2.1.1. Two-step method

The two-step method is widely used in producing nanofluid synthesis considering the limitations of nanoparticle supplies commercially by some companies. In this means, nanoparticles are first created and then dispersed in the base fluids. Ultrasonic vibration is used to reduce the agglomeration of particles intensively. Making nanofluids utilizing the two-step processes is challenging because individual particles tend to quickly agglomerate. This agglomeration is due to attractive van der Waals forces between nanoparticles, and the agglomeration is a critical issue in all nanopowder technology, including nanofluid technology, and a crucial step to success in achieving high-performance heat transfer nanofluids [9]. The methods to prevent the agglomeration of particles, usually using a surfactant that regulates acidity (pH) of the base fluids.
