Melting Time Of Phase Change Material Research Articles

Bionic-response surface combination optimization method for latent heat storage performance improvement

Improving the melting and solidification rate of phase change material is crucial for enhancing the charging or discharging power of a latent heat storage system. This research proposed a novel two-tube heat exchanger latent heat storage unit with longitudinal fins of horsetail stem based on the bionic structure of horsetail stem cross-section. Numerical modeling of transient melting of phase change material in horsetail stem fins by natural convection was established. The model’s accuracy was verified and compared with horsetail stem fins and conventional straight fins. Moreover, we optimized and designed the new fin structure based on the response surface method with minimum melting time as the objective function. The optimization results show that the optimized ponytail fins have a more uniform temperature distribution of the phase change material, significantly eliminating the influence of the heat transfer hysteresis zone, and reaching the steady state more quickly under the heat storage condition. Compared to straight fins, optimized horsetail stem fins reduced the heat storage area by only 3.80% and shortened the phase change material melting time by 44.30%. The solidification time was also reduced by 54.59%. This study provides a new idea for the structural design of phase change heat storage fins.

Pore-scale study of melting characteristic of phase change material embedded with novel open-celled metal foam

Metallic porous structure is a prevailing heat transfer enhancer for the melting of phase change material (PCM), while the effect of the structure on the enhancement performance is yet to be understood. In this work, a pore-scale numerical study on PCM melting embedded in a truncated cuboctahedron porous structure, referred as TCD metal foam, was performed. The solid–liquid interface, temperature and the variation of liquid fraction were analyzed and compared with those with the tetrakaidecahedron porous structure, referred as TKD metal foam. The effects of natural convection, porosity, pore density and heating temperature are explored. It is found the natural convection shortens the PCM melting time by about 7 % with the considered porosity range and thus cannot be ignored. Results also show that the TCD metal foam better enhances PCM melting near the porous cell corners compared to the TKD metal foam. Further analysis shows the TCD metal foam can better enhance melting at the former stage due to the larger surface area, while the TKD metal foam can better enhance melting at the later stage due to the thicker metallic ligaments. With essentially the same melting time at ɛ = 0.941, the half-melting takes 17.2 % of the complete melting time for TCD metal foam and 20.3 % of the complete melting time for TKD metal foam. A critical porosity value exists when comparing the enhancement performance of these two metal foams, below which the better melting enhancement is shifted from the case with TCD metal foam to the case with TKD one. The critical porosities are 0.941, 0.923 and 0.899 at the pore densities of 10, 20 and 30 PPI respectively.

Analysis of melting behavior of layered different phase change materials for a cylinder insert into a channel

Phase change materials (PCMs) have diverse fields of application due to higher thermal inertia. The present study explores the melting behavior in dual-layered different PCMs in a cylindrical lithium-ion battery module placed in a long channel under the hot air stream. The main cylinder is packed with paraffin wax and covered PCM is chosen as calcium chloridehexahydrate (CaCl2-6H2O). The material between two PCMs is considered highly conductive and impermeable. The involved mathematical equations in two-dimensional forms are numerically simulated the applying the finite volume technique. The primary important parameters of melting behavior are the difference in temperature and inlet air velocity. The analysis is carried out for the effective parameters such as the inlet air temperature (Thot = 100 °C and 120 °C) and air velocity (սair = 2.5 and 5.0 m/s). The results revealed that an increase in air velocity reduces the highest and average temperature of the PCM. The changes in melting time of PCMs decline with time. Higher inlet air temperature also causes fast melting of the PCMs over time. The analysis revealed that the application of PCMs is undue when there is no phase change process. The analysis also revealed that an increment in the inlet air velocity causes a decrease in the average temperature. For the same air inlet temperature (Thot) higher air velocity leads to a slower rate of the melting process Therefore, melting time is less by ∼ 30 % (for the inner layer) and 32 % (for the outer layer) with decreasing air velocity. The findings of this study will help the designer to improve the battery thermal management system by modulating the temperature.

Influence of fin shape design on thermal efficiency of phase change material-based thermal energy storage unit

The present numerical study treats the impact of fin shape design on the thermal efficiency of phase change material (PCM)-based thermal energy storage (TES) unit, focusing on the same surface area occupied by fins. Comparing two different finned TES units equipped with rectangular and triangular fin shapes, respectively, showed significant enhancements in PCM melting activity. Comparative analysis demonstrated that triangular fin shape lowers PCM melting time by 12.64% for equivalent fin numbers, and by 15.38% for equal fin lengths due to the enlargement of the heat transfer area provided by the triangular shape. Further examination of fins with triangular shape in terms of spacing and length, under fixed thickness and size parameters, revealed significant reduction in melting time with increasing fins length. Notably, 50.75% decrease in melting time was achieved by decreasing the number of fins to 20 while increasing fin length to 10 mm. Moreover, maintaining a heat transfer fluid (HTF) temperature 20 K higher than the melting PCM temperature maximizes TES thermal efficiency. These outcomes emphasize the importance of optimizing fin shape design for enhancing heat transfer without affecting the energy storage capacity of TES systems, with potential applications in building thermal management.

A novel PCM/expanded graphite composite sphere with high thermal conductivity and excellent shape stability used for a packed-bed thermal energy system

In this research, a novel phase change material (NPCM) sphere was developed and its application in a packed-bed thermal energy storage (PBTES) system during thermal energy storage was studied. Paraffin wax (PW) with a melting point of 40 °C was selected as phase change material (PCM), expanded graphite (EG) as thermal conductivity enhancement material, and epoxy resin (ER) as a surface coating. The results show that the three-dimensional heat conduction network constructed by EG foam improves the thermal conductivity of PW/EG. The thermal conductivity of NPCM is anisotropic. The thermal conductivities perpendicular and parallel to the EG compression direction are 9.03 (W/m·K) and 5.58 W/(m·K). NPCM has excellent shape stability with a leakage rate of only 2.95 %. Then, a PBTE system was built to record the temperature evolution of NPCM spheres at various inlet temperatures and volume flow rates during thermal energy storage, and thermodynamic analysis was performed. The results are as follows. (1) The temperature of the NPCM sphere near the inlet rises more rapidly and the melting time of PCM is shorter. (2) Increasing the inlet temperature improves the heat transfer and shortens the melting time of PCM while increasing the temperature inhomogeneity of the NPCM spheres. Increasing the inlet temperature increases the energy storage capacity. However, higher inlet temperature leads to lower energy efficiency and exergy efficiency. The energy efficiency and exergy efficiency are 49.66 % and 67.64 % for the inlet temperature of 60 °C, respectively. When the inlet temperature increases from 60 °C to 80 °C, the energy efficiency and exergy efficiency decrease by 16.13 % and 16.22 %, respectively. (3) Higher inlet volume flow rate also promotes heat transfer and reduces the melting time of the PCM, but has little effect on the temperature inhomogeneity of the NPCM spheres. Increasing the inlet volume flow rate does not increase the energy storage capacity. Similarly, increasing the inlet volume flow rate also results in a decrease in energy efficiency and exergy efficiency. At the inlet volume flow rate of 19.28 m3/h, the energy efficiency and exergy efficiency are 41.65 % and 56.67 %, respectively. When the inlet volume flow rate increases from 19.28 m3/h to 25.16 m3/h, the energy efficiency reduces by 7.80 % while the exergy efficiency reduces by 7.41 %. This research provides a foundation for the application of the NPCM sphere.

Analysis of phase change material (PCM) melting utilizing environmentally friendly nanofluids in a double tube with spiral fins: A numerical study

Phase Change Materials (PCMs) show great potential for thermal energy storage applications due to their substantial latent heat release during the transition from solid to liquid phases. The objective of this numerical study is to assess the melting process of a phase change material (PCM) within a vertical helical coil designed as a latent heat storage system. Innovative enhancements to the system's performance are introduced through the utilization of environmentally friendly nanofluids, BH (Biogenic Hierarchical)–SiO2/water and OLE (Olive Leaf Extract)–TiO2/water, and three distinct configurations of spiral fins. A three-dimensional model is implemented to investigate the impact of the number of fins, nanoparticle concentration, initial temperature and velocity of the Heat Transfer Fluid (HTF), as well as various fin thicknesses. The porous enthalpy method within ANSYS-Fluent is employed to model the phase-changing process. The results indicate a significant reduction of 66.88 % in the melting time of solid PCM with the inclusion of three spiral fins compared to the configuration without fins. Furthermore, the thermal performance of BH–SiO2 is found to surpass that of OLE–TiO2, attributed to its higher thermal conductivity. Additionally, the analysis reveals that the melting time is more sensitive to the initial temperature of the HTF than its velocity.

Enhancement of PCMs performance using nano-particles in horizontal triple-series shell-and-tube heat exchangers: A numerical study

Integrating Phase Change Materials (PCMs) as a storage system into a parabolic trough collector (PTC) setup can enhance energy security. However, PCMs have a drawback in terms of their low conductivity. To improve reliability, a cascaded array is used for the storage system. The thermal performance of three series shell and tube heat exchangers filled with PCM1 (64–68 °C), PCM2 (57–60 °C) and PCM3 (46–48 °C) during the charging process is evaluated. A 2D simulation model is developed, and 11 computational cases are considered. Firstly, results of utilizing two different designs of heat exchangers are analyzed. The effective geometry is chosen to validate previous experimental findings, and the range of percentage variation is 1.7 to 10.97 %. To optimize the thermal performance of the storage system for residential applications, two distinct nanoparticles of Al2O3 and GNPs are employed with maximum volume fractions of 10 and 3 %, respectively. Findings reveal that the immersion of 10 % Al2O3 accelerates the melting time of PCMs 1, 2, and 3 by 38, 31.6, and 31.6 %, respectively. Also, dispersion of 3 vol% of GNPs shortens the melting time up to 78.1 %. Meanwhile, the PCM's effective average temperature rises the most at this volume fraction, reaching 93.4 °C. On the other hand, it is observed that a higher concentration of Al2O3 (10 vol%) declines the energy and exergy storage of the system by 40.6 and 39.8 %, respectively. Conversely, increasing GNP volume fraction to 2.5 % enhances the system's energy and exergy by 21.1 and 62.9 %, respectively. These advancements enhance the storage system's thermal performance, broadening its potential applications.

Numerical study and optimization of battery thermal management systems (BTMS) Based on Fin-Phase change material (PCM) in variable gravity environments

Phase change materials (PCMs) are widely employed in electronic thermal control systems for spacecraft because of their substantial energy storage competencies. Hence, the impact of gravitational acceleration (GA) on PCM thermal performance holds particular significance. Moreover, given considerations for spacecraft center of gravity, attitude control, and structural design, choosing an optimal battery placement orientation becomes pivotal for maximizing available space utilization. This study employs the enthalpy-porosity method to simulate and assess the heat transfer efficiency of PCM and the thermal behavior of cooling battery thermal management system (BTMS) under different gravity environments (0.05 g, 0.1 g, 1 g, 10 g, and 20 g) and different inclination angles (θ = 90°, 45°, 0°). The research findings indicate that when θ = 90°, as gravity increases from 0.05g to 20g, the complete melting time of PCM at GA = 20g is shortened by 95.05 s (15.00 %) compared to GA = 0.05g. Particularly, when GA = 10 g, increasing θ from 45° to 90° reduces PCM melting time by 59.05 s (9.66 % reduction) compared to θ = 45°, while at θ = 0°, it decreases by 65.75 s (10.75 % reduction). Notably, at θ = 45°, some unmelted solid PCM accumulates in the lower right corner of the enclosure hindering the BTMS heat transfer. Based on PCM melting characteristics, three optimization structures for different θ are proposed. At t = 240 s, PCM melting significantly improves with fins. Comparing Convective Heat Transfer Coefficients (CHTC) curves before and after optimization reveals reduced accumulated effects. However, more fins aren't always better due to BTMS weight considerations. Investigating enhanced CHTC, fin mass, and volume ratio(γ), the optimized model impacts BTMS weight differently for θ values. θ = 45°, a combination of annular and straight fins, is determined optimal using entropy-weighted TOPSIS. This paper innovatively studies PCM melting in BTMS under varied gravitational environments and θ, proposing an enhanced heat transfer scheme for aerospace BTMS design.

Optimization of a thermal energy storage system enhanced with fins using generative adversarial networks method

Optimizing fin configurations is an effective method to improve the performance of a thermal energy storage system. The present research aims to determine the optimal fin spacing and inclination angle to minimize the melting process of a phase change material (PCM) in a rectangular enclosure, which is exposed to a constant temperate finned wall while other walls are adiabatic. Oleic acid (OA) is used as a PCM with a melting temperature of 287–288 K. Computational fluid dynamics (CFD) simulations are employed to comprehensively investigate the thermal behavior of the system by solving continuity, momentum, and energy equations simultaneously. Initially, fifteen different datasets are simulated using CFD methods to explore various fin configurations. After that, fifteen additional datasets are generated to verify the reliability of the generative adversarial networks (GANs) method, which supplements the CFD approach. An ensemble learning approach is implemented to create a hybrid dataset consisting of thirty datasets, and then the optimum dataset is determined. To validate this approach, a single numerical simulation is conducted at the optimum dataset, and the obtained optimum value, minimum melting time of PCM, is compared with the result obtained from CFD simulation. It is identified as the optimal fin configuration, resulting in a fin spacing of 15.75 mm and an inclination angle of −11.6°, highlights the efficacy of the combined CFD and GANs approach. The melting time captured from the numerical simulation and the one produced with GANs differed by about 4.7 %. The current study concludes that the GANs method might be effectively worthwhile in many energy storage applications.

Thermal performance enhancement of multiple tubes latent heat thermal energy storage system using sinusoidal wavy fins and tubes geometry modification

In this paper, performance enhancement of a shell and multiple tube latent heat thermal energy storage system (LHTESS) is numerically investigated by implementing sinusoidal wavy fins and different geometrical designs of heat transfer tubes. The annular space of the shell is filled with the paraffin wax RT35 as phase change material (PCM) and absorbs heat from hot water through the multiple tubes. With the constant total cross-section area of all tubes and fins as the constraint condition, the effect of tube number and tube shape incorporated with the proposed fins on the heat transfer properties of PCM during the melting process is evaluated. The computational results demonstrate that the sinusoidal wavy fins can improve the phase change efficiency compared to the conventional straight fins. The double-pitch sinusoidal wavy fins decrease the total melting time by 9.5% compared to the straight fins for the single-tube case. As the number of HTF tubes increased from one to four, the complete PCM melting time decreased by 38.3%. Geometrical design alterations of heat transfer tubes from circular to petal-shaped are proposed to further improve the thermal performance of multiple tubes LHTESS. The melting rate of PCM is accelerated with an increase in the number of petals. The petal tubes with nine petals can save the charging time up to 24 % in comparison with the circular tubes in a four-tube case with double-pitch sinusoidal wavy fins, and up to 57% compared to the base case with a single circular HTF tube and straight fins.

Effect of novel fin distribution on the melting process of thermal storage units

Thermal storage units play a crucial role in storing excess energy and utilizing it when required. Enhancing the thermal performance of these units is of utmost importance for better thermal energy management. Therefore, this paper suggests introducing new fin distributions to decrease the thermal resistance of the storage unit and, thus, enhance the melting process. An octagonal tube and shell unit with nanoparticle-enhanced phase change material are suggested. Three considered fin distributions to improve the heat transfer inside the unit are straight dual-radial fins, tree-like fins, and roots-like fins. Also, since copper has high thermal conductivity, its nanoparticles are incorporated with the phase change material with different concentrations, i.e., 0, 4, and 8 vol%. The Galerkin finite element technique is employed to model the storage unit. The results show that using roots-like fins has a significant effect in reducing the phase change material melting time by 56% and 91% lower than dual-radial fins and tree-like fins, respectively. The higher nanoparticle concentration (8 vol%) can also improve the thermal storage unit performance by 28.9% compared to the pristine phase change materials. Thus, this study recommends using roots-like fins with nanoparticles in the thermal storage units to enhance thermal performance.

Melting characteristics of phase change material inside graded aluminum foam based on tetrakaidecahedron model: Pore-scale simulations

Metallic ligaments in open-cell metal foams have effectively improved the heat conduction of phase change materials (PCMs). However, when the gradient direction of porosity is perpendicular to the direction of heat conduction, the mechanism by which graded foam (GF) influences the phase transition of PCM remains elusive. To address this issue, this study employs the pore-scale numerical simulation and develops a numerical model to study the impact of GF on the charging of PCM-foam composites. The analysis identifies the local convection and heat conduction as the most crucial factors influencing heat transfer during phase transition. To effectively examine the role of metallic ligaments in the phase transition, simplified tetrakaidecahedron cells are adopted. The results demonstrate that the GF delays the charging of PCM. Specifically, compared to the homogeneous foam, the full melting time (FMT) of PCM in the GF increases by over 29%. Additionally, the integral-mean temperature response rate (ITRR) of PCM in the GF decreases by 20.2% to 22.1%. Within the GF, the PCM requires more time to melt completely in the tetrakaidecahedron cells with high porosity. Moreover, local convection plays a pivotal role, considerably reducing the FMTs of PCMs by over 85% and increasing the ITRRs of these structures by 588.1% to 599.0%.

Accelerated charging dynamics in shell-and-multi-tube latent heat storage systems for building applications

Thermal energy storage (TES) is an emerging technique to store the surplus energy generated during periods of excess supply and utilise it when demand arises. Phase change material (PCM) stands out as a highly efficient TES system. Enhancing heat transfer during phase change is a major challenge in creating effective PCM-based TES systems. This study focuses on enhancing the melting performance of a shell-and-tube latent heat thermal energy storage (LHTES) system. This improvement is achieved by conducting an extensive parametric study involving various geometric factors including tube position from the bottom, vertical tube spacing, tube diameter, different heat exchanger shell aspect ratios, PCM temperature, tube temperature, and PCM type. A three-dimensional model is simplified to a two-dimensional geometry for numerical simulation. The results indicate that the PCM melting time decreased by 20.6 % and 4.4 % with a 20 mm vertical tube distance compared to 15 mm and 25 mm. Among the considered scenarios, the configuration with a doubled number of tubes in width consistently exhibits a higher melt fraction throughout the entire duration. Regarding the aspect ratio, the square-shaped system demonstrates both quicker melting times and a higher energy storage rate. When comparing PCM types, it is evident that RT 35 exhibits a 3.2 % higher heat storage rate and a 44.7 % shorter melting time compared to RT 35 HC.

Empirical Investigation of Thermal Features of Phase Change Material as Thermal Storage System

This paper presents an empirical investigation of the melting processes of phase change material (PCM) in a tube and shell heating exchanger utilizing solar thermal energy. The experiments were conducted outdoors in Al-Mussaib city, Babylon, Iraq (Lat 32.5° North, long 44.3° East), utilizing a north-south (N-S) collector oriented at a tilt angle of 32.5° from the horizontal. This work utilized pure Iraqi black paraffin with 12 kg as PCM. The main empirical rig involves a vacuum tube solar collector (VTSC) utilizing a tube and shell heating exchanger to melt PCM in the shell regime. Different rates of water flow inside the internal heating exchanger's tube, namely (3.5, 5, and 8.5 L/m), were utilized for each season from August 2022 to January 2023. The empirical findings concluded that the internal tube inlet and surrounding temps significantly influence the melting process compared to the rates of water flow. It was found that the melting process of PCM needs about (3 to 4) hours in the summer season. Still, winter needs a longer time, about 14 to 16 hours. Increasing surrounding temp and solar radiation reduces the melting time of phase-change material. The findings of the present work were compared with the earlier investigations and agree with increasing the present work by 23.5 %. The findings from the present study are of practical importance for industries requiring storage materials to improve thermal storage system performance.

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.

Performance comparison and enhancement of the thermal energy storage units under two expansion methods

To improve the performance of the basic thermal energy storage unit, two expansion methods, modular combination and linear structural expansion, are proposed and compared through numerical simulations. The impacts of the two expansion methods on the performance of the storage units are compared by investigating the thermal storage and release processes. Following the numerical study, both expansion methods can increase the heat storage capacity and airflow rates compared to a basic phase change material (PCM) storage unit linearly. However, the linear structural expansion method will increase the PCM melting time from 147 min to 367 min when the heat storage capacity of the basic unit is increased two times, which is about 2.5 times longer duration than using the modular expansion method. As for the heat release process, the results indicate that thermal release performance using linear structural expansion is lower than that of the modular combination along with a decrease in heat release efficiency of about 32.53 %. In conclusion the modular combination method is proved to be more efficient compared to the linear structural expansion method for improving the performance of the PCM storage units.

A novel thermal management system for cylindrical lithium-ion batteries using internal-external fin-enhanced phase change material

This study introduced a phase change material (PCM)-based battery thermal management system (BTMS) using an innovative combination of internal and external fins to create PCM silos around the battery surface, addressing the low thermal conductivity of PCM. The lumped-capacitance thermal model and enthalpy-porosity approach were employed for the battery heat generation and PCM melting process, respectively. The BTMS was evaluated under transient and constant heat generation of the battery at various discharge rates. The effects of fin quantity on thermal management performance, energy density, heat storage capacity, and PCM melting time were investigated. The developed BTMS showed superior performance compared to the battery system with natural air convection cooling and the PCM cooling system without fins. At the end of the PCM complete melting process, the BTMS with 4 internal-external fins decreased the battery surface temperature by 9.90 and 17.45 K compared to the PCM cooling system without fins at the discharge rates of 3C and 5C, respectively. The BTMS with 4 internal-external fins kept the battery surface temperature under the optimum temperature of 318.15 K even at a high ambient temperature of 308.15 K while providing up to 10.02% higher energy density, 11.11% higher heat storage capacity, 32.79% higher fin efficiency, and only 1.08% lower overall fin effectiveness compared to greater fin quantities. The proposed BTMS provided an almost uniform cooling effect on the battery surface compared to the system without fins, which has been largely overlooked in previous studies on BTMSs. Various heat transfer regimes were identified during the PCM melting process. Correlations for predicting the PCM liquid fraction and Nusselt number were proposed as a function of a group of dimensionless numbers. These findings provided valuable insights for designing efficient PCM-based BTMSs.

Simulation and optimization of square fin concentric tube heat storage exchanger

The square fin was used to improve the heat transfer rate of the concentric tube phase change heat exchanger. The effects of fin spacing, fin arrangement, and fin length on the melting process of phase change material (PCM) were studied. The influence and mechanism of non-uniform fin arrangement were discussed in detail. The liquid phase distribution and temperature distribution of PCM with time were analyzed. The results indicated that the heat exchanger with square fins can significantly improve the heat storage rate and shortened the complete melting time of PCM. Compared with heat exchangers without fins, the melting time of PCM in a 40 mm equidistant fin heat exchanger was shortened by 15.85%, and that in a 70 mm, non-uniformly spaced fin heat exchanger was shortened by 36.79%. Due to the different distances between the square fins and the outer boundary of the concentric tube, the temperature distribution near the square fin showed anisotropy, which enhanced the melting rate of PCM. The sensitivity order was fin arrangement > fin length > fin spacing. The research results can provide a reference for the design of phase change heat exchangers.

Experimental study on heat transfer and storage of a heating system coupled with solar flat heat pipe and phase change material unit

Using renewable energy, especially solar energy, is essential to achieve a low-carbon society. PCMs suffer from low thermal conductivity, which hinders the efficiency of phase change thermal storage systems. Heat pipes exhibit vastly superior thermal conductivity, making them a promising candidate for enhancing PCM-based systems. To solve the contradiction between building insulation and importing solar energy into buildings in winter, this study proposes a new building heating ceiling system consisting of a flat-plate heat pipe (FHP) coordinated with a phase change material (PCM), and establishes a platform for a heat stockpiling device integrating the FHP and PCM. This research investigates the impact of heating power and bending angle on the heat transfer efficiency of the heat pipe and phase change heat storage system. The experimental findings demonstrate a direct relationship between increasing heating power and the enhancement of the FHP's heat transfer efficiency. When the FHP is bent at a 5° angle and heating power is increased from 20 W to 80 W, to store heat energy into the PCM cavities, the effective thermal conductivity rises significantly, escalating from 7.26 × 104 W/(m·°C) to 15.1 × 104 W/(m·°C), marking a remarkable 108 % rise. Moreover, although increasing the bending angle leads to heightened effective thermal conductivity of the FHP under constant heat input, and the heat transfer in PCM cavities will be weakened within a bending angle of 15°, experimental results demonstrate that the melting time of PCM still decreases with the increase of bending angle; the heat transfer inertia of phase change materials is dominant.

Numerical simulation and structural optimization of spiral finned tube thermal energy storage

Thermal energy storage (TES) has emerged as a promising solution to enhance nuclear safety by passively removing decay heat during reactor shutdown and accidents, thus preventing overheating of the reactor core and protecting the integrity of containment barriers. The research of TES with different structures has broad application prospects and practical significance. In this study, the melting process of phase change material (PCM) in various TES structures was simulated by the numerical simulation method in two and three dimensions. The mechanism of gravity-driven natural convection enhancing heat transfer was revealed. The effects of different TES structures, fin pitch, fin height, and fin thickness on heat transfer performance were studied. The results showed that many vortices formed by liquid PCM are the main reason for enhancing the natural convection. Adding fins could greatly accelerate the heat storage process. The melting time of PCM in annular and spiral finned tube TES was 47.3% and 61.3% less than that in smooth tube TES, respectively. In the present study, the heat transfer effect was enhanced as the spiral fin pitch became small, the fin height increased and the fin thickness increased. Two opposite effects of fin structure on the natural convection were revealed: (1) positive effect provided by heat transfer enhancement and (2) negative effect produced by blockage.