Latent Heat Capacity Research Articles

The performance effect of PEG-silica fume as shape-stabilized phase change materials on mechanical and thermal properties of lightweight concrete panels

Sustainable construction is of paramount importance and one of the methods is deployment of phase change materials (PCMs) in construction materials due to their large latent heat capacity. This study aims at investigating the mechanical and thermal properties of non-structural lightweight concrete incorporating shape-stabilized phase change materials (SSPCMs). Toward this purpose, silica fume and polyethylene glycol 600 (PEG 600) composite was prepared with direct absorption method and no leakage was observed. Wallboards with two thicknesses including 10 % and 18 % SSPCM and macroencapsulated PCM layers were built and tested under two ambient weather conditions. Results stated that the application of SSPCM in specimens would reduce the inner-side temperature of wallboards to a great extent and the panels with less thickness had a better thermal performance. Regarding mechanical properties, tensile and compressive strength of concrete at early ages decreased by the growth of SSPCM content, while this reduction was compensated by the passage of time.

Thermophysical properties of LiF–LiCl–Li2CO3 eutectic mixture/multi-walled carbon nanotubes for thermal energy storage

Latent heat thermal energy storage based on solid-liquid phase change material has a huge potential in dealing with mismatch between energy demand and supply. LiF–LiCl–Li 2 CO 3 ternary system was screened out for high temperature energy storage material due to its good thermophysical properties. Its eutectic composition ( X LiF = 28.41 mol%, X LiCl = 55.09 mol% and X Li2CO3 = 16.50 mol%) was predicted based on the developed thermodynamic model and verified experimentally. The melting point, phase change latent heat, heat capacity, thernal diffusivity, thermal conductivity and thermal stability of LiF–LiCl–Li 2 CO 3 eutectic mixture were measured. And the influence of the addition of multi-walled carbon nanotubes (MWCNTs) were analyzed. It was found that adding MWCNTs could increase the latent heat, specific heat capacity, thermal diffusivity and thermal conductivity of LiF–LiCl–Li 2 CO 3 eutectic mixture, while didn't significantly change the melting temperature. • An innovation molten salt is successfully designed via computational thermodynamic approach. • Thermophysical properties of the eutectic salt are determined experimentally. • Composite phase change material (CPCM) was prepared and characterized. • Thermal conductivity and heat capacity can be enhanced by doping nanoparticles.

Foam Concrete Produced with Recycled Concrete Powder and Phase Change Materials

In construction industry, phase change materials (PCMs), have recently been studied and found effective in increasing energy efficiency of buildings through their high capacity to store thermal energy. In this study, a combination of Capric (CA)-Palmitic acid (PA) with optimum mass ratio of 85–15% is used and impregnated with recycled concrete powder (RCP). The resulting composite is produced as foam concrete and tested for a series of physico-mechanical, thermal and microstructural properties. The results show that recycled concrete powder can host PCMs without leaking if used in proper quantity. Further, the differential scanning calorimetry (DSC) results show that the produced RCP/CA-PA composites have a latent heat capacity of 34.1 and 33.5 J/g in liquid and solid phases, respectively, which is found to remain stable even after 300 phase changing cycles. In this regard, the indoor temperature performance of the rooms supplied with composite foams made with PCMs, showed significantly enhanced efficiency. In addition, it is shown that inclusion of PCMs in foam concrete can significantly reduce porosity and pore connectivity, resulting in enhanced mechanical properties. The results are found promising and point to the suitability of using RCP-impregnated PCMs in foam composites to enhance thermo-regulative performance of buildings. On this basis, the use of PCMs for enhanced thermal properties of buildings are recommended, especially to be used in conjunction with foam concrete.

Impact of nano‐enhanced phase change material on thermal performance of building envelope and energy consumption

Using phase change material (PCM) in the building envelope can provide energy saving advantages by shaving peak heating and cooling loads. However, the poor thermal conductivity of PCMs limits their application and potential benefits because of inadequate heat storage/release rates. Increasing effective thermal conductivity by adding metal nanoparticles with high thermal conductivity to PCM (NPCM) could be a promising method to accelerate the phase change process, thereby exploiting latent heat more effectively. The potential impact of the utilization of NPCM technology has not yet been adequately explored for building external walls. This study aimed to reveal whether the dispersal of highly conductive nanoparticles in PCM in external building walls helps conserve energy or not. PCM enriched with aluminium oxide nanoparticles (Al2O3) with a content of 1, 2, and 3 vol% was used. The outputs showed that the nanoparticle addition decreased the energy-saving performance of PCM since the reduction in the thermal resistance and latent heat capacity caused by the nanoparticles loading was more profound than the enhancement provided by the improvement of latent heat exploitation caused by the increased thermal conductivity. For example, heating energy saving was reduced by 0.6% when a 3-cm PCM with 1 vol% Al2O3 was used instead of a pure PCM. The negative impact increased to 1.7% by increasing the nanoparticle concentration to 3 vol%. Thus, augmenting the thermal conductivity for higher latent heat activation by adding nanoparticles was not beneficial for building wall applications in a hot-summer Mediterranean climate. Highlights Effect of nanoparticle-enhanced PCM on building energy saving. PCM with Al2O3 content of 0, 1, 2, and 3 vol% embedded in external wall. Yearly energy saving of 20.7% was achieved with pure PCM in the wall. Adding 3 vol% Al2O3 to PCM reduced heating energy saving by 1.7%. Negative effect on energy saving increased with increasing nanoparticle concentration.

Activated carbon nanotube/polyacrylic acid/stearyl alcohol nanocomposites as thermal energy storage effective shape-stabilized phase change materials

Stearyl alcohol (SA) as one of organic phase change materials (PCMs) has promising thermal energy storage prospective. However, the leakage issue during solid-liquid phase change period and low heat harvesting and releasing rate significantly attenuates its TES potential. Towards to overcome these drawbacks, the SA was shape-stabilized using the cross-linked poly acrylic acid (PAA) and activated single walled carbon nanotubes (a-SWCNTs) at three different weigh ratio of 1:1:2, 1:3:4 and 1:5:6 (a-SWCNTs:PAA:SA). The chemical/crystalline and morphologic structures of the produced shape stabilized-nano composite PCMs (SS-NCPCMs) were investigated by FT-IR, XRD and SEM analyses. The latent heat storage (LHS) features and thermal stability of the SS-NCPCMs were measured by DSC and TGA techniques. The thermal cycling effect on the LHS properties and chemical structures of the SS-NCPCMs was also estimated. The DSC findings indicated that the SS-NCPCMs had melting temperature of around 55–56 °C and latent heat capacity of about 135 J/g. TGA measurements disclosed that the thermal degradation temperatures of the nano composite PCMs were prolonged somewhat compared to the SA. A 500 heating-cooling cycling test revealed that the SS-NCPCMs had great chemical and LHS stability. The heat harvesting and releasing performance of the NCPCMs were considerably shortened compared to those of pure SA. The obtained results exposed that the synthesized SWCNTs/PAA/SA composites can be evaluated as promising LHS materials for thermal management of electronic systems, automobile modules, food carriers, solar PV panels etc.

Thermal performance improvement of energy storage materials for low operating temperature solar water heating systems

Recent studies have shown the attractive energy storage capabilities of phase change materials (PCMs); however, PCMs may not be fully effective due to their poor heat transfer characteristics. Moreover, the melting point of PCMs restricts direct integration into a solar collector for low operating solar water heating (SWH) applications. This study investigates the heat transfer enhancement of PCMs as well as aiming to lower their melting point onset to expedite the latent heat storage initiation. The selected types of PCMs are paraffin waxes with melting point temperatures of 28–72 °C. In Phase I, silicone oil is selected as a heat transfer medium to be used with the PCMs to establish natural convection enhancement, which led to maximum melting point depression of approximately 3 °C in the PCM72. In Phase II, the conductive heat transfer enhancement was studied by adding nanoparticles with varying mass concentrations. From this analysis, it was determined that PCM72 with 1% multi-walled carbon nanotubes (MWCNT) has shown an increase of approximately 3.81% in thermal conductivity. The obtained results from this study can lead to overall efficiency improvement of SWH systems by employing the PCM mixtures with low melting point, while keeping the high latent heat capacity, and high thermal conductivity.

Glass fiber reinforced gypsum composites with microencapsulated PCM as novel building thermal energy storage material

A comprehensive study involving the fabrication and characterization of gypsum plasterboards combined with microencapsulated phase change material (mPCM) is introduced to evaluate their benefits regarding thermoregulation management and energy saving performance in buildings. For this purpose, the produced new type of gypsum plasterboard was subjected to the detailed chemical, morphological, mechanical, physical and thermal tests. The gypsum plasterboard incorporated with mPCM (7.5 wt%) and reinforced by glass fiber has latent heat capacities as high as 16.7 and 16.6 J/g at onset melting and solidification temperature of 11.90 °C and 12.09 °C, respectively. TGA analyzes revealed high thermal stability of gypsum plasterboard up to about 140 °C. Outcomes exhibited that mPCM-gypsum plasterboard can substantially diminish cooling load of a building during the daytime even at the high room temperature and offer decline in heat necessity of a house during night-time. During peak room temperature hours, the mPCM-gypsum plasterboard achieved 3 °C lower temperatures than the reference room, and it provided a cooler room temperature for about 7 h during the daytime while a warmer temperature of 0.3 °C was achieved at the cold weather. As a result, the produced gypsum-based composites can be considered as an energy-saving and indoor temperature regulating material in buildings.

Fabrication and Thermal Performance of 3D Copper-Mesh-Sintered Foam/Paraffin Phase Change Materials for Solar Thermal Energy Storage

Due to its large latent heat and high energy storage capacity, paraffin as one of the phase change materials (PCMs) has been widely applied in many energy-related applications in recent years. The current applications of paraffin, however, are limited by the low thermal conductivity and the leakage problem. To address these issues, we designed and fabricated form-stable composite PCMs by impregnating organic paraffin within graphite-coated copper foams. The graphite-coated copper foam was prepared by sintering multilayer copper meshes, and graphite nanoparticles were deposited on the surface of the porous copper foam. Graphite nanoparticles could directly absorb and convert solar energy into thermal energy, and the converted thermal energy was stored in the paraffin PCMs through phase change heat transfer. The graphite-coated copper foam not only effectively enhanced the thermal conductivity of paraffin PCMs, but also its porous structure and superhydrophobic surface prevented the paraffin leakage during the charging process. The experimental results showed that the composite PCMs had a thermal conductivity of 2.97 W/(m·K), and no leakage occurred during the charging and discharging process. Finally, we demonstrated the composite PCMs can be readily integrated with solar thermoelectric systems to serve as the energy sources for generating electricity by using abundant clean solar-thermal energy.

Low-cost magnesium-based eutectic salt hydrate phase change material with enhanced thermal performance for energy storage

Low-cost salt hydrate eutectic phase change materials (EPCMs) are attracting increasing attentions and have shown good application prospects for medium-temperature solar thermal energy storage. Water control during sample preparation, supercooling inhibition, and cycle stability are crucial to ensure the thermal reliability of salt hydrate PCM-based thermal energy storage systems. In this study, a “differential scanning calorimeter (DSC) monitoring system evolution process” is developed to prepare MgCl2·6H2O and Mg-EPCM [MgCl2·6H2O (43.0 wt%)-Mg(NO3)2·6H2O (57.0 wt%)], in which unpurified industrial bischofite is used as a precursor. Melting enthalpy of the prepared MgCl2·6H2O can be raised from 125.6 to 164.2 J/g, which is higher than that of recrystallized MgCl2·6H2O and comparable to those of guaranteed reagent (GR), 3 N (purity: 99.9%), and 4 N (purity: 99.99%) MgCl2·6H2O. Furthermore, melting enthalpy of the prepared Mg-EPCM was improved by approximately 10%, from 126 to 140.1 J/g. The latent heat storage capacity is mainly affected by the preparation method, rather than by the small amounts of impurity elements arising from the precursor (impurity rate: ≤ 0.4%). Moreover, 0.5% Sr(OH)2·8H2O has inhibited the supercooling degree of Mg-EPCM within 1.0 °C, with a melting enthalpy of 139.5 J/g. It is found that Sr(OH)2·8H2O participates in eutectic formation and simultaneously nucleates the system to inhibit supercooling. Thermal cycle testing shows that there is almost no significant degradation after 500 thermal cycles. The low-cost Mg-EPCM developed here exhibits an excellent latent heat capacity and inhibits supercooling, showing great practical potential for latent heat storage systems.

Polyimide/phosphorene hybrid aerogel-based composite phase change materials for high-efficient solar energy capture and photothermal conversion

• We developed a new type of composite PCM for high-efficient solar energy capture. • The composite PCM was based on polyimide/phosphorene hybrid aerogel and PEG . • The introduction of phosphorene enhances solar photothermal absorption and conversion. • The composite PCM presents high solar light-to-heat conversion efficiency. • The composite PCM exhibits great potential for efficient utilization of solar energy. Solar energy is the cleanest and most abundant renewable energy source that can be utilized to displace fossil fuels and provide an effective solution for future energy shortage and climate change. Aiming at enhancing the capture efficiency of solar photothermal energy, we developed a novel type of phase-change composites based on polyimide (PI)/phosphorene (PR) hybrid aerogel and polyethylene glycol (PEG). The composites were prepared by fabricating a series of PI/PR hybrid aerogels with different loadings of PR nanosheets using freeze-drying and thermal imidization techniques, followed by vacuum impregnation of PEG as a phase change material into the aerogel framework. The obtained hybrid aerogels exhibited a lightweight nature with a density of 21.9 mg·cm −3 when 16 wt% PR nanosheets were incorporated, resulting in an extremely high PEG loading of 4067% in the aerogel system. The combination of PI and PR nanosheets leads to a significant enhancement in solar light absorption and photothermal energy conversion for the hybrid aerogel/PEG composites. The loading amount of PEG was also improved remarkably due to an increase in the volume capacity of the hybrid aerogels resulting from the introduction of PR nanosheets. The resultant hybrid aerogel/PEG composites not only exhibit a high latent-heat capacity of over 170 J·g −1 and a high photothermal conversion efficiency of 82.5%, but also show good thermal impact resistance to keep their original shape and form well after heating at 80 °C for 20 min and maintain a high thermal cycle stability after thermally cycled for 500 times. These superior performances make the hybrid aerogel/PEG composites capable of dealing with a wide range of applications in solar photothermal energy capture and storage. This study provides a promising strategy for the design and development of high-performance and lightweight composite PCMs to meet the requirement of applications for efficient utilization of solar energy.

Thermal inertia and energy efficiency enhancements of hollow clay bricks integrated with phase change materials

This article examines the usefulness of incorporating three passive measures into hollow clay walls typically used in Moroccan structures to improve thermal comfort and energy savings in buildings subjected to the climatic conditions of Marrakesh city. The results revealed that coating the internal surfaces of the brick's cavities with a low emissivity paint, filling cavities with insulation material, or utilizing phase change materials (PCM) positively impacts cooling demand and enhances thermal inertia of hollow clay bricks. Thanks to a parametric study, the adequate PCM type and its optimum filling location were determined for maximum benefit from the PCM latent heat capacity to enhance the thermal inertia of the studied wall. The results indicated that filling the middle cavities with a PCM (melting temperature of 32 °C) combined with using a low emissivity paint or filling an insulation material in the internal and external cavities of the brick leads to the maximum enhancement in the thermal inertia characteristics of hollow clay walls. It can be stated that using the optimal configuration permits reducing the internal heat flux density by about 82% and retarding of the external thermal wave to penetrate the indoor environment by about 4 h compared to the traditional hollow clay bricks.

Effects of thermal conductive fillers on energy storage performance of Form-Stable phase change material integrated in Cement-Based composites

Energy consumption to achieve thermal comfort in buildings is one of the significant challenges in the construction industry. Hence, applying thermal energy storage (TES) systems, such as phase change material (PCM), is increasingly being considered as a promising solution. However, the low thermal conductivity of PCM has a negative effect on the thermal cycleand, consequently, the efficiency of the TES system. This study aims to develop a novel form-stable PCM cement composite and investigates the effects of two thermal conductive fillers (TCFs), graphite powder and nano titanium dioxide (nTiO2), on the thermal performance of PCM cement composites. For this purpose, the TCFs at different mass fractions (1 and 3 wt%) were dispersed in the PCM using sonication and impregnated into expanded glass aggregates (EGA). The microstructure studies revealed that TCF was well dispersed in the PCM and PCM-TCF was successfully impregnated into the EGA. The results of thermogravimetric analysis (TGA) and Fourier Transform Infrared Spectroscopy (FT-IR) demonstrated that there was no chemical reaction between PCM and TCFs, and the PCM-TCF were thermally stable in the operating temperature ranges. The differential scanning calorimetry (DSC) analysis showed that the latent heat capacity of PCM-TCF remained reasonable with a maximum deduction of 9.6% and supercooling temperature enhancement up to 3.4 °C. The thermal behaviour analysis obtained from infrared thermography (IRT) imaging showed a 50% improvement in the heat transfer rate of the PCM composite. Moreover, a room model experiment revealed that integrating TCFs into PCM significantly enhanced the performance of EGA/PCM cement mortar. This is evidenced by a reduction in peak indoor temperature of up to 2.5 °C compared to the control sample.

Mechanically strong hectorite aerogel encapsulated octadecane as shape-stabilized phase change materials for thermal energy storage and management

Phase change materials (PCMs) are considered one of the most advanced energy-saving materials owing to their high thermal energy storage density during the phase transition process. To solve the leakage problem and poor thermal properties in PCMs, a three-dimensional (3D) hectorite aerogel, with an abundant porous structure, was synthesized to encapsulate octadecane (ODE) for preparing hectorite/octadecane composite PCMs with shape stability, large latent heat capacity, and good mechanical strength. The mechanical and thermophysical properties of the composite PCMs were investigated in depth in this study. Due to the high porosity characteristic of hectorite aerogel, the composite PCMs exhibited a large latent capacity of 196.70 J/g with an ODE loading rate larger than 85 wt%. It was also found that the aerogel played an important role in maintaining shape stability, as no significant leakage was observed during the phase-change process. In addition, the composite PCMs exhibited a compressive strength of approximately 2.4 MPa, suggesting good mechanical strength. The thermal stability was found to be excellent, considering that the thermal decomposition temperature of the composite was far higher than the phase change temperature. The excellent shape stability and thermal stability contributed to the outstanding recycling performance of the composite PCMs. The thermal management performance of the composite, in a building house model, was also tested to verify its superior thermal regulation function. Thus, these mechanically strong composite PCMs, with stupendous energy storage capacities and good form stabilities, can be applied in the energy storage and thermal management fields, thereby showing great potential for a sustainable society.

Binary composite (TiO2-Gr) based nano-enhanced organic phase change material: Effect on thermophysical properties

The latent heat storage technology using Phase Change Materials (PCMs) has recently been extensively utilized in energy conservation and management to reduce energy consumption. To improve the thermal conductivity of PCMs, they have been incorporated with nanoparticles. In this article, we report, Titanium dioxide-Graphene (TiO2:Gr) binary composite (1 wt% TiO2: 0.1, 0.5, 1 and 2 wt% of Graphene (Gr)) with Paraffin wax (PW) to improve the thermophysical properties added with sodium dodecylbenzene sulphonate (SDBS) as surfactant. Ultraviolet-visible spectrometer (UV–VIS), Fourier transform infrared spectroscopy (FT-IR), Differential scanning calorimeter (DSC), Thermogravimetric analyzer (TGA), Field Emission Scanning Electron Microscopy (FESEM) and Thermal property analyzer (TEMPOS) were used for material characterizations. The latent heat capacity of the PW/Titanium oxide (TiO2) composite and the PW/TiO2-Gr binary composites were improved by 8.62% and 10.02%, respectively, in comparison to base PCM. The thermal conductivity of the composite PCMs with PW/TiO2-1.0 and PW/TiO2Gr-1.0 is 120% and 179% higher than base PW. The FT-IR spectra demonstrated no chemical interaction between the PW and the nanoparticles. TGA results presented improved thermal stability by integration of the TiO2-Graphene particles into the matrix of paraffin wax. The light transmission of the prepared composite was reduced by 58.30% related to base PW, resulted increased light absorption and, subsequently, enhanced photothermal conversion. The composite's improved thermal conductivity and enthalpy make it a strong contender for use in TES and solar photovoltaics thermal systems.

Hollow Filaments Synthesized by Dry-Jet Wet Spinning of Cellulose Nanofibrils: Structural Properties and Thermoregulation with Phase-Change Infills.

We use dry-jet wet spinning in a coaxial configuration by extruding an aqueous colloidal suspension of oxidized nanocellulose (hydrogel shell) combined with airflow in the core. The coagulation of the hydrogel in a water bath results in hollow filaments (HF) that are drawn continuously at relatively high rates. Small-angle and wide-angle X-ray scattering (SAXS/WAXS) reveals the orientation and order of the cellulose sheath, depending on the applied shear flow and drying method (free-drying and drying under tension). The obtained dry HF show Young’s modulus and tensile strength of up to 9 GPa and 66 MPa, respectively. Two types of phase-change materials (PCM), polyethylene glycol (PEG) and paraffin (PA), are used as infills to enable filaments for energy regulation. An increased strain (9%) is observed in the PCM-filled filaments (HF-PEG and HF-PA). The filaments display similar thermal behavior (dynamic scanning calorimetry) compared to the neat infill, PEG, or paraffin, reaching a maximum latent heat capacity of 170 J·g–1 (48–55 °C) and 169 J·g–1 (52–54 °C), respectively. Overall, this study demonstrates the facile and scalable production of two-component core-shell filaments that combine structural integrity, heat storage, and thermoregulation properties.

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.

Polyimide/MXene hybrid aerogel-based phase-change composites for solar-driven seawater desalination

Aiming to explore a high-efficient seawater desalination technique based on solar photothermal energy as the cleanest and most abundant renewable energy source, we developed a novel type of phase-change composites based on a polyimide (PI)/MXene hybrid aerogel as a supporting material and polyethylene glycol (PEG) as a phase change material. The introduction of Ti3C2Tx MXene nanosheets as a high-efficient sunlight absorber not only significantly enhanced solar photothermal energy-conversion efficiency up to 87.28% for the aerogel/PEG composites, but also improved the volume capacity of the hybrid aerogels. This resulted in an extremely high PEG loading rate of up to 97.68 wt% and a high enthalpy efficiency of up to 95.16%. The hybrid aerogel/PEG composites also exhibit an outstanding thermal energy-storage capability under a high latent heat capacity of over 170 J·g−1, high thermal cycle stability, good leakage-resistant performance, excellent thermal impact resistance, and good shape/form stability to deal with the use in seawater desalination. More importantly, the hybrid aerogel/PEG composites show a high seawater evaporation mass of 6.07 kg·m−2, a high evaporation rate of 1.24 kg·m−2·h−1 under one-sun illumination, and a high evaporation efficiency of 50.6% when used in a solar-driven evaporation device. The PI/MXene hybrid aerogel/PEG composites developed by this work exhibit a great potential for application in sustainable seawater desalination.

Pomegranate-like phase-change microcapsules based on multichambered TiO2 shell engulfing multiple n-docosane cores for enhancing heat transfer and leakage prevention

Conventional egg-like core–shell structured phase-change microcapsules present a limitation in thermal conductance and leakage prevention. Aiming at offering a solution to such two issues, we design a unique pomegranate-like structure for the TiO2@n-docosane phase-change microcapsules to enhance their heat transfer transfer and anti-leakage capabilities. The microcapsules were fabricated through a controllable hydrolysis reaction of titanic source in a nonaqueous emulsion-templating system, followed by the polycondensation of its hydrolysates. In the synthesis, the pomegranate-like structure was derived from a double-layered emulsion system based on the internal aggregated small-sized micelles and external large-sized spherical micelle employing a two-step emulsification technique with a nonionic surfactant template. The resultant microcapsules gained high phase-change enthalpies of over 170 J/g at a slow dropwise adding speed of deionized water as a catalyst, and their latent-heat capacity is superior to most of the TiO2-based phase-change microcapsules reported in the literature. Although the pomegranate-like TiO2@n-docosane microcapsules have a relatively lower latent-heat capacity than the conventional egg-like ones, their heat transfer, thermal response, and anti-leakage capability are improved significantly thanks to their unique pomegranate-like structure. Moreover, the pomegranate-like TiO2@n-docosane microcapsules obtained an increase in thermal conductivity by 471% in comparison with pure n-docosane, and their leakage rate decreased by 66.5% compared to the egg-like ones. With superior thermal performance, the novel pomegranate-like phase-change microcapsules developed in this study offer great potential in thermal energy storage and management applications.

High interface compatibility and phase change enthalpy of heat storage wood plastic composites as bio-based building materials for energy saving

Phase change materials (PCMs) is one of the most efficient and reliable methods to store latent heat and reduce energy consumption. This work focused on heat-storage bio-based building materials for energy-saving using encapsulate poly (ethylene glycol) (PEG)/organic diatomite (O-Dt) as the latent heat storage agents, and wood fiber (WF)/high-density polyethylene (HDPE) as the matrix. PEG was encapsulated into the porous structure of Dt, and the obtained form-stable PCM has desired great interface action, high latent heat (105.35 J/g), good packaging capability, and excellent thermal stability. The heat-storage WPCs incorporated with form-stable PCM possessed considerable thermal storage capacity (60.42 J/g) and temperature-regulating ability (12 °C–15 °C). The thermal conductivity of WPC-20% was increased by 26.7% than WPC-0%. The mechanical strength and hydrophobicity of WPCs were increased when the loading percentage of PCM was 5%. Thermal cycling test results demonstrated that the heat storage WPCs had considerable heat storage reliability and chemical stability. The satisfying latent heat capacity and acceptable mechanical strength indicated the heat-storage WPCs could be potentially utilized as building materials for low carbon and energy conservation.

Preparation and thermal conductivity enhancement of a paraffin wax-based composite phase change material doped with garlic stem biochar microparticles

The addition of thermally conductive nanomaterials is an effective strategy for increasing the thermal conductivity of phase change materials (PCMs). However, nanomaterials are expensive and may significantly reduce the latent heat capacity of PCMs. In this study, low-cost and eco-friendly biochar microparticles were prepared from garlic stems, a common food waste in Singapore. The thermal properties of paraffin wax (PW) doped with 1, 3, and 5 wt% garlic stem biochar (GSB) microparticles were investigated. The GSB microparticles prepared at 700 °C had three-dimensional porous and two-dimensional flake-like structures, which contributed to the formation of additional heat transfer pathways in the PW. The addition of 5 wt% GSB microparticles enhanced the thermal conductivity of PW by 27.3% and 7.2% in the solid and liquid phases, respectively. The T-history test revealed that the melting and solidification rates of PW improved by 90 and 115 s, respectively. The improved heat transfer performance was mainly ascribed to the high degree of graphitization and the interconnected porous carbon structure of the GSB microparticles. The phase change temperatures of PW were slightly changed upon the addition of GSB microparticles, and the latent heat capacity was only reduced by 6.1%. These results suggest that the GSB microparticles can be used as a potential alternative to other nanoadditives such as metal- and metal oxide-based nanoadditives.