Assessment on Thermal Storage Performance of Capsule-Type Composite Phase-Change Materials

To address the intermittent challenges of new energy and waste heat recovery as well as counteract the issues of corrosion and overcooling in phase-change materials,this study develops and investigates a medium-temperature phase-change capsule(PCC) through experiments and numerical simulations.The thermal cycle stability testing of the developed PCC,subjected to 150 cycles to evaluate its performance,demonstrated that the capsule's surface remained intact with no signs of leakage.The enthalpy-porosity method combined with the volume-of-fluid method was used to establish a numerical model to simulate the phase-change process in capsules with two structures:one with a central cavity and the other with a top cavity.Results indicated that when using 304 stainless steel as the wall material for both structures,the PCC with the centrally located cavity melted28.3% faster than that with the cavity at the top.When using different materials as wall coverings,the melting rate of the PCC made of polytetrafluoroethylene(PTFE) was 22.1% slower than that of the capsule made of 304stainless steel.Conversely,the modified PTFE PCC melted 15.2% faster than the stainless steel-based PCC.Furthermore,when using PCCs having different diameters,the time differences for complete melting between the PTFE and stainless steel-based PCCs were 118 s and 66 s for the capsules having diameters of 24 mm and 16 mm,respectively,indicating that the time difference decreased with decreasing capsule diameter.