Phase Change Material Domain Research Articles

A shell-tube latent heat thermal energy storage: Influence of metal foam inserts in both shell and tube sides

Enhancing heat transfer in latent heat thermal energy storage systems is of utmost importance to facilitate the efficient absorption and release of thermal energy. The primary objective of the current study is to investigate the influence of a metal foam layer on heat transfer enhancement in both the heat transfer fluid side and the shell side. The research explores the incorporation of a fixed 30 % foam layer, which can either extend along the tube wall or penetrate deeper into the shell, moving away from the heat transfer fluid tube. A local thermal non-equilibrium two-temperature heat equation model is utilized to mathematically model the interactions within the metal foam embedded in the heat transfer fluid tube and the phase change material domain. The governing equations are solved using the finite element method. The results indicate that adjustments to the inlet pressure and the metal foam shape parameter (FL) can significantly reduce the melting time, with a variation of approximately 40 %. Specifically, at a constant inlet pressure of 750 Pa, the energy storage power at a 90 % charging increases from 32.2 W (FL = 0.75) to 48.7 W (FL = 1.37). A modification of FL shape parameter increased the power output by 34 %.

Thermal modeling of porous medium integrated in PCM and its application in passive thermal management of electric vehicle battery pack

The integration of a composite of porous medium with phase change material (PCM) offers significant advantages in thermal management systems, enhancing heat transfer efficiency and addressing various thermal regulation challenges. This approach utilizes the PCM's latent heat absorption and the enhanced thermal conductivity provided by the porous medium, resulting in optimized system performance. Its applicability spans across electronics cooling and building insulation systems. However, predicting the thermal behavior of this composite material is challenging, necessitating computational tools to anticipate its response under different conditions and evaluate its influence on cooling strategies. The objective of this study is to create a computational tool specifically tailored to evaluate constitutive parameters of this composite material, thereby providing a comprehensive description of its thermal behavior. To achieve this goal, the multiscale homogenization principle is employed to assess the composite's effective thermophysical material properties using the representative volume element approach. The repeating unit cell of the aluminum lattice is incorporated into the PCM to define a representative volume element. The finite element method (FEM) is utilized to solve the three-dimensional homogenization problem, yielding an orthotropic effective thermal conductivity due to the inherent symmetry of the repeating material cell. Moreover, the study leverages the apparent heat capacity method to effectively manage the phase transitions within the PCM domain, utilizing smooth and temperature-dependent functions to accurately describe the thermophysical properties of the PCM. Integrating the composite into battery pack thermal management, this study thoroughly examines thermal dynamics by comparing outcomes with and without PCM integration. The transient thermal problem is accurately tackled using the FEM, employing the evaluated effective constitutive parameters of the homogenized composite to minimize computational effort. The results indicate a notable decline in the highest temperatures of the battery pack, leading to a reduction of about 14 °C at the specific moment when the phase change material fully transitions into its liquid form. The obtained results emphasize the effectiveness and practical feasibility of the proposed thermal management strategy. The modeling approach presented provides a robust tool with significant efficiency in reducing computational time for analyzing the thermal behavior of large models, as the utilization of the homogenization technique notably decreases the computational time.

Design and optimization of metal hydride reactor with phase change material using fin factor for hydrogen storage

The solid-state hydrogen storage in metal hydride (MH) is safer and energy efficient than the gaseous and liquid storage methods. The absorption of hydrogen in MH is highly exothermic. Hence, a good heat management system is required to increase the charging rate. The phase change material (PCM) can be integrated into the reactor to reuse the absorption heat for hydrogen desorption. The present numerical study models the concentric cylindrical reactor with magnesium (Mg) as MH surrounded by sodium nitrate (NaNO3) as PCM using COMSOL Multiphysics v6.1. The effect of buoyancy inside the PCM domain is investigated. An iterative approach is used to determine the required amount of PCM. Copper fins are added inside both MH and PCM. The effect of the number of fins, corresponding fin thickness and pitch on hydrogen absorption are determined to optimize the MH reactor. The outcomes reveal that the hydrogen absorption rate increases with fin numbers. The reactor with 10 and 30 fins takes 86.5 and 97.3 % less time than without fins for 90 % hydrogen absorption, respectively. The novel approach is proposed to estimate the fin efficiency (ηf) using temperature profiles of MH and fin during prevailing unsteady heat and mass transfer. The fin factor (Ff) is presented using the ηf and mass of MH. The performance evaluation criterion (PEC) is discussed based on hydrogen absorption relative to the system's weight. Further, the effect of operating parameters like hydrogen supply pressure and the initial temperature is studied on the reactor performance.

Enhancing thermal performance and optimization strategies of PCM-integrated slab-finned two-fluid heat exchangers for sustainable thermal management

This research investigates the influence of phase change material (PCM) distribution, fin density, and PCM type on the thermal performance of a slab-finned cross-flow PCM heat exchanger (HEX). The aim is to develop a highly efficient PCM-HEX system for enhanced thermal intermittency management. Computational fluid dynamics (CFD) simulations are employed to analyze the dynamic behavior of the HEX. Three PCM configurations, 15 variations in fin densities, and three paraffin-based PCMs with distinct melting temperatures are considered. The results reveal that the Type II configuration enhances heating time at high set point temperatures (SPTs), while the Type I configuration extends heating time at low SPTs. Increasing the air mass flow rate (AMFR) reduces the overall discharged thermal energy by 18–19 % for Type II and III configurations and by 10 % for the Type I configuration, indicating the lower sensitivity of Type I to AMFR variations. It is also shown that decreasing the PCM domain's fin density extends the heating time at low SPTs. Additionally, using a PCM with a higher melting temperature enhances the heating time at high SPTs and increases latent energy discharge power. Tetracosane demonstrates the highest efficiency at 54.9 % and maximum total discharged energy reaching 112.4 kJ. The findings of this study have significant implications for the development of optimized PCM heat exchangers in various applications, enabling more efficient and impactful thermal management.

Development of a Numerical Simulation Methodology for PCM-Air Heat Exchangers Used in Decentralised Façade Ventilation Units

This paper presents the development of a methodology for using simulation to test decentralised façade ventilation systems with PCM exchangers and its validation with experimental data. Two approaches were compared to simulate the operation of an exchanger filled with phase-change material. In Method A, the geometry consisted of an air domain and a phase-change material domain, located in the cylinders of the exchanger. In this method, the phase transition was not modelled, but the specific heat was made temperature-dependent, wherein within the limits of the melting point, the specific heat is increased to a level that mimics the amount of latent heat from melting and solidification of the phase-change material. In Method B, the geometry consisted only of the air domain, and the temperature was set on the cylinder wall surfaces at each time step using UDFs. When comparing the methods, the temperature difference at the individual measuring points was no greater than 1 K and the resulting exchanger efficiencies did not differ by more than 5%. It was noted that when the phase-change material was modelled in the software with Method A, the results provided better representation of the values obtained in the experiment. Validation of the models was carried out by comparing the experimental results from the real tests with the simulation results of methods A and B. It demonstrated that both models correctly reflected the operation of the exchanger, and that the efficiency results achieved did not differ by more than 6% compared to the experiment. A comparison of supply temperatures and exchanger efficiencies with numerical simulations using two methods is presented. Visual comparison of the temperature distribution in the flowing air and the temperature distribution on the cylinder walls is also presented. This article adds to existing scientific knowledge of computer simulation of exchangers used in façade ventilation units with phase-change material.

Wet spinning of strong cellulosic fibres with incorporation of phase change material capsules stabilized by cellulose nanocrystals

Incorporating a phase change material (PCM) into fibres allows the fabrication of smart textiles with thermo-regulating properties. Previously, such fibres have been made from thermoplastic polymers, usually petroleum-based and non-biodegradable, or from regenerated cellulose, such as viscose. Herein, strong fibres are developed from aqueous dispersions of nano-cellulose and dispersed microspheres with phase changing characteristics using a wet spinning technique employing a pH shift approach. Good distribution of the microspheres and proper compatibility with the cellulosic matrix was demonstrated by formulating the wax as a Pickering emulsion using cellulose nanocrystals (CNC) as stabilizing particles. The wax was subsequently incorporated into a dispersion of cellulose nanofibrils, the latter being responsible for the mechanical strength of the spun fibres. It was possible to produce fibres highly loaded with the microspheres (40 wt%) with a tenacity of 13 cN tex−1 (135 MPa). The fibres possessed good thermo-regulating features by absorbing and releasing heat without undergoing structural changes, while maintaining the PCM domain sizes intact. Finally, good washing fastness and PCM leak resistance were demonstrated, making the fibres suitable for thermo-regulative applications. Continuous fabrication of bio-based fibres with entrapped PCMs may find applications as reinforcements in composites or hybrid filaments.

Enhancement of the part-load thermal charging performance of a latent heat thermal energy storage unit with variable length fins at effective locations

Rapid thermal charging of the latent heat thermal energy storage unit (LHTESU) based on phase change material (PCM) is restricted by the material's low thermal conductivity. The numerical investigation for the thermal charging process of LHTESU considering a rectangular enclosure under the high-temperature gradient is presented. Constant and variable length fins with different locations are considered inside the enclosure with one vertical sidewall at a constant temperature. For various part-load thermal charging operations, a two-dimensional transient model with enthalpy-porosity technique is employed with natural convection current to evaluate the thermal charging rate and melting characteristics. The simulation outcomes manifest that convective heat transfer significantly impacts PCM melting in the case of variable length fins. Uniform distribution of Variable length fins with the most extended fin near the base of the container has 20% superior thermal charging performance than of constant length in full load thermal charging operations. However, in half-load thermal charging operations, constant-length fins with uniform distribution in the enclosure reduce the maximum thermal charging time and the average temperature of the PCM domain. Further, the result indicates that Cases VF-2 (most extended fins placed significantly close to the bottom and remaining fins inserted with equal gap) and VF-3 (fins insertion only in the lower half of the container) minimized the sensible heating of liquid PCM by directing the heat towards solid PCM. Case VF-3 demonstrated the most robust thermal charging performance by taking the least melting time in all cases for a 90% thermal charging of the system.

Evaluation of Melting Mechanism and Natural Convection Effect in a Triplex Tube Heat Storage System with a Novel Fin Arrangement

In this research, a numerical analysis is accomplished aiming to investigate the effects of adding a new design fins arrangement to a vertical triplex tube latent heat storage system during the melting mechanism and evaluate the natural convection effect using Ansys Fluent software. In the triplex tube, phase change material (PCM) is included in the middle tube, while the heat transfer fluid (HTF) flows through the interior and exterior pipes. The proposed fins are triangular fins attached to the pipe inside the PCM domain in two different ways: (1) the base of the triangular fins is connected to the pipe, (2) the tip of the triangular fins is attached to the pipe and the base part is directed to the PCM domain. The height of the fins is calculated to have a volume equal to that of the uniform rectangular fins. Three different cases are considered as the final evaluation toward the best case as follows: (1) the uniform fin case (case 3), (2) the reverse triangular fin case with a constant base (case 12), (3) the reverse triangular fin case with a constant height (case 13). The numerical results show that the total melting times for cases 3 and 12 increase by 4.0 and 10.1%, respectively, compared with that for case 13. Since the PCM at the bottom of the heat storage unit melts slower due to the natural convection effect, a flat fin is added to the bottom of the heat storage unit for the best case compared with the uniform fin cases. Furthermore, the heat storage rates for cases 3 and 12 are reduced by 4.5 and 8.5%, respectively, compared with that for case 13, which is selected as the best case due to having the lowest melting time (1978s) and the highest heat storage rate (81.5 W). The general outcome of this research reveals that utilizing the tringle fins enhances the thermal performance and the phase change rate.

Effect of a rotating cylinder on convective flow, heat and entropy production of a 3D wavy enclosure filled by a phase change material

• Thermal energy storage is studied in a cubic cavity having phase change materials. • A rotating cylinder is added for mixed convection heat transfer. • Mixed convection is better than the natural one for thermal storage units. • High angular speed in the clockwise direction improves the melting process. • A wavy wall with one undulation is sufficient for good performance. In this manuscript, phase change material (PCM), as a thermal energy storage medium, is considered within a 3D wavy cubic enclosure to investigate the effect of free and mixed convection heat transfer on the PCM melting process. Rotating cylinders also are located in the middle of the enclosure to study the effect of their angular velocity in different conditions. Governing equations are solved by Galerkin Finite Element Method (GFEM) and were confirmed by previous studies. As main outcomes, results with enhanced angular velocity, the average temperature, and entropy generation were significantly decreased. Results showed that as the melting process is helpful for thermal energy storage systems, it is recommended by this study to have a rotating cylinder inside the PCM domain and the undulation number of the hot surfaces not to exceed one. It was shown that the cylinder rotation of −5 rad/s enhances the melting process speed by about 88% compared to the stationary cylinder, and about 186% of melting enhancement can be obtained for the undulation number of 1 instead of 4.

Analysis of Phase Change Material used as Thermal Energy Storage Unit in Catalytic Converter.

Phase change Material(PCM) is widely used to heat storage applications. In this study PCM is used in the catalytic converter application to improve the performance of catalytic converter by maintaining the temperature above the light off temperature. Catalytic converter is inefficient at lower temperature or below the light off temperature the conversion efficiency is very low and practically it is zero. Using PCM conversion efficiency of catalytic converter is increased. PCM is placed above the substrate to absorb the heat from the exhaust gases which are leaving to the atmosphere in order to maintain the substrate temperature above the light off temperature. When the temperature is high at substrate then conversion of pollutants is better. PCM Store the heat by changing the phase from solid to liquid and return the heat to substrate by partial solidification. In this paper, performance of PCM (Mg70Zn24.9Al5.1) which is a eutectic alloy used for high temperature applications was investigated at various loading conditions by doing the simulation on catalytic converter for melting and solidification of PCM and validate the results with experimental work. The melting of PCM domain is simulated using ANSYS fluent 2019 R3 software. The assumptions used for the numerical study, methodology of the work and specification of software is also discussed in this paper. The contours of melting fraction of PCM at regular interval for different loading conditions (i.e. 0%, 50%, and 100% load) are represented for total melting period of the PCM.

Discharge Enhancement in a Triple-Pipe Heat Exchanger Filled with Phase Change Material.

This study aims to study the discharging process to verify the influence of geometry modifications and heat transfer flow (HTF) patterns on the performance of a vertical triplex-tube latent heat container. The phase change material (PCM) is included in the middle tube, where the geometry is modified using single or multi-internal frustum tubes instead of straight tubes to enhance the discharging rate. The effects of the HTF flow direction, which is considered by the gravity and opposite-gravity directions, are also examined in four different cases. For the optimal geometry, three scenarios are proposed, i.e., employing a frustum tube for the middle tube, for the inner tube, and at last for both the inner and middle tubes. The effects of various gap widths in the modified geometries are investigated. The results show the advantages of using frustum tubes in increasing the discharging rate and reducing the solidification time compared with that of the straight tube unit due to the higher natural convection effect by proper utilization of frustum tubes. The study of the HTF pattern shows that where the HTF direction in both the inner and outer tubes are in the gravity direction, the maximum discharging rate can be achieved. For the best configuration, the discharge time is reduced negligibly compared with that for the system with straight tubes which depends on the dimensions of the PCM domain.

A Summary Review on Experimental Studies for PCM Building Applications: Towards Advanced Modular Prototype

The use of phase change material (PCM) as a thermal energy storage system integrated in new buildings, and as retrofits in old buildings, proved its merit as promising renewable energy source. Heating and cooling building applications of PCM have been studied by plenty of scientists, globally, on the basis of numerical and experimental analysis. The performed experiments have mainly focused on one application—active or passive—using permanent prototype design for a certain duration and weather condition. The current study is a new review that focuses on two complementary aspects: (1) Reviewing latest studies in PCM domain and assessing the thermal performance of implemented prototypes within the conducted PCM experimental studies, namely, the effect of the design on the number of acceptable variables and possible PCM applications; and (2) suggesting a new, advanced, flexible, and modular prototype designed to enable several applications of PCM to be adapted and combined within the model. It was implied that the new design allows different configurations that are lacking in the literature and serves for future PCM building applications of thermal analysis towards PCM integration optimization, as an attempt for transforming residential compartments into net zero energy buildings. The designed prototype overcomes the deficiencies found in previous reviewed experimental facilities.

Thermal Analysis and Parametric Investigation of Phase Change Material-Air Cooled Lithium Ion Battery Pack

Abstract A parametric analysis has been conducted for the phase change material (PCM)-air cooled battery pack. The system is composed of 26650 lithium-ion LiFePO4 batteries enclosed by PCM. A one-dimensional thermal model for the PCM domain is developed using the enthalpy method. The finite volume method is employed to solve the energy equation for both cell and PCM domain. The developed computational algorithm has been validated as a result of the simulations for the same conditions with the literature. The discharge process of the batteries has been investigated for 2C, 3C, and 5C rates. Thermal analyses have been performed for passive (natural convection) and active cooling (forced convection). It is aimed to keep the temperature of the battery cell under critical levels. A parametric investigation for crucial parameters like PCM layer thickness, the thermal conductivity of the PCM, arrangement of the batteries has been performed. Simulations have been conducted for the constant air velocity and the pumping power. Thanks to the constant pumping power analysis, thermally best-performing configuration have been sought by eliminating the hydrodynamic effect.

Performance evaluation of melting/solidification mechanism in a variable wave-length wavy channel double-tube latent heat storage system

Abstract Thermal energy storage and recovery in a double-pipe latent heat storage (LHS) system with variable wave-length wavy channels were examined. The presence of wavy channels with variable wave-length makes it possible for the desired aggregation of the solid waves inside the Phase Change Material (PCM) domain. The PCM and the moving water are placed in the outer and inner sides, respectively, in the vertical double tube heat storage unit. Different configurations of variable sinusoidal wave-length were studied compared with fixed wave-length as well as straight channel unit. The wave-amplitude, temperature and Reynolds number of water were also analysed. The significant effects of channel waviness with variable wave-length are presented results in higher heat transfer inside and to/from the PCM domain. Increasing the water temperature and Reynolds number, as well as wave-amplitude, result in a shorter melting/solidification time. Based on the results of the selected case, the time of melting/solidification reduces by almost 70.8/42.8%, respectively, compared with straight wall case. Furthermore, the heat storage/recovery rate is 8.3/3.0 W for melting/solidification, respectively, for the selected configuration which is equal to 2.4/1.7 W for the straight channel case.

Reconfigurable infrared hyperbolic metasurfaces using phase change materials

Metasurfaces control light propagation at the nanoscale for applications in both free-space and surface-confined geometries. However, dynamically changing the properties of metasurfaces can be a major challenge. Here we demonstrate a reconfigurable hyperbolic metasurface comprised of a heterostructure of isotopically enriched hexagonal boron nitride (hBN) in direct contact with the phase-change material (PCM) single-crystal vanadium dioxide (VO2). Metallic and dielectric domains in VO2 provide spatially localized changes in the local dielectric environment, enabling launching, reflection, and transmission of hyperbolic phonon polaritons (HPhPs) at the PCM domain boundaries, and tuning the wavelength of HPhPs propagating in hBN over these domains by a factor of 1.6. We show that this system supports in-plane HPhP refraction, thus providing a prototype for a class of planar refractive optics. This approach offers reconfigurable control of in-plane HPhP propagation and exemplifies a generalizable framework based on combining hyperbolic media and PCMs to design optical functionality.

On a theory for system-level cooling of close electronics enclosures by PCM-filled heat sinks—Exact solution and second law performance limits

This paper takes a fundamental approach on the simple, however widespread, application of closed electronics enclosures that are passively cooled by internally mounted heat sinks filled with phase change material (PCM) and exposed to periodic temperature environments. The regime of interest is that of periodic steady state (PSS). A model that allows for an analytical solution of the Stefan-like problem in the finite PCM domain and of the energy balance coupling of the closed enclosure is devised in dimensionless terms by using a lumped formulation for the enclosure and for the PCM domain, the later being known as zero-phase modeling (Naaktgeboren, 2007). The model is one that allows for internally reversible heat transfers in the PCM and in the enclosure domains, while retaining the finiteness (irreversibilities) of the heat interactions between the environment, the enclosure, and the PCM-filled heat sinks, as well as the heat sources irreversibilities, so as to allow for meaningful outcomes. Results include melting and freezing interface location history—conversely, melting and freezing times—and a design condition for perpetual occurence of phase change; hence, latent heat interactions. Moreover, a figure of merit for passive temperature regulation of real (irreversible) electronics enclosures is proposed as a temperature attenuation effectiveness. The limit imposed by the second law of thermodynamics on the temperature attenuation effectiveness is analytically derived and shown to depend on only two (out of the four) dimensionless parameters of the model. The original expression for the enclosure temperature attenuation effectiveness in the reversible limit, obtained herein, is of theoretical and practical significance.

Numerical modelling of phase-change material used for PV panels cooling

Passive cooling of a PV solar panel using phase-change material (PCM) may play an important role in increasing efficiency of PV cells. Because it does not need a maintenance and does not release greenhouses gases, PCM seems to be a good way to decrease the among of overheating of PV cell. The aims of this paper describes a detailed multiphysical issue in order to understand the effect of PCM (RT25) in keeping PV cell temperature close to ambient. The study is focused on modeling the heat and mass transfer in a PCM domain by modifying the buoyancy term in momentum equation. Due to a phase-change and free convection, transient incompressible flow is taken into account to explain the dynamic variations of the velocity profile and viscosity distribution. With standard condition of irradiation and heat flux on both sides of the PV panel, a melt front has been tracked by the energy equation, which gives a good argument for the temperature evolution during phase-change.

Numerical analysis of metal hydride tank with phase change material

This study discusses the challenges of using heat and hydrogen storage system consisting of a metal hydride tank (MHT) equipped with a phase change material (PCM). A mathematical model was developed to study the bi-dimensional coupled heat and mass transfer inside the hydride bed as well as the PCM domain. The numerical computations have been conducted for two configurations (cylindrical and spherical tanks). Compared to cylindrical tank, the spherical one has the highest MHT-PCM system performance. Additionally, the results have shown that the PCM amount should be carefully optimized. Moreover, the results concerning the impact of MHT-PCM thermal insulation were also discussed.

Finite Difference Approaches for One-Dimension Solid-Liquid Phase Change in Plane and Cylindrical Geometries

Two finite difference methods are presented and discussed, that are applied to the phase change process (freezing) occurring in plane and cylindrical geometries. The first one involves the use of a variable space step grid for each of the time steps of the procedure. An original technique based on Lagrange polynomials is used to determine the actual nodal temperature corresponding to the old temperature field. The second technique uses a fixed grid attached to the phase change material, and the finite difference equations of the nodes neighboring the solid-liquid interface are derived in a special form that involves fractions of the space step. Both techniques are applied to a plane and a cylindrical metallic wall respectively that represents the boundary of the phase change material domain. The numerical results obtained by running the computer codes that we have written for the two techniques show an excellent agreement, the values of the interface rate and of the solid phase fraction at every time step being practically the same.