50-60 ℃에서 녹는점을 갖는 잠열저장물질 중 무기염 수화물로는 비조화 축열제인 sodium acetate trihydrate(SAT)와 유기물로는 stearic acid(SA)를 1 mm이하의 구형입자로 제조한 후 코팅을 수행하였다. SAT의 상분리 및 과냉각 현상을 방지하기 위하여 gelatin과 sodium pyrophospate decahydrate(Na₄P₂O₇·10H₂O)를 첨가하여 poly methyl methacrylate(PMMA)와 wax로 다중코팅하였고, SA는 PMMA, polyurethane(PU), silicon으로 각각 단일 코팅하였다. 광학현미경, Scanning Electron Microscopy(SEM), Thermogravimetry(TG), Differential Scanning Calorimetry(DSC)로 입자의 구형도, morphology, 코팅층의 두께 및 내열성 그리고 용융-동결 싸이클 진행에 따른 흡열-발열 및 과냉각 정도를 확인하였다. 그 결과 10-20 µm 두께로 균일하게 코팅된 구형의 Phase Change Material(PCM) 입자 SEM분석을 통해서 관찰되었으며 코팅후 SAT의 경우 12회 싸이클 진행에 따른 잠열량은 50-60 cal/g으로 일정하나 과냉각은 10℃ 정도가 되는 것을 확인하였다. 반면 SA입자 코팅층의 내열적 안정성은 PU>PMMA>silicon 순으로 나타났으며 PU코팅의 경우 잠열량은 약 35 cal/g으로 일정하였고 과냉각 없이 용융-동결 반복 후에도 코팅층이 안정된 것으로 확인하였다.

Cores(< 1mm diameter) of organic stearic acid(SA) and inorganic sodium acetate trihydrate(SAT) as phase change material(PCM) with a melting point in the range of 50-60 ℃ were manufactured. Single-layer coating was performed for SA cores with poly urethane(PU), poly methyl methacrylate(PMMA), and silicon, respectively, while tertiary-layer coating was performed for SAT cores with PMMA and Wax. In case of SAT, gelatin as thickener and sodium pyrophosphate decahydrate(Na₄P₂O₇·10H₂O) as nucleator were added to prevent the phase separation and the supercooling respectively. Coated PCMs were analyzed by optical microscopy, scanning electron microscopy(SEM), thermogravimetry(TG), and differential scanning calorimetry(DSC) to investigate their morphology, coating thickness, thermal stability. As a result, we obtained the ball-shaped PCM cores with the uniform coating thickness of 10-20μm, constant latent heat of 50-60 cal/g and 35 cal/g in case of SAT and SA respectively. But 10 ℃ of supercooling was observed for SAT after 12th cycle of thaw-freezing test, while no supercooling was observed for the SA coated with PU. Thermal stability of the coating polymers used in SA decreased in the order of PU, PMMA and silicon.

Phase Change Material Encapsulation Thermal Energy Storage

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