Dynamic Viscosity, Surface Tension and Wetting Behavior Studies of Paraffin–in–Water Nano–Emulsions

Abstract

This work analyzes the dynamic viscosity, surface tension and wetting behavior of phase change material nano–emulsions (PCMEs) formulated at dispersed phase concentrations of 2, 4 and 10 wt.%. Paraffin–in–water samples were produced using a solvent–assisted route, starting from RT21HC technical grade paraffin with a nominal melting point at ~293–294 K. In order to evaluate the possible effect of paraffinic nucleating agents on those three properties, a nano–emulsion with 3.6% of RT21HC and 0.4% of RT55 (a paraffin wax with melting temperature at ~328 K) was also investigated. Dynamic viscosity strongly rose with increasing dispersed phase concentration, showing a maximum increase of 151% for the sample containing 10 wt.% of paraffin at 278 K. For that same nano–emulsion, a melting temperature of ~292.4 K and a recrystallization temperature of ~283.7 K (which agree with previous calorimetric results of that emulsion) were determined from rheological temperature sweeps. Nano–emulsions exhibited surface tensions considerably lower than those of water. Nevertheless, at some concentrations and temperatures, PCME values are slightly higher than surface tensions obtained for the corresponding water+SDS mixtures used to produce the nano–emulsions. This may be attributed to the fact that a portion of the surfactant is taking part of the interface between dispersed and continuous phase. Finally, although RT21HC–emulsions exhibited contact angles considerably inferior than those of distilled water, PCME sessile droplets did not rapidly spread as it happened for water+SDS with similar surfactant contents or for bulk–RT21HC.

Comparison of Engine Performance between Nano- and Microemulsions of Solketal Droplets Dispersed in Diesel Assisted by Microwave Irradiation

“…The total surface area among various phases of components of the nanoemulsion was thus significantly larger than the other two fuels, resulting in it being the largest kinematic viscosity among the test fuels. The result agreed well with Cabaleiro et al [29]. The nanoemulsion was also found to have the lowest carbon residue (0.26 wt.…”

Special Issue of the 1st International Conference on Nanofluids (ICNf19)

“…This Editorial note was dedicated to the 1st International Conference on Nanofluids and the 2 nd European Symposium of Nanofluids (ICNf2019). After a short report about the conference, the successful invited submissions [7][8][9][10][11][12][13][14][15] to this Special Issue of Energies were introduced. We believe that the articles in this special issue, whose main parts were presented during the conference, will contribute significantly to the development of nanofluid science and challenges in heat transfer and energy applications.…”

“…The first paper, by Cabaleiro et al [7], reports a comprehensive experimental characterization of phase change material (paraffin-in-water) nano-emulsions. The effect of dispersed phase concentrations of 2, 4 and 10 wt.% on the dynamic viscosity, surface tension and wettability of nano-emulsions is investigated, showing the impact of paraffin droplets and surfactant on these properties.…”

Prediction of Contact Angle of Nanofluids by Single-Phase Approaches

“…They used wettability control to propose new methods to predict specific heat and thermal conductivity of molten salts and their nanofluids accurately. Moreover, Cabaleiro et al [22] found that addition of a phase change material into water decreases the CA up to 52%.…”