Thermal Energy Storage Performance Research Articles

Thermal energy storage with tunnels in different subsurface conditions

Thermal energy storage with tunnels in different subsurface conditions

Enhancing the Power Performance of Latent Heat Thermal Energy Storage Systems: The Adoption of Passive, Fractal Supports

We employ a three-phase thermal lattice Boltzmann model (LBM) to investigate the power performance of latent heat thermal energy storage (LHTES) systems based on the exploitation of phase change materials (PCMs). Different passive thermal supports are considered to increase the melting rate, including innovative, fractal, branch-like structures. Our simulations reveal that the adoption of fractal, branch-like metal supports consistently outperforms other configurations in terms of PCM melting rates. These results open the path towards novel strategies to enhance the power performance of PCM-based TES systems, offering potential benefits for energy storage applications.

Pore-scale melting behaviors in composite phase change material with porosity gradients

Latent heat storage is a promising thermal energy storage solution to tackle the time–space conflict in energy demand. However, the low thermal conductivity of pure phase change material may limit the thermal energy storage performance of latent heat storage systems. In this work, porous support with gradient porosity and high thermal conductivity is incorporated into the phase change material to minimize the total melting time. A pore-scale lattice Boltzmann model for simulating the melting process of composite phase change material is established to investigate the effect of gradient porosity on the dynamic melting process. The results show that the two-dimensional gradient porosity structure can significantly improve the melting rate of composite phase change material. Compared with a uniform porosity structure, the melting time can be reduced by up to 8.58% in this work. By considering the changes in dominant heat transfer mechanisms during the melting process and the asymmetric evolution of the upper and lower parts of the melting front, the two-dimensional gradient porosity structure combines the advantages of horizontal and vertical one-dimensional gradient porosity structure. It is also found that the gradient porosity structures slow down the melting process of composite phase change material when the porosity is too small in the lower right corner of the square cavity or when the two-dimensional gradient porosity is divided too finely. The solid phase change material in this area mainly relies on thermal convection for melting, and it can significantly delay the melting time when the flow velocity is low, with a maximum extension of 26.58% of the melting time as compared to a uniform porosity structure.

Sustainable Energy Progress via Integration of Thermal Energy Storage and Other Performance Enhancement Strategies in FPCs: A Synergistic Review

Flat plate collectors (FPCs) are the leading solar thermal technology for low-medium range temperature applications. However, their expansion in developing countries is still lacking because of their poor thermal performance. Improving the thermal performance of flat plate collectors (FPCs) is a crucial concern addressed in this review This study comprehensively discussed the performance improvement methods of FPCs, such as design modification, reflectors, working fluid, and energy storage materials, by covering current issues and future recommendations. Design factors such as coating and glass cover thickness, thickness of absorber plate and material, air gap between the glass cover and absorber plate, and riser spacing, along with insulation materials, are examined for their impact on FPC performance. Absorber design changes with selective coatings for improving the heat transmission rate between the working fluid and absorber are critical for enhancing collectors’ thermal output. The nanofluids utilization improved FPC’s thermal performance in terms of energetic and exergetic outcomes in the 20–30% range. Moreover, adding a heat storage unit extends the operating hours and thermal output fluctuations of FPCs. Research suggests that employing turbulators and nanofluids as heat transfer fluids are particularly effective for enhancing heat transfer in FPCs. This comprehensive review serves as a critical tool for evaluating and comparing various heat transfer augmentation techniques, aiding in the selection of the most suitable option.

Thermal analysis of a cascaded latent thermal storage tank in a solar domestic water heating system

AbstractTo enhance the thermal characteristics of a solar collector storage system, this study investigates the performance of a rectangular thermal energy storage (TES) tank by incorporating cascade phase change materials (cascade‐PCMs). Three different commercially available PCMs (RT44HC, RT54HC, and RT62HC) with distinct melting temperatures are employed. These cascade‐PCMs are utilized as slabs in vertical rectangular modules, which are integrated into the water TES tank. The heat transfer fluid (HTF) in the flat‐plate solar collector captures solar energy and transfers it to the TES tank, where it is stored as latent thermal energy. A two‐dimensional (2D) numerical model, utilizing the enthalpy‐porosity approach and conservation equations, is developed to analyze the melting and heat transfer processes within the TES tank. The model is validated against previous experimental and numerical data. Performance evaluation of the cascade‐PCMs tank is conducted during a 9‐h charging period (from 8:00 am to 5:00 pm) under Marrakesh weather conditions in Morocco. An optimization study is carried out to determine the optimal height of each cascade‐PCM. The results suggest that an optimal design with heights of 23, 16, and 11 cm for RT44HC, RT54HC, and RT62HC respectively, offers improved melting and storage quality. The thermal characteristics of the TES tank incorporating cascade‐PCMs are compared to those of a TES tank filled with a single phase change material (single‐PCM) during the charging period. The findings indicate that the cascade‐PCMs achieve complete melting, while the single‐PCM only reaches a melting fraction of 0.903 at the end of the charging process. Furthermore, the optimal configuration of the cascade‐PCMs storage tank exhibits slightly higher sensible and latent thermal energy storage capacity compared to the single‐PCM tank. The combination of the solar collector with the cascade‐PCMs storage tank results in a 3.47% higher average collection efficiency when compared to the single‐PCM tank.

Comparative Analysis of Thermal Energy Storage Performance in District Heating Networks: Evaluating the Impact of Different Injection Systems

Comparative Analysis of Thermal Energy Storage Performance in District Heating Networks: Evaluating the Impact of Different Injection Systems

Preparation of novel hollow metal organic framework for enhancing flame retardancy of paraffin/EP thermal energy storage materials

AbstractParaffin is a potential thermal energy storage material, but leakage and flammability are the two major problems affecting its storage and safe use. Here, a novel flame retarded paraffin/epoxy resin composite was developed by using paraffin, epoxy resin and hollow metal organic framework (W‐UiO66‐PPA) as thermal energy storage material, supporting material and flame retardant, respectively. The thermal energy storage and flame retardancy performances were examined with differential scanning calorimetry, vertical burning, limiting oxygen index and cone calorimeter tests. The results show that the paraffin/epoxy resin retains intact without leakage when the content of paraffin reaches 40 wt%, and this material exhibits high melting latent heat and remarkable thermal recycling property. In addition, the flame retarded paraffin/epoxy resin shows excellent flame retardancy, which is attributed to the following three aspects: (1) the hollow structure with open vertices of W‐UiO66 is capable of absorbing and collecting the combustible gasses produced by the combustion of epoxy resin; (2) the Zr and W elements of W‐UiO66 can facilitate catalytic charring and form a dense char layer; (3) phosphorous‐containing free radicals are able to capture OH· and O· free radicals during the combustion of paraffin and epoxy resin, thus interrupting the combustion chain reaction. On the whole, the flame retarded paraffin/EP possesses excellent thermal energy storage, thermal recycling, and flame retardancy properties. Our work provides a fantastic inspiration for the rational design of other flame retarded form‐stable phase change materials.

Thermal energy storage performance of magnesium-based hydrated salts impregnated with activated alumina

ABSTRACT A new thermochemical heat storage composite was prepared for the first time by vacuum impregnation using activated alumina (AA) as the porous matrix and magnesium sulfate (MgSO4) and magnesium chloride (MgCl2) as the heat storage material. The salt content of composites obtained by the vacuum impregnation method was 8.31% higher than that of atmospheric impregnation method. The adsorption and heat storage performance were investigated, the AA − 20 wt% MgSO4 (AS-20) and AA − 20 wt% MgCl2 (AC-20) were outstanding from the single-salt-impregnated composites, especially AS-20 with the heat storage density (HSD) increased by 20.7% compared with atmospheric immersion method. Morphological tests and composition analyses were indicated that the hydrated salt was evenly impregnated into the uniform spherical particles AA matrix. A binary mixed-salt (MgSO4-MgCl2) impregnated AA composites were also prepared, and the sample with the MgSO4:MgCl2 mass ratio of 20:80 in the 20 wt% solution (ASC-20) exhibited the better performance. The adsorption capacity of ASC-20 was 0.301 g/g, the kinetics constant (k s ) was 0.01 s−1, and the HSD was 554 kJ/kg, which were higher than those obtained by single-salt composite and atmospheric impregnation methods. In particular, the k s value of ASC-20 was increased by more than 10 times compared to previous studies. After 10 cycles of testing, the HSD of ASC-20 decreased by 12.5%, and no fracture occurred in the globular particles, showing good thermal stability and structural stability. The new composites obtained by this method is conducive to system application.

Experimental and numerical analyses of gravity-driven granular flows between vertical parallel plates for solar thermal energy storage and transport

Gravity-driven granular flows between vertical parallel plates were considered at elevated temperatures to examine flow behavior and inform solar thermal energy storage and transport infrastructure design and performance. A series of experiments was performed at inlet temperatures of 23, 200, 400, 600, and 800 °C in a high-temperature granular flow experimental rig and spatial and temporal velocity and surface temperature fields were measured. Granular flows were observed to change as a function of temperature. The interaction between the particles and the wall significantly increased with decreases in channel widths. Particle velocities at the outlet of the channel were compared with results from numerical model using the discrete element method. Temperature-dependent flow properties directly related to the assembly were measured and used for granular flow simulation. Flow behavior within the channel was investigated from the simulated results by obtaining particle volume fractions and particle velocities. Wall temperature and outlet granular flow temperature were monitored during the flow experiment and temporal heat loss in the flow was calculated. The granular flow behavior and heat transfer analysis from both the experiment work and simulation provide important mass transfer information for heat transfer modeling at elevated temperature.

Design analysis and performance prediction of packed bed latent heat storage system employing machine learning models

In recent years, the goal of becoming energy independent of fossil fuels has gained prominence. Solar energy is an excellent choice because it has a very less environmental impact in comparison to fossil fuels. The variability of solar radiation creates a divergence between energy demand and supply, making it necessary to implement efficient thermal energy storage systems to bridge the gap and enable solar thermal power plants to become viable solutions for uninterrupted power generation to meet the present and future energy needs. In this study, various data-driven machine learning (ML) models were used to analyze the design and performance of the packed-bed thermal energy storage (PBTES) system. Six different ML models, including linear regression (LR), support vector regression (SVR), K-nearest neighbors (KNN), decision trees (DT), random forests (RF), and extreme gradient boosting (XGB), were employed to evaluate the performance of PBTES. The models were trained and tested using experimental data reported in the literature on PBTES performance. The results of the study showed that the XGB ML model provided the best performance for PBTES analysis and prediction, with a maximum R2 value of 0.982, and minimum MAE, MAPE, and RMSE values of 0.057, 0.182, and 0.16, respectively. The study demonstrated the effectiveness of data-driven approaches in designing and analyzing PBTES performance, which can be useful for developing more efficient and sustainable energy systems. Overall, this study provides valuable insight into the potential of data-driven ML models for the design and performance analysis of PBTES, which could have significant implications for the utilization of renewable energy sources.

Heat transfer enhancement and performance study on latent heat thermal energy storage system using different configurations of spherical PCM balls

Thermal energy storage (TES) systems utilizing latent heat storage substances have gained significant attention recently due to their large heat storage capacity and isothermal behavior during charging and discharging processes. However, many phase change materials (PCM) used for storage exhibit relatively low thermal conductivity. Prolonged surfaces like fins are incorporated in PCM balls to improve heat transfer performance. These fins significantly improve the overall performance of the TES system. This study conducted experiments to evaluate the performance of a latent heat thermal energy storage (LHTES) system using spherical balls filled with PCM, both with and without solid internal fins. Water was used as the heat transfer fluid (HTF) at a constant temperature of 70 °C, while paraffin served as the PCM with a melting temperature of 61 °C. Time-based temperature variation of HTF and PCM has been investigated for various HTF flow rates. Moreover, the effect of non-dimensional numbers, such as Reynolds, Rayleigh, Nusselt, and Stanton numbers, has also been investigated. Performance parameters such as thermodynamic efficiencies and entropy generation are analyzed. The heat storage process aims to get a highly efficient configuration for accumulating the maximum energy possible and higher exergy efficiencies during the charging process. The charging duration is reduced by 47.37 % when comparing the solid internal fin configuration at the higher flow rate (6 L/min) with the no fin configuration at the lower flow rate (2 L/min). At 100 min, the cumulative heat stored is higher in the solid internal fin configurations than in the configurations without fins. Furthermore, the internal fin configurations have less entropy generation than without fin configurations, justifying that providing solid internal fins in PCM balls enhanced the LHTES system performance.

Experimental analysis of a commercial size bio-based latent thermal energy storage for air conditioning

Future smart and efficient energy management systems for space cooling and heating in building applications require novel solutions to store heat to decouple the energy demand and the availability of renewable energy sources. Latent thermal energy storages represent one of the most promising solutions; however, their cost-effective implementation in terms of energy and cost savings and payback time needs to be verified case by case. Thus, simplified, though accurate, performance correlations during both charging and discharging phases are strongly needed to be implemented into the different dynamic simulation tools. This work is intended to present the experimental behavior of a novel 18 kWh latent thermal energy storage that uses the roll-bond technology to efficiently store and release cold energy by exploiting the solid/liquid phase change process of 300 kg of a biobased phase change material having a melting temperature of 9 °C. The effects of the inlet water temperature and flow rate are studied to elucidate how the performance varies and to identify possible control strategies. On the basis of the experimental results, two correlations are proposed to accurately predict the performance of the latent thermal energy storage to be implemented in general dynamic simulation tools that can help in evaluating the system performance and the achievable energy and cost savings.

Experimental and numerical investigations on the thermal performance enhancement of a latent heat thermal energy storage unit with several novel snowflake fins

This article introduces a novel snowflake fin inspired by the crystal structure of snowflake to enhance the heat transfer performance of Latent Heat Thermal Energy Storage (LHTES) units. Initially, a numerical simulation model for transient heat transfer units with snowflake fin was established in a shell and tube LHTES unit. The accuracy and dependability of the model are verified through comparison with experimental results. Then, the effects of three placement methods of LHTES unit (vertical, horizontal-Ⅰ, and horizontal-Ⅱ) on melting and solidification performance are explored. Additionally, the effects of traditional longitudinal fins, snowflake fin, and four novel snowflake fins on melting and solidification behaviors are quantitatively compared. The single-factor method and response surface methodology (RSM) were employed to further optimize the selected optimal novel snowflake fin design. The research results show that the heat transfer performance of the vertically placed LHTES unit is the best. In comparison to traditional longitudinal fins and conventional snowflake fin designs, the novel snowflake fin design reduced the total melting and solidification time by 45.15% and 18.14%, respectively. The optimal size of the branch fins is a radial length of the root of 22.9 mm, self-length of 8 mm, and an angle of 60.3°.

Functionalization, protonation and ligand extension on MIL-53 (Al) MOFs to boost water adsorption and thermal energy storage for heat transformations

Understanding the relationship between the geometry of metal–organic frameworks (MOFs) and the shape of H2O adsorption isotherms is of utmost importance to control the hydrophilic and hydrophobic behaviors of water in MOFs with adsorption/desorption kinetics to realize their applications in thermal energy storage (TES). The MOFs are potential candidates for TES through water adsorption process. The TES can be used as a pivot for heat transformations related to cooling, heat pump, desalination, power generation, water harvesting and dehumidification. The TES performances are mainly determined by water adsorption characteristics such as water uptake/offtake loadings, kinetics and adsorbents-water interaction energy. Therefore, this paper presents a comprehensive analysis on the restructuring of MIL-53 (Al) MOFs for heat transformation applications. In this work, the original MOF is first functionalized with amino or hydroxyl functional groups. Next, the functionalized MOF is protonated with hydrochloric acid. In addition, ligand extension is applied on the original MOF by replacing the original organic linker with the progressively longer linkers. The surface properties of these restructured MOFs are measured by XRD, FTIR, TGA and N2 adsorption analysis. The water uptakes under equilibrium and dynamic conditions are presented in the form of isotherms and kinetic plots. The structural, thermal and cyclic water transfer stabilities of these MOFs are also presented. It is found that the tailored MIL-53 (Al) MOFs modify both the hydrophilicity and hydrophobicity of the original MOFs and improve the water loadings up to 0.9 g/g. The functionalized and protonated MIL-53 (Al) MOFs show higher water transfer with faster kinetics as compared to the parent MIL-53(Al) MOFs. The ligand extended MIL-53 (Al) MOFs provide higher water transfer between humid (relative humidity RH of 80% to 90%) and regenerated (RH of 30%) conditions with promising thermal energy storage density (TESD, up to 1.54 MJ/L).

Effect of charging operating conditions on open zeolite/water vapor sorption thermal energy storage system

Sorption thermal energy storage (STES) is one of the most promising solutions to realize inter-seasonal thermal energy storage for building heating. However, the analysis of charging operation parameters on the thermal energy storage performance of STES system is insufficient. In this paper, a STES experimental bench using zeolite 4A/water vapor as the sorption working pairs was built, and the charging/discharging experiments were conducted. The thermal energy chain during the full charging-discharging process was analyzed. The experimental results indicated that approximately 60% of the thermal energy provided by the heater was directly lost through the reactor outlet in the charging process, which seriously hindered the improvement of the thermal energy storage performance of the STES system, such as the coefficient of performance (COP). In addition, the influence of charging conditions on the thermal energy storage performance of the system was also investigated. Both the improvement of charging temperature and the reduction of charging air humidity are beneficial to enhancing the thermal energy storage performance of the STES system. When the charging temperature was 150 °C, the energy storage density of zeolite reached a maximum of 251 kWh/m3. The COP of system reduced by 28% when the relative humidity of charging air rose from 20% to 70%. The effect of the volume flow rate of charging air on the thermal energy storage performance of the system is insignificant. The COP of system maintained around 0.212 at different charging air volume flow rates.

Numerical energy and exergy evaluation for a multiple-layer latent heat storage unit enhanced with nanoparticles under different seasons

Latent heat thermal energy storage unit alleviates the mismatch between energy supply and demand. However, the sole melting temperature of a phase change material in a single-layer heat storage unit does not adapt well to the environment. Therefore, the mechanisms associated with the better environmental adaptability of a multiple-layer heat storage unit are explored in this study based on energy and exergy evaluations via comparison with single-layer units. An innovative methodology is proposed to discuss transient thermal energy and exergy, and exergy distribution of these heat storage units in different seasons. Results show that the multiple-layer units address the limitations of single-layer units by exhibiting excellent heat storage capacity and quality, as well as uniform melting and exergy distribution. Compared with the single-layer unit with a melting temperature of 49 °C, the multiple-layer unit exhibits a 56.64% higher energy in the winter. Moreover, the exergy is 57.14% higher than that of the single-layer unit with a melting temperature of 33 °C in the summer. This study reveals the mechanism of excellent thermal energy storage performance of the multiple-layer latent heat storage unit in different seasons.

Sorption Thermal Energy Storage Performance of Nanoporous Metal–Organic Frameworks and Covalent Organic Frameworks by Grand Canonical Monte Carlo Simulations

Sorption Thermal Energy Storage Performance of Nanoporous Metal–Organic Frameworks and Covalent Organic Frameworks by Grand Canonical Monte Carlo Simulations

Thermal energy storage performance of hierarchical porous kaolinite geopolymer based shape-stabilized composite phase change materials

Phase change materials (PCMs) are prospective energy materials that are widely applied in building energy conservation, waste heat recovery, infrared stealth technology and solar dynamic power system. The enhancement of heat transfer and leak-proof performance are critical to PCMs. Although geopolymers have been applied in thermal energy storage, meanwhile, hierarchically porous geopolymers have already shown superb performance in various functional applications, to the authors’ knowledge, no report concerning the application of hierarchical porous ones have been issued. This paper concerns the preparation of a shape-stabilized composite PCMs, consisting of hierarchically porous kaolinite-based geopolymer (PKG) embedding polyethylene glycol 4000 (PEG4000), which shows promising prospects in thermal energy storage. Optimized porous geopolymer matrices feature high porosity (>83%), combined with high specific surface area (4.7 m2/g) and thermal conductivity (TC, 1.324 W·m−1·K−1). Furthermore, the shape-stabilized composite PCMs show excellent thermal energy storage properties: loading rate of 80.93 wt%, latent heat of 168.80 J g−1 and TC of ∼0.36 W·m−1·K−1 at 20–30 °C, which is 1.64 times of the TC of pure PEG4000. Finally, the photothermal conversion performances of the shape-stabilized composite PCMs were also simulated.

Heat transfer enhancement of latent heat thermal energy storage with nanoparticle by bubble-driven flow

This study investigated the heat transfer enhancement of phase change material (PCM) with nanoparticles by bubble-driven flow. The addition of nanoparticles can improve conduction heat transfer, while bubble-driven flow can improve convection heat transfer. The 5 wt% nanoparticles increased the thermal conductivity by 6.4 % and viscosity 205 % of phase change material, while decreased the convective flow accordingly. However, bubble-driven flow strengthened the flow velocity by 8.3 times. Since nanoparticles tend to sediment over time in PCM, this issue of sedimentation should be overcome before they are applied in practice. The particle concentration in the vertical direction was analyzed by laser transmission experiment, and as expected, the concentration was the highest at the bottom. The bubble-driven flow uniformized the particle concentration in the vertical direction, which could solve the sedimentation problem. The combined application of nanoparticles and bubble-driven flow to phase change material both improved conductive and convective heat transfer, and provided uniform distribution of particle concentration. A latent heat thermal energy storage (LHTES) unit was designed for combined application study, and a charging performance experiment was conducted. Nanoparticle only improved the average charging power by 1.09 times, while bubble-driven flow only improved it by 1.27 times. Bubble-driven flow and nanoparticles applied altogether increased the average charging power by 1.41 times. Therefore, it was confirmed that the combined application of nanoparticles and bubble-driven flow can effectively improve the heat transfer performance of the latent heat thermal energy storage. Thus, this method is expected to be applied to a wide range of industries.

Leaf-vein bionic fin configurations for enhanced thermal energy storage performance of phase change materials in smart heating and cooling systems

In the present study, we investigated the effect of different structures of a novel leaf vein bionic fin and various arrangements in the tube on the complete melting time of phase change materials (PCM) in a triplex-tube thermal energy storage (TES) system. RT82 was adopted as the phase change material. The enthalpy-porosity method was employed for this numerical study. The numerical model was validated against experimental data from a previous reference. The simulation results demonstrate that the novel fins deliver significant reductions in the duration of complete melting. Based on fin-branched vein numbers of 1, 2 and 3, increasing the fin angle from 30° to 60° can reduce the complete melting time by up to 14.3%. Additionally, adjusting the fin arrangement can save up to 6.35% of the complete melting time. The proper arrangement of the fins can improve the heat transfer performance of the PCM. The non-dimensional quantities analysis of the calculated results shows that the melting time is negatively correlated with the non-dimensional angle. As the non-dimensional parameter, fin arrangement number decreases from 1, the complete melting time corresponding to the fins of different structures first decreases and then increases for the phase change material.