Microencapsulated Phase Change Materials Research Articles

Systematic investigation on preparation and characterization of silica shell microencapsulated phase change materials based on sodium silicate precursor

A kind of paraffin@silica (Pn@SiO2) microencapsulated phase change materials (MEPCM) were prepared by sol-gel method using sodium silicate as silica precursor. The investigation of this synthesis technique demonstrates that pH value and core/shell ratio play key role in optimizing the morphology and microstructure of Pn@SiO2 microcapsules to achieve optimal thermal storage properties. Therefore, we systematically investigated the effects of pH value and core/shell ratio on the microstructure, crystallization behavior and phase transition properties of Pn@SiO2. It was determined that at pH 3 and Pn/SiO2 ratio of 5:1, the synthesized Pn@SiO2 exhibited well-defined core-shell structure and regularly spherical morphology. The encapsulation rate reached 74.14 % with latent heat of about 186.4 J/g due to the formation of perfect microstructure and morphology. In addition, Pn@SiO2 presents excellent heat storage capacity, high thermal stability and good shape stability, and shows reliable and durable phase-change performance. In summary, sodium silicate was used as the SiO2 precursor for the first synthesis of MEPCM with high encapsulation rate and regularly spherical morphology.

A Review of the Mathematical Models for the Flow and Heat Transfer of Microencapsulated Phase Change Slurry (MEPCS)

Microencapsulated phase change slurry (MEPCS), prepared by mixing microencapsulated phase change materials (MEPCMs) with water or other carrier fluids, is widely used in different applications such as for thermal regulation or heat storage systems. The transient thermal-hydraulic behavior accompanying the phase change process of the MEEPCS has a significant impact on the system performance. However, the heat and mass transfer during the phase change of the MEPCS is a complex multiscale process, due to the complex phase change of small particles and the complex coupling between the particles and carrier fluids. The numerical methods have been proved to be efficient and powerful means to investigate such complex phase change problems. However, the mathematical model is the critical factor determining the accuracy of the numerical methods, and is still under development. This review summarized the mathematical models proposed for the thermal-hydraulic processes of the MEPCS, compared the adaptabilities of different models, and provided suggestions for the selection of models.

Phase Change Composite Microcapsules with Low-Dimensional Thermally Conductive Nanofillers: Preparation, Performance, and Applications

Phase change materials (PCMs) have been extensively utilized in latent thermal energy storage (TES) and thermal management systems to bridge the gap between thermal energy supply and demand in time and space, which have received unprecedented attention in the past few years. To effectively address the undesirable inherent defects of pristine PCMs such as leakage, low thermal conductivity, supercooling, and corrosion, enormous efforts have been dedicated to developing various advanced microencapsulated PCMs (MEPCMs). In particular, the low-dimensional thermally conductive nanofillers with tailorable properties promise numerous opportunities for the preparation of high-performance MEPCMs. In this review, recent advances in this field are systematically summarized to deliver the readers a comprehensive understanding of the significant influence of low-dimensional nanofillers on the properties of various MEPCMs and thus provide meaningful enlightenment for the rational design and multifunction of advanced MEPCMs. The composition and preparation strategies of MEPCMs as well as their thermal management applications are also discussed. Finally, the future perspectives and challenges of low-dimensional thermally conductive nanofillers for constructing high performance MEPCMs are outlined.

Microencapsulation of polymeric phase change materials (MPCM) for thermal energy storage in industrial coating applications

Abstract In recent years, energy has become an important factor in overall development. Most of the energy comes from fossil fuels which are nonrenewable and harmful to our environment. It has become important to develop new application technologies that utilize thermal energy storage (TES) technology. Energy storage technology based on PCMs is a cutting-edge research area with a wide range of potential applications. But the biggest problem of phase change material is its leakage problem, for that the researchers have set up a solution i.e., the microencapsulation techniques. This paper gives an overview of the synthesis of (MPCM) microencapsulated phase change material by using different methodologies and their applications in industrial coatings. Corrosion is the biggest problem in industrial coatings which reduces the working time span and overall performance of the coatings. The incorporation of the micro-PCMs in industrial coatings increases workability as well as the overall performance of the coatings. This review covers the use of MPCM in various industrial coating applications, challenges, and their future directions are also discussed.

Energy impact of heat pipe-assisted microencapsulated phase change material heat sink for photovoltaic and thermoelectric generator hybrid panel

As the importance of energy saving continues to increase owing to climate change, various Internet of Things sensors, related to building temperatures, humidity, and energy usage, are being employed in buildings, such as in building energy management systems. Aiming to satisfy the rapidly increasing electric energy demands of buildings, studies have combined various building-integrated photovoltaic (BIPV) and thermoelectric generators (TEGs) to recover sunlight and heat wasted from building envelopes. However, in most previous studies, active methods for heat rejection were applied to increase the temperature difference between both ends of the TEG and cooling of the solar panel. The actual constructability problems, such as leakage problems, were insufficiently addressed. Therefore, this study proposed a BIPV-TEG system with increased constructability and heat dissipation efficiency using a heat pipe and microencapsulated phase change material (mPCM). In addition, this study analyzed the thermal behaviors and improvements in power generation efficiency through field tests by manufacturing a prototype. The results of the outdoor experiment indicated that the BIPV-TEG-PCM prototype improved power generation efficiency by approximately 2% in the intermediate season and 2.5% in the summer relative to the efficiency of a general PV panel. Moreover, using a single TEG, approximately 3.06 Wh of the heat wasted in the building envelope can be recovered as a form of electricity annually.

A medium-temperature, tubeless heat exchanger based on alloy microencapsulated phase change material (MEPCM)/ceramic composites

High-performance heat storage materials and devices are urgently needed to meet the demand for efficient heat storage. Herein, a novel SnBi58 alloy microencapsulated phase change material (MEPCM)/ceramic composite with flow channels inside is fabricated for medium-temperature heat storage, which combines the characteristics of sensible heat storage (SHS) and latent heat storage (LHS). Then a tubeless heat exchanger based on the composite is constructed, and its heat storage performance is experimentally studied. The results show that the thermal conductivity of the composite-based heat exchanger is doubled (up to 3.09 W/(m·K)) and the heat storage density is increased by 30.4% to 559.1 MJ/m3 compared with the ceramic-based heat exchanger. Meanwhile, the heat storage performance of the heat exchanger can be improved with the increase of inlet temperature and mass flow rate, and it is more sensitive to the response of the inlet temperature. Furthermore, the average heat storage duty of the heat exchanger reaches 1183 W/(m3·°C), which is 3.56 times the mean value of other heat storage devices. Finally, test results confirm the high thermal reliability of the composite, which can meet the tubeless heat exchange requirements.

Phase change material microcapsules with DOPO/Cu modified halloysite nanotubes for thermal controlling of buildings: Thermophysical properties, flame retardant performance and thermal comfort levels

Although the microencapsulated phase change material (MPCM) with organic core-shell structure is an effective means to encapsulate phase change material (PCM), it has the defects of low thermal conductivity and flammability. Herein, the flame retardant halloysite nanotubes (c-HNTs) doped by 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and Cu nanoparticles were successfully inserted in the MPCM to form a highway to heat transfer. The related examination and surface morphology showed that the DOPO structure anchored by Cu nanoparticles was grafted on the surface of halloysite nanotubes (HNTs) and the c-HNTs were successfully embedded in MPCM. The thermogravimetric analysis (TGA) proved that c-MPCM has the best thermal stability when compared to other samples, which is caused by the presence of c-HNTs. The differential scanning calorimetry (DSC) test indicated that MPCM delays the heat transfer to the capric acid while the HNTs improve this situation as thermal conduction channels. Then, the MPCM samples were added to the epoxy resin (EP). In the cone calorimetry test, we found that the heat and smoke release rate of EP composite is obviously reduced. Finally, the temperature control ability test of MPCM demonstrated that the EP composite with c-HNTs has the minimum temperature fluctuation. These properties will greatly stimulate the application of c-MPCM in insulation materials.

Numerical investigation of double-walled direct absorption evacuated tube solar collector using microencapsulated PCM and nanofluid

In the present study, the thermal performance of direct absorption solar evacuated tube collectors utilizing CuO nanofluid, CuO/Al2O3 binary nanofluid, and CuO nanofluid combined with microencapsulated phase change material (MPCM) is investigated. The impact of base fluid types (water and ethylene glycol (EG)), nanofluid volume fraction, and flow velocity, are analyzed by the numerical simulation of the collector. Also, two models (single-phase and mixture) are used for simulating the MPCM slurry. Due to the insignificant difference between the results of the single-phase and two-phase models, the single-phase model is recommended to reduce computational time. It is found that the most significant differences in outlet temperature occur using 0.06 % Al2O3+ 0.002 % CuO/water nanofluid and 0.06 % Al2O3+ 0.002 % CuO/EG nanofluid which are equal to 28.34 K, and 36.64 K, respectively. The collector efficiency using binary nanofluids is higher than using CuO nanofluids in both water- and EG-based nanofluids. Results indicate that combining MPCM and CuO nanofluid increases the collector efficiency by 4.53 % and lowers the heat loss by 5.84 %. The simultaneous application of MPCM and CuO nanofluid has the highest efficiency among all working fluids.

Numerical modeling of the effects of the radial and axial location of added micro-encapsulated phase change materials in vertical borehole heat exchangers

A numerical model of a vertical borehole heat exchanger (BHE) with micro-encapsulated phase-change material (PCM) was used to examine the thermal effect of the radial and axial location of the added PCM within the borehole. In the radial direction, PCM could be placed at the center of the borehole, at the borehole periphery, or interspersed within the grout. In the axial direction, PCM could be concentrated either in the top, bottom, or mid portions of the borehole grout, or again interspersed evenly. PCM could also be added to the borehole heat transfer fluid. Each location has its own thermal, and therefore economic, advantages and disadvantages, and thus this present work investigated these effects toward decreasing borehole length. Analysis of results showed that the best radial location for the PCM is intermixed within the grout, even though that configuration has a disadvantage of increasing the overall borehole thermal resistance. In the axial direction, it was found that the thermal behavior of the PCM varied over the borehole length, and thus adding the PCM-grout mixture to only the bottom half-depth of the borehole reduced the thermal benefit by only about 19%. Thus, it is concluded that strategic placement of PCM within borehole grout can significantly improve the economics of its use in vertical GCHP systems, but at current costs of PCM, its use in borehole grouts remains an economic challenge.

A review of the thermal storage of phase change material, morphology, synthesis methods, characterization, and applications of microencapsulated phase change material

Abstract In the thermal energy storage area, microencapsulated phase change material (MPCM) is getting more popular among researchers. When phase change materials (PCMs) shift from one phase to another at a specific temperature, a significant quantity of thermal energy is stored. The PCM application focuses on upgrading worldwide energy conservation efforts in light of the rapidly dwindling fossil fuels. The thermal energy supplied by PCM is significantly influenced by the choice of supporting materials and encapsulation methods. A solution to the volume change issues of PCM, phase separation, and leakage is the PCM microencapsulation technique. One of the most common methods to increase the effectiveness of thermal storage material is attained by using PCM with microencapsulation. The preparation processes and thermal characteristics of the MPCM are summarized in this paper. This paper gives information about MPCM with its types, properties, testing, and characterizations. Tables describe specific examples of PCM with thermal properties. Applications in various fields are defined. This review gives as much information to help and be useful for new researchers in the field of thermal management systems to guide their future research.

Studies on Myristyl Alcohol based microencapsulated phase change material for thermal energy storage applications

ABSTRACT In this paper, a novel Myristyl Alcohol (MAL) phase change material (PCM) microencapsulated with calcium carbonate (CaCO3) shell through a self-assembly process is developed. Despite having strong thermal energy storage capabilities, pure MAL PCM has low thermal conductivity and phase change leakage issues, which limit its usefulness for thermal energy storage applications. To avoid leakage and improve thermal conductivity, pure MAL PCM is encapsulated with a CaCO3 shell for different core/shell mass ratios. The morphology, chemical structure, and crystalline structure of the microencapsulated phase change material (MAL-MEPCM) samples are analyzed by the SEM, FTIR, and XRD. The SEM morphology reveals that the generated microcapsules have spherical, needle-shaped, and floral forms. The DSC thermograms reveal the latent heat (melting) values of 223.36 and 155.40 J/g with an encapsulation efficiency of 69.42% for pure MAL PCM and MAL-MEPCM, the maximum core/shell mass ratio. The TGA thermograms confirm good thermal stability. Even after 200 thermal cycles, the samples have consistent chemical stability and phase change properties, as evidenced by FTIR and DSC results. The prepared MAL-MEPCM samples have higher thermal conductivity than the pure MAL PCM and thus enhance thermal energy storage performance.

Effect of carbon nanotube and microencapsulated phase change material utilization on the thermal energy storage performance in UV cured (photoinitiated) unsaturated polyester composites

The utilization of phase change materials in the synthesis of polyester is an economically viable approach for the production of polymer composites with remarkable thermal and mechanical characteristics, thereby facilitating thermal energy savings. This study manufactured a series of unsaturated polyester resin (UPR)/carbon nanotubes (CNT)/MPCM composites via mechanical mixing and ultrasonication processes and the produced composites were cured with ultraviolet (UV) curing technology. The unsaturated polyester resin was utilized as a support matrix, and to improve the thermal conductivity of MPCM-UPR composites, CNT were introduced into the matrix. This paper discusses the effect of CNT and MPCM on the mechanical, thermal, and thermal regulative performance of polyester composites. A 10 wt% incorporation of MPCM led to an almost 77 % and 15 % drop at Charpy impact strength and Shore D hardness values of reference UPR, respectively. Similarly, the introduction of substitution of 0.005 wt% of CNT reduced the impact strength of the specimen with 10 % MPCM by 31 %, while it increased the Shore D hardness by almost 5 %. Although the thermal conductivity of reference resin was reduced by 15 % with a 10 % addition of MPCM, CNT content increased the thermal conductivity values by almost 20 % regardless of MPCM concentration. The onset melting and freezing temperatures of MPCM were found to be 21.71 and 22.74 °C, respectively; while for the composites with and without CNT, this value ranged between 20.70 and 22.39 °C and 22.45–22.90 °C, respectively. Thermoregulation test results indicate that MPCM improved the thermal energy storage capacity of composites. The results of this research will be of great significance in order to gain a more comprehensive understanding of the thermal properties of polyesters with MPCM/CNT, thus allowing for the utilization of this material as a latent heat thermal energy storage system for energy conservation.

Heat and mass transfer in different concrete structures: a study of self-compacting concrete and geopolymer concrete

AbstractThermal characteristics of concrete are one of the main topics in concrete technology researches. They were extensively studied since the 1980s to predict the behavior of the concrete in fire and the performance of massive concrete. However, this topic was raised again after 2010 as a part of sustainable, energy effective and ecofriendly buildings studies. The aim of this research is to present a comparison between the thermal characteristics of self-compacted concrete (SCC) and the geopolymer concrete (GPC) using collected previous researches. More than fifty references were collected, sorted and analyzed in the last forty years. The results showed that (GPC) has better thermal characteristics, such as thermal conductivity, heat capacity, fire resistance, while (SCC) has better mechanical properties, such as compressive strength, early strength and elastic modulus. Besides that, from ecological point of view, partially replacing of ordinary Portland cement (OPC) with microencapsulated phase change materials (MPCM), such as fly ash, silica fume, slag and metakaolin, remarkably decreases the CO2 footprint of construction industry.

Forced Convection of Nanofluid-Microencapsulated Phase Change Material Mixtures in Mini-Channels: Importance of the Mini-Channel Height

Energy storage and heat enhancement are the main focus of many projects in the industry. Phase change material is receiving a lot of interest in the energy sector. In particular, storing energy for later use or heat extraction has been the focus of many types of research in this field. Nanofluid and microencapsulated phase change material (MEPCM) flow is an exciting field, mainly when the mixture fluid circulates in mini channels. Many applications, including cooling surfaces, have been investigated. This paper examines how to store energy without using extra space for a particular design. Four different fluids are circulating in mini-channels which are distilled water, 0.5%vol Al2O3 in water, 0.5% Al2O3 +4% MEPCM/water, and 0.5% Al2O3 +20% MEPCM/water. The flow is assumed laminar and steady-state. Results revealed that the amount of energy absorbed when using 0.5% Al2O3 +20% MEPCM/water mixture exceeds 0.5%vol Al2O3 in the water mixture. By varying the mini-channels heights, maintaining constant test volume of the cavity, it was found that the flow in the minichannels and above the mini-channels exhibit the more extensive heat removal capacity. This occurs when the mini-channels height occupies half the test cavity height corresponding to an aspect ratio equal to 6. Among the four fluids under investigation, 0.5% Al2O3 +20% MEPCM/water is the most effective fluid for heat removal and energy storage.

A new strategy for simultaneous photoluminescence and thermal energy storage/release: Microencapsulated phase change materials via nano-Y2O3 modified PW@CaCO3

A multifunctional microencapsulated phase change material (PW@CaCO3/Y2O3) with both photoluminescence and thermal energy storage/release properties has been prepared by in situ polymerization. The material is based on the phase change material paraffin wax (PW) as its core, and the highly thermally conductive inorganic material CaCO3 is selected as the shell material to which a nano-Y2O3 material is attached. Five samples with different amounts of nano-Y2O3 incorporated in the shell are prepared. The microscopic morphology, chemical composition, crystal structure, thermal energy storage properties, thermal conductivity, thermal stability, as well as fluorescence spectra and intensities of the samples are experimentally measured and compared. The luminescence properties of nano-Y2O3 and the light enhancement phenomenon of microencapsulated phase change materials are also analyzed. The thermal properties are investigated, and it is found that the PC-Y3 sample (i.e., the mass ratio of PW:CaCO3:nano-Y2O3 is 100:100:3.0) exhibits the best thermal performance among the five samples with a melting enthalpy of (87.5 ± 2.5) J/g, an encapsulation efficiency of (61.9 ± 1.2)%, a thermal energy storage efficiency of (62.1 ± 1.5)%, an average specific heat capacity of (1.38 ± 0.21) kJ/(kg K) in solid phase (10–20 °C) and (1.46 ± 0.02) kJ/(kg K) in liquid phase (70–80 °C), and a thermal conductivity of (1.55 ± 0.01) W/(m K) in solid phase that is six times that of the solid PW. A study of the optical properties revealed that the microcapsules emitted blue light at an excitation wavelength of 290.0 ± 2.2 nm. The fluorescence intensity appeared to be enhanced with the addition of nano-Y2O3. This microencapsulated phase change material has potential applications in areas where synchronization of fluorescence and thermal modulation is required; for example, some specific fluorescent sensors that are very sensitive to heat should operate at a fixed low temperature.

Development of smart polyurethane foam with combined capabilities of thermal insulation and thermal energy storage by integrating microencapsulated phase change material

Development of smart polyurethane foam with combined capabilities of thermal insulation and thermal energy storage by integrating microencapsulated phase change material

Numerical simulation of heat and mass transfer of a wall containing micro-encapsulated phase change concrete (PCC)

Before planning to equip buildings with energy systems, it is essential to first understand and control the behavior of the premises (via control of heat and water transfer phenomena) (air conditioners, heat pumps, heat exchangers, etc.). Given the amount of solar radiation to which it is exposed in summer and its significant contribution to energy loss in winter, the thermal insulation of the ceiling appears effective. The objective of this work is to study the heat and mass transfer through a ceiling wall containing micro-encapsulated phase change materials under realistic climatic conditions based on meteorological data in Tunisia. This article is about a numerical study that uses software (DIGITAL Visual FORTRAN 95) to predict the effect of incorporating a layer of PCM on thermal behavior, mass, and occupant thermal comfort, as well as energy consumption for summer and winter periods.

Temperature regulation and rheological properties assessment of asphalt binders modified with paraffin/ SiO2 micro-encapsulated phase change materials

Solar energy, as a renewable energy source, can be maximized through phase change materials, thus making it possible to mitigate the urban heat island. The paraffin/ SiO2 micro-encapsulated phase change material (MPCM) with 53.64 °C phase transition temperature was synthesized in this paper via in-situ dehydration and condensation reaction, and the cooling effect in asphalt binder was investigated by implementing various experiments. The micro characterization results of MPCM show that the SiO2 shell resoundingly encapsulated the paraffin and the average particle size of MPCM was 94.8 nm. Fourier transform infrared spectroscopy (FT-IR) and X-ray diffractometer (XRD) results show that the interaction between MPCM and asphalt binder was a physical blending process. Furthermore, the initial degradation temperature of 240 °C means its remarkable thermal stability and confirms the applicability of MPCM to asphalt binders theoretically. It was found that the melting and solidifying enthalpies of MPCM are 110.5 J/g and 108.7 J/g, respectively, from the differential scanning calorimeter (DSC) results, while the maximum melting and solidifying enthalpies of MPCM-modified asphalt binders can be achieved at 13.76 J/g and 11.04 J/g respectively. The MPCM-modified asphalt binders possess a higher specific heat capacity than base asphalt binders, especially at the range of phase transition temperatures (20–60 °C), suggesting the predominant thermal regulation effects. The heating rate of modified asphalt binders is reduced at the temperature ranging from 45 to 55 °C due to the phase transition of MPCM. Dynamic shear rheometer (DSR) results demonstrate that the rutting resistance of modified asphalt binders was better than the base asphalt binder at low-temperature and low frequency only at the content of 8 % and 10 %. Thus, we concluded that the paraffin/ SiO2 MPCM is applicable for cooling asphalt pavement and the rheological properties of MCPM in asphalt pavement need further research.

Structure-property correlation of thermally activated nano-size phase change material in the cementitious system

Recently, energy-efficient building design has emerged as a prominent research focus for maximizing energy savings. In light of this, various attempts are made to improve the thermal mass of buildings. Increasing the heat capacity of construction materials with the incorporation of phase change material (PCM) has been considered an easy and effective technique to increase the thermal mass of concrete structures. However, the incorporation of microencapsulated phase change material (MPCM) into cementitious system possesses drawbacks of weaker hydration activity and leakage problems. Therefore, this study has been aimed to explore the chemical and morphological evolution of thermally activated nanoencapsulated phase change material (NPCM) with principal hydrated phase of ordinary Portland cement (OPC) at 60 °C. With an average size of ∼450 nm, silica encapsulated paraffin-based NPCM is synthesized via facile in-situ polycondensation method. 1% NPCM has boosted the hydration reaction with the occurrence of a low quantity of C3S + C2S, whereas a denser cement matrix with minimum pore structures has been accomplished due to better pozzolanic activity and existence of CaCO3 on the surface of NPCM. The emergence of needle-shaped CaCO3 polymorph on the NPCM surface proves that NPCM acts as secondary nucleation sites for the formation of additional C–S–H, which has manifested pore-filling effects as well as further leakage protection. The activation of NPCM at high-temperature curing has ascertained excellent structural and durability performances over an extended period. Thus, this study may bring out better insight to the researchers toward the direction of energy storage materials applications in building structures.

Preparation of n-Octadecane@MF resin microPCMs and its application in temperature control of esterification reactions

Reaction thermal runaway accidents occur frequently and occupy a high proportion in chemical accidents. Reducing accidents by controlling reaction temperature is of great implication to enhance the safety level of chemical processes. Phase change materials (PCMs) have a good energy storage potential, which can rapidly convert the reaction exotherm in the reaction process into its own phase change latent heat, urgently control the reaction temperature, and enhance the process thermal safety level. In this study, using n-octadecane as the core and melamine-formaldehyde (MF) resin as the shell, microencapsulated phase change materials (microPCMs) was made, which has a smooth spherical shape, good thermal stability, and a phase change enthalpy up to 162.87 J/g. The homogeneous esterification reaction of 2-butanol (2 B) and propionic anhydride (PA) was selected as the target reaction, and then the reaction was scaled up equivalently to investigate the effect of amplification to the reaction system. The results indicated that the temperature control of the esterification reaction system by microPCMs is the synergy between physical inhibition and chemical inhibition. The reaction temperature could be controlled by adding microPCMs, and the temperature control effect improved with the increase of microPCMs addition. In large scale reactors, microPCMs still has certain temperature control ability after being added.