Thermal Storage System Research Articles

Innovative flexible thermal storage textile using nanocomposite shape-stabilized phase change materials

A novel flexible thermal storage system based on organic phase change materials (PCMs) deposited on a non-woven polyester (PET) substrate is described in this article. Thermally regulating effects were created via encapsulation of polyethylene glycol (PEG) in carbon nanofibers (CNFs) to manufacture a shape-stable phase change material (SSPCM). Improvement in the thermal conductivity (TC) of the system was obtained by incorporating reduced graphite oxide nanoparticles (rGONP) into the CNFs. A new method was applied to load and secure the manufactured SSPCMs on the fibrous substrate so that an acceptable level of flexibility was preserved (change in bending length less than 30%). The sample performance was evaluated by measuring its thermal properties. The physical properties, wash fastness, abrasion resistance, morphology, and PCM leakage of the samples were also assessed. The results point to a good thermal storage ability of the samples with characteristic phase change temperature ranges of 30.1–31.4 °C and 19.2–24.3 °C for melting and freezing, respectively, and a latent heat of 8.9–22.9 J g−1 for meting and 11.2–21.4 J g−1 for freezing. The use of the CNF-rGONP for PEG enhanced the TC of the system by 454%, thus providing a rapid thermal response, and efficiently prevented the leakage of PEG. Finally, the loading and fixation method on the non-woven substrate allowed an acceptable level of durability with less than 4% of weight loss during washing and abrasion tests. This system provides a promising solution for rapid response, flexible thermal storage wearables.

Finned-tube-integrated modular thermal storage systems for HVAC load modulation in buildings

Finned-tube-integrated modular thermal storage systems for HVAC load modulation in buildings

Dynamic modeling and techno-economic assessment of hybrid renewable energy and thermal storage systems for a net-zero energy greenhouse in South Korea

Dynamic modeling and techno-economic assessment of hybrid renewable energy and thermal storage systems for a net-zero energy greenhouse in South Korea

Heat charging and discharging of coupled MgH2–LaNi5 based thermal storage: Cycling stability and hydrogen exchange reactions

Heat charging and discharging performances and cycling stability of the coupled MgH2–LaNi5 thermal storage system are investigated. Heat storage reaction is studied by tracking temperatures and pressures of hydride beds as well as hydrogen mass flow rates exchanging between MgH2 and LaNi5. Upon 20 heat storage cycles, MgH2–LaNi5 pair reveals remarkably cycling stability with the energy densities during heat charging and discharging of 797 ± 37.5 and 680 ± 28 kJ/kg, respectively. The hydrogen content exchange between MgH2 and LaNi5 during heat storage cycles is up to 57 % of theoretical hydrogen capacity. The possibilities to enhance the hydrogen contents participating in the heat storage reaction are discussed. The heat charging and discharging performances at different positions in the hydride beds of MgH2–LaNi5 pair are characterized. Not only thermodynamic compatibility of MgH2 and LaNi5 but also kinetics as well as hydrogen and heat transfer in MgH2 beds considerably influence heat storage performance.

Design and dynamic simulation of a molten salt THS coupled to SFR

With the increasing ratio of renewables in the grid, a low-carbon and stable base load source that also is capable of load tracking is in demand. Sodium cooled fast reactors (SFRs) coupled to thermal heat storage system (THS) is a strong candidate for the need. This research focuses on the designing and performance validation of a two-tank THS based on molten salt to integrate with a 280 MWth sodium cooled fast reactor. Designing of the THS includes the vital component, sodium-to-salt heat exchanger which is a technology gap that needs to be filled, and designing and parameter selection of the tanks and related pumps. Modeling of the designed THS is conducted followed by the description of operation strategies and control logics of the THS. Finally, the dynamic simulation of the designed THS is conducted based on Fortran. Results show, the proposed power system meets the need of the design requirements to store heat for 18 h during a day and provide 500 MWth for peak demand for the rest of the day.

Investigating the thermo-economic performance and modeling of a parabolic solar collector with phase change material in the receiver tube in a solar desalination

Solar desalination is a suitable and cost-effective system for producing drinkable water from salt water. The main goal of this study is improving the thermal performance of the solar desalination with latent thermal storage system and the panel detector. The heat loss from the solar collector increases due to the fluctuations in the intensity of solar radiation and the use of phase change materials is a suitable solution for storing energy during peak hours and releasing it when the solar radiation intensity is reduced or absent. Thus phase change material (paraffin) placed in the focal tube in the form of a 6 mm spiral pipe with a pitch of 7 cm. Thermal performance of the collector was carried out at three fluid flow rates of the working fluid at 1.9, 1.3 and 4.2 l/min with phase change material and without phase change material in four consecutive days from 10:00 to 14:00. The results of the showed that the solar water desalination equipped with phase change materials had the highest thermal efficiency at the fluid flow rate of 4.2l/min and the lowest with a flow rate of 1.9 l/min. The results showed that the using phase change material improves the thermal efficiency by 3.05 %. Produced fresh water during 4 h was 0.722l/m2 and it significantly reduced the hardness of drinking water. The solar collector simulated by Anysy and the simulated results showed a good correlation between the predicted and experimental data with reasonable accuracy (R2 > 0.97).

Multi-objective optimization of multi-energy complementary system based on cascade utilization of heat storage

A multi-energy complementary system driven by solar energy and central grid is proposed to supply electricity and cooling/heating, in which a dual-tank thermal storage system is integrated to achieve cascaded solar heat energy utilization. The system integrates parabolic trough solar collectors, high-temperature and low-temperature thermal storage tanks, and an organic Rankine cycle to form an operational loop. The low-temperature thermal storage tank drives an absorption heat pump independently. Excess photovoltaic power drives the ground source heat pump for heating/cooling. Three indicators are defined and compared to show the renewable energy penetration rate in the complementary system. A multi-objective optimization model considering economic performance and renewable energy rate is constructed to optimize the system configurations. Three sets of objective functions are compared through the optimization Pareto frontiers. Then, the TOPSIS method is employed to select the optimum configuration through setting different weights of optimization objectives. Compared with the reference system, the proposed multi-energy complementary system improves the energy, economic and environmental benefits by 59.21%, 24.27% and 11.31%, respectively. Through a variety of equipment (PV, ORC, AHP, TES), solar energy supplies 86.2% and 72.2% of total electricity and heat loads, respectively.

On the entropy analysis and hydrothermal behavior of buoyancy-driven magnetized hybrid nanofluid flow within a semi-circular chamber fitted with a triangular heater: Application to thermal energy storage for energy management

Entropy generation is treated as a noteworthy criterion for effective operation in thermal storage systems. Buoyancy-driven laminar flows within the semi-circular chamber have wide-ranging applications within the aviation industry, solar thermal receivers, heat exchangers, chemical mixing chambers, electronic components, etc. Nanofluids do explore significant heat transport capabilities in industrial, technical, and commercial sectors. The stable dispersion of metallic or oxide tiny nano-level particles and water, named hybrid nanofluids signifies the extended version of classical nanofluids. Hybrid nanofluids reveal superior thermal conductivity and are significantly used as an advanced heat transport medium in thermal storage, solar receiver, electronic cooling, heat pipes, space, biomedical, etc. With such an objective, the performed analysis unfolds the hydrothermal and entropy investigation of magnetically driven buoyancy-induced Al2O3–TiO2–water hybrid nanofluids through a semi-circular chamber having a triangular heater fitted from the bottom wall. The curved periphery is made cold, while the remaining triangular parts and bottom walls are made heated and insulated, respectively. Several triangular-size heaters are set to the lower wall and variations in entropy plus hydrothermal scenario are noted. Leading equations are transferred to dimensionless form using apposite similarity transformation. The Galerkin finite element discretization procedure is merged to execute the numeric simulation. Both numeric and experimental studies are clutched to compare the present result’s accuracy. Various velocities, streamlines, isotherms, Bejan numbers, entropy profiles, and Nusselt number profiles are presented to address the parametric influence of Hartmann numbers, solid particle concentrations, and Rayleigh numbers.

A perspective on high‐temperature heat storage using liquid metal as heat transfer fluid

AbstractEnergy storage systems are essential to secure a reliable electricity and heat supply in an energy system with high shares of fluctuating renewable energy sources. Thermal energy storage systems offer the possibility to store energy in the form of heat relatively simply and at low cost. In concentrating solar power systems, for instance, molten salt‐based thermal storage systems already enable a 24/7 electricity generation. The use of liquid metals as heat transfer fluids in thermal energy storage systems enables high heat transfer rates and a large operating temperature range (100°C to >700°C, depending on the liquid metal). Hence, different heat storage solutions have been proposed in the literature, which are summarized in this perspective. Based on these, future technical advances are suggested such as reducing the liquid metal share in the heat storage, using waste material as storage medium or using liquid metal as heat transfer fluids not only in sensible, but in latent or thermochemical energy storage systems. The use of waste material in a packed bed configuration with 5% porosity, for example, can bring down the storage material costs to 2%–3% of the costs of a liquid metal‐only storage system. Furthermore, future application fields beyond concentrating solar power are proposed: supply of industrial process heat, waste heat integration and power‐to‐heat‐to‐power processes.

Effect of climate on the optimal sizing and operation of seasonal ice storage systems

Seasonal thermal storage systems can reduce the temporal mismatch between renewable energy availability and energy demand. Ice storage systems exhibit a non-linear behaviour in the heat exchange and storage processes, complicating the formulation of optimal design and operation problems. In this work, we propose a mixed-integer quadratically-constrained programming formulation, which minimizes the Levelized Cost of Energy for space heating and cooling, including sizing of a supporting PV array. The optimization was repeated for different storage volumes, finding the system optimal operation in each case –and thereby the optimal system sizing. The heating and cooling demands were computed from an archetypal office building, placed in three reference locations with cold and semi-arid, warm and humid continental, and temperate and humid continental climates. Results show that the optimal PV size decreases with growing ice storage volume, and an ice storage works best in a temperate continental climate, covering up to 47% of the cooling demand with a 250 m 3 storage.

Experimental and numerical investigation of the melting process of solar salt in a spherical capsule

Solar salt is commonly employed as phase change material in various industrial applications, particularly in latent heat-based thermal storage systems such as packed beds in solar thermal power technologies. Here, a series of experimental and numerical studies are conducted of the melting process of a binary nitrate salt inside a spherical capsule under a wide range of large Stefan numbers, specifically ranging from 0.56 to 1.12. For a deep understanding of the melting behavior inside the sphere and its heat transfer characteristics under different constant wall temperatures and sphere sizes, the visualized high-temperature phase change experiment along with a 2D axisymmetric numerical model are presented. To confirm modelling reliability, the numerical model well-realized the sinking phenomena visualized in the experiment with a suitable mushy-zone parameter value of 6*108 kg/(m3·s). Subsequently, the temperature field, flow field, melting front, total transfer rate and melting time are explored. Further, a detailed parametric investigation is applied, including the effects of dimensionless parameters such as Gr, Ste on the melting process. And finally, the dimensionless correlation is succeeded to be proposed for unconstrained melting process with 0.56 ≤ Ste ≤ 1.12 and 1.80E+04 ≤ Gr ≤ 2.02E+05.

Experimental analysis of a power-to-heat storage with high-temperature phase change materials to increase flexibility and sector coupling

To boost the flexibility, sector coupling and manageability of renewable energy systems, a unique power-to-heat storage (electric charging, thermal discharging) is proposed. The hybrid thermal energy storage system, including phase change materials, is built using flat pillow-plates and heating rods. Experimental testing is conducted to assess the prototype's electrical and thermal performance. In addition, a parametric study involving several charging and discharging control strategies is proposed in this context.The suggested hybrid thermal storage system provides a total storage capacity of 4.87kWh using nitrate salts as phase-change material (eutectic mixture of KNO3 and NaNO3). The charging efficiency ranges from 65 to 90%, depending on the charging/discharging strategy, and the discharging period can be shortened by more than 1 h. Additionally, active management of the heating rod temperature reduces the charging period by half, making the storage system highly flexible. This demonstrates the ability of this system to aid in modularity and flexibility for effective energy management in the context of renewable energy and industry thanks to an increased storage capacity.

Improving thermal performance of groups of energy screw piles with phase change materials

Underground thermal storage systems have potential to play an important part in the transition to renewable energy. Studies on combining building foundations with thermal storage are often limited to concrete piles, especially when involving phase change materials. In a recently published work, the authors presented a novel energy pile built using a screw pile filled with phase change materials. While the previous work considers all energy screw piles with same pile fillings, meaning a trade-off of low thermal conductivity and high heat capacity, screw piles in this work have two different functions: one screw pile filled with grout acts as the heat exchanger (energy pile) and its neighbour, filled with Phase Change Materials, act as a thermal battery (thermal storage pile). U-loop pipes are embedded only into the energy piles and connected to a Ground Source Heat Pump, so thermal energy from buildings will be stored in both the ground and the thermal storage piles. Numerical results show that this system can store up to 189.8 MJ/m3 heat energy during one year of operation. The Coefficient of Performance of the heat pump increases slightly, up to 3.4 %, which results from an improvement of the cooling mode performance.

Study of storage thermal energy of latent heat Application to the solar collector

The energy production provided by a heat excess or discontinuous source (solar, waste heat...) involve the utilization of a thermal storage in the thermodynamic or recuperation chain. These last years, studies on thermal storage systems have been developed in order to bring technical and economic elements. The study includes two parts. The first one concern a numerical analysis of a latent-heat thermal energy storage unit is conducted. The element of storage is a rectangular closed cavity filled with a phase change material (PCM) initially at the solid state. At t = 0 a heat flux is applied through one of the vertical walls of the cavity. Other one, experimental steady treats a new type of solar collector was developed and tested to valid numerical models.

Effect of structural characteristics on the transport characteristics of solid particles in the thermal storage and release system of circulating fluidized bed

Coal-fired power generation stands as the most economically viable modulating power source in present-day China. It holds the potential to offer prospective solutions to the challenges posed by the rapid expansion of intermittent, unpredictable, and unstable renewable energy sources. Solid particle thermal storage technology emerges as an effective means to enhance the flexibility of coal-fired circulating fluidized bed power units. To attain an optimized structure for the solid particle thermal storage and release system in circulating fluidized bed units, experimental research was conducted on a 0.1 MWth circulating fluidized bed test platform. This study delved into the impact of ash storage bin geometries and the shapes of their feed-discharge valves on the control properties of solid particle transportation. The experimental outcomes reveal that employing inverted m-shaped valve and dual U-shaped valves for feed control, alongside U-shaped valves and N-shaped valves for discharge control, both enable efficient and rapid storage and release of solid particles within the circulating fluidized bed. Under similar air distribution conditions, the inverted m-shaped valve exhibits lower conveying energy consumption than the dual U-shaped valves, while the N-shaped valve excels in control characteristics over the U-shaped valve. Furthermore, the inverted m-shaped valve and the N-shaped valve demonstrate optimal overflow port heights, and the ash storage bin exhibits an optimum height-to-diameter ratio.

Heat transfer enhancement and applications of thermal energy storage techniques on solar air collectors: A review

Solar air collectors have been used in a variety of industrial applications, prompting a study and summary of various studies on the topic. Solar collectors’ exceptional energy conversion and storage outputs have piqued curiosity in the field of energy research. The current review study focuses on solar thermal application advancements and provides an overview of thermal energy storage devices and solar collectors. This paper presents and discusses a variety of solar collectors, both concentrating and non-concentrating. The energy storage media utilized in these plants, phase change material with melting temperatures exceeding 300°C, was exam-ined. The goal of this study is to provide the necessary information for advanced investiga-tions in the development of cost-effective high-temperature thermal storage systems. Finally, a summary of the presentation, as well as potential solar power plants are reviewed.

Optimal sizing and operation of seasonal ice thermal storage systems

Ice storage systems can be used as an efficient cooling source during summer, as well as a heat source for heat pumps during winter. The non-linear behavior of the heat exchange process in storage makes formulations for optimizing the design and operation of these technologies complex. In this work, we propose a quadratically-constrained mixed-integer programming formulation, that can capture the latent and sensible behavior of the storage and its impact on the delivery of heating and cooling. A building demonstrator integrating an ice storage device was used as a case study. Monitoring data were used to validate the simplified ice storage model employed in the optimization. Results showed that the most common optimal storage cycle requires freezing the water during late winter and when the air temperature falls below 0∘C. Increasing the storage volume increases both storage efficiency and the amount of free cooling available during summer. For these reasons, economies of scale can make larger systems more competitive than smaller ones. Storage size and thermal insulation level affect the duration of the charging and discharging phases. Thermal insulation improves seasonal efficiency and free cooling significantly. A higher CO2 emissions price does not yield significant benefits in terms of emissions reductions. High investment costs and the seasonal variation in CO2 intensity of electricity reduce the economic and environmental competitiveness of long-term ice storage systems, respectively.

Optimizing mixed cool thermal storage systems across a connected community

A high level of electric demand flexibility must be integrated into our building infrastructure to enable greater renewable energy penetration in the grid. In the U.S., 9 % of electricity generated is used to cool buildings in a periodic manner, making this end-use an ideal target for active management through cool thermal energy storage (CTES) technologies. Historic uses for CTES are designed around central chilled water plants, but these systems cool less than 25 % of U.S. commercial floorspace. Emerging technologies are under development to serve the many smaller distributed cooling systems, such as rooftop units (RTUs), and have the potential to add CTES to an additional 66 % of cooled commercial floorspace. However, these unitary thermal storage systems (UTSS) lack the modeling and analysis tools to evaluate them in the future interactive grid context. This study develops the modeling and optimization tools necessary to simultaneously examine central and distributed ice storage systems within the multi-building, connected community context. An integrated simulation-optimization workflow is created to allow for rapid customized analysis. Results demonstrate the energy and flexibility tradeoffs of various implementations.

Method for screening paired metal hydrides with appropriate phase change material for a thermochemical energy storage system

Thermochemical energy storage (TES) systems using coupled metal hydrides (MHs) have long been recognized as an option for sustainable energy systems such as solar power plants. The MHs-TES system consists of two linked MH beds (energy storage bed and hydrogen storage bed) that exchange hydrogen during the heat storage/release cycles. The heat reaction of the hydrogen storage bed is stored in a PCM as latent heat, which is recovered during the heat release step. One of the main issues of the MHs-TES system is selecting the best-suited combination of MHs and compatible PCM to satisfy application requirements. Herein, an approach is proposed for screening the right pairs of hydrides and the suitable PCM. To assess this procedure's effectiveness, a 2D-mathematical model is developed, and a computer code is established. In addition, using this code, the dynamic behavior of the MHs-TES system and the effect of the hydrogen storage bed temperature on the system's performance are examined. The Mg2Fe alloy as HTMH bed, and two LTMH beds as LTMH (LaNi4.25Al0.75 at medium temperature and LaNi5 at low temperature) are used. With an efficiency of 86.5%, the results show that Mg2Fe/LaNi5 is a viable MHs combination for a thermal storage system.

Augmenting the thermal response of helical coil latent-heat storage systems with a central return tube configuration

Low-temperature stratification, high-volumetric storage capacity, and less-complicated material processing make phase-changing materials (PCMs) very suitable candidates for solar energy storage applications. However, their poor heat diffusivities and suboptimal containment designs severely limit their decent storage capabilities. In these systems, the arrangement of tubes conveying the heat transport fluid (HTF) plays a crucial role in heat communication between the PCM and HTF during phase transition. This study investigates a helical coil tube-and-shell thermal storage system integrated with a novel central return tube to enhance heat transfer effectiveness. Three-dimensional computational fluid dynamics simulations compare the proposed design against a baseline helical coil system without a return tube under equivalent conditions. Outcomes quantify the return tube's efficacy in augmenting heat transfer uniformity and accelerating phase transition. Adding the return tube markedly boosts heat storage and recovery rates, increasing charging by 88% and discharging by 56% versus the baseline. Moreover, total phase transition time reduces by 48% for melting and 36% for solidification with the return tube. The accelerated charging stems from sustained convective heat transfer inside the return tube even as the molten layer thickens. Meanwhile, enhanced solidification results from ongoing cooling of inner regions. Isotherm analysis visualizes the return tube's efficacy in maintaining thermal uniformity throughout the phase transition process. Overall, the return tube significantly improves PCM thermal response, demonstrating a novel but straightforward approach to address heat transfer limitations in latent thermal storage systems.