Change Thermal Energy Storage Material Research Articles

Thermal property optimization and shape stabilization of sugar alcohols phase change thermal energy storage materials reinforced by sintering synthesized alumina porous ceramics

Sugar alcohols phase change thermal energy storage materials have many advantages such as high latent heat, non-toxicity and abundance, which are extremely potential in the field of thermal energy storage. However, the application of sugar alcohols in thermal energy storage is greatly restricted by high supercooling. In this work, alumina porous ceramics (APC) were successfully prepared by replication template method, and then the prepared APC were modified by 3-aminopropyltriethoxysilane to obtain APC-SiX. The APC and APC-SiX were used to improve the thermal properties of erythritol (ET), d-mannitol (DMT) and d-dulcitol (DDT), respectively. Based on the results, the supercooling degree and solidification stability degree of sugar alcohols were suppressed observably, among which, the supercooling suppression for ET was the most significant. The supercooling degree and solidification stability degree of ET were suppressed to 3.3 ± 0.1 °C and 0.7 ± 0.2 °C, respectively. Besides, the thermal conductivity of the sugar alcohols was also obviously enhanced. Furthermore, the high latent heat, excellent cycling thermal stability and anti-leakage of sugar alcohols composite phase change materials (PCM) are also available. This conclusion is important for supercooling regulation and thermal property optimization of sugar alcohols, and indeed, can promote the utilization of sugar alcohols in thermal energy storage.

Novel and durable composite phase change thermal energy storage materials with controllable melting temperature

The development of high temperature phase change materials (PCMs) with great comprehensive performance is significant in the future thermal energy storage system. In this study, novel and durable Al-Si/Al2O3-AlN composite PCMs with controllable melting temperature were successfully synthesized by using pristine Al powder as raw material and tetraethyl orthosilicate as SiO2 source. The Al2O3 shell and Al-Si alloy were in-situ produced via the substitution reaction between molten Al and SiO2. Importantly, the crack caused by the incomplete encapsulation of the Al2O3 shell could repair itself by the nitridation reaction of internal molten Al and thereby forming a highly dense Al2O3-AlN composite shell. The produced dense Al2O3-AlN composite shell could significantly improve the thermal cycling stability of composite PCMs, and thus, the thermal storage density decrease of the Al-Si/Al2O3-AlN (59.8 J/g to 77.7 J/g) was far less than that of the Al-Si/Al2O3 (118.5 J/g) after 3000 thermal cycles. Moreover, the synthesized Al-Si/Al2O3-AlN still exhibited a controllable melting temperature (571.5–637.9 ℃), relatively high thermal storage density (105.6–150.7 J/g), great dimensional stability and structural stability after 3000 thermal cycles. Hence, the synthesized Al-Si/Al2O3-AlN composite PCMs, as promising preferential thermal energy storage materials, can be stably used in the energy utilization efficiency improvement of various systems for more than 6 years.

A turbidity titration procedure for the nucleation mechanism determination of sodium sulfate decahydrate (Glauber salt) in unseeded aqueous solution

As a noteworthy salt hydrate, sodium sulfate decahydrate or Glauber salt can be used as a phase change thermal energy storage material. Kinetic parameters of sodium sulfate decahydrate salt solution are evaluated experimentally. Instead of the traditional polythermal and isothermal methods, a novel constant temperature experimental method (based on the turbidity titration) was adopted to experimentally illustrate the induction time and metastable zone width, in unseeded batch crystallization for sodium sulfate decahydrate salt solution at different temperatures (7, 9, 10, 13, 16, 19, 22 °C) and supersaturation ratio (1.01–1.43). We determined crystallization thermodynamics parameters, solubility, and supersolubility, of sodium sulfate decahydrate salt solution under atmospheric pressure and at different temperatures. The solubility data could be well fitted by the solubility carve of sodium sulfate decahydrate in the phase diagram of sodium sulfate. Statistical analysis shows that there was consistency in the result data of solubility. Two models, classical nucleation theory (primary homogeneous) and secondary nucleation, were employed to analyze the experimental data. The secondary nucleation model helped determine the order of nucleation and nucleation kinetic constants.

Development of phase change materials using hydrolyzed Al-Bi composite powder for solar energy storage

The hydrogen generation technology using the hydrolysis of Al-based composite powders has recently gained an increasing attention. However, the emission of hydrogen generation waste residue stream is an urgent problem to be addressed in the actual manufacture. For this purpose, this study reported the development of phase change thermal energy storage materials using hydrogen generation waste residue stream from Al-based composite powder hydrolysis. Specifically, the rapid hydrolysis reaction of Al-Bi composite powders was used to generate hydrogen, and subsequently tetraethoxysilane of different masses was added to the hydrogen generation waste residue stream to prepare Al-Si/Al2O3 composite phase change materials (PCMs) with controllable melting temperature. The results indicated that the hydrogen generation yield of Al-Bi composite powders during the fabrication of composite PCMs was 537.3–565.7 mL/g. Importantly, the prepared composite PCMs, with a controllable melting temperature of 573.2–654.2 °C, thermal energy storage density of 30.9–37.3 J/g, great repeatable utilization performance and structural stability, were potential thermal energy storage materials for concentrated solar power plants. Thus, this study not only achieved the reuse of hydrogen generation waste residue stream but also offered a new method for preparing Al-based composite PCMs.

Photothermal properties and photothermal conversion performance of nano-enhanced paraffin as a phase change thermal energy storage material

The paraffin incorporation in device of glass envelope allows the thermal regulation, increasing the thermal comfort and energy efficiency of buildings. Addition of nanoparticles has an advanced application prospect in the field of solar energy collection and storage capacity of glass envelope systems filled with paraffin. The present study conducts an experimental and numerical investigation in order to study photothermal properties of the paraffin incorporated ZnO or CuO nanoparticles. An experimental and theoretical model is also established to analyze the effect of nanoparticles on the thermophysical and optical properties of nano-enhanced paraffin. The results show that due to the presence of the nanoparticles, the transmittance of nano-enhanced paraffin decreases. On the other hand, temperature increment results in a small rise in the transmittance of nano-enhanced paraffin. The results also indicate that the utilized nanoparticles exhibit a higher attenuation to light, and the scattering effect cannot be avoided, where the maximum scattering proportion is 6.3%. Improvements of 5.87 and 13.12% in thermal conductivity of nano-enhanced paraffin at the volume fraction of 5 × 10−4 vol% are obtained using ZnO and CuO nanoparticles, respectively. The evaluation of the photothermal performance based on the temperature variations shows that the CuO/paraffin can absorb more solar energy. The optimum photothermal performance can be satisfied by the nanoparticle volume fraction ranging from 5 × 10−4 to 1.5 × 10−3 vol%.

Interfacial thermal conductance across hexagonal boron nitride & paraffin based thermal energy storage materials

It is of vital importance to understand the interfacial thermal conductance between the high thermal conductivity fillers and the phase change thermal energy storage materials in order to enhance the energy storage efficiency. The interfacial thermal conductance across low-dimensional hexagonal boron nitride layers (h-BN) and n-octadecane was calculated with reverse non-equilibrium molecular dynamics methods in this paper. The influences of size effect, molecular arrangement of n-octadecane, layer number of h-BN as well as the defects modified with various functional groups on the interfacial thermal conductance within the temperature range from 273.15 to 373.15 K were investigated, respectively. The results showed that the interfacial thermal conductance of all systems increase with rising temperature and the size effect is inconspicuous. And systems with n-octadecane molecules parallel to the h-BN surface possess the highest interfacial thermal conductance with respect to the vertical and amorphous arrangements. In addition, the interfacial thermal conductance will reduce when the layer number of h-BN increases. In terms of the effect of defects, the systems with h-BN containing the defects modified with hydrogen atoms, i.e., lighter atom, possess higher interfacial thermal conductance. At last, for interpreting deeper mechanism, the vibration power spectrum of the velocity autocorrelation function and the components in different directions were also calculated.

Evaluation of stearic acid/coconut shell charcoal composite phase change thermal energy storage materials for tankless solar water heater

Abstract This work presents a cost-effective and environment-friendly form-stabilized phase change material (PCM) and corresponding solar thermal application in the tankless solar water heater (TSWH). Coconut shell charcoal (CSC) as supporting material was modified by moderate oxidant of H2O2 with different concentrations, and then stabilized stearic acid (SA) to prepare composite PCMs through vacuum impregnation. It found that CSC support causes a 15.70% improvement of SA loadage after treated by 15% H2O2 due to coefficient enhancement by physical interaction and surface modification. The modified CSC15 support appears more super macropores which contribute to the impregnation of SA than non-modified CSC0 support verifying from SEM and BET results. And the content of oxygen functional groups was increased after oxidation modification, also motivating SA stabilization by hydrogen bond interaction in XPS analysis. FTIR results proved there is no chemical reaction happened between SA and CSC. Moreover, the latent heat and phase transition temperature of the as-prepared SA/CSC15 composite are 76.69 J g−1 and 52.52 °C, respectively. All composites exhibit excellent thermal stability under a working temperature of 180 °C and form stability during phase change. Thermal energy storage-release test within 70 °C presents the composite has fast heat transfer efficiency than pure SA. The composite filled in TSWH system has 0.75 W m−1 K−1 thermal conductivity which is 2.88 times higher than that of pure SA (0.26 W m−1 K−1). Besides, the TSWH system with a flow rate of 0.004 kg s−1 could heat water effectively after sunset and the energy obtained from the thermal storage system within 1830 s testing times is about 0.15 kW h. In all, SA/CSC composite with good physical-thermo properties has potential in thermal energy storage application, especially in solar energy storage.

A study on preparation and properties of carbon materials/myristic acid composite phase change thermal energy storage materials

ABSTRACTMicroscale graphite (Gr) and nanoscale multi-walled carbon nanotubes (MWCNTs) were chosen to modify the organic phase change material (PCM) of myristic acid (MA). The Gr/MA and MWCNTs/MA composite PCMs were prepared by adding the carbon materials at different mass fractions into MA. The experimental results indicated that both Gr and MWCNTs could enhance the thermal conductivity of MA. For the 3 wt% loading, the solid thermal conductivity of MA increased by 37.42% with Gr and 62.26% with MWCNTs. The FT-IR spectra showed that the reactions between carbon materials and MA were physical. The DSC results illustrated that the phase change latent heats of the composite PCMs decreased gradually with the additives increasing. Gr and MWCNTs strengthened the thermal stability of MA. The heat release rates of the composite PCMs accelerated. Three hundred thermal cycles of the chosen composite PCMs revealed that the prepared composite PCMs presented good thermal cycling stability.

Experimental study on preparation of a novel foamed cement with paraffin/ expanded graphite composite phase change thermal energy storage material

This study proposed a novel foaming cement heat preservation block with heat storage, peak clipping, and temperature adjustment functions. To produce such cements, a paraffin/expansion graphite composite phase change heat storage material with a phase transition temperature of 41.9℃ and a enthalpy value of 207.6 J/g was prepared. Then the composite phase change material (PCM) loaded paraffin at 44℃ into expanded graphite and then was mixed cement uniformly. The porous structure of the foamed cement has light weight and good heat preservation capacity so that then composite PCM can effectively store heat energy and shave the load peak. To investigate the characteristics of the proposed material, this focuses on the physical structure, thermal storage capacity and thermal insulation performance when the material mass fractions of PCM are 10%、15%、20%、25% and 30%. The experimental results show that with the increase of the mass fraction of PCM, the thermal storage capacity and thermal insulation properties of the foamed cement increases. In addition, there is no chemical reaction between the materials. The results show a the proposed material has a potential in creating efficient thermal insulation walls.

Stearic acid/expanded graphite as a composite phase change thermal energy storage material for tankless solar water heater

Tankless solar water heater (TSWH) integrated phase change materials (PCMs) is a promising field due to its low cost, low heat loss, and compact structure. To obtain a composite PCMs that suitable for tankless solar water heater application, the expanded graphite (EG) in different mass fraction (2 wt.%, 6 wt.%, and 10 wt.%) were added to stearic acid (SA) via melting impregnation. The thermophysical properties including phase change temperature, latent heat, and thermal conductivity of the SA/EG composites were characterized by DSC and thermal conductivity tests. The melting and freezing heats of SA/EG6 composite were 163.5 J g−1 and 167.3 J g−1, respectively. The thermal conductivity of SA/EG6 was as high as 9.6 times that of pure SA. Meanwhile, the infrared images suggested the addition of EG enhance the heat release capability of composites as well as improve the uniformity of heat transfer process of SA/EG6. At last, a developed compact solar water heater was used to estimate the thermal performance of as-prepared composites. The experimental results shown that the melting time of SA/EG6 was shorten 63.3% compared with that of the SA and the heat releasing rate of SA/EG6 was the highest, suggesting the SA/EG6 composites can be applied in TSWH system.

The Effect of Nanometer Oxide Additive on the Heat-Conducting Property of Barium Hydroxide Octahydrate.

Nanometer silicon dioxide additive can improve the thermal performance of barium hydroxide octahydrate as the phase change thermal energy storage material. Through measuring the changes of phase change temperature, degree of supercooling, thermal conductivity, the different effects of nanometer silicon dioxide additives of different mass fraction on barium hydroxide octahydrate thermal performance are compared. It can be seen that the precipitation of barium hydroxide octahydrate with nanometer silicon dioxide additive of 0.5% mass fraction improves greatly. The thermal conductivity of barium hydroxide octahydrate with nanometer silicon dioxide additive of 0.5% mass fraction increases to a very slight degree.

Thermophysical properties of some organic phase change materials for latent heat storage. A review

Past three decades are characterized by intensive investigations and the development of phase change materials for thermal energy storage. Latent heat storage is one of the most perspective methods of increasing efficiency in energy conservation and effective using sources of heat. Among available latent heat storage materials, the organic materials draw the attention of many researchers. It should be noted that the development of phase change materials advances the investigations of their thermophysical properties sufficiently. Knowledge of thermophysical properties is necessary condition for practical applications. The data on thermophysical properties of potential latent heat storage materials is dissipated in many scientific sources that are inaccessible, in many cases, for potential consumers of phase change thermal energy storage materials. This paper summarizes the results of previous investigations on transitions temperatures, heat of fusion, heat capacity, and thermal conductivity, long-term characteristics of many organic substances, their compositions, and compounds.

Temperature-dependent thermal properties of a paraffin phase change material embedded with herringbone style graphite nanofibers

In many studies, carbon nanoparticles with high values of thermal conductivity (10–3000W/mK) have been embedded into phase change thermal energy storage materials (PCMs) in order to enhance their bulk thermal properties. While a great deal of work to date has focused on determining the effect of these nanoparticles on a PCM’s solid phase thermal properties, little is known about their effect on its liquid phase thermal properties. Thus, in this study, the effect of implanting randomly oriented herringbone style graphite nanofibers (HGNF, average diameter=100nm, average length=20μm) on the bulk thermal properties of an organic paraffin PCM (IGI 1230A, Tmelt=329.15K) in both the solid and liquid phase is quantified. The bulk thermal conductivity, volumetric heat capacity and thermal diffusivity of HGNF/PCM nanocomposites are obtained as a function of temperature and HGNF volume loading level. It is found that the property enhancement varies significantly depending on the material phase. In order to explain the difference between solid and liquid phase thermal properties, heat flow at the nanoparticle–PCM and nanoparticle–nanoparticle interfaces is examined as a function of HGNF loading level and temperature. To do this, the solid and liquid phase thermal boundary resistances (TBRs) between the nanoparticles and the surrounding PCM and/or between contacting nanoparticles are found. Results suggest that the TBR at the HGNF–PCM interface is nearly double the TBR across the HGNF–HGNF interface in both solid and liquid phases. However, both the HGNF–PCM and HGNF–HGNF TBRs are at least an order of magnitude lower when the PCM is in its solid phase versus when the PCM is in its liquid phase. Finally, the effect of nanofiber concentration on the PCM’s latent heat of fusion and melt temperature is investigated in order to determine the applicability of the HGNF/PCM nanocomposite in a wide variety of energy systems.

Thermal properties of paraffin/graphite composite phase change materials in battery thermal management system

The thermal properties of paraffin/graphite composite phase change materials for power nickel metal hydride batteries were experimentally investigated. Two different modes for heat dissipation were designed in this experimental study: air cooling and cooling with phase change materials. Paraffin/graphite composite phase change thermal energy storage materials were prepared and tested by differential scanning calorimetry. It appeared that the battery thermal management system with phase change materials had better performance than air cooling, especially when the scale of paraffin/graphite composite material approximates 4:1.

Preparation and characterizations of HDPE–EVA alloy/OMT nanocomposites/paraffin compounds as a shape stabilized phase change thermal energy storage material

A kind of shape stabilized phase change nanocomposites materials (PCNM) based on high density polyethylene (HDPE)/ethylene-vinyl acetate (EVA) alloy, organophilic montmorillonite (OMT), paraffin and intumescent flame retardant (IFR) are prepared using twin-screw extruder technique. The structures of the HDPE–EVA alloy/OMT nanocomposites are evidenced by the X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that an ordered intercalated nanomorphology of the HDPE–EVA alloy/OMT nanocomposites is formed. Then the structures of the shape stabilized PCNM are characterized by scanning electron microscopy (SEM). The HDPE–EVA alloy/OMT nanocomposites act as the supporting material and form the three-dimensional network structure. The paraffin acts as a phase change material and disperses in the three-dimensional network structure. Its latent heat is given by differential scanning calorimeter (DSC) method. The SEM and DSC results show that the additives of IFR have little effect on the network structure and the latent heat of shape stabilized PCNM, respectively. The thermal stability properties are characterized by thermogravimetric analysis (TGA). The TGA analysis results indicate that the flame retardant shape stabilized PCNM produce a larger amount of char residue at 800 °C than that of shape stabilized PCNM, although the onset of weight loss of the flame retardant shape stabilized PCNM occur at a lower temperature. The formed multicellular char residue contributes to the improvement of thermal stability performance. The probable combustion mechanisms are also discussed in this paper.

Study on paraffin/expanded graphite composite phase change thermal energy storage material

Abstract A paraffin/expanded graphite composite phase change thermal energy storage material was prepared by absorbing the paraffin into an expanded graphite that has an excellent absorbability. In such a composite, the paraffin serves as a latent heat storage material and the expanded graphite acts as the supporting material, which prevents leakage of the melted paraffin from its porous structure due to the capillary and surface tension forces. The inherent structure of the expanded graphite did not change in the composite material. The solid–liquid phase change temperature of the composite PCM was the same as that of the paraffin, and the latent heat of the paraffin/expanded graphite composite material was equivalent to the calculated value based on the mass ratio of the paraffin in the composite. The heat transfer rate of the paraffin/expanded graphite composite was obviously higher than that of the paraffin due to the combination with the expanded graphite that had a high thermal conductivity. The prepared paraffin/expanded graphite composite phase change material had a large thermal storage capacity and improved thermal conductivity and did not experience liquid leakage during its solid–liquid phase change.