Microencapsulated PCMs

Quite similar to direct discharge storages are slurry types (Figure 141). They differ from direct discharge types only because the heat transfer fluid also contains microencapsulated PCM. The micro encapsulated PCM increases the stored heat per volume of heat transfer fluid, which again has to be a fluid... 

From an energetic point of view, it would be desirable to produce cold at somewhat higher temperatures. Then other PCM with higher melting points in the 5-10 °C range are preferred. Such slurries can be produced using microencapsulated PCM. Figure 142 shows such a slurry produced by BASF. 

Slurries from microencapsulated PCM can of course also be produced for heating applications. 

Modular heat storages use macro encapsulated PCM instead of microencapsulated PCM to increase the storage capacity. During discharge the macro encapsulated PCM however remains in the storage. 

The storage consists of plaster with microencapsulated PCM (Figure 194). To release the heat, capillary sheets are integrated into the plaster and connected to ground water. 

M.N.A. Hawlader, M.S. Uddin, and M.M. Khin, Microencapsulated PCM thermal-energy storage system, Applied Energy, 74(l-2) 195-202, January-February 2003. 

In 2010, Wang s and Fang s teams in China independently showed that PCM with enhanced thermal conductivity and phase-change performance can be successfully fabricated by sol-gel microencapsulation of wax such as n-octadecane and paraffin in silica microspheres obtained from TEOS polycondensation. The thermal conductivity of the microencapsulated n-octadecane is also significantly enhanced due to the presence of the high thermally conductive silica shell. However, the silica microcapsules prepared from TEOS only have poor mechanical properties, with the brittle shell of the microencapsulated PCM easily cracking. 

Wang, X. Niu, J. Heat transfer of microencapsulated PCM slurry flow in a circular tube. AIChEJ 54( ) (2008) 1110-1120. 

Another example of a comfortable garment is made from microencapsulated PCMs, packed into a space between two fabric layers in order to produce a garment with passive, regenerative thermal protection. The garment offers improved comfort due to not only enhanced thermal control but also by enabling the transport of humidity through the PCM layer and away from the body. 

Pause The basic and dynamic thermal insulation of fabrics coated with or without microencapsulated PCM was studied. 26... 

Frisby Inc. Coated fabrics and wet spinning polyaorylio fibre containing microencapsulated PCM came onto the market. 32... 

Bryant and Colvin produced a fibre with integral microcapsules with PCMs or plastic crystals. The fibre has enhanced thermal properties at predetermined temperatures. The microcapsules can range in size from about 1 to about 10 microns. In fabricating the fibre, the desired microencapsulated PCMs are added to the liquid polymer, polymer solution or base material and the fibre is then expended according to conventional methods such as dry or wet spinning of the polymer solutions and extrusion of the polymer melts. According to the report, the maximum content of PCM in the polyacrylic fibre is about 10%. The minimum filament denier is 2.2dtex. ... 

The fibres made through the microencapsulated PCM composition spinning method also have some disadvantages such as a relatively low latent heat value and very complicated operation. In addition, particle size and size distribution of microencapsulated PCMs also affect the spinnability and mechanical properties of thermo-regulating fibres. This method is restrained in large-scale applications. 

There are two different ways to prepare microencapsulated PCM, the physical and the chemical method. Figure 8.4 shows the flowchart of these two different manufacturing techniques of micro-encapsulated PCM. Physical methods result in a relatively large size, and rough surface microcapsules compared to chemical methods [1,12], Among the chemical methods, better structure and smaller shell are obtained by the in-situ polymerization technique. 

Flow chart showing different manufacturing techniques of microencapsulated PCM [1],... 

Maao-encapsulation is the usual way to encapsulate PCM for TES applications. On the other hand, the manufacture of microencapsulated PCM is more complex than the macro-encapsulated PCM because the size is lower than 1 mm. Despite this, microencapsulation has a higher rate of heat... 

Arce P, Cdstellon C, CasteU A, Cabeza LF. Use of microencapsulated PCM in buildings and the effect of adding awnings. Energy Build 2012 44 88-93. 

Li et al. [12] analyzed the thermal characteristics of a three layer wall with microencapsulated PCM polyester fabric by numerical simulations. The simultaneous heat and moisture transfer through a porous building material containing PCM was taken into account by the mathematical model. The study provided an effective way to investigate the thermal properties of porous materials containing PCM, but the simulations were very complicated. The wall consisted of a wooden middle layer to which porous textile material was fixed at the inner and outer side as shown in Figure 11.2. 

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