Pickering anhydrous emulsions as heat transfer fluids with cold energy storage characteristics for refrigeration and freezing

Abstract

The study presents a new class of Phase Change Emulsions (PCE) formulated with polyethylene glycol 400 as the disperse phase, D‑limonene as the continuous phase, and hydrophobic fumed silica nanoparticles (Aerosil® R805) as Pickering stabilisers. Model emulsions containing ∼10 wt.% Phase Change Material (PCM) were characterised through calorimetry, thermogravimetry, thermal conductivity measurements, rheology, laser diffraction, and optical microscopy to evaluate their energy‑storage capacity, thermal stability, microstructure, and flow behaviour. The emulsions exhibited homogeneous droplet dispersions and stable sub‑zero phase‑change transitions, with a minimum nanoparticle content of ∼0.05 wt.% required to prevent crystallisation‑induced coalescence. Increasing silica concentration reduced droplet size and enhanced interfacial stabilisation but also promoted viscosity growth and shear‑thinning behaviour. Compared with commercial secondary refrigerants, the PCEs offered a markedly broader operational window (−85 °C to +20 °C) and up to 2.4‑fold higher cumulative volumetric enthalpy change. Forced‑convection analysis further showed that lightly stabilised formulations achieve favourable heat‑transfer effectiveness and pumping‑power balance, positioning these emulsions as promising candidates for ultra‑low‑temperature refrigeration and thermal‑buffering applications.