Thermal Energy Storage Performance Research Articles

A review and prospective of fin design to improve heat transfer performance of latent thermal energy storage

A review and prospective of fin design to improve heat transfer performance of latent thermal energy storage

A brief strategy for designing self-encapsulated Al-Si base phase change materials with high thermal energy storage performance

A brief strategy for designing self-encapsulated Al-Si base phase change materials with high thermal energy storage performance

Albizzia pollen-inspired phase change capsules accelerate energy storage of packed-bed thermal energy storage system

Packed-bed thermal energy storage (PBTES) system using phase change capsules has been widely applied for thermal energy harvesting and management to alleviate unbalanced energy supply and demand problems. However, the slow thermal energy charging is always a daunting challenge limiting its fast development. Here, a bionic phase change materials (PCMs) capsule by mimicking the natural structure of albizzia pollen is proposed. The heat storage performance and economy of capsules with different internal fin structures are investigated numerically and experimentally. The thermal charging of pollen-type PCMs capsules is the fastest, whose melting time prominently reduces by 19 %, 24 %, 41 % and 61 % compared to the plate-type, ring-type, column-type, and pure PCMs capsules, respectively. That is because the contact area between the skeleton and the capsule wall is increased and the average distance between PCMs and the heat transfer surface is shortened. The pollen-type capsules exhibit the best economy with the exergy efficiency is improved by 15 % compared to pure PCMs capsule. By optimizing the ratio of fin length to radius (L/R) to 5/6, the melting time can be further reduced by 62 % and the exergy efficiency can be improved by 16 % owing to the enhanced heat transfer rate in the center of the pollen-type capsules. A PBTES system is further built based on optimized pollen-based capsules, and faster heat storage rate is successfully demonstrated in experiments. These results provide alternative solutions for optimizing PBTES systems and improving their thermal energy storage performances.

Collective behavior of boreholes and its optimization to maximize BTES performance

Borehole layout strongly affects the behavior of borehole heat exchangers (BHEs) and changes the performance of a borehole thermal energy storage (BTES). This study investigates the existence and importance of the optimum collective behavior of BHEs to maximize the performance of BTES. Charge benefit ratio, storage efficiency and configurational benefit factor are proposed as performance indicators for better and finer performance evaluations of BTES systems. A small-scale BTES consisting of ten boreholes arranged on a concentric double-ring layout is considered as an application. Performance variations with the inner and the outer radii of the borehole field are analyzed for the first five years of operation. The temperature fields of different configurations show the transition from collective to individual behavior of boreholes, which leads to an optimal radial configuration maximizing the performance indicators. It is seen that the indicators strongly depend on both inner and outer radii and they reach their maximums for the same distinct radial configuration. The optimum arrangement can almost double the thermal performance indicators. It is thus of great importance to optimize collective behavior to maximize the usage of stored thermal energy. The results are qualitatively general and represent the common behavioral patterns of BTES systems.

Numerical simulation on thermal behavior of partially filled metal foam composite phase change materials

As a kind of material with high thermal conductivity, metal foam embedded in phase change materials (PCM) can significantly improve the thermal energy storage performance of PCM, so as to better serve the latent heat thermal energy storage (LHTES). However, the presence of metal foam will suppress the natural convection of PCM, reduce its LHTES capacity and increase the total cost. In view of the above problems, this study designed LHTES units with metal foam filled at the top or the bottom with different height ratios. The melting heat transfer characteristic was studied by numerical simulations. Results show that the flow rate of liquid paraffin in the bottom filling configuration is one to two orders of magnitude higher than that in the top filling configuration, which plays a positive role in natural convection and is more conducive to heat transfer enhancement. However, the top filling configuration performs better in the heat storage capacity. The metal foam with a filling height ratio of 0.75 can increase the heat storage capacity by 7.47% while saving 25% material. On this basis, we proposed a new criterion, named the comprehensive strengthening goodness factor (CSGF), for evaluating the heat transfer performance of LHTES system. CSGF is different from the general criterion in that it can evaluate the heat storage capacity and the economic performance at the same time. Under the evaluation of CSGF, the optimum metal foam-paraffin configurations for different occasions were selected.

Improving the Cold Thermal Energy Storage Performance of Paraffin Phase Change Material by Compositing with Graphite, Expanded Graphite, and Graphene

Improving the Cold Thermal Energy Storage Performance of Paraffin Phase Change Material by Compositing with Graphite, Expanded Graphite, and Graphene

Amine-based thermal energy storage system towards industrial application

Thermal energy storage (TES) bridges the intermittence of renewable energy to generate steady and efficient clean energy. While amine-based CO2 capture is a leading technology for CO2 emission reduction, we innovatively employed the amine technology for long-term thermal energy storage, namely amine-based TES (ATES). The system utilises the thermally reversible amine-CO2 reaction as the energy storage working pair, where low-grade thermal energy is used to break the amine-CO2 chemical bond with the heat stored and released via exothermic amine-CO2 reaction to produce high-quality thermal energy when required. Using benchmark absorbent monoethanolamine (MEA), we simulate and optimize the ATES system, and demonstrate that ATES exhibits desirable thermal energy storage performance with high-quality heat output up to 131 °C, high thermal energy conversion efficiency of >70%, moderate energy density of 210 kJ/kg and long-term storage, which outperforms the water-based sensible thermal storage technology. More importantly, the ATES is built on commercially viable amine process and heat exchange system, indicating its great potential for commercial applications, such as space heating and industrial waste heat storage.

Experimental investigation of the effects of inclination, fin height, and perforation on the thermal performance of a longitudinal finned latent heat thermal energy storage

Longitudinal fins have been proven to be one of the most economical and easiest means to improve the thermal characteristics of latent heat thermal energy storage systems. Currently, most studies on this topic are numerical, and several research questions regarding the effects of angular position, fin height, and perforation remain unanswered. In this paper, we conducted experimental studies on four solid finned tubes of varying fin heights (10, 20, 25, and 30 mm), and three perforated finned tubes with different hole sizes (4, 8, and 12 mm). We also examined four different angular positions (0°, 30°, 60°, and 90°). Angular positions of 0° and 30° showed a high rate of average temperature rise during charging, while it had no substantial effect on discharging. The optimal fin height was found to be 65% of the annulus for the melting process, while the solidification process did not exhibit the optimal fin height. Perforation improved the thermal performance marginally. For the same fin volume, small diameter holes were recommended over large holes, as the perforated fins with hole diameters of 4 mm and 8 mm had reduced the pre-melting time by 12.65% and 3.16%, respectively, compared to solid fins.

Lego-Inspired Glass Capillary Microfluidic Device: A Technique for Bespoke Microencapsulation of Phase Change Materials.

We report a Lego-inspired glass capillary microfluidic device capable of encapsulating both organic and aqueous phase change materials (PCMs) with high reproducibility and 100% PCM yield. Oil-in-oil-in-water (O/O/W) and water-in-oil-in-water (W/O/W) core-shell double emulsion droplets were formed to encapsulate hexadecane (HD, an organic PCM) and salt hydrate SP21EK (an aqueous PCM) in a UV-curable polymeric shell, Norland Optical Adhesive (NOA). The double emulsions were consolidated through on-the-fly polymerization, which followed thiol-ene click chemistry for photoinitiation. The particle diameters and shell thicknesses of the microcapsules were controlled by manipulating the geometry of glass capillaries and fluid flow rates. The microcapsules were monodispersed and exhibited the highest encapsulation efficiencies of 65.4 and 44.3% for HD and SP21EK-based materials, respectively, as determined using differential scanning calorimetry (DSC). The thermogravimetric (TGA) analysis confirmed much higher thermal stability of both encapsulated PCMs compared to pure PCMs. Polarization microscopy revealed that microcapsules could sustain over 100 melting-crystallization cycles without any structural changes. Bifunctional microcapsules with remarkable photocatalytic activity along with thermal energy storage performance were produced after the addition of 1 wt % titanium dioxide (TiO2) nanoparticles (NPs) into the polymeric shell. The presence of TiO2 NPs in the shell was confirmed by higher opacity and whiteness of these microcapsules and was quantified by energy dispersive X-ray (EDX) spectroscopy. Young's modulus of HD-based microcapsules estimated using micromanipulation analysis increased from 58.5 to 224 MPa after TiO2 incorporation in the shell.

Thermal performance of cold thermal energy storage system with fin and fin–foam structures

The heat transfer performance of most cold thermal energy storage (CTES) devices is limited by the low thermal conductivity of phase change materials (PCMs) and the increase in the thickness of PCMs. A comparative work was performed to explore the heat transfer performance of CTES systems with a fin structure (Fin-CTES) and a fin–foam structure (Fin–foam-CTES). The heat transfer performance, temperature distribution, and thermal effectiveness of Fin-CTES and Fin–foam-CTES at different inlet temperatures and volume flow rates of heat transfer fluid were investigated and compared. Results demonstrated that the overall heat transfer performance of Fin–foam-CTES is better than that of Fin-CTES. However, compared with the PCM in Fin-CTES, that in Fin–foam-CTES has a greater degree of supercooling, reaching 4.35 °C at the maximum. In the discharging (melting) process, Fin-CTES and Fin–foam-CTES have almost similar heat transfer effectiveness, in which the maximum difference is only 0.0107. That is, the enhanced heat transfer effect of the natural convection of the liquid PCM and the metal foam is basically the same during the discharging process.

Thermal energy storage in concrete utilizing a thermosiphon heat exchanger

The performance of a lab-scale concrete thermal energy storage (TES) module with a 2-kWh thermal capacity is evaluated at temperatures up to 400 °C. The TES module uses conventional normal weight concrete with thermal and mechanical properties that are tailored for use as a solid thermal energy storage media. A thermosiphon heat exchanger is used to provide rapid heat transfer into the concrete module, which is reinforced with a steel pipe outer shell. The charging and discharging cycles are examined to assess the thermal performance of the concrete and thermosiphon. Based on the results of testing, the thermosiphon is able to repeatably charge the concrete module from 300 to 400 °C over a 4-h period. After 2250 total hours of charge and discharge cycles, there was no observed delamination between the concrete and the thermosiphon or the steel jacket reinforcement. Non-destructive measurements of the concrete indicated no significant degradation of the solid storage media. The experimental results are then used to validate a numerical model of the concrete TES module for parametric study. Varying insulation conditions were analyzed using this model to determine practical configurations for regular operation of the proposed concrete TES module.

Performance of sorption thermal energy storage in zeolite bed reactors: Analytical solution and experiment

Sorption thermal energy storage (STES) has the advantage of high energy storage density and low heat loss, which has been considered as one of the promising solutions to achieve carbon neutrality in buildings. An insight into the thermal energy storage performance of reactors enables the optimization of STES systems. In addition, the analytical solution is concise and understandable in physical significance. In the present work, the perturbation theory was introduced to derive the analytical solutions for the fluid and solid temperatures in the reactor during the discharging process. Subsequently, a zeolite 13X STES system was built to conduct charging and discharging experiments. Based on the derived analytical solution, the fluid temperature at different axial positions in the reactor and energy storage density (ED) of zeolite were calculated and compared with the measured data. The results showed that there was a good agreement between the experimental test and the analytical solution, in which the maximum deviation of the energy storage density was less than 4 %. The analytical solution could obtain specific functional expressions for STES performance parameter of ED and further receive the results quickly.

Experimental investigation on electrical power and thermal energy storage performance of a solar hybrid PV/T-PCM energy conversion system

This paper presents the experimental investigation under real environmental conditions of a solar hybrid energy conversion system consisting of latent heat thermal storage (LHTS) and a PV/T panel. In this context, the heat energy from the sun was transferred to the heat transfer fluid (HTF) by means of a heat collector positioned so as not to affect the solar radiation absorption of the PV/T panel. A closed-loop liquid circulation system was developed between the heat collector and the phase change material (PCM) container to transfer the heat transferred from the sun to the PCM container. In addition, the upper surface was designed with optical material in order to increase the energy storage capacity of the PCM container. In the experimental study, a PV/T panel with a maximum electrical power generation capacity of 40 W, measuring 424 × 674 × 25 mm at a 36° azimuth and tilt angle, was used. Commercial RT55 was used as PCM, and tap water was used as HTF. The experimental study was performed between 9:09 and 18:17 on a sunny day under atmospheric conditions. The results of the paper show that a maximum of 30.56 W of electrical power can be produced from the PV/T panel at 14:00, whereas a maximum of 1.2 W of heat energy can be stored in the PCM container at 11:00. On the other hand, the total power of the solar hybrid energy conversion system reached its maximum value of 31.54 W at 12:00. In addition, the rate of energy stored in the PCM within the solar hybrid energy conversion system reached its highest value at 10:00, with 4.5%.

Current, Projected Performance and Costs of Thermal Energy Storage

The technology for storing thermal energy as sensible heat, latent heat, or thermochemical energy has greatly evolved in recent years, and it is expected to grow up to about 10.1 billion US dollars by 2027. A thermal energy storage (TES) system can significantly improve industrial energy efficiency and eliminate the need for additional energy supply in commercial and residential applications. This study is a first-of-its-kind specific review of the current projected performance and costs of thermal energy storage. This paper presents an overview of the main typologies of sensible heat (SH-TES), latent heat (LH-TES), and thermochemical energy (TCS) as well as their application in European countries. With regard to future challenges, the installation of TES systems in buildings is being implemented at a rate of 5%; cogeneration application with TES is attested to 10.2%; TES installation in the industry sector accounts for 5% of the final energy consumption. From the market perspective, the share of TES is expected to be dominated by SH-TES technologies due to their residential and industrial applications. With regard to the cost, the SH-TES system is typically more affordable than the LH-TES system or the TCS system because it consists of a simple tank containing the medium and the charging/discharging equipment.

Utilization of carbonized water hyacinth for effective encapsulation and thermal conductivity enhancement of phase change energy storage materials

In this work, a biochar carrier was developed to adsorb phase change materials and enhance thermal conductivity. Six kinds of modified carbonized water hyacinth were prepared by freeze drying (or vacuum drying) combined with high-temperature carbonization. The pore volume and specific surface area (SSA) of FC900 are the highest, reaching 0.3153 cm3/g and 479.966 m2/g, which are 32% higher than those of VC900. The load rates of FC900 and VC900 on lauric acid-myristic acid-paraffin section (LMPS) are 75% and 65% respectively. Meanwhile, the phase transition enthalpy of LMPS/FC900 is 104.36 J/g, which is 20.75% higher than that of LMPS/VC900, and the phase transition temperatures are 25.93 and 26.77 °C respectively. After 500 times of heat storage and release experiments, LMPS/FC900 maintains a stable phase change peak, which has good thermal performance stability. Notably, the thermal conductivity of LMPS/FC900 is 0.4168 W/(m·K), which is 56.93% higher than that of LMPS. Otherwise, under the constant temperature environment of 50 °C, the heating time of LMPS/FC900 is 11.89% longer than that of LMPS/VC900, which has more excellent temperature control performance. This study concludes that the carbonization temperature of 900 °C and freeze-drying measures are the best preparation process for carbonized water hyacinth, and LMPS/FC900 has good thermal conductivity and phase change energy storage performance.

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.

Dynamic creep and stress performances of the packed-bed thermal energy storage tank with molten salt EPCM particles

In the concentrating solar power (CSP), the high-temperature creep and stress concentration greatly affect the safety performance of the packed-bed thermal energy storage (TES) tank with encapsulated phase change materials (EPCMs). Therefore clearly analyzing the dynamic creep and stress distribution is an effective way to optimize the mechanical performance of EPCM-TES tank. In the study, a commercial scale EPCM-TES tank applied in 50MWe tower plant is designed. Then an integration model coupling FVM and FEM applied in EPCM-TES structure is established, where the real mechanical loads and cyclic temperature distribution are considered in stress analysis model. Based on the coupled model, the dynamic creep and stress performances of the EPCM-TES tank in charging and discharging are studied. The results are concluded as follows. (1) In charging, when the tank wall is gradually heated, the creep damage is produced on wallboards installed above 4.4 m height. Because of the tank wall continue to be heated by the high-temperature EPCMs fillers after charging, the creep phenomenon further occurs on the rest of wallboards installed below 4.4 m height. In discharging, when the tank wall is cooled by cold salt, the creep damage of the whole wallboard can be avoided. (2) The creep damage time of tank wallboards varies greatly along the height direction. In 25ys design life, the maximum creep time happens on top wallboard which is 105,000 h and occupies almost 47.9 % of the total operation time. (3) Most wallboards installed above 2.2 m height are always in elastic state with lower stress level in charging and discharging, whereas the plastic damage induced by stress concentration always occurs at the fillet weld location of bottom wallboard in charging. The study provides insights on the optimization design of the molten salt EPCM-TES tank in CSP for lower stress level and creep damage time.

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 cold-crystallization temperature of 51.7 °C and enthalpy of 178.1 J/g. The supercooled composite PCMs without latent heat release can be maintained at room temperature (10–25 °C) 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.

Sea urchin skeleton-inspired triply periodic foams for fast latent heat storage

The latent heat storage technology has been widely applied in various thermal management fields, but its extensive deployment is limited due to the poor thermal conductivity of phase change material. Here, inspired by the microstructure and functions of sea urchin skeleton, four different metal foam skeletons based on triply periodic minimal surface (TPMS) are introduced to enhance latent heat thermal energy storage performances, which are evaluated by both experiment and numerical simulation. The metal foam-PCM (MFPCM) based on the Primitive structure has the fastest thermal energy storage rate with melting time prominently reduced by 20% compared to the traditional structure (Lattice). The underlying mechanism can be attributed to a more continuous and compact internal structure of TPMS compared with traditional MFPCM by thermal resistance analysis. In addition, the effect of gradient porosity is investigated as well, and the positive gradient in porosity has the fastest melting rate. The present study provides a new idea to design high-performance MFPCM and promotes the application of bionics in accelerating latent heat thermal energy storage.

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.