Preparation Of Thermal Energy Storage Composite Materials And Study On Dynamic Heat Transfer Characteristics Modeling Of Microencapsulated Phase Change Material Slurries

This article mainly elaborated the preparation and the properties of phase change material composites. The thermal properties, chemical structure and micro structure of the phase change material composites were measured and analyzed. The dynamic heat transfer characteristics of the microencapsulated phase change material slurries are analyzed. A theoretical model and heat transfer equations are set up. The effects of the Ste number, mass fraction, the phase transition temperature interval and the Re numbers on the dimensionless wall temperature and heat transfer coefficient are discussed by numerical analysis.1. Preparation and characterization of thermal energy storage composite materialsThe n-octadecane/molecular sieve5A composites as form-stable thermal storage materials were prepared by adsorbing liquid n-octadecane into the molecular sieve5A. In the composites, the n-octadecane was used as thermal storage material, and the molecular sieve5A acted as the supporting material. Fourier transformation infrared (FT-IR) spectroscope and scanning electronic microscope (SEM) were used to determine the chemical structure and microstructure of the n-octadecane/molecular sieve5A composites. The thermal properties and thermal stability were investigated by a differential scanning calorimeter (DSC) and a thermogravimetry analyzer (TGA). The FT-IR analyses indicated that there is no chemical interaction between the n-octadecane and molecular sieve5A. The SEM results showed that the n-octadecane was well adsorbed into the porous network of the molecular sieve5A and there is no leakage of the n-octadecane from the composites even when it is in the melting state. The DSC results indicated that the n-octadecane/molecular sieve5A composites exhibited the same phase change characteristics as the n-octadecane and their latent heats increased with the increase of the n-octadecane content in composites. The TGA results presented that the molecular sieve5A can improve the thermal stability of the composites as form-stable thermal energy storage materials.Shape-stabilized lauric acid/activated carbon composites as phase change materials were prepared by adsorbing liquid lauric acid into activated carbon. In the composites, the lauric acid was used as a phase change material for thermal energy storage, and the activated carbon was used as an adsorbent that acted as the supporting material. Fourier transformation infrared spectroscope, X-ray diffractometer, scanning electronic microscope and thermal conductivity apparatus were used to determine the chemical structure, crystalloid phase, microstructure and thermal conductivity, respectively, of the composites. The thermal properties and thermal stability were investigated by a differential scanning calorimeter and a thermogravimetry analyzer. The microstructural analysis results showed that the lauric acid was well adsorbed into the porous network of the activated carbon. The thermal conductivity measurement results presented that the thermal conductivity of the composites was enhanced. The differential scanning calorimetry analysis results indicated that the composites exhibited the same phase change characteristics as those of the lauric acid and their latent heats increased with increase of the lauric acid content in composites. The thermogravimetric analysis results presented that the activated carbon can improve the thermal stability of the composites.Microencapsulated stearic acid (SA) with silicon dioxide (SiO2) shell as shape-stabilized thermal energy storage materials were prepared using sol-gel methods. In the shape-stabilized thermal energy storage materials, the stearic acid was used as the core material that is the latent heat storage phase change material, and the silicon dioxide acted as the shell material which prevented the leakage of the melted stearic acid. Fourier transformation infrared spectroscope and scanning electronic microscope were used to determine chemical structure and microstructure of microencapsulated stearic acid with silicon dioxide shell, respectively. The thermal properties and stabilities were investigated by the differential scanning calorimeter and thermogravimetric analyzer, respectively. The SEM results showed that the stearic acid was encapsulated in the shell of the stearic acid. The DSC results indicated that the microencapsulated stearic acid with the silicon dioxide shell thermal energy storage materials solidify at52.62℃with a latent heat of161.99kJ/kg and melt at53.53℃with a latent heat of170.98kJ/kg when the encapsulation ratio of the stearic acid is90.7%. The TGA results presented that the silicon dioxide shells can improve the thermal stability of the microencapsulated stearic acid thermal energy storage materials.Microencapsulated paraffin with silicon dioxide (SiO2) shell as shape-stabilized thermal energy storage materials were prepared using sol-gel methods.The paraffin was used as the core material, and the SiO2prepared with methyl triethoxysilane (MTES) acted as the shell material. The morphology and particle size of the microcapsules were investigated by scanning electron microscopy. The chemical characterization of the microcapsule was measured by Fourier transformation infrared spectroscope. The crystalloid phase of the microcapsules was measured by X-ray diffraction method. And the thermal properties and thermal stability of the microcapsules were analyzed with differential scanning calorimetry and thermal gravimetric analysis. The FT-IR, XRD and SEM results showed that the paraffin was encapsulated in the shell of the SiO2. The DSC results showed that the typical microcapsules melt at57.96℃with a latent heat of156.86kJ/kg and solidify at55.78℃with a latent heat of144.09kJ/kg as the microencapsulation ratio is82.2%. The TGA and DTG results showed that the microcapsules have a good thermal stability. The SiO2shells can improve the thermal properties and the thermal stability of the microcapsules.2. Dynamic heat transfer characteristics modeling of microencapsulated phase change material slurriesMicroencapsulated phase change materials (MPCM) have been recognized as effective materials to enhance heat transfer, and to improve heat storage performance in thermal energy system. Microencapsulated phase change material slurry (MPCS) can apply to heat transport and thermal energy storage systems. In order to fully develop the application of MPCS in thermal energy system, more researches on preparation and characteristics of MPCS have been done. This paper presents a review on microencapsulation methods and thermal characteristics of MPCS. It focuses on the thermal properties and heat transfer characteristics of MPCS flowing in horizontal circular pipe. Some phase change materials and microencapsulation methods are analyzed and discussed. Theoretical models for analyzing heat transfer characteristics of MPCS flowing in the pipe are presented. Several factors affecting the heat transfer characteristics of MPCS are also summarized.Convective heat transfer characteristics of microencapsulated phase change material slurries (MPCSs) flowing in a circular tube under constant heat flux are studied and a feasible heat transfer model is presented. The heat transfer coefficient of MPCS and the wall temperature of the circular tube are simulated. The simulation results agree qualitatively with the experimental results. The effects of Ste number, mass concentration, phase change temperature range, and Re number on heat transfer characteristics are discussed. The results indicate that the Ste-number and mass fraction are the most important parameters influencing heat transfer properties compared to the phase change temperature range and Re-number which less affect these characteristics.