Improving the sub-cooling and thermophysical profile of isopropyl palmitate for refrigeration applications

• GnP2/IPP nanofluids proposed for refrigeration and cold storage applications. • Enhanced dispersion stability using cetyltrimethylammonium bromide. • Solid-liquid phase transitions comprehensively examined for all dispersions. • 2.7 K sub-cooling reduction and 4.4 % thermal conductivity enhancement at 2 wt% GnP2. • Proposed nano-enhanced isopropyl palmitate improves refrigeration efficiency. Phase change materials have been suggested for use in refrigeration systems or thermal energy storage. However, their low thermal conductivity as well as high sub-cooling hinder the use of these materials in such applications. This study presents the experimental design and characterization on phase change transitions, isobaric heat capacity, density, thermal conductivity, thermal diffusivity, and rheological behaviour of phase change materials based on isopropyl palmitate (IPP) that have been improved with the addition of nanoparticles. Four dispersions of graphene nanoplatelets (GnP2) in IPP were prepared, ranging from 0.25 to 2 wt% and stabilized with cetyltrimethylammonium bromide (CTAB) at a surfactant:nanoparticles mass ratio of 1:1. Similar hydrodynamic sizes of the dispersed nanoadditives for three weeks were confirmed, showing good temporary colloidal stability. A 10% reduction in sub-cooling was observed for the 1 wt% (CTAB:GnP2 1:1)/IPP sample and isobaric heat capacity decreased by up to 10% in the 2 wt% (CTAB:GnP2 1:1)/IPP sample. Enhancements in thermal conductivity of up to 4.4% were evidenced for the 2 wt% (CTAB:GnP2 1:1)/IPP nano-enhanced phase change material. Moreover, increasing temperature caused an exponential drop in shear viscosity, with maximum diminution of 61% for the base IPP. Similar behaviour was observed for (CTAB:GnP2 1:1)/IPP nanofluids at all studied concentrations. The decrease in sub-cooling and improved thermophysical properties reinforce nano-enhanced isopropyl palmitate’s suitability for refrigeration and cold storage.