Abstract
Phase change materials (PCMs) often suffer from leakage, low thermal conductivity, and low latent heat, which impair thermal storage performance. This study addresses these issues through an optimized microencapsulation technique based on ethyl cellulose and a 4 wt% sodium chloride (NaCl) aqueous core, whose freezing point is approximately −2.6 °C, making it suitable for subzero cold chain applications. The encapsulated PCMs were prepared by a two-step W₁/O/W₂ emulsion method. The effects of emulsifier concentration, secondary emulsification speed, and the volume ratio of the primary emulsion (W₁/O) to the external aqueous phase (W₂) on emulsion stability and microcapsule properties were investigated. The preferred conditions among those tested were 2 wt% emulsifier, 300 rpm secondary emulsification speed, and a W₁/O: W₂ volume ratio of 1:3. The resulting microcapsules exhibited a latent heat of 158 J/g, a yield of 81.58%, and an average particle size of about 200 μm. Phase-change microcapsule suspensions were prepared, and their viscosity, thermal conductivity, and stability were examined. The thermal conductivity of the suspensions increased with temperature but decreased with increasing microcapsule concentration, mainly because the ethyl cellulose shell has a lower thermal conductivity than the base fluid. At −3 °C, the 0.2 wt% suspension showed a 9.52% lower thermal conductivity than the base fluid.