Methyl myristate PCM nanoemulsions for low-temperature thermal management in laminar flow

• Nanoemulsions with non-paraffinic PCMs tested for low-temperature heat transfer. • Stable droplets with reduced subcooling achieved via optimized formulation. • Thermal energy storage improved by up to 25 % compared to base fluid (4–17 °C). • PCM droplets boost heat transfer up to 70 % due to possible secondary convection. • 6 wt% emulsion offer optimal balance of heat transfer and flow resistance. Nanoemulsified phase change materials are emerging as efficient thermal fluids for enhancing energy storage across diverse applications. This study explores the development and performance of nanoemulsions for laminar flow heat transfer. The slurries were based on an ethylene glycol:water solution (25:75 by weight), into which 2–10 wt% of a tailored organic blend (rich in methyl myristate and containing methyl stearate, n -nonadecane, and cetyl alcohol) was dispersed. A dual-surfactant system (sodium dodecyl sulfate and Brij™ S2) ensured colloidal stability and nanometric droplets (∼140–180 nm). Calorimetric studies revealed transitions starting near 9-10°C (melting) and 8-9°C (crystallization). The 10 wt% dispersion demonstrated up to 25 % greater thermal energy storage than the base fluid over 4–17 °C range. Rheological analyses indicated mostly Newtonian behavior, with slight shear-thinning at low temperatures in the most concentrated sample. Viscosity evaluations based on pressure drop analyses supported these findings. Heat transfer tests in a horizontally heated tube showed that, outside the droplets transition, Nusselt numbers closely followed classical laminar flow predictions. However, near the melting point of dispersed phase, a significant enhancement in heat transfer was observed, attributed to latent heat adsorbed by the nanoemulsified mixture. Additionally, the lower section of the pipe exhibited values up to 70 % above to what expected according to classical equations, likely due to buoyancy-induced secondary flows that may enhance mixing and thermal boundary layer disruption. An overall assessment of thermo-fluidic performance reveals that 6 wt% emulsions achieves the most effective compromise between enhanced heat transfer and manageable flow resistance.