New Methodology Developed for DSC for the Analysis of Phase Change Materials - METTLER TOLEDO

New Methodology Developed for DSC for the Analysis of Phase Change Materials

The level of thermal comfort nowadays needed in buildings has led to an increase in energy consumption in the residential and service sectors. Thermal energy storage (TES) is an important alternative for reducing high energy consumption. Phase change materials (PCMs) have been studied as suitable materials for storing thermal energy due to their high heat storage capacity.

 

Introduction

The authors of this article have developed and tested a phase change material (PCM) incorporated in a polymer matrix. Unexpected difficulties however arose in the measurement of the thermal properties of this material using differential scanning calorimetry (DSC). The thermal effects of the polymer matrix and the PCM overlapped.

A new method was therefore developed to overcome this problem. This consisted of using a reference crucible containing the polymer matrix as a blank instead of the usual empty crucible. This enabled a clear signal of the PCM to be obtained.

 

PCM

Phase change materials (PCMs) are ideal for storing thermal energy due to their large heat storage capacity at the phase change: The thermal energy is released again below the temperature of the phase change.

Paraffin materials can be used as PCMs to climatize rooms due to their heat storage capacity of about 130 kJ/kg and their melting temperature of 15 to 30 °C [1]. In most countries, this temperature range is accepted as being optimal for thermal comfort in buildings.

Consequently, PCMs based on paraffin materials are integrated as composite materials in thermal insulation systems. These materials increase the thermal inertia of the building envelope and combined with insulation material reduce energy consumption and temperature fluctuations [2].

The thermal behavior of composite materials normally used in building envelopes is difficult to characterize due to the large dimensions and heterogeneity of the materials. For this reason, thermal analysis of PCMs is necessary at an early stage of the design of building because it is a key point for the thermal characterization of the building envelope.

 

DSC

Differential thermal analysis (DSC) is one of the most powerful techniques [3] for measuring thermal properties such as the specific heat capacity (cp), and the enthalpy and temperature of phase transitions. This has been discussed by Castellón et al. [4]. The main limitations of the technique when used for this particular application are the sample requirements, namely small size, purity, and homogeneity [5]...



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Results and Conclusions

Composite materials were first analyzed by DSC in the conventional way using an empty crucible as the reference sample. The initial results showed rather poorly defined DSC curves (Figure 1).

In addition, the measured thermal properties of the PCMs did not correspond to the expected values. This was attributed to the overlap of contributions of the matrix and PCM in the DSC curve response signal. To eliminate the overlap due to the matrix signal, two different blank reference samples were used; one was the pure polymer matrix, the second the polymer matrix and the EAFD filler.

The first important result of this study is that DSC curves were improved through the use of the new blank samples. Thanks to the new methodology, the peaks were better defined and the PCM peak was separated from the matrix signal.

Another important conclusion is that the overlap of the signals is due to the polymer matrix because there was no significant difference in the result when the polymer matrix or the polymer matrix with EAFD was used as the reference.

To sum up, a new experimental methodology for analyzing composite materials containing PCM by DSC has been developed and tested. Improvements in the signal and hence accurate curve evaluation have been achieved.

This is a very important point because the method allows signals to be differentiated when composite materials are used. This methodology is strongly recommended for applications in which the matrix signal has to be separated from signals of other components.



New Methodology Developed for DSC for the Analysis of Phase Change Materials | Thermal Analysis Application No. UC374 | Application published in METTLER TOLEDO Thermal Analysis UserCom 37