Characterization of Thermophysical Properties of Phase Change Materials Using Unconventional Experimental Technologies

Abstract

The growing interest in developing applications for the storage of thermal energy (TES) is highly linked to the knowledge of the properties of the materials that will be used for that purpose. Likewise, the validity of representing processes through numerical simulations will depend on the accuracy of the thermal properties of the materials. The most relevant properties in the characterization of phase change materials (PCM) are the phase change enthalpy, thermal conductivity, heat capacity and density. Differential scanning calorimetry (DSC) is the most widely used technique for determining thermophysical properties. However, several unconventional methods have been proposed in the literature, mainly due to overcome the limitations of DSC, namely, the small sample required which is unsuitable for studying inhomogeneous materials. This paper presents the characterization of two commercial paraffins commonly used in TES applications, using methods such as T-history and T-melting, which were selected due to their simplicity, high reproducibility, and low cost of implementation. In order to evaluate the reliability of the methods, values calculated with the proposed alternative methods are compared with the results obtained by DSC measurements and with the manufacturer’s technical datasheet. Results obtained show that these non-conventional techniques can be used for the accurate estimation of selected thermal properties. A detailed discussion of the advantage and disadvantage of each method is given.

Thermal Characterization of Medium-Temperature Phase Change Materials (PCMs) for Thermal Energy Storage Using the T-History Method

“…In their research, Martínez et al [ 29 ] give a value of 5.36 kJ/kgK for the solid state, which is even higher than the values obtained in this study and by the manufacturer. The value of the latent heat obtained in this work amounts to approximately 177 kJ/kgK for the heating and 178 kJ/kgK for the cooling process ( Figure 19 b), in good agreement with both Martínez et al [ 29 ] and the manufacturer’s data [ 33 ], specified as 168.30 ± 3.29 kJ/kgK and 170 kJ/kgK, respectively. However the results of latent heat obtained by He et al [ 30 ] in the DSC measurement are higher (226.2 kJ/kg for heating and 223.3 kJ/kg for cooling).…”

“…In the experimental tests of RT55 (see Figure 18 ), the value of the specific heat for the liquid at 58 °C was approximately 2.06–2.12 kJ/kgK (see Figure 19 a) and is similar to the value given by Martínez et al—2.43 kJ/kgK [ 29 ], and comparable to the manufacturer’s value of 2 kJ/kgK. On the other hand, the value of specific heat for the solid form at 48 °C is approx.…”

“…4.24–4.54 kJ/kgK ( Figure 19 a) which is higher than manufacturer’s value of 2 kJ/kgK. In their research, Martínez et al [ 29 ] give a value of 5.36 kJ/kgK for the solid state, which is even higher than the values obtained in this study and by the manufacturer. The value of the latent heat obtained in this work amounts to approximately 177 kJ/kgK for the heating and 178 kJ/kgK for the cooling process ( Figure 19 b), in good agreement with both Martínez et al [ 29 ] and the manufacturer’s data [ 33 ], specified as 168.30 ± 3.29 kJ/kgK and 170 kJ/kgK, respectively.…”

“…Moreover, Figure 22 shows the enthalpy curves, while Figure 23 presents distributions of energy stored. These results are also compared with the published results of other researchers (Martinez et al [ 29 ] and He et al [ 30 ]) and with the manufacturer’s data [ 30 ].…”

“…Published T-history method results are collected in Table 2 for the following selection of middle-temperature PCMs: C58 [ 19 ], OM55 [ 21 ], Na 2 S 2 O 3 ·5H 2 O [ 24 ], mixture of 37.5 wt% NH 4 NO 3 and 62.5 wt% of Mg(NO 3 ) 2 ·6H 2 O [ 24 ], myristic acid [ 24 ], lauric acid [ 24 , 25 ], mixture 58.7 wt% Mg(NO 3 ) 2 ·6H 2 O + 41.3 wt% MgCl 2 ·6H 2 O [ 24 ], Mg(NO 3 ) 2 ·6H 2 O [ 24 ], sodium acetate hydrate CH 3 COONa·H 2 O [ 25 ] and trihydrate CH 3 COONa·3H 2 O (SAT) [ 20 , 24 , 26 ], Greek market paraffin [ 27 ], GR41 [ 28 ], RT45 [ 29 ], RT55 [ 29 , 30 ], RT58 [ 31 , 32 ], bischofite [ 32 ], D-mannitol [ 32 ] and hydroquinone [ 32 ].…”