Performance of a Stable Hybrid TiO ₂ /SiO ₂ Nanocomposite in the Thermophysical Characterization of Organic PCM (Stearic Acid) for Thermal Energy Storage

Hybrid nanomaterials, a combination of particles, bring more synergistic interaction and functionality to conventional fluids such as phase change materials (PCMs). As a result, the thermal energy storage potential of these systems is significantly higher than that of conventional PCMs. However, commercial particles usually suggest nonuniform dispersion under the action of particle−parti`cle agglomeration, sedimentation, and large size clusters. These limitations can be addressed if particles remain of uniform size and agglomeration free after mixing in PCM. This study reports the development of a hybrid TiO 2 −SiO 2 nanocomposite of customized size (20–80 nm) by a single-step sol−gel method followed by their impact on thermal performance of PCM:stearic acid (SA). Six different nano-enhanced PCMs (n-PCM: A1−A6) were developed using mixture ratios of 90:10 and 80:20 (SA:nanocomposite), which were stable colloidal suspensions owing to their zeta potential value of >30 mV. The inclusion of TiO 2 −SiO 2 significantly improved the thermal properties of SA, where increasing particle size was related to enhancement in thermal conductivity (by ∼32%), heat flow (by ∼18%), and charging−discharging performance (by ∼35.3%), but only up to a certain size limit of ∼60–70 nm. Particle sizes greater than 70 nm showed a reverse effect due to the possible tendency of particle−particle associations, resulting in decreased connectivity and disrupted heat conduction pathways for efficient heat transfer. Compared to SA, the maximum melting (63.9 °C) and freezing temperature (55.1 °C) were obtained for the n-PCM sample (A2), consisting of 10 and 20% loading of TiO 2 −SiO 2 with particle sizes of 59 and 66 nm, respectively. In addition, the weight loss and enthalpy retention of n-PCM samples were superior to those of SA. SA showed a weight loss of 1.6 g after 100 cycles, which was only 0.32 g for the A1 sample. Thus, enthalpy retention in sample A1 was 26% higher than that in SA after 100 cycles. Thus, this study shows the potential of hybrid TiO 2 −SiO 2 nanomaterial of customized size in improving the thermal energy storage of conventional PCMs, e.g., stearic acid.