Thermal Energy Storage System Research Articles

On The Potential Use of Copper-Modified Geopolymer Incorporating Lead-Smelter Slag for Thermal Energy Storage

Thermal energy storage (TES) system has been widely employed in concentrated solar power (CSP) plants to ensure the system efficiency. With excellent thermal characteristics, electrolytic copper powder (ECP), graphene oxide (GO) and lead-smelter slag (LSS) aggregate – a mining waste material, have been utilised in this study, aiming to fabricate metallurgical geopolymer material as a storage medium in the TES system. This paper investigated the effect of ECP contents (0, 5%, 10%, 15%, 20%) on the strength, specific heat, thermal conductivity and thermal stability of GO-engineered geopolymer mixes incorporating LSS aggregate. With 10% ECP inclusion, the flow rate and compressive strength improved significantly. Increasing ECP content improved the thermal conductivity but reduce specific heat of geopolymers. The results revealed that ECP was a promising component to be incorporated into geopolymer to enhance its physio-mechanical characteristics and thermal stability. The combination of ECP, GO and LSS to produce geopolymer materials for TES system can provide an eco-friendly solution to the CSP plants and the industry waste recovery.

Numerical Study of an Energy Storage Container with a Flat Plate Phase Change Unit Characterized by an S-Shaped Flow Channel

China’s rapid economic development and rising energy consumption have led to significant challenges in energy supply and demand. While wind and solar energy are clean alternatives, they do not always align with the varying energy needs across different times and regions. Concurrently, China produces substantial amounts of industrial waste heat annually. Effective recycling of this waste heat could substantially mitigate energy supply and demand issues. The Mobile Thermal Energy Storage (M-TES) system is a key solution to address these challenges, as it helps manage the uneven distribution of energy over time and space. This article establishes a packaged M-TES based on a plate-type phase change unit. Based on different placement methods of the plate-type phase change unit, different inlet temperatures and phase change temperature differences, and different inlet and outlet directions, the complete charging and discharging process of the packaged phase change thermal storage system was simulated using ANSYS FLUENT 2022 R1 software. The results showed that during the heating process of the entire system, the horizontal placement of the plate-type phase change unit and the inlet and outlet methods of the heat transfer fluid (HTF) significantly improved the heating effect of the system, increasing it by 15.9%. Increasing the temperature difference between the inlet temperature of the heat transfer fluid and the melting temperature of the phase change material (PCM) from 4 K to 19 K can increase the melting rate of PCM by approximately 54.9%

Numerical study and experimental validation of a porous biochar supported form stable composite for thermal energy storage

This study numerically investigates the performance of the melting process for a biochar-based phase change material latent heat energy storage system. The melting processes of a composite made from softwood biochar combined with paraffin RT28, were compared numerically using the equilibrium porous medium model in ANSYS Fluent. The set up was validated through results from previous literature and experimental work. The enhancement in melting was compared to the pure PCM melting scenario and the effects of different paraffins, boundary conditions and inclination angle were investigated for real world application. Softwood biochar composites significantly surpass the performance of paraffin alone, reducing the melting time by 79 %. Different paraffins within the softwood composite produced different melting times, ranging from 2565 s to 4790 s. In terms of inclination angle adjusting to 90° produced steadier heating and reduced the melting time by 63 % in the composite. These findings offer insights into optimising latent heat thermal energy storage systems for improved performance and reduced energy wastage, highlighting the potential of biochar composites in sustainable energy solutions.

Enhancing Fire Protection in Electric Vehicle Batteries Based on Thermal Energy Storage Systems Using Machine Learning and Feature Engineering

Thermal Energy Storage (TES) plays a pivotal role in the fire protection of Li-ion batteries, especially for the high-voltage (HV) battery systems in Electrical Vehicles (EVs). This study covers the application of TES in mitigating thermal runaway risks during different battery charging/discharging conditions known as Vehicle-to-grid (V2G) and Grid-to-vehicle (G2V). Through controlled simulations in Simulink, this research models real-world scenarios to analyze the effectiveness of TES in controlling battery conditions under various environmental conditions. This study also integrates Machine Learning (ML) techniques to utilize the produced data by the simulation model and to predict any probable thermal spikes and enhance the system reliability, focusing on crucial factors like battery temperature, current, or State of charge (SoC). Feature engineering is also employed to identify the key parameters among all features that are considered for this study. For a broad comparison among different models, three different ML techniques, logistic regression, support vector machine (SVM), and Naïve Bayes, have been used alongside their hybrid combination to determine the most accurate one for the related topic. This study concludes that SoC is the most significant factor affecting thermal management while grid power consumption has the least impact. Additionally, the findings demonstrate that logistic regression outperforms other methods, with the improving feature to be used in the hybrid models as it can increase their efficiency due to its linearity capture capability.

Advanced smart HVAC system utilizing borehole thermal energy storage: Detailed analysis of a Uppsala case study focused on the deep green cooling innovation

This article presents and thoroughly examines an innovative, practical, cost-effective, and energy-efficient smart heating, ventilation, and air conditioning (HVAC) system. The fundamental component of this concept is a state-of-the-art method called Deep Green Cooling technology, which uses deep drilling to utilize the ground's heating and cooling potential directly without the need for machinery or heat pumps. This method satisfies demands with the least energy use, environmental impact, and operational costs. In order to effectively oversee and regulate energy production, storage, and utilization, the system consists of an intelligent control unit with many smart controllers and valves. Renewable energy deployment is made easier, and the intelligent automation unit is more compatible with the help of a high-temperature cooling resource with a high supply temperature of 16 °C. The technical, environmental, and financial aspects of the suggested smart office building system in the southern region of Uppsala, Sweden, are evaluated using TRNSYS software. According to the results, boreholes provide more than 28.5 % of the building's energy requirements by utilizing the ground's ability to generate affordable, dependable seasonal thermal energy. The district heating network satisfies the remaining demand, amounting to 787.2 MWh, highlighting the benefits of combining conventional and renewable energy sources for increased supply security and dependability. The borehole thermal energy storage system meets the building's entire cooling need, underscoring the importance of high-temperature cooling systems. The most expensive part of the system is the borehole thermal energy storage, which accounts for over half of the total investment. The system has an appropriate payback period of ten years, proving its long-term profitability and cost-effectiveness, thanks to removing the machinery and heat pump. With 3138 MWh of ground-source heating and cooling, the system saves 17,962 USD by reducing CO2 emissions by about 143.7 t, sufficient to grow 16.3 ha of trees throughout the payback period.

Buoyancy-driven heat transfer and entropy analysis of a hydromagnetic GO-Fe3O4/H2O hybrid nanofluid in an energy storage enclosure partially filled with non-Darcy porous medium under an oblique magnetic field

Purpose Thermal energy storage systems use thermal energy to elevate the temperature of a storage substance, enabling the release of energy during a discharge cycle. The storage or retrieval of energy occurs through the heating or cooling of either a liquid or a solid, without undergoing a phase change, within a sensible heat storage system. In a sensible packed bed thermal energy storage system, the structure comprises porous media that form the packed solid material, while fluid occupies the voids. Thus, a cavity, partially filled with a fluid layer and partially with a saturated porous layer, has become important in the investigation of natural convection heat transfer, carrying significant relevance within thermal energy storage systems. Motivated by these insights, the current investigation delves into the convection heat transfer driven by buoyancy and entropy generation within a partially porous cavity that is differentially heated, vertically layered and filled with a hybrid nanofluid. Design/methodology/approach The investigation encompasses two distinct scenarios. In the first instance, the porous layer is positioned next to the heated wall, while the opposite region consists of a fluid layer. In the second case, the layers switch places, with the fluid layer adjacent to the heated wall. The system of equations for fluid and porous media, along with appropriate initial and boundary conditions, is addressed using the finite difference method. The Tiwari–Das model is used in this investigation, and the viscosity and thermal conductivity are determined using correlations specific to spherical nanoparticles. Findings Comprehensive numerical simulations have been performed, considering controlling factors such as the Darcy number, nanoparticle volume fraction, Rayleigh number, bottom slit position and Hartmann number. The visual representation of the numerical findings includes streamlines, isotherms and entropy lines, as well as plots illustrating average entropy generation and the average Nusselt number. These representations aim to provide insight into the influence of these parameters across a spectrum of scenarios. Originality/value The computational outcomes indicate that with an increase in the Darcy number, the addition of 2.5% magnetite nanoparticles to the GO nanofluid results in an enhanced heat transfer rate, showing increases of 0.567% in Case 1 and 3.894% in Case 2. Compared with Case 2, Case 1 exhibits a 59.90% enhancement in heat transfer within the enclosure. Positioning the porous layer next to the partially cooled wall significantly boosts the average total entropy production, showing a substantial increase of 11.36% at an elevated Rayleigh number value. Positioning the hot slit near the bottom wall leads to a reduction in total entropy generation by 33.20% compared to its placement at the center and by 33.32% in comparison to its proximity to the top wall.

Melting Behavior Effect of MXene Nanoenhanced Phase Change Material on Energy and Exergy Analysis of Double and Triplex Tube Latent Heat Thermal Energy Storage

Abstract The impacts of melting behavior on the thermal performance of triple tube thermal energy storage (TT-TES) and double tube thermal energy storage (DT-TES) systems employing cetyl alcohol and 3% v/v. MXene nano-enhanced PCM (NEPCM) are compared and numerically evaluated in this work. For both the DT-TES and TT-TES systems, the following were investigated in connection to melting time: system efficiency, discharged energy, heat transfer rate, exergy destruction, entropy generation number, exergetic efficiency, melting fraction, and melting temperature contours. In addition, the effect of Stefan, Rayleigh, and Nusselt numbers on Fourier numbers are compared for the DT-TES and TT-TES systems with MXene NEPCM. MXene-based nano-enhanced PCM melting in TT-TES displayed 6.53% more Stefan number than cetyl alcohol. DT-TES with pure cetyl alcohol phase change material (PCM) consumes 0.4% more energy at 7800 s than MXene NEPCM. Pure melting of MXene-based nano-enhanced PCM in a TT-TES had 4.16% higher storage exergy than cetyl alcohol. The entropy generation number of pure melting of MXene-based nano-enhanced PCM in TT-TES is 7.93% lower than that of cetyl alcohol. Pure melting of MXene-based nano-enhanced PCM in TT-TES reduces storage energy by 1.95% over cetyl alcohol. Pure cetyl alcohol has 76.99% optimal system efficiency at 5400 s melting time and MXene NEPCM 77.04% at 4800 s in DT-TES. The charging temperature for pure cetyl alcohol PCM in TT-TES is 0.7% lower than in DT-TES. Furthermore, pure melting of MXene-based nano-enhanced PCM in a TT-TES has 1.95% lower storage energy than cetyl alcohol. For a given volume of MXene-based nano-enhanced cetyl alcohol PCM, melting occurs more rapidly in a TT-TES system.

Okra functional biomimetic composite phase change materials integrated with high thermal conductivity, remarkable latent heat, and multicycle stability for high temperature thermal energy storage

High-temperature phase change materials (h-PCMs) offer viable solutions for efficient thermal energy storage systems within large-scale industrial facilities. However, h-PCMs still face enormous challenges owing to low thermal conductivity and restricted thermal storage efficiency. Herein, we report okra functional biomimetic high-temperature composite phase change materials (h-CPCMs) that exhibit excellent comprehensive thermal storage properties and operational reliability, inspired by the okra seed storage process. The okra biomimetic SiC ceramic skeleton, featuring unique macropores and crosslinked axially fibrous thermal transfer pathways, significantly boosts the thermal storage efficiency of loaded molten-salt-based h-PCMs. The resulting h-CPCMs exhibit excellent thermal conductivity with a maximum value of 31 W/(m·K) accompanied by a notable latent heat of 207 J/g. Of note, the h-CPCMs with high porosity maintain superior thermal storage properties after 500 cycles. The overall thermal storage performance under 400–700 °C outperformed that of h-CPCMs reported in previous works. Furthermore, utilizing a self-designed thermal storage performance testing device, the thermal storage power density of h-CPCMs performs a 101 % enhancement compared to pure h-PCMs, suggesting a significant improvement in thermal storage efficiency. This work provides valuable insights and advancements for the further design of highly performance h-CPCMs.

A novel approach to improve double-tube thermal energy storage: Impacts of inner tube twisting and its location

Thermal energy storage (TES) systems are a crucial component of solar energy harvesting cycles. Our objective in this study is to enhance the efficiency of a double-tube TES that utilizes lauric acid, a phase change material (PCM), and heated water as a heat transfer fluid (HTF). For the first time, this study examined the effects of utilizing a twisted inner tube inside a double-tube TES containing HTF. The finite volume method based on the enthalpy porosity model was used to investigate the effects of three different cross-sectional aspect ratios (AR = 0.5, 0.75, and 1) of the inner tube, at three different normalized locations along the vertical axis (Y = 0, −0.2, and − 0.4). The results were evaluated based on liquid fraction, temperature, velocity, total melting time, and average Nusselt number. The obtained results revealed that the AR effect of the inner tube varies depending on its location along the Y-axis. It is established that placing the tube at lower Y values in cases where a helical tube is present will yield significantly better results than higher Y values. Finally, the best case with the lowest total melting time occurred when the inner tube was located at Y = -0.4 and AR = 0.5. This case resulted in a total melting time decrease of up to 63 % compared to the reference case (AR = 1 at Y = 0).

Design-Point Techno-Economics of Brayton Cycle PTES for Combined Heat and Power

Abstract Pumped thermal energy storage (PTES) systems are grid batteries that use heat pumps to create both hot and cold thermal energy stores when there is excess electricity and then use a power cycle to convert the thermal energy into electricity when there is demand for electricity. In normal operation, Joule-Brayton PTES discharges low-grade heat at temperatures useful for thermal energy consumers like district and industrial heating. Furthermore, PTES designs, like conventional combined heat and power (CHP) technology, can be modified to sacrifice some round-trip efficiency (RTE) to increase the temperature of heat rejection. This paper uses design-point performance and cost models that provide a detailed understanding of the efficiency and cost trade-offs of rejecting heat at various temperatures in ideal-gas Brayton PTES configurations. First, we keep the heat rejection in its nominal location in the PTES system. Next, we move the heat rejection to the discharge turbine exit. We define design-point metrics that isolate both the cost and performance penalty associated with the hotter heat rejection and attribute it exclusively to the heat economic metrics. We find that the levelized cost of heat, including the cost of thermal energy storage (TES) buffering the PTES and heat off-taker, compares favorably versus electric technologies and is less than the cost of natural gas for low temperature scenarios and competitive with the cost of natural gas in some regions of the contiguous United States in high temperature scenarios.

Off-design operation and performance of pumped thermal energy storage

In this article, we describe off-design models and control strategies for a Pumped Thermal Energy Storage (PTES) system that uses liquid thermal energy storage: specifically molten salt for hot storage and methanol for cold storage. Off-design conditions arise when load-following, or due to variations in storage tank temperatures or ambient temperatures. We propose a control strategy that uses inventory control to manage the mass flow rate in the thermodynamic cycles, which facilitates load following. We also propose a control strategy for the storage fluid mass flow rates, which are varied to ensure the molten salt is maintained at its design temperature. This maximizes efficiency and minimizes problems with salt freezing or degradation. The cold storage fluid mass flow rate is varied so that the cold tanks have the same state-of-charge as the hot tanks. This leads to variations in cold fluid temperature, but these variations are shown to be acceptably small (e.g. 7.5 % increase), and this control method is shown to be simpler and more efficient than an alternative strategy where tanks become unbalanced. The ambient temperature and storage tank temperatures are moved ±50 °C from the design values and the impact on power, duration, and tank temperatures is quantified. Results demonstrate that the proposed control strategy is stable and self-correcting – that is, storage temperatures converge on stable values after two-to-three charge-discharge cycles. When inputs return to design values, the system returns to its design point after two charge-discharge cycles. We also demonstrate that inventory control enables delivery of the target power output even when off-design conditions exist that would normally reduce the power output.

A novel approach for solidification enhancement of phase change materials through direct contact with a boiling fluid: An experimental investigation and visualization

Due to their remarkable properties, such as high latent heat and stable temperatures during phase transitions, phase change materials (PCMs) are widely used in thermal energy storage (TES) and thermal management systems (TMSs). However, their low thermal conductivity has limited their broader application across various industries. This study experimentally explores, for the first time, the effects of injecting boiling fluid (BF) into the PCM container as a new method to enhance heat transfer during the solidification process of PCM. To this end, Paraffin wax and acetone with saturation temperature lower than paraffin’s freezing point are selected as PCM and BF, and the influence of four various parameters, namely the initial PCM temperature (75, 85, and 95 °C), the height of the PCM inside the container (15 cm, 25 cm, and 35 cm), the flow rate of the BF (0.32, 0.46, and 0.57 L/min), and the nozzle diameter (2 mm, 3 mm, and 4 mm), on the solidification behavior of PCM, temperature distribution inside the container, and heat transfer enhancement (released energy and Nusselt number) is thoroughly scrutinized. In order to visualize and further evaluate the two simultaneous phase transitions (vaporization of the BF and solidification of the PCM), a Hele-Shaw cell with a height, width, and thickness of 50, 20, and 1 cm is considered as the PCM storage system. The findings indicate that when the BF is injected into the paraffin storage, the high heat transfer coefficient of boiling superbly improves the thermal behavior of PCM, and the solidification process occurs in a much shorter time. Also, boiling of the acetone inside the container and its direct contact with paraffin leads to a significant mixing inside the container and the creation of vortices and turbulent flow in the system, which further improves the freezing phenomenon. Furthermore, it was observed that regardless of other parameters, the flow rate of BF is the most crucial parameter, and after that, the height of the paraffin and the initial temperature have the greatest impact. By employing the highest flow rate, the proposed technique is capable of freezing 0.7, 0.5, and 0.3 L of paraffin in 48, 33, and 18 s, respectively, indicating multiple times of improvement in the full solidification time compared to previous studies.

Analysis of charging performance of thermal energy storage system with graded metal foam structure and active flip method

The latent heat thermal energy storage (LHTES) technology based on solid-liquid phase change material (PCM) is characterized by high energy storage density, small volume change, and constant operation temperature, which is widely employed in waste heat recovery, solar thermal utilization, and equipment thermal management. This paper introduces active flipping and graded porous to strengthen natural convection and heat conduction to alleviate the issue of low thermal conductivity and non-uniform phase change of PCM. Based on the fixed grid system, the enthalpy-porosity method combined with time-dependent gravity and non-Darcy porous effect is employed to solve the solid-liquid phase change problem under different porosity gradients, dimensionless flipping times (t*), and modified Ra (Ra*) numbers. Furthermore, the effects of the Ra* on the optimal t* and porosity gradient are also discussed. The results show that the flipping method can significantly enhance flow and heat transfer within the container, improve temperature field uniformity, and increase the proportion of latent heat storage. With the increase of porosity gradient and t*, the melting time initially decreases and then increases and the optimal thermal performance is achieved at a 6 % porosity gradient and t* = 0.4. Compared to the uniform porous structure without flipping, it can shorten melting time by 49.37 % and improve thermal energy storage rate (TESR) by 76.23 %. Additionally, the optimal porosity gradient is 6 % under different Ra*, but the optimal t* decreases with the increase of Ra*. This paper explores the charging performance of the thermal energy storage system with the graded metal foam structure and active flip method, which can contribute to the study of heat transfer enhancement in LHTES technology.

Synergizing compressed air energy storage and liquefied natural gas regasification in a power-to-biofuels plant

The present study is dedicated to the thermodynamic evaluation of an innovative system for the generation of biomethanol and natural gas, utilizing the processes of biomass gasification and high-temperature electrolysis. The recovery of waste heat from a compressed air energy storage (CAES) system serves as a crucial thermal energy source. Recognizing the periodic nature of CAES operations, a thermal energy storage (TES) system has been used to ensure a consistent supply of heat to the biomethanol production facility. The liquefied natural gas (LNG) regasification unit and an open Brayton cycle play a dual role, contributing not only to power generation and natural gas production but also to enhancing biomethanol production through the utilization of flue gases. The results of a thermodynamic modeling conducted within the Aspen Plus program demonstrate the production of 69251 ton/year of natural gas, 1424 ton/year of biomethanol, with a CO2 consumption of 3452 ton/year, resulting in an impressive overall energy efficiency of 95.27 %. The electrolyzer exhibits the highest power consumption at 1035 kW. Sensitivity analysis showed that net input electricity increases with an enhanced number of solid oxide electrolysis cell (SOEC) cells, while biomethanol capacity rises due to enhanced electrolysis size and hydrogen production rate.

Adsorption and nucleation mechanism of molten carbonate on nano-SiC surface

Molten carbonate is an important thermal storage media for high temperature thermal energy storage system. However, the specific heat capacity (SHC) of carbonate is less than 2 J/g K, which limits its application prospects. Nano-SiC was used to improve the SHC of carbonate at high temperature in our previous work. The SHC of binary carbonate increased by 83 % with the addition of nano-SiC. However, the improvement mechanism is not clear. In this study, the adsorption and nucleation mechanism of molten carbonate on nano-SiC surface were clarified. The DFT calculation results show that the adsorption energy of Li+, Na+ and CO32− is −310, −259 and −654 kJ/mol, respectively, which means the addition of nano-SiC causes a non-uniform distribution of molten carbonate ions around its surface. This affects the subsequent nucleation and results in carbonate segregation. Na2CO3 is the most thermodynamically favorable to adsorb and nucleate, followed by LiNaCO3, and Li2CO3 is the most difficult. The crystalline phase changes of carbonate on nano-SiC surface from solid to liquid phase during melting process were obtained in-situ and the results are consistent with the DFT calculations. Therefore, the adsorption and nucleation mechanism of molten carbonate on nano-SiC surface is well elucidated by the calculations and experiments of this study.

Thermal performance of cascaded latent heat thermal energy storage units constructed based on solid-liquid interface information

A novel approach to constructing cascaded latent heat thermal energy storage units is proposed to enhance the thermal performance of horizontally placed shell-and-tube phase change heat storage systems. This method is based on the solid-liquid interface variation patterns during the solidification and melting processes. It creates interfaces between different phase change materials within the cascaded latent heat thermal energy storage unit to shorten melting time and increase thermal performance by optimizing the unit's internal structure to balance heat transfer rates across all areas. The enthalpy-porosity method was used to numerically study the phase change phenomenon. The inner tube of the units was set as an isothermal boundary, and the outer shell was insulated. Findings from this cascaded latent heat thermal energy storage system demonstrate that, compared to single-latent heat thermal energy storage units, the average heat transfer rates during solidification and melting increased by 27.3% and 36.7%, respectively. The average heat transfer rate during solidification improved by 11.7% compared to traditional concentric circular cascaded latent heat thermal energy storage units. These results indicate that this method can significantly enhance the thermal performance of latent heat thermal energy storage units, providing valuable insights for future structural optimization.

Thermal conductivity enhancement of polyethylene glycol/NF composite as stabilized phase change materials for thermal energy storage

Polyethylene glycol (PEG) has the advantages of large latent heat of phase transition, a wide range of phase transition, and cheap price, but the application of PEG in the latent thermal energy storage (TES) systems is hindered due to its lower heat transfer rate and leakage. Porous metal foam has excellent thermal conductivity and high strength, which can effectively improve the problems of PEG. In this study, PEG/nickel foam (NF) composite phase change materials (PCM) were prepared by vacuum molten impregnation method using NF as substrate. It was found that PEG had good compatibility with NF, and the highest impregnation rate of PEG6000/NF reached 85.73 %. The thermal conductivity of PEG2000/NF can be increased to 1.58 1.58 W·m−1 K−1, nearly 4 times larger than that of pure PEG. The phase change temperature range of the composite PCM is 51–63 °C, and the phase change enthalpy is 67.8–126.3 J·g−1. Furthermore, the PEG/NF composite demonstrated outstanding photothermal conversion properties and high thermal stability, which can be widely used in the field of building temperature control and device heat dissipation.

Numerical investigation of packed granular beds subjected to thermal cycling with application to thermal energy storage systems: a continuous approach

Numerical investigation of packed granular beds subjected to thermal cycling with application to thermal energy storage systems: a continuous approach

Prediction of thermo-physical properties and evaluation of thermal energy storage performance of phase change materials based on silicone rubber/graphite (Q/G) composites

ABSTRACT Phase change composite materials (PCCMs) are a type of thermal energy storage system known for their high latent heat of fusion. In this study, PCCM samples based on peroxide-cured silicone rubber (Q) were prepared using a simple soaking procedure in molten Paraffin Wax (PW). At any fixed amount of peroxide, the rubber base samples were filled with varying amounts of graphite powder (G), 4 to 8 Wt.%, to improve the thermo-physical properties. The effect of peroxide and graphite content was then evaluated on the PW loading, PW leakage, and thermal storage performance of the resulting Q/G/PW composites. It was found that the highest ratio of the PW loading to PW leakage occurs at a peroxide content of 6 Wt.%. Moreover, the graphite particles demonstrate a significant role in PW trapping inside the rubber structure and lowering the PW leakage. Finally, the thermal studies showed that the Q/G/PW composite containing 6 wt.% of peroxide and 4 wt.% of graphite has the highest latent heat of 111.5 J/g with a PW loading of 15.2%. This sample also had the lowest thermal diffusivity and the slowest cooling and heating rate.

Application of the image‐well method for transient borehole thermal energy storage systems with complex boundaries

AbstractThis study introduces a new analytical framework that employs the image‐well method to simulate the spatial and temporal temperature distribution in vertical borehole thermal energy storage (BTES) systems. The model accommodates complex boundary shapes and conditions, including insulation, convection, and constant temperature, without requiring iterative solutions at each time step. The model's accuracy and utility are demonstrated through an application to a borehole heat exchanger cluster arranged in an octagonal shape with insulating boundaries, based on a BTES site in Drake Landing (Canada). Model predictions are validated against a finite element model, showing a root‐mean‐square error of 0.012°C. A global sensitivity analysis highlights the influence of thermal parameters on system performance, identifying the heat flux of the borehole heat exchanger as the most sensitive parameter. Overall, this approach combines the advantages of analytical and numerical techniques to provide a clear and efficient tool for evaluating BTES systems, offering significant potential for advancing sustainable energy solutions.