Enhanced properties of stone coal-based composite phase change materials for thermal energy storage

Phase change materials (PCMs) can be incorporated with low-cost minerals to synthesize composites for thermal energy storage in building applications.Stone coal (SC) after vanadium extraction treatment shows potential for secondary utilization in composite preparation.We prepared SC-based composite PCMs with SC as a matrix,stearic acid (SA) as a PCM,and expanded graphite (EG) as an additive.The combined roasting and acid leaching treatment of raw SC was conducted to understand the effect of vanadium extraction on promoting loading capacity.Results showed that the combined treatment of roasting at 900℃ and leaching increased the SC loading of the composite by 6.2%by improving the specific surface area.The loading capacity and thermal conductivity of the composite obviously increased by 127%and 48.19%,respectively,due to the contribution of 3wt% EG.These data were supported by the high load of 66.69%and thermal conductivity of 0.59 W·m^(-1)·K-1of the designed composite.The obtained composite exhibited a phase change temperature of 52.17℃,melting latent heat of 121.5 J·g^(-1),and good chemical compatibility.The SC-based composite has prospects in building applications exploiting the secondary utilization of minerals.

The establishment of Boron nitride@sodium alginate foam/polyethyleneglycol composite phase change materials with high thermal conductivity, shape stability, and reusability

Adopting organic phase change materials(PCMs) for the management of electronic devices is restricted by low thermal conductivity. In this paper, the composite PCMs are established by freeze-drying and vacuum impregnation. Herein, polyethylene glycol(PEG) is induced as heat storage materials, boron nitride(BN) is embedded as filler stacking in an orderly fashion on the foam walls to improve thermal conductivity and sodium alginate(SA) is formed as supporting material to keep the shape of the composite stable. X-ray diffractometry, scanning electron microscopy-energy dispersive spectrometer, thermal gravimetric analysis, thermal conductivity meter, differential scanning calorimeter, and Fourier transform infrared were used to characterize the samples and thermal cycles were employed to measure the shape stability. The results exhibit the BN@SA/PEG composite PCMs have good chemical compatibility, stable morphology, and thermal stability. Due to the high porosity of foam, PEG endows the composite PCMs with high latent heat(149.11 and 141.59 J·g^(-1)). Simultaneously, BN@SA/PEG shows an excellent heat performance with high thermal conductivity(0.99 W·m^(-1)·K^(-1)), reusability, and shape stability, contributing the composite PCMs to application in the energy storage field. This study provides a strategy to manufacture flexible, long-serving, and shape-stable PCMs via introducing BN@SA foam as a storage framework, and these PCMs have great potential in thermal management in the electronic field.

Spatiotemporal phase change materials for thermal energy long-term storage and controllable release

Phase change materials(PCMs)have attracted much attention in the field of solar thermal utilization recently,due to their outstanding thermal energy storage performance.However,PCMs usually release their stored latent heat spontaneously as the temperature below the phase transition temperature,rendering thermal energy storage and release uncontrollable,thus hindering their practical application in time and space.Herein,we developed erythritol/sodium carboxymethylcellulose/tetrasodium ethylenediaminetetraacetate(ERY/CMC/EDTA-4Na)composite PCMs with novel spatiotemporal thermal energy storage properties,defined as spatiotemporal PCMs(STPCMs),which exhibit the capacity of thermal energy long-term storage and controllable release.Our results show that the composite PCMs are unable to lose latent heat due to spontaneous crystallization during cooling,but can controllably release thermal energy through cold crystallization during reheating.The cold-crystallization temperature and enthalpy of composite PCMs can be adjusted by proportional addition of EDTA-4Na to the composite.When the mass fractions of CMC and EDTA-4Na are both 10%,the composite PCMs can exhibit the optical coldcrystallization temperature of 51.7℃ and enthalpy of 178.1 J/g.The supercooled composite PCMs without latent heat release can be maintained at room temperature(10-25℃)for up to more than two months,and subsequently the stored latent heat can be controllably released by means of thermal triggering or heterogeneous nucleation.Our findings provide novel insights into the design and construction of new PCMs with spatiotemporal performance of thermal energy long-term storage and controllable release,and consequently open a new door for the development of advanced solar thermal utilization techniques on the basis of STPCMs.

Mica-stabilized polyethylene glycol composite phase change materials for thermal energy storage

Mica was used as a supporting matrix for composite phase change materials(PCMs)in this work because of its distinctive morphology and structure.Composite PCMs were prepared using the vacuum impregnation method,in which mica served as the supporting material and polyethylene glycol(PEG)served as the PCM.Fourier transform infrared and X-ray diffraction analysis confirmed that the addition of PEG had no effect on the crystal structure of mica.Moreover,no chemical reaction occurred between PEG and mica during the vacuum impregnation process,and no new substance was formed.The maximum load of mica-stabilized PEG was 46.24%,the phase change temperature of M_(400)/PEG was 46.03℃,and the latent heat values of melting and cooling were 77.75 and 77.73 J·g^(−1),respectively.The thermal conductivity of M_(400)/PEG was 2.4 times that of pure PEG.The thermal infrared images indicated that the thermal response of M_(400)/PEG improved relative to that of pure PEG.The leakage test confirmed that mica could stabilize PEG and that M_(400)/PEG had great form-stabilized property.These results demonstrate that M_(400)/PEG has potential in the field of building energy conservation.

Preparation of Paraffin/γ-Al2O3 Composites as Phase Change Energy Storage Materials

Paraffin/γ-Al2O3 composites as phase change energy storage materials were prepared by absorbing paraffin in porous network of γ-Al2O3.In the composite materials,paraffin was used as a phase change material(PCM)for thermal energy storage,and γ-Al2O3 acted as supporting materials.Characterizations were conducted to evaluate the energy storage performance of the composites,and differential scanning calorimeter results showed that the PCM-3 composite has melting latent heat of 112.9 kJ/kg with a melting temperature of 62.9 ℃.Due to strong capillary force and surface tension between paraffin and γ-Al2O3,the leakage of melted paraffin from the composites can be effectively prevented.Therefore,the paraffin/γ-Al2O3 composites have a good thermal stability and can be used repeatedly.

Thermal energy storage inside the chamber with a brick wall using the phase change process of paraffinic materials:A numerical simulation

Phase change materials are one of the potential resources to replace fossil fuels in regards of supplying the energy of buildings.Basically,these materials absorb or release heat energy with the help of their latent heat.Phase change materials have low thermal conductivity and this makes it possible to use the physical properties of these materials in the tropical regions where the solar radiation is more direct and concentrated over a smaller area.In this theoretical work,an attempt has been made to study the melting process of these materials by applying constant heat flux and temperature.It was found that by increasing the thickness of phase change materials’layers,due to the melting,more thermal energy is stored.Simultaneously it reduces the penetration of excessive heat into the chamber,so that by increasing the thickness of paraffin materials up to 20 mm,the rate of temperature reduction reaches more than 18%.It was also recognized that increasing the values of constant input heat flux increases buoyancy effects.Increasing the Stefan number from 0.1 to 0.3,increases the temperature by 6%.

Modified sepiolite stabilized stearic acid as a form-stable phase change material for thermal energy storage

Sepiolite(ST) was used as a supporting matrix in compiste phase change materials(PCMs) due to its unique microstructure, good thermal stability, and other raw material advantages. In this paper, microwave acid treatment were innovatively used for the modification of sepiolite. The modified sepiolite(ST_(m)) obtained in different hydrochloric acid concentrations(0.25, 0.5, 0.75, and 1.0 mol·L^(-1)) was added to stearic acid(SA) via vacuum impregnation method. The thermophysical properties of the composites were changed by varying the hydrochloric acid concentration. The SA-ST_(m0.5)obtained by microwave acid treatment at 0.5 mol·L^(-1)hydrochloric acid concentration showed a higher loading capacity(82.63%) than other composites according to the differential scanning calorimeter(DSC) analysis. The melting and freezing enthalpies of SA-ST_(m0.5)were of 152.30 and 148.90 J·g^(-1), respectively. The thermal conductivity of SA-ST_(m0.5)was as high as 1.52 times that of pure SA. In addition, the crystal structure, surface morphology, and microporous structure of ST_(m)were studied, and the mechanism of SAST_(m0.5)performance enhancement was further revealed by Brunauere Emmett Teller(BET) analysis. Leakage experiment showed that SAST_(m0.5)had a good morphological stability. These results demostrate that SA-ST_(m0.5)has a potential application in thermal energy storage.

Numerical Investigation of the Thermal Behavior of a System with a Partition Wall Incorporating a Phase Change Material

The work deals with the thermal behavior of a conventional partition wall incorporating a phase change material(PCM).The wall separates two environments with different thermal properties.The first one is conditioned,while the adjacent space is characterized by a temperature that changes sinusoidally in time.The effect of the PCM is assessed through a comparative analysis of the cases with and without PCM.The performances are evaluated in terms of dimensionless energy stored within the wall,comfort temperature and variations of these quantities as a function of the amount of PCM and its emplacement.

Tightened1D/3Dcarbonheterostructure infiltratingphase change materials for solar-thermoelectric energy harvesting:Faster and better

Extensive use of thermal energy in daily life is ideal for reducing carbon emissions to achieve carbon neutrality;however,the effective collection of thermal energy is a major hurdle.Thermoelectric(TE)conversion technology based on the Seebeck effect and thermal energy storage technology based on phase change materials(PCMs)represent smart,feasible,and research-worthy approaches to overcome this hurdle.However,the integration of multiple thermal energy sources freely existing in the environment for storage and output of thermal and electrical energy simultaneously still remains a huge challenge.Herein,three-dimensional(3D)nanostructured metal-organic frameworks(MOFs)are in situ nucleated and grown onto carbon nanotubes(CNTs)via coordination bonding.After calcination,the prepared core-shell structural CNTs@MOFs are transformed into tightened 1D/3D carbon heterostructure loading Co nanoparticles for efficient solar-thermoelectric energy harvesting.Surprisingly,the corresponding composite PCMs show a record-breaking solar-thermal conversion efficiency of 98.1%due to the tightened carbon heterostructure and the local surface plasmon resonance effect of Co nanoparticles.Moreover,our designed all-in-one composite PCMs are also capable of creating an electrical potential of 0.5 mV based on the Seebeck effect without a TE generator.This promising approach can store thermal and electrical energy simultaneously,providing a new direction in the design of advanced all-in-one multifunctional PCMs for thermal energy storage and utilization.

Integrating thermal energy storage and microwave absorption in phase change material-encapsulated core-sheath MoS_(2)@CNTs

Developing advanced nanocomposite integrating solar-driven thermal energy storage and thermal management functional microwave absorption can facilitate the cutting-edge application of phase change materials(PCMs).To conquer this goal,herein,two-dimensional MoS_(2) nanosheets are grown in situ on the surface of one-dimensional CNTs to prepare core-sheath MoS_(2)@CNTs for the encapsulation of paraffin wax(PW).Benefiting from the synergistic enhancement photothermal effect of MoS_(2) and CNTs,MoS_(2)@CNTs is capable of efficiently trapping photons and quickly transporting phonons,thus yielding a high solar-thermal energy conversion and storage efficiency of 94.97%.Meanwhile,PW/MoS_(2)@CNTs composite PCMs exhibit a high phase change enthalpy of 101.60 J/g and excellent lo ng-term thermal storage durability after undergoing multiple heating-cooling cycles.More attractively,PW/MoS_(2)@CNTs composite PCMs realize thermal management functional microwave absorption in heat-related electronic application scenarios,which is superior to the single microwave absorption of traditional materials.The minimum reflection loss(RL) for PW/MoS_(2)@CNTs is-28 dB at 12.91 GHz with a 2.0 mm thickness.This functional integration design provides some insightful references on developing advanced microwave absorbing composite PCMs,holding great potential towards high-efficiency solar energy utilization and thermally managed microwave absorption fields.

Numerical Study on the Combined Use of Corten Steel and Phase Change Materials in Container-Type Houses

A study is presented on the feasibility of an approach based on the combination of Phase Change Materials(PCM)with metal walls in container-type houses.This line of research finds its motivations in recent trends in the energy and building sectors about energy consumption reduction.Another important objective concerns possible improvements in the comfort provided by such houses during the summer period.The results obtained through numerical solution of the governing equations accounting for heat transfer and latent heat effects associated with the PCM show that the indoor temperature can be reduced with a varying degree of success depending on the considered conditions.

Preparation of Palygorskite-based Phase Change Composites for Thermal Energy Storage and Their Applications in Trombe Walls

Palygorskite/paraffin phase-change composites were prepared by the combination of purified palygorskite clay and sliced paraffin. Then, this composite was used in the Trombe wall to improve its energy storage ability. Further, its energy storage ability was compared to that of ordinary concrete wall through contrastive test. The experiments show that palygorskite clay is a type of clay mineral with strong adsorption ability, and the purity of natural palygorskite clay can reach up to 97.1% after certain purification processes. Paraffin is well adsorbed by palygorskite, and the test results show that the optimal adsorption ratio is palygorskite： paraffin = 2：1（mass ratio）. Palygorskite/paraffin phase change composites can be obtained by using palygorskite as the adsorbing medium to adsorb paraffin. The composite materials exhibit good heat storage（release） performance, which can store heat with increasing environment temperature and release heat with decreasing temperature. This property not only increases the inertia to environment temperature change, but also promotes the energy migration in different time and space, thus achieving a certain energy-saving effect. The application of palygorskite/paraffin phase change composite materials to the Trombe wall can significantly reduce the fluctuation of indoor temperature and enhance the thermal inertia of indoor environment. From the aspect of energy storage effect, the Trombe wall fabricated using PCMs is significantly superior to the concrete wall with the same thickness.

Role of Composite Phase Change Material on the Thermal Performance of a Latent Heat Storage System: Experimental Investigation

Paraffin wax is a perfect phase change material(PCM)that can be used in latent heat storage units(LHSUs).The utilization of such LHSU is restricted by the poor conductivity of PCM.In the present work,a metal foam made of aluminium with PCM was used to produce a composite PCM as a thermal conductivity technique in PCM⁃LHSU and water was used as heat transfer fluid(HTF).An experimental investigation was carried out to evaluate the heat transfer characteristics of LHSU using pure PCM and composite PCM.The study included time⁃dependent visualization of the PCM during the melting and solidification processes.Besides,a thermocouple network was placed inside the heat storage to record the temperature profile during each process.Results showed that better performance could be obtained using composite PCM⁃LHSU for both melting and solidification processes.The melting time of composite PCM⁃LHSU was about 83%faster than that of a simple PCM⁃LHSU,and the percentage decreasing in the solidification time was about 85%due to the provision of metal foam.

Heat transfer and parametric studies of an encapsulated phase change material based cool thermal energy storage system

This work investigates the transient behaviour of a phase change material based cool thermal energy storage (CTES) system comprised of a cylindrical storage tank filled with encapsulated phase change materials (PCMs) in spherical container integrated with an ethylene glycol chiller plant. A simulation program was developed to evaluate the temperature histories of the heat transfer fluid (HTF) and the phase change material at any axial location during the charging period. The results of the model were validated by comparison with experimental results of temperature profiles of HTF and PCM. The model was also used to investigate the effect of porosity, Stanton number, Stefan number and Peclet number on CTES system performance. The results showed that increase in porosity contributes to a higher rate of energy storage. However, for a given geometry and heat transfer coefficient, the mass of PCM charged in the unit decreases as the increase in porosity. The St number as well as the Ste number is also influential in the performance of the unit. The model is a convenient and more suitable method to determine the heat transfer characteristics of CTES system. The results reported are much useful for designing CTES system.

Parametric Study on Phase Change Material Based Thermal Energy Storage System

The usage of phase change materials (PCM) to store the heat in the form of latent heat is increased, because large quantity of thermal energy is stored in smaller volumes. In the present experimental investigation, sodium thiosulphate pentahydrate is employed as phase change material and it is stored in stainless steel capsules. These capsules are kept in fabricated tank and hot water is supplied into it. The experimental design is prepared by considering the parameters: flow rate, heat transfer fluid inlet temperature and PCM capsule shape. Experiments are conducted according to the experimental design and responses are recorded. The effect of selected parameters on TES using PCM is studied by analyzing experimental data. The experimental data are also analyzed using Fuzzy Logic to find the optimal values of flow rate, heat transfer fluid inlet temperature and PCM capsule shapes. The present work utilizes Fuzzy Logic to find the optimal parameters for designing the effective Thermal Energy Storage System (TES).

Fly Ash/Paraffin Composite Phase Change Material Used to Treat Thermal and Mechanical Properties of Expansive Soil in Cold Regions

Phase change materials(PCMs)can store large amounts of energy in latent heat and release it during phase changes,which could be used to improve the freeze-thaw performance of soil.The composite phase change material was prepared with paraffin as the PCM and 8%Class C fly ash(CFA)as the supporting material.Laboratory tests were conducted to reveal the influence of phase change paraffin composite Class C fly ash(CFA-PCM)on the thermal properties,volume changes and mechanical properties of expansive soil.The results show that PCM failed to establish a good improvement effect due to leakage.CFA can effectively adsorb phase change materials,and the two have good compatibility.CFA-PCM reduces the volume change and strength attenuation of the soil,and 8 wt.%PCM is the optimal content.CFA-PCM turns the phase change latent heat down of the soil and improves its thermal stability.CFA-PCM makes the impact small of freeze-thaw on soil pore structure damage and improves soil volume change and mechanical properties on a macroscopic scale.In addition,CFA-8 wt.%PCM treated expansive soil has apparent advantages in resisting repeated freeze-thaw cycles,providing a reference for actual engineering design.

Enhanced Thermal Performance of Roofing Materials by Integrating Phase Change Materials to Reduce Energy Consumption in Buildings

This work focused on characterizing and improving the thermal behavior of metal sheet roofing.To decrease the heat transfer from the roof into a building,we investigated the efficiency of four types of phase change materials,with different melting points:PCMІ,PCM II,PCM III and PCM IV,when used in conjunction with a sheet metal roof.The exterior metal roofing surface temperature was held constant at 50℃,60℃,70℃and 80℃,using a thermal source(halogen lights)for 360 min to investigate and compare the thermal performance of the metal sheet roofing with and without phase change materials for each condition.The thermal behaviors of the phase change materials were analyzed by differential scanning calorimeter(DSC).The results showed the melting points of PCMІ,PCM II,PCM III and PCM IV were around 45℃,50℃,55℃and 59℃,respectively.The integration of PCM IV into the metal roofing sheet increased the thermal performance by reducing the room temperature up to 2.8%,1.4%,1.0%and 0.7%when compared with the normal metal roof sheet,at the controlled temperatures of 50℃,60℃,70℃and 80℃,respectively.The thermal absorption of the phase change materials also caused a time delay in the model room reaching a steady temperature.The integration of phase change materials with metal roofing sheets resulted in better thermal performance and conservation of electrical energy by reducing the demand for cooling.

Time-Temperature Charge Function of a High Dynamic Thermal Heat Storage with Phase Change Material

A thermal heat storage system with an energy content of 40 kWh and a temperature of 58°C will be presented. This storage system is suitable for supporting the use of renewable energies in buildings and for absorbing solar heat, heat from co-generation and heat pumps or electric heat from excess wind and solar power. The storage system is equipped with a plate heat exchanger that is so powerful that even with small temperature differences between the flow temperature and the storage temperature a high load dynamic is achieved. The storage system has a performance of 2.8 kW at 4 K and 10.6 kW at a temperature difference of 10 K. Thus, large performance variations in solar thermal systems or CHP plants can be buffered very well. Further a storage charge function Q(T, t) will be presented to characterize the performance of the storage.

Preparation of Composite Phase Change Material Based on Sol-Gel Method and Its Temperature-Adjustable Textile

In this study,the sol-gel method was introduced to prepare the composite phase change material (CPCM). The CPCM was added to fabric with coating techniques and the thermal activity of modified fabric was studied. In addition,the thermal property and the microstructure of CPCM were also discussed in detail by means of polarization microscope and differential scanning calorimeter,respectively. According to the analysis of main influencial factors of the property of CPCM,the optimal preparing technique was determined. It was proved that CPCM could exhibit a good thermal property while phase transformation process took place,and a better appearance of the fabric modified with CPCM could be obtained due to the fact that in a warm circumstance,the liquid-state phase change material could be firmly enwrapped and embedded in the three-dimensional network all the time during the phase transformation. Besides,the fabric treated with CPCM had a high phase-transition enthalpy and an appropriate phase-transition temperature. As a result,a desirable temperature-adjustable function appeared.

Numerical Study of Thermal Performance of Phase Change Material Energy Storage Floor in Solar Water Heating System

The conventional solar heating floor system contains a big water tank to store energy in the day time for heating at night,which takes much building space and is very heavy.In order to reduce the water tank volume even to cancel the tank,a novel structure of integrated water pipe floor heating system using shape-stabilized phase change materials(SSPCM)for thermal energy storage was developed.A numerical model was developed to analyze the performance of SSPCM floor heating system under the intermittent heating condition,which was verified by our experimental data.The thermal performance of the heating system and the effects of various factors on it were analyzed numerically.The factors including phase transition temperature,heat of fusion,thermal conductivity of SSPCM and thermal conductivity of the decoration material were analyzed.The results show that tm and kd are the most import influencing factors on the thermal performance of SSPCM floor heating system,since they determine the heat source temperature and thermal resistance between SSPCM plates and indoor air,respectively.Hm should be large to store enough thermal energy in the day time for nighttimes heating.The effects of kp can be ignored in this system.The SSPCM floor heating system has potential of making use of the daytime solar energy for heating at night efficiently in various climates when its structure is properly designed.