关键词: 十五烷, 相变材料, 微胶囊, 原位聚合法, 潜热型功能流体, 相变焓

Abstract:

To prevent the leakage of materials during the phase-change process, low-temperature phase-change microcapsules with pentadecane (Pen) as the core material and urea-formaldehyde resin (UF) as the wall material were prepared using insitu polymerization. The effect of heating rate, polymerization pH, and polymerization speed on the microcapsules preparation was studied. The morphology, chemical composition, thermodynamic properties, and the particle-size distribution of microcapsules were tested using SEM, FT-IR, DSC, and Malvern laser particle-size analyzer. A heating rate of 1.0 ℃/min, polymerization pH value of 3.5, and polymerization speed of 500 r/min are the optimal preparation conditions for pentadecane microcapsules. The microcapsules prepared under the above conditions have spherical morphology, smooth surface, a few UF particle adherence, and the particle-size distribution is uniform. The phase-change temperature and latent heat of the microcapsules are 8.20 ℃ and 115.3 J/g, respectively. The average particle size of the microcapsules is 50.0 μm, and the encapsulation rate reaches 77.3%. The experimental results show that the core and wall materials are held by physical forces. The microcapsules have good heat storage performance and thermal stability. Pentadecane microcapsules are dispersed with different mass fractions of ethanol solution as the base solution. A stable latent-heat functional fluid (LHFF) is obtained using a static experiment for 24 h. The LHFF is the most stable in the base solution with 70 wt% ethanol. The thermal conductivity and viscosity of the LHFF are tested and analyzed using a thermal conductivity tester and rotational viscometer. The thermal conductivity of the LHFF increases with an increase in temperature and decreases with an increase in the mass fraction of microcapsules. The viscosity of the LHFF decreases with an increase in temperature and increases with an increase in the mass fraction of microcapsules. As the secondary refrigerant of the air conditioning system, LHFF can improve the performance of the refrigeration unit, reduce the energy consumption of the pump, and improve the economy of cold storage of the air conditioning system.

Key words: pentadecane, phase change materials, microcapsules, in situ polymerization, latent heat functional fluids, phase change enthalpy