**2. Pre-design: important factors**

Since non-pure substances have lower costs than pure materials, they are used in commercial PCM. The characterization of the PCM and its encapsulation material are required to choose the optimal PCM and to design the heat exchanger for each application. The thermophysical properties of the PCM as a function of temperature are essential to the numerical model. Such information is not available for commercial PCM. This section therefore aims at the development of an adequate methodology to characterize PCM. Subsequently, the design of an experimental setup is explained, directed towards the determination of the enthalpy vs. temperature curves, by using the T-history method. The setup was built and a methodology was proposed to verify the T-history setups. The same methodology is applied to determine thermal conductivity, another essential thermal

scarce literature on the melt fraction studies of PCM used in the various applications for storage systems. Many of these applications have been studied widely in the last years; most are related to buildings and several to heat exchange between PCM and air as the heat

 Ceiling cooling systems and floor heating systems including a PCM storage device were studied by authors like Turnpenny et al., 2001, and Yanbing & Yinping, 2003. Free-cooling has demonstrated to be an attractive application for latent heat storage using PCM. This application is reported in the work carried out by Butala & Stritih,

Solar air heating systems are important in many industrial and agricultural

 Other interesting possibilities are temperature maintenance/control in rooms with computers or electrical devices, and the pre-cooling of inlet air in a gas turbine

In any case, it is crucial to achieve efficient heat exchange between the heat transfer fluid and the PCM. This point is strongly affected by the heat exchanger geometry, as the TES unit has limited periods of time to solidify. Lazaro, 2009, compared the PCM-air heat exchange geometries studied by different researchers (Arkar et al., 2007; Turnpenny et al., 2000; Zalba et al., 2004; Zukowsky 2007). The author pointed out the difficulty of comparing between the different results provided by the authors, since each one show the results in its own way. Therefore, Lazaro concluded the need to standardize for proper comparison. Lazaro et al., 2009b, also presented experimental results for melting stage of real PCM-air heat exchangers pointing out the importance of the geometry. Geometry issues also affect the pressure drop of the TES unit and the air pumping requirements of the system, i.e., the electrical energy consumption. Regarding experimental studies, the evaluation of the thermal behaviour of the TES unit under statistical approaches or mathematical fitting leads to expressions that are very useful tools when designing such units. Among others, Butala & Stritih, 2009, and Lazaro et al., 2009b, followed this methodology when they evaluated their

In this chapter, a specific case study on slab geometry of a PCM-air heat exchanger is presented for temperature maintenance in rooms. However, the methodology posed here

Since non-pure substances have lower costs than pure materials, they are used in commercial PCM. The characterization of the PCM and its encapsulation material are required to choose the optimal PCM and to design the heat exchanger for each application. The thermophysical properties of the PCM as a function of temperature are essential to the numerical model. Such information is not available for commercial PCM. This section therefore aims at the development of an adequate methodology to characterize PCM. Subsequently, the design of an experimental setup is explained, directed towards the determination of the enthalpy vs. temperature curves, by using the T-history method. The setup was built and a methodology was proposed to verify the T-history setups. The same methodology is applied to determine thermal conductivity, another essential thermal

can be extrapolated to other different PCM geometries and system setups.

applications, such as those reported in the papers by Kürklü, 1998.

transfer fluid:

results.

2009, and Lazaro et al., 2009a.

**2. Pre-design: important factors** 

(Bakenhus, 2000).

property regarding heat transfer. As a result of the application of the existing methods to analyze the liquid and solid phases, the most suitable method is chosen and the setup was started up. Besides the energy storage capacity and the thermal conductivity as a function of temperature, other properties are also important to be known, such as the compatibility of the PCM with the encapsulation material.
