Latent Heat Thermal Energy Storage Unit Research Articles

Multi-objective optimization of metal foam parameters for enhanced performance of LHTES unit in shell-and-tube configurations

Latent heat thermal energy storage (LHTES) units utilize phase change materials (PCMs) to effectively store thermal energy and address the challenges of solar energy intermittency and instability. Heat transfer characteristics largely influence the thermofluidic efficiency of the LHTES unit during phase transitions. To improve the typically low heat transfer capabilities of PCMs, high-conductivity metal foams are introduced to enhance bulk heat conduction. This study focuses on optimizing the parameters of composite PCM (CPCM) embedded in the LHTES unit, specifically examining metal foam height (H), angle (θ), and porosity (ϵ), primarily affecting the performance of the CPCM. A series of Taguchi-based orthogonal experiments were conducted to analyze the effects of these variables. The results indicate that metal foam height has a notable influence on the CPCM performance, significantly reducing melt fraction variations caused by changes in cross-sectional geometry. ANOVA analysis shows that the metal foam height contributes 49.02% to improve operational time and 73.62% to enhance melt fraction. The study also identifies the optimal values for the metal foam parameters (H, θ, ϵ) that most effectively improve the LHTES unit thermal performance. Based on various indices, an economic assessment of the optimal configuration further supports the proposed design. Overall, the findings provide a recommended configuration to enhance the LHTES unit performance, contributing valuable insights for developing efficient TES systems and supporting sustainable energy management.

Experimental study on the charging and discharging performance of a thermal energy storage unit using low temperature phase change material

The latent heat thermal energy storage (LHTES) unit offers a versatile solution for storing waste heat and solar thermal energy across various temperature ranges. Despite its potential, limited experimental research has been conducted on LHTES units operating at low temperature ranges. This study addresses this gap by experimentally investigating the performance of an LHTES unit using water as the heat transfer fluid (HTF) and myristic acid (PCM) with a phase change temperature of 53–55 °C. The rectangular configuration of the TES unit was chosen for its practical advantages in industrial and residential applications, facilitating efficient space utilization and uniform thermal distribution. Experiments were conducted with various HTF volumetric flow rates (200, 300, and 400 LPH) using a constant temperature heat source. PCM and HTF temperature profiles at three segments of the TES unit were used to evaluate key parameters essential for designing a storage system, including thermodynamic analysis, Nusselt number, stratification analysis, storage/recovery efficiency, and charging/discharging efficiency. These parameters provide valuable insights into the performance of the LHTES unit. The outcomes indicate that increasing the HTF flow rate from 200 to 400 LPH decreases the charging/discharging duration by 40.73 % and 38.24 %, respectively. At the higher flow rate (400 LPH), convective mixing increases, reducing stratified layer stability. Furthermore, increasing the HTF flow rate leads to a reduction in peak Richardson numbers by 31.6 % and 27.8 % during charging/discharging, indicating a transition towards diminished stratification and increased turbulence in the HTF flow. In conclusion, while the TES unit exhibited better performance at a lower HTF flow rate (200 LPH), practical applications demand efficient fast charging and discharging. Despite this, minimal differences in efficiencies, energy, and exergy rates across flow rates suggest practical viability in various test conditions.

Evaluation of wavy wall configurations for accelerated heat recovery in triplex-tube energy storage units for building heating applications

Efficient thermal energy storage (TES) is crucial for integrating intermittent renewable energy sources and managing fluctuations in energy supply and demand. Among TES methods, latent heat TES (LHTES) using phase change materials (PCMs) is highly promising due to its high energy storage density and nearly isothermal operation during phase transitions. However, the inherently low thermal conductivity of PCMs hinders heat transfer rates, negatively impacting charging and discharging performance. This study investigates novel wavy channel geometries for the PCM container in a triplex-tube LHTES unit to enhance heat transfer and improve solidification rates during the discharge process. A comprehensive computational model based on the enthalpy-porosity method is developed to simulate the PCM (paraffin wax RT35) solidification inside wavy channels with sinusoidal, zigzag, and step-function profiles. The effects of channel geometry, heat transfer fluid (HTF) velocity, and inlet temperature on solidification rate and heat recovery are systematically evaluated. Results demonstrate that the step-function geometry significantly accelerates solidification compared to straight channels, reducing discharge time by 65.1 % and increasing heat recovery rate by 147.9 %. Decreasing waviness width from 15 mm to 5 mm further reduces solidification time by 70.1 %, while increasing waviness height from 5 mm to 15 mm leads to a 74.4 % reduction. Moreover, increasing HTF flow from Re = 250 to 1000 enhances heat recovery by 92.3 %, and lowering inlet temperature from 20 °C to 10 °C improves it by 76.9 %. The findings provide valuable insights for designing efficient LHTES units with wavy channel geometries for renewable energy integration and thermal management applications.

A comparative analysis on charging performance of triplex-tube heat exchanger under various configurations of composite phase change material

In present work, the melting performance of triplex-tube latent heat thermal energy storage (LHTES) unit was numerically studied using equal volumes of PCM and metal foam composite PCM (CPCM) in various arrangements. For the n-eicosane (as PCM), the study was conducted at the fixed Rayleigh number (Ra) = 4.08x107, Prandtl number (Pr) = 62.9, and Stefan number (Ste) = 0.14. The results showed that positioning the metal foam on the bottom side and distributing segmented CPCM with alternating PCM zones effectively improved the system performance. Moreover, this also prevents the overheating of thermal layers in the LHTES unit. While the model labelled M2 exhibited the highest economic efficiency among all isotropic models, its low dimensionless thermal energy storage (TES) density (i.e., q’ ∼ 0.6) led this study to focus on models falling under the category having a TES density of ∼ 0.8. Compared to a pure PCM model, the configurations under equal volume ratio category demonstrated up to ∼ four times higher TES rate (p’) and the significant reduction of ∼ 75 % in melting time. The optimized isotropic model achieved the highest TES rate per unit cost with peak value of ∼ 3 at a price ratio (N) of 1. Lastly, the testing of metal foam anisotropy on the chosen design showed a substantial increase in melting/heat storage rates. The largest drop of ∼ 33 % in the total melting time was noticed for model M2 as compared to isotropic case.

Improving phase change heat transfer in an enclosure partially filled by uniform and anisotropic metal foam layers

Anisotropic metal foams exhibit exceptional potential for improving the efficiency of latent heat thermal energy storage (LHTES) units by enhancing heat transfer and thermal energy storage rates. This study explores the largely uncharted area of thermal behavior of anisotropic metal foams in varied configurations and enclosure designs. The research focuses on an LHTES unit with a specific channel configuration, constructed using copper and containing three layers of copper metal foam, one of which is anisotropic and infused with paraffin wax. The finite element method was utilized to manage the complexities emerging from phase change, and the anisotropic angle varied from 0 to 90° in three different placements of the AMFL: top, middle, or bottom of the enclosure. The ideal design was achieved with an AMFL in the middle with a 0°angle, resulting in a 3.7 % reduction in melting time and approximately a 2.3 % reduction in solidification time. However, AMFL designs at the middle placement with a 75° anisotropic angle were less effective, hampering the melting and solidification processes, thus potentially extending charging and discharging times. The study concludes that the placement and angle of the AMFL layer are vital for the heat transfer capabilities of phase change materials. AMFL at the middle with a 0° angle optimally leverages temperature gradients, enhancing heat transfer compared to other investigated cases. An AMFL in the middle with a 0° angle exhibits approximately 7.1 % and 6.3 % improvements for melting fractions of 0.9 and 0.95, respectively, underscoring its potential for efficient thermal energy storage.

Response to the design conditions of a tube-bundle thermal energy storage unit with paraffin-copper foam composite as a storage medium

Owing to its potential to limit the issues of intermittency and instability in solar energy by means of phase-change materials (PCMs), latent heat thermal energy storage (LHS) has met increasing attention and been widely employed in thermal-based systems. Most PCMs, however, inherently exhibit poor heat conductance leading to modest rate of charging. To master this drawback, highly conductive metal foams are utilized to upgrade the bulk heat conductance of a PCM resulting in an enhanced rate of heat transport; hence, accelerating the melting process. This enhancement way is employed to promote the response of a tube-bundle thermal energy storage unit configured of staggered tubes filled with high-porosity copper foam embedded in paraffin wax as a storage medium. To charge the thermal energy storage (TES) unit proposed, a relatively hot stream of water is allowed to flow across the bundled tubes through the voids in-between. To check how feasible the proposed design is, the tubes enclosing the TES medium and the water flow in the shell surrounding have been simulated by ANSYS Fluent CFD code. A variety of design factors has been examined to explore their influence on the charging performance attained including structural properties of the metal foam employed along with the configuration of the tube-bundle considered. The foam structural characteristics inspected are the porosity ∅∈(0.89∼0.97) and pore density ω∈(5∼80)PPI, while various tube-bundle configurations have been tested in terms of the packing density N∈(15∼65)TubesLines/meterwidth as well as the shape of PCM tubes used b/a∈(0.25∼1). Results indicate that for a certain tube-bundle configuration, the best response is acquired when denser foam with lower porosity is used, while the best performance can only be achieved with higher porosity due to the better TES capacity offered. For certain foam structural properties of (∅=0.93&ω=80PPI), it has been observed that increasing the packing density can save up to 56 % of the time taken for charging completion with up to 200 % increase in storage capacity leading to up to 48 % improvement in the system overall performance. It has also been found that using paraffin embedded with copper foam as a TES medium accelerates the melting process considerably and saves more than half the time taken to charge the corresponding TES unit based on pure paraffin. It is also worth mentioning that the currently suggested LHS unit is not only of simple configuration, but practically efficient as well, with outstanding gross performance OP∈(104∼105). Through a proper manipulation of design conditions, it has been found that the charging response can be notably improved leading to substantial promotion in the overall performance realized.

Natural convection and field synergy principle analysis of the influence of fins redistribution on the performance of a latent heat storage unit in a successive charge and discharge

The present study focuses on analyzing the impact of enhancing the heat exchanges on the shell side by surface extension on the kinetics of melting/solidification in a latent heat thermal energy storage (LHTES) unit. Particular attention is paid to the influence of fins redistribution on the performance of the LHTES unit, natural convection, and Phase Change Material (PCM) melting/solidification kinetics. The particularity of this study lies in the improvement of the LHTES unit performances in a successive charging-discharging operation by only redistributing the fins while keeping the same total heat transfer surface, PCM volume, and compactness. The first part of the study consists of evaluating the impact of fin redistribution for the same total heat transfer surface on the LHTES unit performance. Attention was paid to the fully charging and discharging times and the heat duty absorbed or released during the melting or solidification process. For this purpose, 4 configurations of LHTES units having 4 and 8 radial fins with the same total transfer surface were analyzed, with the aim of ensuring a maximum performance on charging process. In a second part, an improved configuration was proposed in order to minimize the successive charging and discharging time for a cyclic operation of the LHTES unit. The coordination factor derived from the field synergy principle, PCM liquid fraction, the heat duty exchanged, phase change kinetics, and liquid PCM velocity were used as performance key factors. They were used to analyze and compare the different configurations in order to find the best configuration for a successive charging-discharging operation. The selected improved configuration has been found to enhance both the charging and discharging processes. It leads to the reduction of the successive charging-discharging overall duration by 10 % to 47 % compared to the other configurations investigated with the same heat transfer surface. The enhanced LHTES unit developed in the present study is intended to improve the thermal comfort of buildings by valorizing and storing renewable and waste energies.

Numerical investigation and optimization of the melting performance of latent heat thermal energy storage unit strengthened by graded metal foam and mechanical rotation

In this paper, a combined passive graded metal foam and active mechanical rotation strategy is proposed to simultaneously solve the problem of slow melting rate and non-uniform phase change problem of the latent heat thermal energy storage (LHTES) technology. The enthalpy-porosity method and fixed grid structure are employed to numerically investigate the effects of porosity range, the number of graded layers, and the rotational angular velocity. Moreover, the response surface method (RSM) is further selected to optimize the structural parameters and obtain the function of melting performance and various factors. The result shows that there is an optimal porosity range and the total melting time decreases first and then increases with the increase of porosity range. When the porosity range is 12 % and the graded layer is three, it can shorten the melting time by 35.54 % and increase the thermal energy storage rate (TESR) by 51.57 %. In addition, the melting performance is gradually improved as the number of graded layers increases. The strengthening effect of graded metal foam with just four layers is close to that of the maximum layers considered in this paper. The trend of the influence of rotation speed on the melting performance of the LHTES unit is consistent with the porosity range, indicating the existence of the optimal rotational speed. The RSM optimization structure, with a 14.969 % porosity range, 5-layer graded number, and 2.267 rpm rotational speed, shortens the melting time by 42.42 % and increases the TESR by 62.75 % compared with the stationary case with uniform metal foam. This work verifies the effectiveness of active rotation coupling with passive graded porous structures, which could provide a new strengthening approach to enhance LHTES.

Numerical study of solidification and melting behavior of the thermal energy storage system with non-uniform metal foam and active rotation

This paper focuses on the strengthening study of the latent heat thermal energy storage (LHTES) unit and proposes a coupling strengthening method with non-uniform graded metal foam and active rotation. The non-uniform graded metal foams are employed to enhance heat conduction, and the rotation method is selected to make full use of natural convection. The solidification and melting behavior under the coupling effect of non-uniform metal foam and active rotation are numerically analyzed. The aluminum foam is partially concentrated and divided into two parts (concentrated part and diluted part) and is divided into the even-layered or uneven-layered porous structures according to the different regions area. Under the same volume of phase change material (PCM), the effects of layered forms (even-layered and uneven-layered approach), concentrated porosity, concentrated ratio, and rotational speed are performed. It can be concluded that the metal foam should concentrated near the inner tube and the uneven-layered structure can further improve the phase change heat transfer performance compared to the even-layered structure. Moreover, the thermal performance of the LHTES unit improves firstly and then decreases as the concentrated porosity, concentrated ratio, and rotational speed increase. The optimal values are obtained at 0.86 concentrated porosity, 0.3 concentrated ratio, and 0.5 rpm rotational speed. Compared with the static case with uniform metal foam, the melting time, solidification time, and total melting and solidification time can be significantly reduced by 40.30 %, 28.66 %, and 33.18 %, respectively. Similarly, the thermal energy storage rate can be correspondingly increased by 62.57 %, 40.82 %, and 54.11 %, respectively.

Investigation of phase change heat transfer in a rectangular case as function of fin placement for solar applications

This paper attempts to maximize solar energy utilization by employing a latent heat thermal energy storage (LHTES) unit integrated with a solar receiver of concentrating collectors or thermal management unit for photovoltaic panels. The study investigated an LHTES unit with a rectangular shape and equipped with a T-shaped fin subjected to heat flux. The paper examined the effect of eight T-fin positions under the applied heat flux on the thermal performance of phase change material (PCM). The PCM melting process was modeled using the enthalpy-porosity method using the finite element approach. The obtained numerical results revealed that PCM melting rate strongly depends on fin position, with superiority for fins located at the upper part of the chamber when heat flux is used as the primary heating source. Under applied heat flux, locating the fin at the upper section of the vertical LHTES unit enhanced the melting rate of the PCM, reaching 10 % better than the fin's middle and bottom positions, which is against the cases reported for the fixed temperature heating process that prefer bottom fins. Thus, these results recommend using T-shaped fins in the upper parts of PCM-based units used for solar collector receivers and thermal management of photovoltaic panels.

Design and experimental investigation of topology-optimized fin structures for enhanced heat transfer in latent heat thermal energy storage units

In order to enhance the heat exchange rate between the heat transfer fluid and the phase change material (PCM), the placement of fins in the latent heat thermal energy storage (LHTES) unit is an effective means. To this end, this paper introduces a novel fin structure that can evolve along the optimization process using a topology optimization strategy, aiming to optimize the spatial layout of the fins and maximize the thermal performance of the LHTES unit. The numerical results demonstrate that the topological fins (TOF) outperform the conventional rectangular fins (CF) in effectively enhancing the temperature and liquid phase fraction of the PCM. Following this, the TOF was fabricated using selective laser melting and tested in an experimental platform containing three types of LHTES units to examine its thermal properties. The findings from the experiments indicate that the TOF exhibits superior thermal performance and can achieve a more uniform heat exchange with the PCM. Specifically, under the heat storage and release conditions of 90 °C–60 °C, the heat transfer efficiency of the TOF unit is enhanced by 57.8 % compared to that of the finless unit, and by 25.26 % compared to that of the CF unit. Similarly, under the heat storage and release conditions of 85 °C–65 °C, the heat transfer efficiency of the TOF unit is improved by 67.54 % compared to the finless unit, and by 22.84 % compared to the CF unit. Consequently, in engineering applications, LHTES units equipped with TOF can achieve faster heat storage and release, and exhibit greater responsiveness to load changes in the energy system.

Improving heat storage performance of shell-and-tube unit by using structural-optimized spiral fins

Spiral fins have been widely used to enhance the heat transfer of latent heat thermal energy storage (LHTES) systems. However, owing to the inhomogeneous melting of solid-liquid phase change materials (PCMs) driven by convective heat transfer, the uniform spiral fins always have poor enhancing performance. In the present work, we proposed structural-optimized spiral fins, including optimized fin thickness, optimized fin height, and optimized fin pitch, to uniformly and efficiently transfer the heat from fins to PCM. By comparing their melting results with the original-uniform model, we found that negative models with larger fin volume at the bottom are more efficient in accelerating the melting process, and they can maximally reduce the complete melting time of PCM by 15.01% compared with the original one. On the contrary, the positive model with a smaller fin volume at the bottom slows down the melting of the LHTES unit. The heat transfer mechanism along the whole melting process is analyzed by comparing the thermal parameters (including liquid fraction, average temperature, average liquid velocity, and heat flux) of the original and optimized models. The enhancements of the negative models are owing to their benefits to the developments of convective heat transfer in the top region and conductive heat transfer at the bottom. According to the results of this paper, researchers can design novel high-performance LHTES systems using optimized spiral fins.

Design and assessment on a bottom-cut shape for latent heat storage tank filled with metal foam

The utilization of phase change materials (PCMs) holds tremendous potential of heat storage domain. The PCM's refractory at the latent heat thermal energy storage (LHTES) unit bottom hinders the heat storage efficiency, despite the significant improvement in thermal conductivity achieved through the addition of metal foam. This study employs numerical simulation to examine the impact of applying bottom cross-cut on PCM's spatial distribution in a horizontal LHTES unit. The manuscript analyzes parameters including melting fraction, complete melting time, Rayleigh number, natural convection heat transfer gain, melting phase interface, velocity and temperature distributions, and heat storage. The findings indicate that the proximity to the heating tube results in a reduction of solid volume at the LHTES unit bottom. A 0.6 bottom cross-cut ratio leads to an 18.84 % faster heat storage rate compared to a concentric-circle unit. Furthermore, a bottom cross-cut ratio of 0.5 enhances natural convection heat transfer gain by 3.28 times.

Design and Research of Heat Storage Enhancement by Innovative Wave Fin in a Hot Water–Oil-Displacement System

Energy storage technology provides a new direction for the utilization of renewable and sustainability energy. The objective of this study is to introduce a novel, wavy, longitudinal fin design, which aims to improve heat transfer in the melting process of a Latent Heat Thermal Energy Storage (LHTES) unit. The main goal is to mitigate the negative effects caused by the refractory zone at the end of the melting phase. A two-dimensional numerical model of LHTES unit is established by using the enthalpy porosity method and verified by experimental data. Through the quantitative comparison between the traditional rectangular fin and the innovative wave fin, the influence of wave fin on the heat transfer mechanism in the heat storage process is revealed. The results show that the average heat storage rate of five and six wave fins is 3.70% and 12.98% higher than that of conventional rectangular fins, respectively, and the average temperature response of six wave fins is 17.78% higher than that of conventional rectangular fins. The addition of the wave fin weakens the negative effect of the refractory zone, but prolongs the heating time of the initial melting point.

Numerical analysis and optimization of the heat transfer enhancement from the heat transfer fluid side in a shell-and-tube latent heat thermal energy storage unit: Application to buildings thermal comfort improvement

This study investigates the impact of enhancing the convective heat transfer on the Heat Transfer Fluid (HTF) side by passive flow manipulation on the melting and solidifying kinetics of a Phase Change Material (PCM) in a shell-and-tube Latent Heat Thermal Energy Storage (LHTES) unit. The PCM used is PureTemp 23 (PT23), a commercial bio-sourced product. The targeted application is the development of a LHTES unit for improving the thermal comfort in buildings through a combined heating and cooling approach. The study is carried out using the commercial code STARCCM+ and the enthalpy-porosity method, with appropriate implementation of the buoyancy source term. The numerical approach used for phase change modeling has been validated by comparisons with reference data from the open literature. Delta Wing pairs (DWg) and Delta Winglet pairs (DWt) vortex generators (VGs), were first inserted into the tube in which the HTF flows. Parametric analysis on the aspect ratio, position, and VGs number were performed, and optimization was done on the attack and rolling angles. The Performance Evaluation Criteria (PEC) index, which takes into account the heat transfer enhancement achieved and the related pressure losses, was used as an assessment criterion to evaluate the heat transfer augmentation of the studied enhanced tube with VGs. The results show that maxima can be reached for the different parametric studies carried out. While PEC increases with the attack angle until a maximum beyond which it decreases, it decreases consistently with the rolling angle. Once the enhanced optimal tube equipped with a shell containing the PCM, the results of the detailed study made on the kinetics for charging and discharging period of the enhanced LHTES unit reveal important gain for the storage unit. The heat transfer enhancement achieved result into more than 110 % increase in the PCM's melting/solidifying kinetics in the shell, thanks to an increase in the heat duty exchanged between the HTF and the PCM, leading to a considerable reduction of complete melting/solidification time. It was observed that the enhanced and optimized LHTES unit developed in the present study has a huge potential for improving buildings seasonal thermal comfort.

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.

The Effect of Different Configurations of Copper Structures on the Melting Flow in a Latent Heat Thermal Energy Semi-Cylindrical Unit

Utilizing latent heat thermal energy storage (LHTES) units shows promise as a potential solution for bridging the gap between energy supply and demand. While an LHTES unit benefits from the latent heat of the high-capacity phase change material (PCM) and experiences only minor temperature variations, the low thermal conductivity of PCMs hinders the rapid adoption of LHTES units by the market. In this regard, the current work aims to investigate the thermal behavior of a semi-cylindrical LHTES unit with various copper fin configurations (including horizontal, inclined, and vertical fins) on the melting flow. The novelty of this research lies in the fact that no prior studies have delved into the impact of various fin structures on the thermal performance of a semi-cylindrical LHTES system. The nano-enhanced phase change material (NePCM) fills the void within the unit. The warm water enters the semicircular channel and transfers a portion of its thermal energy to the solid NePCM through the copper separators. It is found that the system experiences the highest charging capability when the fins are mounted horizontally and close to the adiabatic upper wall. Moreover, the presence of dispersed graphite nanoplatelets (GNPs) inside the pure PCM increases the charging power and temperature of the LHTES unit.

An in-depth study on melting performance of latent heat thermal energy storage system under rotation mechanism by fluctuating heat source

The Organic Rankine Cycle (ORC) is a reliable and efficient means of converting solar energy into electricity. The challenges brought about by the unpredictable nature of solar energy can be effectively mitigated by utilizing latent heat thermal energy storage (LHTES) technology, specifically by implementing heat source pretreatment. This paper investigates the thermal storage properties of a rotating triplex-tube LHTES unit under different sinusoidal fluctuating heat sources. A transient numerical model is built to analyze the effects of sinusoidal wall temperature amplitude and angular velocity on the melting characteristics of the unit, including melting time, heat storage rate, and temperature response. The design is further analyzed using the Taguchi method. The results show that the angular velocity of the sinusoidal wall temperature has a greater effect on the average heat storage rate and melting time than the amplitude. When the amplitude is set to 10 and the angular velocity to 0.02, the melting time is decreased by 8.7%, while the average heat absorption rate and average temperature response increase by 10.21% and 12.27%, respectively. Additionally, the sensible and total heat energy absorption increase by 2.23% and 0.62%, compared to the initial heat source condition. Furthermore, the heat transfer is enhanced through the introduction of Al2O3 nanoparticles at varying percentages. The unit heat storage rate improves significantly with an increasing percentage of nanoparticles. Specifically, when 2.5% and 5% Al2O3 nanoparticles are added, the melting time of the unit is reduced by 3.77% and 15.07%, respectively, while the average heat absorption rate increases by 2.43% and 10.39%.

Comprehensive performance analysis and structural improvement of latent heat thermal energy storage (LHTES) unit using a novel parallel enthalpy-based lattice Boltzmann model

Latent heat thermal energy storage (LHTES) utilizing phase change material (PCM) is one of the critical enablers in developing sustainable and low-carbon energy systems. To fill the knowledge gap, this paper presents an enthalpy-based solid–liquid model through the lattice Boltzmann method (LBM) with a multi-relaxation-time (MRT) approach, aiming to simulate convective phase change in LHTES units with and without porous media in Cartesian or axisymmetric domains. To improve accuracy and efficiency, the model integrates a differential scanning calorimetry (DSC) correlated equation for enthalpy modeling, couples with a 1D heat-transfer-fluid (HTF) model for boundary treatment of HTF side, and employs a parallel LBM scheme for efficient parametric studies. The validation demonstrates the model’s success in predicting PCM phase change, with errors below 10%. A comprehensive numerical analysis is then conducted to quantitatively evaluate the effect of convection on PCM melting. Novel metrics, such as acceleration rates (ac) of PCM melting and threshold Rayleigh numbers (Radc) at various aspect ratios, are introduced. Furthermore, PCM melting in the porous cylindrical unit is explored. Findings reveal up to 86% acceleration in melting compared to pure PCM at 80% energy storage, and the porous media with porosity above 0.9 is recommended for thermal enhancement. Moreover, this paper analyzes the negative effect of uneven temperature distributions caused by convection on LHTES unit efficiency. A modified LHTES unit geometry is proposed to offset this negative effect, and the study demonstrates successful mitigation of uneven temperature distributions, achieving up to 57 % acceleration in PCM melting.

The heat transfer enhancement of the converging-diverging tube in the latent heat thermal energy storage unit: Melting performance and evaluation

Latent heat thermal energy storage (LHTES) has emerged as a promising approach to settle the intermittent and fluctuant of renewable energy but heat transfer enhancement is necessary due to the low thermal conductivity of the phase change material (PCM). This study numerically investigated the heat transfer enhancement effect of the typically converging-diverging tubes (CDTs) inside a shell-and-tube LHTES unit. The evolution of melting behavior was analyzed to describe the heat transfer enhancement mechanism of the CDT. Based on the enhancement effect and pump power consumption associated with the CDT, a modified performance evaluation criterion (PEC) was established to evaluate the feasibility of current designs. The arrangement of CDTs was found to significantly improve the heat transfer performance of LHTES. The triangle CDT exhibited the maximum melting time reduction of 20.77%. The heat transfer enhancement effect of CDT was attributed to the enhanced natural convection of PCM and forced convection of heat transfer fluid. The analysis of the evaluation ensures the feasibility of the new criterion and its specific application field. Moreover, it was worth to note that the triangle CDT achieved the best cost performance of 0.363 ω, where ω represented the return factor.