Abstract

Thermal oils are widely used in several industrial applications such as solar thermal power plants and petroleum industry. Nowadays, there is an intensive research worldwide in order to enhance the heat transfer properties of these oils. The use of nanofluids (fluids containing nanoparticles) is an emerging technique for heat transfer intensification. In this context, the fabrication of nanoparticles in thermal oils by chemical methods is a well-established technique. However, less attention have been paid to its fabrication by physical methods. In this contribution we study the fabrication of gold nanoparticles in a thermal oil known as Therminol VP-1 by pulsed laser ablation in liquids. The process involves two stages, the ablation and re-fragmentation. A Ti:Sapphire laser that emits pulses of 30 fs FWHM, with mean wavelength of 800 nm, and repetition rate of 1 kHz, is used as light source. The fluence for both stages was 1 J/cm² . To determine the particle size distribution we applied the non-destructive dynamic light scattering technique at a 173º scattering angle in a Zetasizer NANO ZS analyzer. We showed that the nanoparticles produced just after the ablation reach sizes around 120 nm, whereas for the sample that is re-fragmented the sizes of nanoparticles decreased after the irradiation until 58.8 nm. Commonly, chemical methods achieve nanoparticles of around 100 nm, but they present pollution problems. In contrast, the nanoparticles produced by our method do not have these problems because no stabilizer or redactor is used in the process.