Latent Heat Thermal Energy Storage System Research Articles

Technical assessment of phase change material thermal expansion for passive solar tracking in residential thermal energy storage applications

Phase changing materials (PCMs) have been widely investigated for Latent Heat Thermal Energy Storage (LHTES) applications in the last decades, due to their inherently high volumetric storage density and thermal control features. Nonetheless, PCMs and their related LHTES systems still require significant scientific and technical advancements and more efficient market penetration strategies, to be able to play a key role in the massive transition towards renewable energy that is expected to take place in EU in the near future. Some of the most investigated PCMs for low to medium temperature LHTES belong to the alkanes/paraffins family, which is characterized by a relatively high volumetric expansion solid-to-liquid phase transition. This is generally considered a side effect, which should be accounted for to avoid damaging the containment structure. However, it could also represent an opportunity to add extra functionalities and increase the overall efficiency of LHTES systems.In this paper, we evaluate the feasibility of using the mechanical work generated by the volumetric expansion cycles in a paraffin-based LHTES device for photovoltaic (PV) solar tracking purposes, thus assuming a novel paradigm for the efficient integration between thermal and PV solar installations. To this aim, the temporal evolution of temperature and density fields inside the PCM are modeled through a finite-difference/finite-volume numerical approach. Accurate charge/discharge profiles of the TES are implemented, considering data from a previously investigated solar-assisted heating/cooling plant for a typical residential application in southern Italy. Outcomes from this analysis allow to estimate the tracking capability of the chosen PCM in terms of number/surface of actuated PV panels.

Bubble-driven flow enhancement of heat discharge of latent heat thermal energy storage

In this paper, the use of bubble-driven flow on phase change material (PCM) is proposed to improve the discharge performance of a latent heat thermal energy storage system (LHTES). The upward momentum of bubbles due to its density difference can agitate liquid PCM and increase the flow velocity of liquid PCM to enhance heat transfer between the heat transfer fluid (HTF) and the PCM. To analyze the mechanism of enhanced heat transfer, visualization techniques of particle image velocimetry (PIV) and shadowgraphy were used. The result showed that the discharge time of LHTES decreased by 6%–12%. The increased flow velocity by bubble-driven flow could be observed and the expanded phase change region away from the solid/liquid interface could be identified. The average convective heat transfer coefficient is increased by maximum 1.79 times during the heat discharge period. This mechanism could accelerate the solidification process and enhance the energy discharge rate of the LHTES. Bubble-driven flow could be successfully applied to PCM to improve LHTES discharge performance.

Application of phase change material in thermal energy storage systems

The energy sustainability is one of the recent fields of research among scientist and engineers throughout the world. Solar energy is abundantly available and can be used to generate power. A major problem faced by technologies using solar radiation for energy generation is the unavailability of sunlight during night hours or when the sky-view has been obstructed by natural weather phenomena such as rain, cloudy weather, etc. Solar energy is not always produced at the peak power usage times which usually occurs during summer afternoons and evenings. To firm renewables, that is, to ensure energy on-demand irrespective of the time of the day is one of the biggest challenges facing the energy industry. Storing energy can contribute to smoothing out variations attributed to the amount of sunlight incident onto concentrating solar-thermal power systems or photovoltaic systems and allow for smoother flow of energy on the grid. Latent heat thermal energy storage system (LHTES) is one of the vital ways to store thermal energy with the help of phase change materials (PCM). The current paper gives an overview about the LHTES, and different methods of enhancing the thermal conductivity of PCM.

Melting Characteristics of a Phase Change Material Mixed with Nano Particles of Cobalt Oxide Bounded in a Trapezoidal Structure

A novel trapezoidal design for storage of heat energy through melting of phase-change material (PCM) is investigated. Latent heat thermal energy storage system (LHTES) is a promising option to diminish mis-match between energy consumption and supply. For this purpose, Paraffin: Rubitherm-35 (RT35) material is successively melted in aluminum structure which is heated from one side and the other sides are kept adiabatic. Melting of PCM is observed experimentally and melt fronts are photographed for various time lengths. The fluid-solid module in COMSOL Multiphysics 5.4 has been utilized. The transient heat conduction with enthalpy function is hired. Simulations are carried out for enhancement of thermal conductivity through addition of nano-entities of cobalt oxide . The melting time is notably reduced with inclusion of nano-entities to enhance thermal conductivity. The time spans for melt start and total melt in case of pure PCM are 375 and 4500 (s) respectively whereas for the nano mix case, these are 150 and 3000 s. Thus 33% shorter time length is noticed for charging of the PCM trapezoidal matrix with nano entities of are mixed. The results from simulation and lab observations depict similar patterns and are in quite close comparison.

Optimization of Nano-Additive Characteristics to Improve the Efficiency of a Shell and Tube Thermal Energy Storage System Using a Hybrid Procedure: DOE, ANN, MCDM, MOO, and CFD Modeling

Using nano-enhanced phase change material (NePCM) rather than pure PCM significantly affects the melting/solidification duration and the stored energy, which are two critical design parameters for latent heat thermal energy storage (LHTES) systems. The present article employs a hybrid procedure based on the design of experiments (DOE), computational fluid dynamics (CFD), artificial neural networks (ANNs), multi-objective optimization (MOO), and multi-criteria decision making (MCDM) to optimize the properties of nano-additives dispersed in a shell and tube LHTES system containing paraffin wax as a phase change material (PCM). Four important properties of nano-additives were considered as optimization variables: volume fraction and thermophysical properties, precisely, specific heat, density, and thermal conductivity. The primary objective was to simultaneously reduce the melting duration and increase the total stored energy. To this end, a five-step hybrid optimization process is presented in this paper. In the first step, the DOE technique is used to design the required simulations for the optimal search of the design space. The second step simulates the melting process through a CFD approach. The third step, which utilizes ANNs, presents polynomial models for objective functions in terms of optimization variables. MOO is used in the fourth step to generate a set of optimal Pareto points. Finally, in the fifth step, selected optimal points with various features are provided using various MCDM methods. The results indicate that nearly 97% of the Pareto points in the considered shell and tube LHTES system had a nano-additive thermal conductivity greater than 180 Wm−1K−1. Furthermore, the density of nano-additives was observed to be greater than 9950 kgm−3 for approximately 86% of the optimal solutions. Additionally, approximately 95% of optimal points had a nano-additive specific heat of greater than 795 Jkg−1K−1.

Phase Change Process inside Toroidal Tube Heat Exchanger with Internal Fins

Inadequate melting of phase change material (PCM) in concentric tube and shell and tube heat exchangers appeal motivations for innovative latent heat thermal energy storage (LHTES) systems. In the current research, a novel application of toroidal tubes inside the LHTES system for charging of PCM is presented. The proposed heat exchanger geometry is numerically investigated with the help of enthalpy – porosity approach. Toroidal tubes are assumed to be filled with PCM (i.e., coconut oil) and fabricated inside cylinder accommodating the heat transfer fluid (HTF). To establish and accelerate homogenous melting, flat thin fins are attached inside the toroidal tubes, and transient simulations are performed. The system performance is investigated for variations of (i) fin numbers (Nf), (ii) fin length (L0), and (iii) fin orientations (Fo) in terms of (i) melt fraction (MF), (ii) average PCM temperature, (iii) energy stored by PCM, and (iv) Nusselt number (Nu). Simulation results indicate that fin orientation stands out as the dominant factor for heat transfer enhancement compared to fin numbers and fin length. In the toroidal tube LHTES system, it is found that even though fin numbers and fin length are identical, correctly oriented fins (i.e., case 8) can provide 50.52% more rate of energy storage than a system with random fin orientation (i.e., case 5). Moreover, the optimum fin orientation (i.e., case 8) can (i) save 65.28% time for 100% melting and (ii) provide 168% more rate of energy storage than a system without fins. Based on the melting progression pattern, the current study encourages the use of multiple PCMs having dissimilar melting point temperatures with fins.

Optimization of shell and tube thermal energy storage unit based on the effects of adding fins, nanoparticles and rotational mechanism

According to the high storage capacity of latent heat thermal energy storage (LHTES) systems, finding a suitable solution to compensate for the weakness of these systems is logical. The main weakness of these systems is the low thermal conductivity of phase change materials (PCMs) as the storage reservoir of thermal energy. Many methods have been proposed previously to overcome this limitation. Most of these methods can be divided into three types that including changes in the geometric configurations, improving thermophysical properties of PCMs and applying external conditions to improve the LHTES systems' performance. Nonetheless, limited studies have been conducted with combination approaches between these methods. In line with this, the present study investigates the effect of combining three different types of improvement methods in the applicable ranges simultaneously. These methods are selected based on utilizing three different ways to heat transfer rate enhancement. So that these ways include increasing heat transfer area (by adding fins), increasing natural convection effect (by adding rotational mechanism) and improving the thermal conductivity of PCM (by adding Cu nanoparticles). Results show that the combination of these methods has a significant effect on the improving performance of LHTES system during charge and discharge processes. So that increasing productivity of each method leads to decreasing melting and solidification times and following this heat transfer rate enhancement. Based on comparing results, rotational speed increment has the highest effect on increasing heat transfer rate in charge and discharge processes. Moreover, since storage and release capacities are important parameters in the LHTES systems, to shed further light on the impact of utilizing combination methods on reducing these capacities, an optimization process is conducted by the response surface methodology (RSM). Optimization results present an optimal case based on the highest heat transfer rate with the highest storage and release capacities in charge and discharge process. Comparing results between simple and optimal cases show that applying optimal conditions leads to enhancing heat transfer rate significantly based on decreasing melting and solidification time at about 74% and 70%. While based on this comparison, storage and release capacities are reduced by just 2.5% and 4.1%, respectively.

An experimental study on the effect of annular and radial fins on thermal performance of a latent heat thermal energy storage unit

Latent heat thermal energy storage (LHTES) has been used to deal with the cyclical nature of energy production through solar means. One problem with LHTES systems is the PCM having a low thermal conductivity. This results in low heat transfer rate prolonging the charging and discharging cycles. In the current study, the thermal characteristics of a latent heat thermal energy storage system enhanced with annular and radial fins are investigated experimentally. Rubitherm RT-55 is used as the phase change material (PCM) and is enclosed within a vertical cylindrical container. Water is used as the heat transfer fluid (HTF) which is circulated in a copper pipe that passes through the center of the container. Different numbers of annular and radial fins attached to the central pipe, all containing the same volume of copper are studied. The effects of these configurations on the thermal performance of the latent heat thermal energy storage system during the charging and discharging processes is monitored. The no-fin benchmark case took 47.87 h to charge the LHTES unit and 42.5 h to discharge. The ten-annular fins charged the system 84.1% faster and discharged the system 68.21% faster. The twenty-annular fin case reduced the charging time by 85.8% and the discharging by 68.58%. The four-fin radial case was found to decrease the charging time by 81.9% and 70.0%; whereas the eight-fin radial case was found to have the greatest decrease the charging and discharging times, being 86.6% and 80.1%, respectively.

Numerical simulations and experimental investigations to study the melting behavior of beeswax in a cylindrical container at different angular positions

Phase Change Materials (PCMs) are widely used in Latent Heat Thermal Energy Storage Systems (LHTES). This work aims to study the melting behavior of low-temperature phase change materials in cylindrical containers placed at different angular positions. Simulations were performed using ANSYS FLUENT by applying the enthalpy porosity model to analyze melting of beeswax in a cylindrical glass tube subject to an isothermal wall condition. The tube was placed at angular positions of 0°, 30°, 60° and 90° to the horizontal in order to study the effect of angular position on melting behavior. The simulation results were then validated by performing experiments and capturing images at regular intervals of time to track the solid-liquid interface. Image processing using MATLAB was performed on the captured images to study the variation of melt fraction as a function of time. It is observed that the experimental results were in good agreement with the simulations. From these studies, it was observed that the total melting time increases with the angle of tilt from 0° to 90° Initially, the melting progressed similar to the analytical solutions of one-dimensional phase-change heat transfer. As the melting continued, the experimental and numerical results deviated from the analytical solutions and the rate of melting increased due to convection effects. The results obtained in this study can be used to predict the melting behavior of PCMs in a solar flat plate collector kept at different angular inclinations. This result can be kept in mind while designing a thermal energy storage system to set an appropriate angle to match the cycle time of the system.

On the effect of porosity and functional grading of 3D printable triply periodic minimal surface (TPMS) based architected lattices embedded with a phase change material

Triply Periodic Minimal Surface (TPMS) topologies have recently gain widespread attention due to their promising performance in several areas like structural strength enhancement, heat transfer augmentation, scaffold and tissue engineering, etc. to name a few. Evolution in 3D printing technology has realized the manufacturing of these complex topologies in an extremely simplistic and straightforward manner. Recent research progress has shown that upon impregnations with phase change material (PCM), lattices based on TPMS topologies exhibited better heat transfer performance than the conventional metal foam in Latent Heat Thermal Energy Storage (LHTES) systems. However, the effect of lattice's porosity and functional grading is not understood and requires further investigation. In order to bridge this gap. This numerical study aims at studying the effect of porosity and functional grading of TPMS-PCM lattices on heat transfer performance. Three TPMS structures namely Primitive, Gyroid and IWP are considered in this study. The porosity study analyzes the heat transfer performance of TPMS structures at three distinct levels of porosity i.e., 60%, 75% and 90% with the 75% porosity case being the benchmark. Furthermore, to study the effect of functional grading, 75% uniform porosity configuration of each TPMS configuration was compared with 75% overall porosity configurations having first a positive and then a negative functional gradient in the porosity. It was found that both porosity and functional grading have a significant effect on both conductive and convective heat transfer enhancement. A reduction in porosity significantly reduces the PCM melting time owing to enhancement in the heat transfer. On the other hand, a positive gradient in the porosity outperforms both uniform porosity and negative porosity gradient cases. Moreover, in both porosity and functional grading studies, the extent of heat transfer enhancement is topology-dependent i.e., each TPMS structure exhibits a different extent of heat transfer enhancement that can be traced back to its topology. This study may therefore serve as a guideline for design and selection of a suitable TPMS candidate according to the applied boundary conditions/problem constraints of the respective LHTES system.

Melting characteristics of a longitudinally finned-tube horizontal latent heat thermal energy storage system

This study aims to analyze the effect of fin geometry on the thermal performance of longitudinally finned-tube horizontal latent heat thermal energy storage (LHTES) systems. The longitudinal fins with different fin heights, thickness, and numbers were applied in the horizontal shell-and-tube LHTES system and the paraffin was packed in the annulus. The melting fronts, average temperature, and velocity profiles of Phase Change Material (PCM) were graphically illustrated and compared for charging processes. It was found that the incorporation of longitudinal fins in a small quantity (2.85% of total volume) could reduce the complete melting time by 34% in comparison to the bare-tube configuration. Melting characteristics were compared using average liquid fraction, average PCM temperature, and stored energy. It was recommended that the fin height should not exceed half of the annulus gap. The optimum fin volume was identified by comparing the enhancement ratio for examined configurations. Furthermore, for the same fin volume configurations, this study evaluated (i) whether a large number of short fins are beneficial or a smaller number of long fins and (ii) whether thick short fins are beneficial or thin long fins? Comparison results showed that a small number of long fins were more beneficial than that of more short fins and the melting characteristics of thin long fins were superior to that of the thick short fins. Finally, the optimum fin configuration was justified, and the priority sequence was suggested for the design of longitudinally finned-tube energy storage systems.

Thermal performance evaluation of a latent heat thermal energy storage unit with an embedded multi-tube finned copper heat exchanger

ABSTRACT The experimental thermal characterization during charging and discharging of a prototype compact latent heat thermal energy storage system (LHTESS) with an embedded horizontally oriented finned multi-tube copper heat exchanger is presented. The thermal store was filled with a commercial-grade, CrodaTherm™ 60, phase change material (PCM) with a nominal melting temperature of 60°C. The proposed heat exchanger (HX) configuration mitigates the effect of low PCM thermal conductivity and increases the rates of heat transfer to and from the store during the charging and discharging processes compared to multi-tube copper HX without fins. The experimental testing regime assessed the impact of heat transfer fluid (HTF) volume flow rate and inlet temperature on I) transient PCM temperature distribution, II) the total charging/discharging time and III) instantaneous/average power during the charging and discharging processes. The experimental results showed that the HTF volume flow rate and inlet temperature play a significant role in the thermal performance of the LHTESS during the charging/discharging process. During the charging process, the influence of increasing HTF inlet temperature is greater than that due to increasing HTF volume flow rate. Moreover, it is shown that during the first 30 minutes of the discharging process, the average power output was 4.3, 5.1 and 5.3 kW for HTF volume flow rate of 2.5 and 7.2 and 10.5 l/min, respectively.

Thermal performance enhancement of compound parabolic concentrator solar collector using latent heat thermal energy storage

Employment of compound parabolic concentrator (CPC) solar collector with evacuated tubes enables effective collection of solar energy. The main objective of the present experimental work is to investigate thermal performance of CPC solar collector coupled with sensible and latent heat thermal energy storage (TES) system. Depending on obtained thermal stratification in sensible TES system, a commercial phase change material (PCM)—OM 65 has been selected and packed only at top quarter section of the TES system. Results showed an appreciable cumulative energy storage of 21 MJ d−1 due to existence of desired temperature driving potential during charging. A higher thermal stratification has been achieved in latent heat TES system, reducing the “MIX” number and supplying the heat transfer fluid at lower temperature to the collector. Due to enhanced useful heat energy gained, thermal efficiency of CPC collector reaches a maximum of 49% while coupling with latent heat TES system. The outcome of the study highlights the potential role of CPC and PCMs in solar thermal system, particularly for water heating applications.

Pareto optimal design of a finned latent heat thermal energy storage unit using a novel hybrid technique

A finned latent heat thermal energy storage (LHTES) unit is considered for optimization through a hybrid procedure based on computational fluid dynamics (CFD), grouped method of data handling (GMDH) type of artificial neural network (ANN), non-dominated sorting genetic algorithms (NSGA-II), and multi-criteria decision-making (MCDM). Considering that optimized fins have a tremendous impact on the efficiency of finned LHTES systems, this paper considers the design variables the geometrical parameters of fins (number, length, and volume fraction). Furthermore, two of the most significant thermal energy storage (TES) systems, phase change time and total stored energy are considered objective functions. The primary purpose is to minimize the phase change time and maximize the stored energy. For this purpose, first, the effects of design variables on objective functions are studied by CFD simulations. Afterward, by importing the numerical data into the GMDH-type ANN code, polynomials are derived to predict the values of the objective functions in terms of design variables. Then, Pareto optimal points are presented using the NSGA-II algorithm and GMDH predictive models. Finally, the objective functions' design points per weight are proposed using TOPSIS and VIKOR MCDM methods. The considered finned LHTES unit showed that about 60% of the Pareto optimal points have a dimensionless fin length above 0.98. Also, the volume fraction of fins was observed below 0.1 for about 79% of the optimal cases. Besides, 81% of the total optimal cases had 4 or 5 fins.

A novel analytical approach to study the charging characteristics of a shell and tube thermal energy storage system

AbstractThis study presents a novel analytical solution of the phase change problem in a shell and tube arrangement of latent heat thermal energy storage (LHTES) system. The transient melting behavior of phase change material (PCM) is captured using time‐dependent boundary conditions and moving interface energy equation. An approximate mathematical model is developed with the help of dimensionless number (η), exponential integral function, Lambert W function, and Swamee and Oijha approximation. The proposed analytical solution is used for investigating the thermal performance of low, medium, and high melting temperature PCM for building, solar absorption cooling, and concentrated solar power (CSP) applications, respectively. The results obtained from the analytical approach are compared with a numerical model based on the enthalpy method. It is found that the root mean square difference between the average PCM temperature obtained from analytical solution and detailed numerical analysis is 3.3°C, 1.2°C, and 0.1°C for the low, medium, and high‐temperature systems, respectively. The temporal variation of melt front position and the effect of inner tube temperature are further investigated using the analytical solution. The mathematical model could be proposed as an effective tool for the assessment of shell and tube LHTES systems.

Enhanced thermal performance of finned latent heat thermal energy storage system: fin parameters optimization

Integration of thermal energy storage (TES) systems in concentrated solar power (CSP) plants plays an important role, followingly, the mismatch between energy production and demand can be adjusted. Generally, latent heat thermal energy storage (LHTES) can ensure important amounts of energy compared to sensible heat thermal energy storage systems (SHTES), which has oriented researchers, engineers, and decision makers toward using this technology because of its high energy density. Otherwise, using phase change materials (PCMs) in LHTES systems can considerably reduce their performance as PCMs have relatively low thermal conductivity values, which makes it very necessary to take measures for enhancing the thermal conductivity or heat transfer inside of these LHTES units. This study simulated, modeled and optimized a proposed system for heat transfer enhancement, which is a shell-and-tube storage units with annular fins, by using the finite element method during the charging and discharging processes. In addition, NaNO3–NaNO2 was used as PCM while the Delco Term Solar E 15 was used as heat transfer fluid (HTF). The main objective of this work is to provide the optimal geometry parameters of the studied system in terms of length, number, step, and fin thickness by comparing many fin geometries. According to the results, an increase around 65.04% in the charging (melting) time and 58.36% in the discharging (solidification) period was achieved by the integration of optimal fins. The recommended fin parameters corresponding to the highest thermal performance were; length = 14 mm, thickness = 1 mm, step = 3.45 mm, and number = 66.

Optimization and design criterion of the shell-and-tube thermal energy storage with cascaded PCMs under the constraint of outlet threshold temperature

In the concentrating solar power generation (CSP), the latent heat thermal energy storage system (LHTES) is under the constraint of the outlet threshold temperatures, which caused lower effective utilization rate (Uma) of the phase change material (PCM). The objective of the present work is to improve the performance of the shell-and-tube LHTES which is under the constraint of the outlet threshold temperatures in charging and discharging processes. In this study, a transient, two-dimensional, and axisymmetric model of a shell-and-tube LHTES is established. Based on the model prediction, first, the sensitivity analysis of the geometry parameters to the performance of the LHTES shows that with the increase of the specific surface area and the porosity, the Uma monotonically increases, but the investment cost for LHTES per unit of stored heat (cTES) has a minimum value. Then based on the influence of the number and filling thickness of cascaded PCMs, a design criterion of the cascaded PCMs distribution is proposed for the shell-and-tube LHTES constrained by the outlet threshold temperatures, and the effectiveness of this design criteria is verified. Based on the proposed design criterion, the Uma of the optimal shell-and-tube LHTES with 5-cascaded PCMs can reach 77.6%, which is 3.1 times larger than that of a non-cascaded LHTES. Its cTES is only about 2/5 of a non-cascaded LHTES. The results of optimizing the geometry parameters of the TES device and the distribution of cascaded PCMs can be beneficial to the shell-and-tube LHTES which is under the constraint of outlet threshold temperatures in the real utilization of CSP.

PARAFFIN AS PHASE CHANGE MATERIAL FOR THERMAL ENERGY STORAGE, HEATING APPLICATION

Liberally accessible sun based vitality utilization for residential and mechanical applications are ruined since of its discontinuous nature. The thermal energy storage (TES) framework utilizing both sensible and inactive warm has numerous advantages like expansive warm capacity in a unit volume and its isothermal behavior amid the charging and releasing forms. Since of these focal points, in later a long time, a part of investigate work has been going on to overcome issues like moo warm exchange the rates between warm exchange liquid and stage alter fabric (PCM) in both charging and releasing forms of the PCM-based TES framework. In the present experimental investigation results of a combined sensible and latent heat TES system integrated with a varying (solar) heat source is presented. Investigations are carried out in the TES system for different phase change materials (paraffin) by varying HTF flow rates and for various paraffin mass (2, 4, and 6) kg. Experiments are performed charging processes. The results show that the 2 kg paraffin mass shows better performance compared to other paraffin mass.

Numerical investigation of melting enhancement for paraffin in an innovative finned-plate latent heat thermal energy storage unit

Latent heat thermal energy storage (LHTES) is essential for eliminating the discrepancy between energy supply and demand as well as for improving the utilization rate of low-grade industrial waste heat. This paper aims to solve the problem of long energy charge time in finned-plate LHTES device. In the present study, the LHTES unit is designed with three different orientations of the fin plates: A denotes a horizontal unit with fins; B and C denote vertical units with transverse and longitudinal fins, respectively. First, the melting process with different sizes and distributions of fins is investigated and the effect of fin thickness on the melting time is analysed. When obtaining the optimized fin parameters, two potential strengthening strategies (rippling fins and fins of non-equal length) are applied to further improve the melting performance of the device. The results show that long and thick fins can remarkably ameliorate the melting performance of paraffin, and the melting rate for the three orientations is of the order A>C>B. Compared with the finless structure, the melting rate increased by 4.52, 3.63, and 3.62 times for the three orientations of A, B, and C, respectively, for a fin length of 50 mm and fin number equal to 10. The use of rippling fins can reduce the melting time up to 4.1%, 5.4%, and 10.7% for the three orientations of A, B, and C, respectively, compared to using equal-length homogeneous fins with a thickness of 3 mm. Moreover, for orientations A and B, by adjusting fin length arrangement or using full fins, 11.4 and 46% reduction in melting time could be achieved compared with the configuration with a fin length of 50 mm and a thickness of 3 mm. The proposed innovative finned-plate LHTES device provides a useful reference and groundwork for the future large-scale utilization of the LHTES system.

Thermal characterization of 3D-Printed lattices based on triply periodic minimal surfaces embedded with organic phase change material

Owing to their high latent heat of fusion and thermal stability, organic phase change materials (PCMs) are lucrative candidates for utilization in latent heat thermal energy storage systems (LHTES). However, since their low thermal conductivity inhibits their direct usage in such systems, they are often impregnated into a thermally conductive metallic matrix, which exhibits an effective thermal conductivity superior to that of PCM alone. In this study, metallic lattices based on Triply periodic minimal surfaces (TPMSs) are utilized as thermal conductivity enhancers for organic PCMs. TPMS are a class of periodic cellular materials that have been recently studied in several structural, thermo-mechanical, and other applications showing promising performance. However, their utilization with PCM in LHTES systems is a relatively uncharted area of research. Using selective laser sintering technique; four metallic TPMS structures were fabricated, i.e., diamond, gyroid, I-graph and wrapped package-graph (IWP), and primitive, and were later impregnated with two organic PCMs (i.e., RT62HC and RT64HC). The thermal conductivity of both PCMs and TPMS-PCM composite were measured using Transient Plane Source (TPS) method. It was found that the TPMS structures enhanced the thermal conductivity of the PCMs. Moreover, for a fixed porosity and unit cell size, the effective thermal conductivity was found to be a function of the TPMS architecture. A preliminary numerical analysis to compare the heat performance of PCM-alone and PCM embedded with TPMS (primitive) showed clear superiority of the TPMS-PCM composite over the PCM-alone case. Therefore, the utilization of TPMS structures in LHTES could be promising in a bid to increase the performance of organic PCMs.