AN669 – Melting and Crystallization of Phase Change Materials (PCM) by MicroDSC

EINFÜHRUNG

Ein Phase Change Material (PCM) ist ein Stoff mit einer hohen Schmelzwärme und Erstarrungstemperatur, der in der Lage ist, große Energiemengen zu speichern und freizusetzen (siehe Abb. 1). Neben anderen energiesparenden Anwendungen werden PCM verwendet, um effizientere Isolationssysteme zu entwickeln. Tatsächlich können diese Substanzen in Materialien wie Ziegeln oder anderen Wand-, Boden-, Dach- und Deckenmaterialien eingekapselt werden. Durch sukzessives Schmelzen und Kristallisieren können sie zur Temperatursenkung eingesetzt werden.

AN-669

Fatty acids, paraffins, organic substances, or inorganic salts can be employed if they have high enough latent heat and temperatures of phase change adapted to the application. Moreover, the sensible heat, or the heat capacity change over the temperature range of the considered phase change can play animportant role. Of course, those relevant thermal properties have to be known precisely and with a high accuracy. The MicroDSC technique with the capacity of applying very low scanning rates for a better simulation of the process is very well indicated for such a study.

AN-669

AN-669b

EXPERIMENTAL

Sample is a homogeneous blend of polyolefins under the shape of soft beads. It weights 90.39mg of corresponding to about 10 beads. It is heated from -20°C to 50°C followed by cooling from 50°C to -20°C at 1°C.min-1 and 0.04 °C.min-1

RESULTS

HeatFlow = f(Temperature) and derived enthalpy variation curves are showed on Figures 4 and 5. Latent heat, onset, offset and peak maximum temperatures are indicated in Table 2. Temperatures at which 90% of the product is crystallized (T90) during cooling operations is also indicated in Table 2. μDSC3 Evo 3D sensor allows handling large samples, with odd shapes. It can scan temperatures at extremely low rates, that are representative of real conditions of use of PCMs and approach thermodynamically stable conditions necessary for the determination of the heat stored at any temperature [2].

AN-669C

[1] O’Conner, J. und Weber, R., “Thermal Management of Electronic Packages Using Solid-to-Liquid Phase Change Materials”, ISPS Proceedings, pp. 72 – 80, 1997.
[2] H. Mehling, H.-P. Ebert, P. Schossig, 7. IIR-Konferenz über Phasenwechselmaterialien und Aufschlämmungen für Kälte- und Klimaanlagen