quality of particles from the CSTR is similar to that of the batch method. Stable nanofluids have been prepared by re- dispersing the nanopowder in water and EG. Moderate enhancement (similar to 5%) in thermal conductivity for Cu-EG nanofluids and small enhancement (similar to 2%) for Cu-water nanofluid have been observed with 0.6 vol% of copper loading.