Thermal- and Phase-Change Characteristics of Self-Assembled Ethanol/Polyalphaolefin Nanoemulsion Fluids

The strategy of adding solid particles to fluids for improving thermal conductivity has been pursued for more than one century. Here, a novel concept of using liquid nanodroplets for enhancing thermal performance has been developed and demonstrated in polyalphaolefin nanoemulsion fluids with dispersed ethanol nanodroplets. The ethanol/polyalphaolefin nanoemulsion fluids are spontaneously generated by self-assembly and are thermodynami- cally stable. Their thermophysical properties, including thermal conductivity and viscosity, and impact on convective heat transfer are investigated experimentally. The thermal conductivity enhancement in these fluids is found to be moderate but increases rapidly with increasing temperature in the measured temperature range of 35-75°C. A very remarkable increase in the convective heat transfer coefficient, by a factor of up to 2.2, occurs in the nanoemulsion fluids due to the explosive vaporization ofthe ethanol nanodroplets at the superheat limit (i.e., spinodal states, about 122°C higher than the atmospheric boiling point for ethanol). Such an explosive liquid-vapor phase transition might augment the fluid heat transfer through the heat of vaporization (which intuitively raises the base fluid specific heat capacity) and the fluid mixing induced by the sound waves. The development of such phase-changeable nanoemulsion fluids would open a new direction for thermal fluids studies.