Phase change temperature range

In addition to ice (water), more than 500 natural and synthetic PCMs are known. These materials differ one from another in terms of their phase change temperature range and their heat-storage capacities. 

In contrast, the use of thicker and less-dense textile structures leads to a delayed and therefore more efficient heat release of the PCM. Furthermore, the phase change temperature range and the application temperature range should correspond in order to realize the desired thermal benefits. 

Suitable phase change temperature => to assure storage and extraction of heat in an application with a fixed temperature range. 

Applications of PCM cover many diverse fields. As mentioned before, the most important selection criterion is the phase change temperature. Only an appropriate selection ensures repeated melting and solidification. Connected to the melting and solidification process is the heat flux. The range of heat flux in different applications covers a wide range from several kW for space heating with water or air, domestic hot water and power plants to the order of several W for temperature protection and transport boxes (Figure 124). 

The MD calculations using the Tersoff model are carried out under constant-volimie and -temperature conditions. The melting temperatures predicted by tiie Tersoff model are much hi er tiim tiie real phase-change temperatures. The model is, however, widely applied in tiie recent simulations, because it can reproduce well the structural and dynamical properties of elemental semiconductors such as silicon md cM bon ranging from crystalline to amorphous structures In tiie Tersoff model, tiie potential energy between two neighboring atoms i and j can be expressed as... 

The combined effect of temperature and sorbate is to lower the temperature phase transition temperature and increase its width. In the phase transition temperature range, both phases now coexist with all the material being crystalline. Above the transition temperature, there are only minor changes reflecting lattice expansion due to temperature within the orthorhombic (12 T atom) phase. 

Meanwhile, Chen and co-workers also investigated the effect of PCM content on the thermal properties of the electrospun PCM/polymer fibers [14]. Figure 9.6 showed the DSC curves of LA powder and electrospun LA/PET composite fibers with different LA/PET mass ratios and the corresponding data of thermal properties. Clearly, the latent heats (A//f and Alfc) of the four LA/PET composite fibers were lower than that of LA powder (169.41 J/g and 165.12 J/g, respectively) because PET in the composite fibers has few contribution to the latent heat at this temperature range, and the latent heats of the fibers increased with the increase of LA/PET mass ratio. However, the phase transition temperatures (Tm and Tc) of all the electrospun LA/PET composite fibers have no obvious variations compared with those of LA (less than 1 °C). It indicated that the PCM/polymer mass ratio plays an important role on the latent heat of the form-stable PCM/polymer composite fibers but has less effect on their phase-change temperature. 

By contrast, the hqnid-phase Schmidt unmbers range from about 10" to lO and depeua strongly on the temperature. The effect of temperature on the liquid-phase mass-transfer coefficient is related primarily to changes in the hquid viscosity with temperature, and this derives primarily from the strong dependency of the hqnid-phase Schmidt number upon viscosity. 

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