Preparation of paraffin and fatty acid phase changing nanoemulsions for heat transfer

•Stable paraffin nanofluids (∼50nm particle size) were prepared ultrasonically.•Stearic and myristic acid nanoemulsions were prepared by low energy PIC method .•Ionic and nonionic surfactants together produced best fatty acid fluid stability.•Melting temperatures of stable nanofluids were 3–4°C lower than those of bulk PCMs. In the present work, phase change material (PCM) nanofluids were developed for heat transfer applications. Three PCMs, stearic acid, myristic acid and paraffin, were dispersed in water using two different emulsification methods; high-energy ultrasound processing and low-energy phase inversion composition (PIC). In ultrasound processing desired amounts of reagents are stirred vigorously in the presence of an optimized surfactant, while in the PIC method, spontaneous curvature of surfactants is tuned in regulation of the geometry at the interface of two immiscible phases by controlling the concentration of reagents. In this study, paraffin nanofluids with an average particle size of ∼50nm were produced successfully by ultrasound processing. In addition, fatty acid nanofluids were prepared using the PIC procedure, in which slow water addition and partial neutralization of fatty acids were utilized to achieve the phase inversion. Stable stearic acid nanofluids were successfully prepared with optimized surfactant composition, whereas all myristic acid emulsions tested were unstable. For both of the fatty acid nanofluids, combination of ionic and nonionic surfactant resulted in best stability. Thermal and structural properties of the prepared nanofluids were also characterized.