In order to integrate phase change materials with building envelope materials and make their application into practical stage, the commonly used methods are impregnation, direct addition and encapsulation.
(1) Impregnation method: This method is to immerse porous building materials in molten phase change materials and use capillary action to adsorb phase change materials. The advantages of this method are simple process, easy material acquisition, and the preparation of phase change building materials from ordinary building materials at any time, anywhere and as needed. Because the main material can be about the surface tension of liquid phase change material, the phase change material will not flow. In addition, gypsum board can be compatible with a variety of phase change materials, such as methyl ester, short chain fatty acid, SUNIC acid and lauric acid mixture.
(2) Direct addition method: This method refers to the direct addition of phase change materials as a component in the preparation of building materials. The advantages of direct addition are simple process, low cost and uniform distribution of phase change materials. Feldman et al. mixed 21% - 22% butyl stearic acid into gypsum to prepare phase change gypsum board and applied it to indoor ceiling. The experimental results show that phase change gypsum board can greatly reduce indoor temperature fluctuation.
(3) Packaging method: In order to prevent the side effects of phase change materials such as erosion of building materials, phase change materials can be packaged and then compounded with the matrix of building materials. Macro package and micro package are two main methods. Macroscopic packaging is to encapsulate phase change materials in containers such as pipes, bags, boards, etc. Microencapsulation is to encapsulate phase change materials (PCMs) particles in polymer films, and the materials are compatible with each other. The advantage of this method is that the heat transfer area of the material is large, so the heat transfer effect is good, but the strength of the envelope structure may be reduced.
Another kind of composite material prepared by encapsulation is the shape-stabilized phase change material, which has attracted much attention in recent years. It is composed of phase change material (core material) and polymer material and encapsulation material (capsule material). Polymer materials have high melting point, and play a supporting role in the composite materials to form a spatial network structure, which is encapsulated by capsules. The whole composite material has a certain strength and is not easy to leak. Its stored energy can be comparable to that of ordinary phase change materials. Numerical simulation of heat transfer in phase change materials
At present, ANSYS is the main software for phase transformation analysis. The software is developed by a famous finite element company in the United States. It is a large general finite element software with functions of structure, fluid, electric field, magnetic field, sound field and thermal analysis. Phase transition is accompanied by latent heat absorption and release, so it is a non-linear transient thermal analysis problem. One of the most important functions of ANSYS is to analyze phase transition. ANSYS considers latent heat of materials by defining enthalpy (product of density and specific heat and integration of temperature) and simplifies the calculation process.
Sun Xiao and others used Ansys'powerful non-linear analysis function to simulate the temperature change process of the composite phase change wall made of paraffin and gypsum, pointing out that the ribbed structure is helpful for the latent heat storage of phase change materials. Chai Guorong builds a mathematical model based on ANSYS software, calculates and analyses the heat transfer characteristics and energy saving effect of phase change walls composed of concrete with different thickness and phase change materials with different thickness. The calculation results show that, compared with two different thickness concrete walls, increasing the shape-stabilized phase change material has a good energy-saving effect; the optimal thickness of the shape-stabilized phase change material needs to be determined from all aspects; with the increase of the thickness of the shape-stabilized phase change material, the fluctuation amplitude of the wall surface temperature decreases approximately linearly. Conclusion
The theoretical research of phase change materials has become more and more mature, but the types of phase change materials suitable for various engineering fields are still limited. How to develop phase change materials suitable for different occasions, with high latent heat, small expansion and shrinkage, non-toxic, non-corrosive, non-degradable, non-odor, and low cost to meet commercial production is still the direction of future efforts. In addition, the preparation of phase change materials still remains in the traditional methods and processes. The encapsulation technology such as microcapsules is a promising method recently proposed by scholars. How to better integrate phase change materials into matrix materials is still the focus and difficulty of research.
With the rapid development of computer technology, more and more scholars use computer to simulate phase change problems, and the correctness of simulation results has been well verified, which brings more convenient means for phase change materials research besides experimental methods. So how to build a more accurate mathematical model, open up the angle of analysis and find the general law will be a good research direction for future generations. In addition, there are very few software for phase change analysis, so it is very important to develop software programs with better performance.
TRUNNANO (Luoyang Trunnano Tech Co., Ltd ) is a professional new nano material manufacturer with over 12 years experience in chemical products research and development. If you are looking for high quality new nano material, please feel free to contact us and send an inquiry.
