Paraffin wax–water nanoemulsion: A superior thermal energy storage medium providing higher rate of thermal energy storage per unit heat exchanger volume than water and paraffin wax

TES Nanoemulsions: A Review of Thermophysical Properties and Their Impact on System Design

“…However, for emulsions with low concentrations ranging between 10 and 30%, this relationship was linear, which was most likely due to reduced interactions between nanodroplets. For a 33 wt% paraffin wax-water emulsion, Sivapalan [138] reported a 7-to 9-times-higher viscosity than that of water in the temperature range of 25-60 • C. The trends reported in different studies are similar, but their increases may be quite different, which can be attributed to possible differences in the nanoemulsions' structure. Very few nanoemulsions have been reported to have atypical behavior due to increases in the particle concentration [57], exhibiting a maximum at a specific water particle concentration in water/polyalphaolefine (PAO) nanoemulsions, attributed to the nonlinear inner structure changes, revealed by small-angle neutron-scattering curves.…”

“…Larger increases of up to six times with respect to the base fluid were reported in other studies [102] for water in an n-decane nanoemulsion stabilized by sorbitane monolurate, with a good fit shown between the experimental data and the Maxwell equation only when the thermal conductivity of the emulgator was accounted for. Sivapalan [138] reported a continuous decrease in the thermal conductivity of up to 37% with an increase in the paraffin wax concentration in water of up to 50 wt%, even though an increase in the heat capacity was registered. Cabaleiro [30] also reported a decrease in the thermal conductivity of PCME for a paraffin-in-EG+water (RT21HC/EG+W) nanoemulsion and found a good compatibility with the Maxwell model for low volume fraction values, when the droplets were in a solid state.…”

“…It is clear that the Maxwell equation can be used when nanodroplets are not prone to strong deformations, particle-fluid interactions, Brownian motion, and other possible effects, which depend on the diameter, concentration, temperature of dispersed phase droplets. However, when the nanoparticle concentration is increased beyond a certain Sivapalan [138] reported a continuous decrease in the thermal conductivity of up to 37% with an increase in the paraffin wax concentration in water of up to 50 wt%, even though an increase in the heat capacity was registered. Cabaleiro [30] also reported a decrease in the thermal conductivity of PCME for a paraffin-in-EG+water (RT21HC/EG+W) nanoemulsion and found a good compatibility with the Maxwell model for low volume fraction values, when the droplets were in a solid state.…”

“…This trend is favorable for heat transfer PCM applications since it leads to a lower pumping power in a fluid with enhanced thermal properties. In nanoemulsions, the variation in viscosity with temperature has been investigated by a number of authors [57,58,138]. The decrease in viscosity with the increase in temperature was found to become more accentuated the higher the concentration of nanodroplets was, probably due to the extra energy provided increasing the Brownian motion and thus resulting in a reduction in viscosity [131,138,139,147].…”

Exploring the Properties of User-defined Phase Change Materials for Thermal Energy Storage

“…Sivapalan et al [7] perform an experimental investigation on paraffin wax-water nanoemulsions for use as thermal energy storage media. They selected paraffin wax with a melting point of 58-60°C and used it to create 10 wt%, 20 wt%, 33 wt% and 50 wt% concentrations.…”