Preparation And Performance Of Nanoencapsulated Phase Change Materials As Cool Storage Media

Due to the rising cost of fossil fuels and environmental concerns, more and moreattention has been paid to energy conservation lately. Thermal energy storage (TES) usingphase change materials (PCM) can solve the problem in time and spatial mismatch betweenthe energy supply and the consumption of energy, and play an important role in increasingefficiency of energy utilization. Latent functionally thermal fluid (LFTF), which encapsulatedphase change material dispersed in heat transfer fluid, is a solid-liquid two-phase fluid.Because the latent heat released from phase change materials can enlarge heat capacity offluid, and the existence of micro-convection around the PCM capsules can enhance heattransfer efficiency, therefore, the LFTF is novel multifunctional fluid which can combine thethermal storage and the thermal transmission in one.In this paper, the nanoencapsulated phase change materials (NEPCMs) with polystyrene(PS) as shell and n-tetradecane (Tet) as core were synthesized by ultrasonic technique andminiemulsion in-situ polymerization. The influence of polymerization factors such asultrasound power and time, hydrophilic co-monomer, emulsifier, co-emulsifier, initiator, chaintransfer agent, and the ratio of n-tetradcane and styrene on the morphology, particle size andthermal property of nanocapsules were systematically investigated. The samples werecharacterized by particle size analyzer, transmission electron microscope (TEM), fouriertransform infrared spectroscopy (FTIR), differential scanning calorimeter (DSC) andthermogravimetric analyzer (TG). The results showed that, due to the strong hydrophobicityof polystyrene chain, it isn't easy to separate and encapsulate, while adding hydrophilicco-monomer, it is easy to form steady capsules; the composite surfactants contribute to formuniform and steady nano-latex; the proper amount of chain transfer agent might facilitatephase separation and form regular capsules; using 2,2′-azobisisoheptonitrile (ABVN) as initiator, the capsules with good encapsulation can be obtained, while using potassiumpersulfate (KPS), the solid bead is easy to form; the ratio of Tet and St has a great effect onthe themal property and the strength of polmer shell, which change phase change enthalpy.The optimized experimental conditions were that 50% (rated power is 900w) poweradjusted value of ultrasonic, 10 min ultrasonic time, 5hr reaction time, 1:1 ratio of Tet and St, 2.5% hydrophilic ethyl acrylate (EA) co-monomer, 0.1% dodecanethiol (DDT) chain transferagent, 3% composite surfactants which composed sodium dodecyl sulfate(SDS) andpoly-(ethylene glycol) monooctylphenyl ether(OP-10) by 1:1 in weight ratio and 0.4%2,2′-azobisisoheptonitrile(ABVN). Under this conditions, the average particle size of prepared nanocapsules was 132 nm and the phase change enthalpy was 98.71 kJ?kg-1.The test result forlatex showed that the nanocapsule emulsion (15% mass fration) has low viscosity (8.3cP at25℃), good thermal conductivity(0.8467 W/m·K at 25℃) and excellent specificheat(4.8J/g·℃at 7℃). After more than forty times freezing-melting circulation, the latexhas well thermal property and mechanical stability which is suitable as cool storage media.