Preparation of a stable nanocomposite phase change material (NCPCM) using sodium stearoyl lactylate (SSL) as the surfactant and evaluation of its stability using image analysis

• A new method was proposed for the preparation of a stable Al2O3-paraffin nanocomposite.
• Sodium stearoyl lactylate was used to stabilize paraffin-nanoAl2O3 composites.
• Image analysis was proposed for evaluating the stability of nanocomposites.

In this study, a new method was proposed for the preparation of a stable Al2O3-paraffin nanocomposite phase change material (NCPCM). Sodium stearoyl lactylate (SSL) was used as the surfactant to improve the dispersion of Al2O3 nanoparticles (2.5, 5, 7.5, and 10 wt.%) in paraffin with a SSL/Al2O3 mass ratio of 1:3.5. After preparation, one group of the samples was placed in an incubator at a temperature of 60 °C for one week to evaluate its stability during the time elapsed. The other was left alternately in two incubators, one at 60 °C and the other at 25 °C over time intervals of 1 h in order to evaluate the stability of the sample after given numbers of melting/freezing cycles. This latter treatment has been seldom ever reported elsewhere. For NCPCM stability evaluation, the samples were broken into two parts equal in volume and the change ratios of surface layer Al3+ concentration are determined. Also, image analysis is used for evaluating the stability of nanofluids. The results obtained from the two methods are found to be in good agreement. Image analysis is, therefore, proposed as a nondestructive method with good accuracy, especially for evaluating the stability of high concentration nanofluids.