Parametric study on the thermal performance enhancement of a thermosyphon heat pipe using covalent functionalized graphene nanofluids

Heat transfer characteristics of copper sintered heat pipe explored using a modified graphene nanoplatelets (GNP)-containing nanofluid with great dispersion stability as a novel working fluid. Firstly, a water dispersible GNP with specific desire was synthesized by the reaction of GNP sheets with the diazonium salt (DS) of sodium 4-aminoazobenzene-4-sulfonate. An X-ray photoelectron spectroscopy (XPS) test shown successful covalent functionalization of GNP using DS which provided special water dispersibility characteristics. The results indicate that the thermal conductivity enhancement was up to 17% by adding modified GNP sheets in the base fluid. It also, exhibited a maximum sedimentation of 16% after 840 hrs. Further research works were carried on thermal performance of heat pipe by varying nanofluid concentrations, filling ratio, input heating powers and inclination angles of heat pipes. The results proof that the maximum enhancements of the effective thermal conductivity and reduction in thermal resistance for purposed nanofluid atφ = 5% were 105% and 26.4%, respectively. Moreover, these good features of the GNP/DS nanofluid make it a very promising working fluid to enhance the thermal performance and efficiency of the current heat pipe systems

Facile Preparation of Carbon Microcapsules Containing Phase-Change Material with Enhanced Thermal Properties

This study describes the hydrothermal synthesis of a novel carbon/palmitic acid (PA) microencapsulated phase change material (MEPCM). The field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM) images confirm that spherical capsules of uniform size were formed with a mean diameter of 6.42 μm. The melting and freezing temperature were found to be slightly lower than those of pure PA with little undercooling. The composite retained 75% of the latent heat of pure PA. Thermal stability of the MEPCM was found to be better than that of pure PA. The thermal conductivity of MEPCM was increased by as much as 41% at 30°C. Due to its good thermal properties and chemical and mechanical stability, the carbon/PA MEPCM displays a good potential for thermal energy storage systems

Encapsulation of organic phase change materials within metal oxides for thermal energy storage systems / Sara Tahan Latibari

Solar energy is receiving a lot of attention nowadays since it is a clean, renewable, and sustainable energy. A major limitation of solar energy is that it is available for only about 2000 hours a year in many places. Thermal energy storage is a major contributor to bridge the gap between energy demand (consumption) and energy production (supply) by solar power. The utilization of high latent heat storage capability of phase change materials is one of the keys to an efficient way to store thermal energy. Several kinds of organic PCMs like fatty acids have been applied recently as they have a high latent heat and appropriate thermal properties. However, direct use of such PCMs in practical thermal applications is not easy due to their low thermal conductivity, flammability, instability, and leakage problems. To overcome these problems, PCMs have been encapsulated in various organic and inorganic shell materials. An inorganic shell material with high thermal conductivity and superior strength not only enhances the thermal transfer performance of the PCM system but also improves the durability and working reliability of them. This study presents state of the art of nano/microencapsulated PCMs (NE/MEPCMs) for thermal energy storage applications and provides an insight into our efforts to develop novel nano/microencapsulated phase change materials with enhanced performance and safety. Specific attention was given to the encapsulation process of some inorganic materials for the first time and the improvement of thermal conductivity and thermal stability of the prepared materials. In addition, the thermal energy storage properties and performance are discussed for thermal energy applications. In this research three types of nano/microcapsules were prepared with organic fatty acids as the core phase change material and SiO2 (silica), TiO2 (titania), and Al2O3 (aluminum oxide) as the inorganic shell materials through a sol-gel method. The structural, morphological and thermal features of the newly developed NE/MEPCMs iv were evaluated by a series of modern instruments and characterization technologies, including DSC, TGA, FT-IR, TEM, SEM and XRD. The thermal reliability of prepared nano/microcapsules was investigated using a thermal cycler for a large number of heating and cooling processes. In this research the influences of several types of parameters during the preparation method on the morphology, thermal performance and thermal conductivity of the prepared materials have been studied. The experimental results indicate that the fatty acids were successfully encapsulated in the shell materials in spherical shapes. Encapsulated fatty acids confirmed the outstanding phase-change performance with specific heat and thermal stability enhancement. The thermal conductivities of the encapsulated PCMs are significantly improved compared to pure PCMs. In conclusion, the outstanding latent heat, high thermal conductivity, thermal stability and reliability of the prepared nano/microcapsules make these materials appropriate phase change materials for thermal energy storage applications like slurry systems

Preparation of Phase Change Microcapsules with the Enhanced Photothermal Performance

The performance of solar-thermal conversion systems can be improved by incorporation of encapsulated phase change materials. In this study, for the first time, CrodathermTM 60 as a phase change material (PCM) was successfully encapsulated within polyurea as the shell supporting material. While preparing the slurry samples, graphite nanoplatelet (GNP) sheets were also incorporated to enhance the thermal and photothermal properties of the prepared materials. The morphology and chemical properties of these capsules were characterized by scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectrum, respectively. The results show the spherical-like and core-shell structure of capsules with an average diameter size of 3.34 μm. No chemical interaction was observed between the core and the supporting materials. The thermal characteristics of the microencapsulated PCMs (MEPCMs), analyzed by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), indicate that the prepared samples with 0.1 weight percentage of GNP possess the latent heat of 95.5 J/g at the phase transition temperature of about 64 °C. Analyzing the rheological properties of the prepared slurry with 16 wt % of MEPCMs proves that the prepared material meet the requirements given by the heat transfer applications. The thermal storage capacity, good thermal stability, and improved photothermal performance of the prepared material make it a potential candidate for using in direct absorption solar thermal applications