**5.2 Microencapsulation**

Encapsulation is a tiny particle has the particle size <1 mm where in PCM as a core material which is surrounded by inorganic shell such as Titanium, Silica etc. Polymers such as a Melamine – formaldehyde (MF), Urea Formaldehyde (UF), Poly-styrene (PS), Polyurethane (PU), Methyl methacrylate (MMA) etc. Microencapsulation of phase change materials can be prepared in two methods one is physical method and chemical method (**Figure 6**) [32].

**Figure 6.**

*Methods for preparation of microencapsulation of PCM.*

**Figure 7.**

*Improvement of effective thermal conductivity of PCMS for energy storage. \*SW: Sugar WAX, PW: Paraffin wax, PA: Palmitic acid.*

This technique controls the volume change during solid to liquid, resists interaction with environment and enhances the heat transfer area [33]. The inorganic shells can improve the effective thermal conductivity of organic PCMs. Effective thermal conductivity is plays vital role in energy storage unit [34].

Addition of 2–4% of high thermal conductivity material to the PCM can be enhance its thermal properties [35] as shown in **Figure 7**. It will be helpful better performance of energy storage unit.

#### **6. Durability of phase change materials**

Accelerated thermal cycle test is essentially required for before applying in solar water heater and solar air conditioner. Thermal cycle test is referring to heating from ambient temperature to melting point of phase transition until completely becomes liquid and cools down to below melting point until becomes the solid. The total heating period and cooling period is called accelerated test. It works once in a day and reflects life of the phase change materials (**Figure 8**). Silakhori et al. [36] conducted accelerated test for paraffin wax and determined melting point and

*Phase Change Materials for Renewable Energy Storage Applications DOI: http://dx.doi.org/10.5772/intechopen.98914*

**Figure 8.** *Performance of accelerated thermal cycle test.*

latent heat of fusion after 1000 cycles. 1.6–7% of melting point of paraffin wax was observed. Alkan et al. [37] conducted thermal cycle test of microencapsulated docosane for thermal stability with polymethyl methacrylate (PMMA). There is no significant changes occurred in key parameters 5000 cycles. Ahmet Sari et al. [38] performed the accelerated thermal cycling test for microencapsulated n-octacosane for 5000 cycles. There is no change observed in chemical structures of microcapsules. Sude Ma et al. [39] carried out conducted the thermal cycling test of paraffin wax with PMMA up to1000 cycles. No change in observed in thermal stability of microcapsules.

Yang et al. [40] performed accelerated test of different fatty acids such as lauric acid, myristic acid, palmitic acid and stearic acid for 10,000 thermal cycles. Thermal properties of fatty acids have not changed significantly after repeated cycles Sheili et al. [22] performed thermal cycle test of eutectic mixture of capric and lauric acid. no substantial changes in eutectic mixture after 360 cycles. Chinnasamy V and Appukuttan S [41] determined thermal properties of eutectic mixture of lauric acid /myristyl alcohol after 1000 cycles. It was determined that, there was no changes observed in thermal properties. Zuo et al. [42] found that eutectic mixture of lauric acid/1-tetradeconal were stable thermal properties were stable up to 90 thermal cycle tests. Zhang et al. [43] prepared ternary fatty acid mixture of PCMs with lauric acid, Mysteric acid, and palmitic acid. Melting point and heat of fusion were stable up to 50 cycles.
