Composite Thermal Energy Storage Materials Research Articles

Experimental study of phase transition heat of composite thermal energy storage materials paraffin wax/expanded graphite

In this paper, the effect of the expanded graphite (EG) matrix on the phase transitions enthalpy of phase change material (PCM) is studied experimentally. For this purpose, the paraffin wax (PW) containing EG (up to 6.5 wt%) was explored in terms of the effective heat capacity and a diffuse phase transitions enthalpy difference over the 25–65 °С temperature range. Composite PCMs PW/EG was prepared using a new method and were inherent in high pores fill factor. The main advantage of the proposed method is preliminary vacuuming of the PW and EG with subsequent mixing and sonication under vacuum. The EG choice was based on the hypothesis that the EG matrix contributes to modifying the PW internal structure due to the PW molecules' adsorption on the EG surface during PCM cooling and solidification. Consequently, a significant change in PW/EG caloric properties vs. pure PW was observed. The EG presence in PW reverses the enthalpy hysteresis in the heating-cooling cycle vs. pure PW. The enthalpy difference during PW heating and melting in the range of 30–60 °С is higher than during its cooling and solidification: 336.2 J∙g−1 vs. 214.9 J∙g−1. On the contrary, the enthalpy difference of melting for PW/EG of 3.6 wt% in the range 30–60 °С was 171.2 J∙g−1 vs. 273.8 J∙g−1 during solidification. The obtained results are explained by the different dynamics of processes of PW melting and solidification in EG matrix pores. The presence of the 3.2–6.5 wt% of EG in PW contributes to an increase in solidification enthalpy difference in the range 30–60 °C on 27–33 % vs. pure PW. A decrease in the melting enthalpy difference for PW/EG on 44–50 % vs. pure PW was recorded in the range of 30–60 °C. In addition, thermal conductivity was measured to confirm the advantages of PW/EG as PCM. Thermal conductivity for PW/EG with EG content of 3.6 and 6.5 wt% at 25 °C was 8.9 and 9.6 times higher than for pure PW. Similarly, 8.8 and 10.9 times thermal conductivity increase was observed at 65 °C. The composite PCM containing 3.6 wt% of EG in PW obtained by developed method can be recommended as a rational composition in benefit of the thermal conductivity and caloric properties for utilization in high-performance TES systems.

Synthesis and Characteristics of Microencapsulated Myristic Acid with TiO2 as Composite Thermal Energy Storage Materials

To solve the issues of flowing and leaking of myristic acid (MA) as phase change energy storage material in practical application, a novel microencapsulated composite phase change energy storage material was prepared by sol-gel method using myristic acid (MA) as core material and titanium dioxide (TiO2) as shell material. The chemical structure, crystal structure, micromorphology, phase change characteristics and thermal stability of phase change microencapsulated energy storage materials were characterized by using Fourier transform infrared spectrometer (FT-IR), X-ray diffraction analyzer (XRD), field emission scanning electron microscope (FE-SEM), differential scanning calorimetry (DSC), thermogravimetric analyzer (TGA). The consequents illustrated that the ideal sample melted at 54.97 °C with the latent heat of 55.76 J/g and solidified at 49.85 °C with the latent heat of 54.55 J/g. In general, the prepared microencapsulated phase change materials possessed good thermal properties and thermal stabilities. It is predicted that the shape-stabilized MA/TiO2 composites have great potential for thermal energy storage.

Conductive heat transfer in lamellar phase change material composites

Composite thermal energy storage materials consisting of highly thermally conductive and capacitive constituent elements can thermally buffer transient heat pulses. The ability to quantitatively describe these composite systems is valuable in the design of thermal management components to determine how a thermal load affects the necessary geometric aspects. Here, we develop numerical and analytical reduced-order solutions of 1D conductive heat transfer in lamellar multi-component thermal energy storage materials. Investigation of the limit in which conduction is the dominant term is important for the case where length-scales are small enough to limit convection or where the phase change material maintains a solid or high viscosity state at high temperatures. The response of lamellar PCM systems is herein described using (1) an effective medium approximation, and (2) a 1D “fin equation” approximation. Analytical solutions are compared against a higher resolution finite difference analysis numerical model in order to determine the length- and time- scales over which each expression is valid. The result of this work is a set of approximate solutions of transient thermal behavior in thermal energy storage composites, which can aid in the deliberate design of composite thermal energy storage materials to achieve desired performance characteristics. Remarkably, application of this approach predicts composite structures which absorb heat at much higher rates than pure metal conductors.

Preparation and Characteristics of Microencapsulated Lauric Acid as Composite Thermal Energy Storage Materials

A novel microencapsulated phase change material was prepared by sol-gel method using lauric acid (LA) as core material and titanium dioxide (TiO2) as shell material. The composites were characterized by field emission scanning electron microscope (FE-SEM), Fourier transformation infrared spectrometer (FT-IR), differential scanning calorimeter (DSC) and thermogravimetric analyzer (TGA). The results of the FE-SEM and FT-IR indicated that LA was well coated in the shell of TiO2 and no chemical reaction occurred between them. The results of the DSC denoted that the composites with 43.5 % encapsulation ratio of the LA melted at 44.39 ℃ with the melting enthalpy of 67.54 J/g and solidified at 43.64 ℃ with the solidification enthalpy of 65.17 J/g. The results of the TGA signified that the thermal stability and fire resistance of the microcapsules were greatly enhanced under the protection barrier of TiO2. The thermal decomposition of the microencapsulated LA with TiO2 shell hardly occurred under 200 ℃. That is to say, the composites possess good thermal stability in the operating temperature range. In conclusion, the prepared microencapsulated composites can be incorporated into solar energy storage like solar air heaters and into electronic devices as heat sinks.

Influence of Cu powders on the properties and characteristics of nano-MgO based aluminate cementitious materials

From the perspective of practical application, the development of desirable thermal and mechanical performance of solid sensible materials for thermal energy storage (TES) is highly needed. Here, we report the improved properties of nano-MgO optimized aluminate cementitious materials incorporated with Cu powders for TES. The composite TES materials were heated at 105, 350, and 900 °C, respectively. The results show that as the Cu powders content increases the thermal conductivity and volume heat capacity significantly increase, but there is a gradual decrease in compressive strength. Through the characterizations such as calorimetric test, XRD, FESEM, TG-DSC, and MIP, a significant feature of mass compensation also has been obtained, which might result from the oxidation reaction of the Cu powder at elevated temperatures.

Effect of nano-MgO on thermal and mechanical properties of aluminate cement composite thermal energy storage materials

Thermal and mechanical properties of high temperature aluminate cementitious thermal energy storage materials enriched with nano-MgO (NM) are investigated. According to the development of thermal storage materials and their application environment requirement in solar thermal power, the specimens were subjected to heating at 105, 350, and 900°C. It was observed that the addition of NM provided a great improvement on the thermal properties of the composite pastes which were heated principally at 350 and 900°C. When the NM content was 1wt%, the thermal conductivities are 34.8% and 23.6% higher than that of pure paste at 350 and 900°C, respectively. Meanwhile, at 2wt% NM particles loading, the optimum value of volume heat capacity is obtained, which are 19.8% and 40.8% higher than that of pure paste at 350 and 900°C, respectively. Moreover, compressive strength of the composite paste with 1wt% NM presents approximately 30.5%, 27.8%, and 23.8% higher than that of pure paste at 105, 350, and 900°C, respectively. XRD, TG-DSC, SEM, and MIP were used to characterize the phases, mass/heat changes, microstructure and pore distribution of the hardened cement pastes, respectively.

Preparation and characteristics of microencapsulated stearic acid as composite thermal energy storage material in buildings

Microencapsulated stearic acid (SA) with silicon dioxide (SiO2) shell as composite thermal energy storage material was prepared using sol–gel methods. In the composite thermal energy storage material, the stearic acid was used as the core material that is the latent heat storage phase change material (PCM), and the silicon dioxide acted as the shell material which prevented the leakage of the melted stearic acid. Fourier transformation infrared spectroscope (FT-IR) and scanning electronic microscope (SEM) were used to determine chemical structure and microstructure of microencapsulated stearic acid with silicon dioxide shell. The thermal properties and thermal stability were investigated by the differential scanning calorimeter (DSC) and thermogravimetric analyzer (TGA). The SEM results showed that the stearic acid was encapsulated in the shell of the silicon dioxide shell. The DSC results indicated that the microencapsulated stearic acid with the silicon dioxide shell as composite thermal energy storage material solidifies at 52.6°C with a latent heat of 162.0kJ/kg and melts at 53.5°C with a latent heat of 171.0kJ/kg when the encapsulation ratio of the SA is 90.7%. The TGA results presented that the silicon dioxide shells can improve the thermal stability of the microencapsulated stearic acid as composite thermal energy storage material.

Experimental Investigation of PCM-LWA Composite for Building Wallboard

In this paper, a experimental investigation of application of room wallboard containing Phase-Change-Material / Lightweight-Aggregate composite (PCM-LWA) was carried out. A PCM-LWA composite thermal energy storage material was prepared by absorbing the paraffin. In such a composite, the paraffin serves as a latent heat storage material and the porous lightweight aggregate acts as the supporting material. Mixture of cement paste and epoxy were used to seal the PCM-LWA surface. Through comparing temperature curves of a general room model and the model using wallboards containing PCM-LWA, it can be known that the highest temperature of the room model using the wallboards containing PCM can be controlled in a narrow range. Therefore, room model assembled with the walls containing phase change material can effectively reduce the highest indoor temperature and the range of reduced temperature is about 2~4°C.

Preparation of Phase-Change-Material/Lightweight Aggregate Composite as an Energy Storage Material

In this paper, a phase-change-material/lightweight aggregate (PCM-LWA) composite thermal energy storage material was prepared by absorbing the lauryl alcohol, which is one kind of phase change materials, into porous lightweight aggregates (LWAs) that have an excellent absorbability. In such a composite, the lauryl alcohol serves as a latent heat storage material and the porous lightweight aggregate acts as the supporting material. In order to prevent the melted lauryl alcohol leak from the porous LWAs, surface seal processing for the PCM-LWA was necessary. In this research, pure cement paste and polymer modified cement paste were used to seal the PCM-LWA surface. Through comparison between the differential scanning calorimetry (DSC) tests for lauryl alcohol and PCM-LWA, it can be known that the solid-liquid phase change temperature of the composite PCM-LWA was slightly higher than that of the lauryl alcohol, and latent heat of the PCM-LWA was smaller than that of the pure PCM.

Calorimetric studies of thermochemical heat storage materials based on mixtures of MgSO 4 and MgCl 2

Attapulgite granulate impregnated with mixtures of MgSO 4 and MgCl 2 hydrates was investigated for suitability as a composite thermal energy storage material. These mixtures were chosen because of the very different deliquescence relative humidities of the salts. The thermochemical heat storage of these materials was characterized by measurements of isothermal heat of sorption and thermogravimetry (TG). The salt mixtures showed a different sorption behavior compared to pure MgSO 4. The reduction of the deliquescence relative humidity of the mixture by the partial substitution of MgSO 4 by MgCl 2 increases the capacity of condensation and therefore the released heat. The energy density of the composite heat storage material containing a salt mixture of 20 wt% MgSO 4 and 80 wt% MgCl 2 was 1590 kJ/kg measured by calorimetry (at 30 °C/85% RH) with a desorption temperature of 130 °C.