Phase Change Material Particles Research Articles

CFD simulation of a solar collector integrated with PCM thermal storage

AbstractThermal energy storage is indeed a valuable solution for addressing the time lag or mismatch between energy supply and demand. The study aims to computationally model the melting and solidification processes of phase change material (PCM) using ANSYS Fluent that utilizes the finite volume technique. The simulations provide insights into the shapes of the liquid fraction, corresponding times, and temperature distribution of the PCM particles under the given conditions. The study considers factors such as solar radiation, thermal conductivity, density, latent heat, and the melting temperature of the PCM. The study finds that paraffin wax melts more quickly under a higher average maximum solar irradiance of 985 W/m2, while a lower solar radiation of 300 W/m2 has the opposite effect. Enhanced heat transfer resulting from conduction within the molten PCM, especially at a thermal conductivity of k = 0.25 W/m·K, accelerates the melting process. The thermal conductivity of the PCM affects the overall performance of the thermal energy storage system. The study highlights the potential application of thermal storage for drying purposes. Through the controlled release of stored heat energy, thermal storage enables the provision of heat in the absence of sunlight.

Preparation, characterisation and property modification of a calcium chloride hexahydrate phase change material slurry with additives for thermal energy transportation

Efficient thermal energy distribution and rational energy management are effective solutions to address the significant and fast-ascending energy consumption in building heating, ventilation, and air conditioning (HVAC). Phase change material (PCM) slurries with excellent thermal energy transportation and storage characteristics have been recognised as promising secondary refrigerants to simultaneously facilitate efficient heat/cold transport and effective thermal energy storage in air conditioning systems. Among various PCM slurries, salt hydrate PCM slurries have attracted increasing attention in recent years due to their many inherent advantages. This paper presented the preparation, characterisation, and property modification of a CaCl2·6H2O slurry based on a methodology proposed for optimal salt hydrate PCM slurry development. Theoretical modelling was first carried out to assess the availability of salt hydrate PCM slurries based on the phase diagram and solid fraction, followed by a series of property measurements to reveal the mechanisms and address the problems behind the phase transition, crystal particle morphology, stability and rheologic characteristics, using nucleating agents, surfactants and stabilisers. It was found that the salt hydrate PCM slurry developed provides a unit volume enthalpy twice that of water over the phase change temperature range of 5°C, together with acceptable fluidity. The results also showed that the PCM particle size can be well controlled, and the slurry can be stabilised, with the assistance of surfactants and stabilisers. Compared to other types of PCM slurries, the proposed salt hydrate PCM slurry has the advantages of being cost-effectiveness, easy preparation, adjustable phase change temperature, etc., which is promising to facilitate energy saving and rationalisation in building HVAC.

Turbulent Heat Transfer of Hybrid Nanofluid with Nano-Encapsulated Phase Change Material in a Square Channel

Investigation of turbulent mixed convection of different working fluids, namely, pure water, CuO/water nanofluid, n-octadecane/water nanofluid (or slurry), and a hybrid water-based suspension of CuO and n-octadecane nanoparticles in a uniformly heated vertical square channel is carried out. The shear stress transport/kappa-omega model is applied to simulate the turbulent flow. Eulerian–Lagrangian two phase model and homogeneous model are employed to simulate the nanofluid flow. It is shown that Eulerian–Lagrangian two-phase model predicts higher Nusselt number and friction factor than single-phase model and the results of two-phase model are closer to experimental data. It is found that a new hybrid nanofluid with dispersed nano-encapsulated phase change material particles provides better thermal and hydrodynamic performances compared to other nanofluids. Slurry containing 5% n-octadecane provides an improvement of nearly 37.2%, while hybrid nanofluid (1% CuO + 5% n-octadecane) offers added convective heat transfer enhancement of almost 60%. With increasing volume fraction, friction factor becomes slightly larger than that of pure water. For 5% n-octadecane/water and 1% CuO + 5% n-octadecane/water nanofluids, friction factor increases by 2.5% and 1.7%, respectively. Due to dominance of thermal entropy generation, total entropy generation reduces by increasing Reynolds number and volume fraction.

A Dual Encapsulation Strategy for High-Temperature Micro PCM Particles with High Cyclic Durability.

Addressing critical issues such as high-temperature corrosion, leakage, degradation, and subpar cyclic performance is imperative for phase change materials (PCMs), prompting the development of appropriate encapsulation techniques to surmount these challenges. In this study, a dual encapsulation strategy is proposed for high-temperature micro PCM particles. Al-Si core is microencapsulated via the "solvent evaporation-heating curing" method. Subsequently, TiO2 is employed as the skeleton material for form-stable encapsulation of PCM microcapsules by "cold pressed sintering". Detailed analysis of the crystalline phase transformation mechanism in the sintering synthesis pathway of TiO2 underscore its potential as a robust structural material with exceptional thermal stability. Furthermore, the incorporation of hexagonal boron nitride (hBN) results in a substantial enhancement of the thermal conductivity of the composites, increasing by 121.1-131.3%. The prepared form-stable phase change microcapsules (FSPCMs) are subjected to 5000 thermal cycles in the air atmosphere. There is no observed PCM leakage or composite ruptures in the FSPCM. Moreover, the oxidized mass gain is merely 3.3%, signifying exceptional oxidation resistance. Thermophysical analysis indicates that FSPCM can retain 91.3% of the enthalpy after 2000 cycles, with over 80% preservation after 5000 cycles, underscoring its remarkable cyclic thermal durability.

MELTING PROCESS SIMULATION OF PHASE CHANGE MATERIAL LAYER USED IN THE BUILDING ENVELOPE

The melting process of phase change material (PCM) for thermal energy storage purposes has been studied and simulated in this paper. Using the ANSYS (Fluent) 2023 R1 software, the melting of a rectangular PCM zone with left and right sides exposed to convection heat and the other sides adiabatic is simulated. The study also discusses the program specifications, numerical modeling equations, and assumptions. For a total melting duration of 360 min, the contours of the liquid fraction, temperature, density, and velocity of phase change material particles are shown at regular intervals of 30 min. The contours aid in identifying how the melting interface changes in shape and motion as melting time increases. It also describes how the melting fraction changes over time, which provides information regarding the amount of melted PCM at various points.

Novel microencapsulated ternary eutectic alloy-based phase change material

Recent applications of phase change materials (PCMs) include energy storage, transportation, and management. Multicomponent PCMs represent a primary tool for regulating operating temperatures across a broad range to accommodate diverse requirements across various temperature ranges. Moreover, the microencapsulation of PCMs promotes their manageability and functionality. However, microencapsulated PCMs (MEPCMs) with ternary eutectic alloy systems are yet to be reported. Moreover, various technical challenges impede the integration of components during PCM fabrication. In this study, a core–shell-type MEPCM with a ternary eutectic Al–Cu–Si alloy system was successfully developed for the first time. The MEPCM was prepared over two simple steps: (1) the formation of a precursor shell on the PCM particles using boehmite treatment and (2) the heat oxidation treatment to form a stable oxide shell. The fabricated MEPCM exhibited a melting point of 517 °C and a latent heat of 353 J g−1. MEPCMs operating at this temperature have not previously been reported. Furthermore, the heat storage density of the fabricated MEPCM was significantly higher than that of other reported MEPCMs. Additionally, the fabricated MEPCM exhibited high durability under 100 cycles of heat storage and release tests, retaining >90 % of its latent heat capacity. Therefore, for the first time, this study successfully developed a core–shell-type MEPCM with a ternary eutectic system.

Cyclic heat-generation and storage capabilities of self-heating cementitious composite with an addition of phase change material

This study explored the efficiency of the phase-change materials (PCM) to improve the heat storage capacity of carbon nanotube (CNT) and carbon fiber (CF) based self-heating cementitious composites. Composites were prepared with 0.8 wt% CNT and 0.2 wt% CF as conductive fillers, and five different PCM contents (0, 5, 10, 20, and 30 wt%), and their electrical conductivities, thermal conductivities, and compressive strengths were measured. To determine the self-heating capability, the heat-generation and heat-storage capabilities of the composites were investigated using monotonic and cyclic heating/cooling tests. The results of these tests were analyzed through a differential scanning calorimetry and micro-computed tomography, which showed that the PCM particles with high latent heat were well dispersed in the composites, improving the heat storage capacity. Therefore, it can be said that the addition of PCM may improve heat storage capacity and enhance energy efficiency of the cement-based self-heating composites.

A facile synthesis approach of silica aero-gel/eicosane particles and its potential application on polyester fabric to impart thermoregulation properties

This article aims to study the thermo-regulating properties of infiltrated Phase change material (PCM) micro-particles treated on polyester fabric. The melt infiltration method was implemented for the synthesis of the Silica aero-gel/Eicosane particles by dispersing eicosane in silica aero-gel. Synthesized particles were incorporated into the polyester knitted fabric by both exhaustion dyeing and coating method to impart the thermoregulation characteristics. The crystalline structure and the particle size of aero-gel infiltrated PCM particles were measured by X-ray diffraction (XRD) analyzer. The presence of eicosane particles deposited on the fabric surface was confirmed by the Fourier Transform Infrared Spectroscopy (FT-IR) and Scanning Electron Microscope (SEM). Finally, while the sample was subjected to heating, both the dyed and coated fabric showed resistance against the rise of temperature due to the presence of phase transition PCM micro-particles compared to the untreated raw fabric sample.

Magnesium oxychloride cement with phase change material: Novel environmentally-friendly composites for heat storage

To solve heat energy storage of building enclosure systems, phase change materials (PCMs) were implemented into magnesium oxychloride cement (MOC) to form a MOC-PCM composite. Such composites possess sufficient mechanical strength for specific usage and high heat storage efficiency. The chemical and physical properties of raw materials were investigated as well as fresh composite mixture rheology. On matured samples, structural, mechanical, hygric, and thermal properties were tested. The results suggest that the enrichment of MOC with PCM particles causes an increase in porosity, hence a decrease in the specific density of the composites. With each addition of PCM the reduction of mechanical properties of the composite material occurs, where the maximum reduction in flexural and compressive strength for the sample with 40 wt % of PCM is around 80%. The low strength of the composite is compensated by excellent thermal properties that are required for its intended application. The enthalpies of phase changes increased linearly with the dosage of PCM and can contribute to the passive moderation of temperature fluctuations. The developed composites can find use in building engineering in the form of indoor cladding panels, facing slabs ceiling boards, etc. Which can be beneficially applied for example in the passive cooling of attic rooms and retrofitting of the present building stock.

Study on the rheological properties and phase-change temperature regulation of asphalt modified by high/low-temperature phase change material particles

The temperature sensitivity of asphalt can be improved by blending phase change materials into asphalt through the effect of phase change temperature control. In this study, two types of phase change material particles with excellent heat resistance were prepared by vacuum adsorption method. Based on material preparation, phase change material particles with different phase change temperature intervals were blended into asphalt to prepare a composite modified asphalt. Furthermore, the composite modified asphalt's rheological properties and temperature regulation effects were analyzed. The results showed that the incorporation of phase change material particles improved the rutting factor of the composite modified asphalt. The aging resistance of the composite modified asphalt increased significantly with the increase of the proportion of low-temperature phase change material particles. Bending beam rheometer (BBR) test results showed that incorporating high/low-temperature phase change material particles did not significantly affect the low-temperature rheological properties. According to temperature regulation simulation, it was found that the temperature change rate affects the temperature regulation effect of the composite modified asphalt. With increasing the temperature change rate, the maximum temperature difference increases, the latent heat accumulation temperature value (LHATV) decreases, and the latent heat temperature regulation index (LHTI) increases.

Passive thermal regulation with 3D printed phase change material/cellulose nanofibrils composites

Application of phase change materials (PCM)-containing composite represents a promising passive thermal control strategy to provide indoor thermal comfort without using powered equipment. Yet, the trade-off between high thermal storage density and good thermal stability is the major obstacle that restricts the thermal regulation performance of the current PCM-containing products. This study proposed a facile approach to prepare PCM/cellulose nanofibrils (CNF) ink for 3D printed composite monolith, with very high PCM loading, good thermal stability, and robust mechanical properties. By incorporating a small amount of CNF gel as the stabilizer and viscosity modifier, the CNF-microencapsulated paraffin (model PCM) obtained essential printability to construct tailorable structure using Direct Ink Writing technology. After ice templating and freeze drying, the microencapsulated PCM particles were in-situ embedded in a CNF-assembled scaffold, forming a PCM/CNF composite. The lightweight nature of such scaffold (35.0 mg/cm3 for pure CNF matrix) endowed the composite monolith with high PCM loading (up to 82% with respect to the composite) and high thermal storage capacity (up to 153 J/g). Due to the 3D-interlinked CNF matrix and the coated CNF on PCM particles, the composite monolith not only exhibited high Young's modulus of up to 1.14 MPa but also showed exceptional thermal stability with negligible variation in microscopic morphology and thermal storage capacity, after high temperature conditioning at 80 °C for 30 h.

Al–Ni alloy-based core-shell type microencapsulated phase change material for high temperature thermal energy utilization

Latent heat thermal energy storage (LHTES) using alloy-based phase-change materials (PCMs) is a promising technique for stabilizing the power supply of grid-connected renewable energies. In particular, recently developed alloy-based microencapsulated PCMs (MEPCMs) are attracting considerable attention owing to their ease of handling and ability to overcome the problems of corrosion and melting leakage experienced by alloy PCMs. To expand high-temperature LHTES, more MEPCMs need to be developed. In this study, an MEPCM was developed using Al-5 wt.%Ni alloy (melting point 640°C). Microencapsulation was performed in two steps: 1) Al hydroxide layer formation on the surface of PCM particles by boehmite treatment in boiling water for 1 h or 3 h and 2) Al 2 O 3 shell formation by heat oxidation treatment in an O 2 atmosphere. The prepared MEPCM consisted of an α-Al 2 O 3 shell and an Al–Ni alloy core. The sample after 1 h of boehmite treatment and heat oxidation treatment had melting and solidification latent heat capacities of 241 J g –1 and 251 J g –1 , respectively. The developed MEPCM maintained its original shape and high latent heat capacity, even after 100 cycles of melting and solidification. The developed Al–Ni alloy-based MEPCM is expected to be applied to next-generation LHTES, in which a large-scale and ultrafast heat exchange system is employed in a small space by cascade configuration with other MEPCMs with different melting points. In addition, the formation of the Al–Ni alloy core/α-Al 2 O 3 shell structure was investigated thermodynamically, providing insights that will promote the development of Al- X alloy-based MEPCMs in the future. • Al–Ni alloy based microencapsulated phase change materials (MEPCMs) were developed. • The prepared MEPCM consisted of an α-Al 2 O 3 shell and an Al–Ni alloy core. • The MEPCM exhibited high thermal storage capacity about 241 - 251 J g -1 . • The MEPCM had melting temperature of 640°C. • They are good candidates for high-temperature thermal energy storage application.

Influence of the Physical State of Microencapsulated PCM on the Pressure Drop of Slurry in a Circular Channel.

Phase Change Material (PCM) is mainly used in thermal energy storage. The addition of small PCM particles to the working fluid circulating in the heat exchange systems allowed to increase the amount of transported energy thanks to the use of latent heat—the heat of phase change. Encapsulating PCM in microcapsules avoids the disadvantages of PCM emulsions and makes the resulting slurry an attractive heat energy carrier. The paper presents the effect of the aggregate state of PCM enclosed in microcapsules on the flow resistance of the slurry through a rectilinear tubular channel. The tests were carried out with the use of a tube with an internal diameter of 4 mm and a measuring section length of 400 mm. A slurry of 21.5 wt.% PCM microcapsules (MPCM) was used as the working fluid in distilled water. A slurry with temperatures of 18.4 °C (PCM encapsulated in a solid state), 26.1 °C (PCM is in a phase change), and 30.5 °C (PCM in a liquid state) flowed through the measuring section. The mass flow rate of the MPCM slurry reached 70 kg/h (Remax = 2150). It was shown that the higher the Re number, the higher the value of the flow resistance, and the more clearly this value depended on the temperature of the slurry. Detailed analyses indicate that the observed changes were not the result of a change in the viscosity of the slurry, but its density depending on the state of the PCM. Significant changes in the density of the slurry in the range of the phase transition temperature are the result of significant changes in the volume of the microcapsule containing the phase change material in different aggregate states.

Experimental Study on Concentration Effects on the Supercooling of Phase Change Material-in-Water Nanoemulsions

In energy storage, energy transfer and thermal management applications, phase change material (PCM) nanoemulsions are promising; however, supercooling has always been an important issue in the research and application of PCMs. When supercooling occurs, the efficiency of energy storage applications may possibly be reduced. In this study, n-octadecane and n-eicosane (as core materials), and nonionic surfactants (hydrophile-lipophile balance value = 8) were used to prepare n-octadecane and n-eicosane emulsions with a mass concentration of 1–9%. The effects of particle size and operation temperature on emulsion viscosity were investigated, and the relationships between supercooling and the PCM particle size, PCM concentration and process cooling rates were analyzed. The results showed that small PCM particles could form a 2nd freezing point far from the melting point, resulting in a large supercooling degree. As the process cooling rates increased, the supercooling became more pronounced. However, when the high-concentration emulsion was mainly composed of small particles and subjected to low cooling rates, the concentration effect was significant, thereby decreasing the supercooling effect.

High-performance macro-encapsulated composite for photothermal conversion and latent heat storage

The request for green circular economy stimulates the use of solar energy. Capture and storage-release of solar energy can be simultaneously achieved by integrating photothermal conversion particles into phase change materials (PCMs) to obtain dual functional composites. Herein, a simple, cheap strategy for preparing 3D macro-encapsulated composite is proposed. Firstly, based on sizes difference, in situ grow nanoscale CuS coating on the surface of foamy Cu. The obtained CuS-Cu porous carrier adsorbs Na2S2O3·5H2O-CH3COONa·3H2O eutectic PCM to form semi-shape-stabilized PCM@CuS-Cu. Then, CuS-B4C modified epoxy resin (MEP) thin-layer macro-encapsulates PCM@CuS-Cu to fabricate PCM@CuS-Cu@MEP permanent shape-stabilized composite. The uniform distribution of CuS particles improves the heat transfer and photothermal conversion abilities of composite, as well as its exothermic accuracy shown as a low supercooling degree of only 0.740 °C. Photothermal conversion efficiency of PCM@CuS-Cu@MEP is 81.83 %, increased by 12.70 times compared with that of PCM (5.97 %). The MEP helps the composite to have leak-free performance under 60 °C for 72 h, and thermal reliability revealed as consistent thermal properties, crystal phase, composition after 100 heating-cooling cycles. The job provides a novel strategy to uniformly disperse PCM and photothermal conversion particles in space, ensuring the efficiently conversion and storage-release of energy.

Melting behavior and migration characteristics of microencapsulated phase change material particles in galinstan flow and application in minichannel heat sink

Mini/microchannel cooling performance can be improved with microencapsulated phase change material (MPCM) slurry as coolant by utilizing latent heat absorption capacity of MPCM. Compared with existing water, using liquid metal (LM) as basefluid can combine the advantages of high apparent heat capacity of MPCM particles and high thermal conductivity of LM. Thus, the prepared MPCM-LM slurry is proposed as coolant for minichannel heat sink. The melting of particles near the bottom enhances heat transfer performance of two-phase MPCM-LM slurry, but migration and aggregation cause the increase of pressure drop. Furthermore, the two-phase model is adopted to investigate the melting behavior and migration characteristics of MPCM particles in galinstan flow and the effect of particle volume percent on minichannel cooling performance. The results show that particles present boundary-to-center melting behavior in MPCM-galinstan slurry, resulting in the larger reduction degree in bulk mean temperature compared to MPCM-water slurry. Different from uniform distribution for small-diameter particles, the large-diameter particles migrate upward, leading to top-aggregation distribution and up-down asymmetry of velocity profile. Finally, the increase of particle volume percent significantly reduces heat capacity thermal resistance of heat sink, and maximum reduction is 59.02% for MPCM-galinstan slurry with φ s = 20% compared to pure galinstan.

Development of temperature-responsive transmission switch film (TRTSF) using phase change material for self-adaptive radiative cooling

To overcome the problem of unable automatic turn on and off response to the ambient temperature of current static radiative cooling systems, we prepared a series of temperature-responsive transmission switch film (TRTSF) samples using n-octadecane as phase change material (PCM) and polydimethylsiloxane (PDMS) as carrier material. The phase change cycle permeability analysis showed that the TRTSF samples with PCM content above 30.0 w.t.% exhibit a serious leakage problem due to a large number of holes on surface. The TRTSF samples with 10.0–30.0 w.t.% PCM content were further analysed by Differential scanning calorimetry (DSC) and Thermogravimetry (TG), and compared with the theoretical PCM contents, which verified the reliability of the curing results of PCM in TRTSF from various aspects. The ultraviolet–visible light-near-infrared (UV–VIS-NIR) and mid-infrared (MIR) transmittance characterization of TRTSF revealed that the switching effect was obvious during solid–liquid phase change process. TRTSF microstructure analysis revealed that the particle size distribution of PCM microspheres was between 1 μm and 6 μm. The UV–VIS-NIR band (wavelength at 0.25–1.1 μm) transmittance of PCM decreased to less than 3.7% after solidification due to the interfacial reflectance of solid PCM particles increased to more than 66.8% even in monolayer, thus the solid PCM particles would produce Mie scattering and isolate the internal and external radiation heat transfer. However, the TRTSF can be used as the radiative cooling emission layer since its optical properties were similar to the PDMS when the PCM is in liquid phase. Overall, the TRTSF film prepared in this study successfully adapted the temperature switching properties, also, is expected to be further used for the development of self-adaptive radiative cooling systems.

The effect of micro-encapsulation on thermal characteristics of metallic phase change materials

Micro-encapsulated phase change material with metallic core can work under high temperature for energy storage purpose, making it an appealing candidate for renewable energy technologies, such as thermal energy storage for concentrating solar power plants. The objective of this work is to study the impact of encapsulation on the thermal performance of the micro-encapsulated phase change materials under various operating conditions. To evaluate the thermal performance of the micro-encapsulated phase change material particles, the governing equation of transient heat conduction with phase change in spheres with composite walls is solved numerically. The impact of encapsulation shell on the convective heat transfer rate, total energy absorption, latent heat ratio, energy density, and duration of phase change is presented and analyzed under different operating conditions. Three different core materials including tin, aluminum and copper with distinct Stephan numbers are investigated. In addition to the encapsulation shell effect, this model can be used to study micro-encapsulated phase change materials with different material compositions, core to shell ratios, and it can be used to analyze the impact of air gaps in between materials. Understanding the thermal performance at particle level is essential, and the results of this study could potentially be used as input for thermal energy storage system level analysis, such as the charging and discharging processes. • Encapsulation enhances convection due to the increased surface area • Thicker shell shortens core melting time • Heating time depends on the ratio of heat capacitance and convection rate • Optimal shell thickness exists for achieving high energy storage and fast absorption

Oscillatory natural convection in a square enclosure containing a PCM suspension

In this study, a numerical simulation is performed to explore oscillatory natural convection in a square enclosure with a phase change material (PCM) suspension using the implicit finite difference method. The following parameters are considered: aspect ratio of the physical model = 1; ratio of the buoyancies caused by temperature and concentration gradients = 1; Rayleigh number = 103-106; initial mass fraction (or concentration) of PCM particles = 0–0.1; Stefan number = 0.005–0.1; and subcooling factor = 0–1.0. The results show that high Rayleigh numbers can easily cause oscillations in the flow field and temperature distribution. However, even under low Rayleigh number conditions, when the initial mass fraction or subcooling is increased or the Stefan number is decreased, oscillations occur.

Shape-stabilized phase change material convective melting by considering porous configuration effects

Phase change material (PCM) encapsulation within a porous medium, known as the shape-stabilized PCM (SS-PCM), is a kind of novel technique for maintaining the PCM during the melting process and improving the conductive heat transfer. However, the performance of the SS-PCM in thermal energy storages and slurries is highly dependent on the thermophysical properties of PCM and the stabilizer’s structure. In this state-of-art study, the convective melting within a circular porous region, as a representative for an embedded PCM particle, is investigated. The main characteristic parameters of SS-PCM, including porosity, permeability, effective thermal conductivity and latent heat of fusion, have been under scrutiny by developing enthalpy-based Lattice-Boltzmann code. The results revealed that the Rayleigh-Benard convection can be shaped at powerful flow circulation that has a significant impact on the melting trend and time. Moreover, improving the thermal conductivity by using highly conductive porous material is reasonable up to a certain optimum point depending on the application. Meanwhile, the porosity of the stabilizer and latent heat capacity of the PCM have shown an inverse impact on the melting performance. They are the main factors in changing heat transfer mechanism, between conduction and convection, and heat storage model, between sensible and latent.