Solid-liquid Phase Change Process Research Articles

Data-driven multi-fidelity topology design of fin structures for latent heat thermal energy storage

This work develops a data-driven multi-fidelity topology design (MFTD) method for designing fins in a latent heat thermal energy storage tube. The high-fidelity simulation resolves the actual solid-liquid phase change process using the enthalpy method, while the low-fidelity topology optimization (TO) simply considers the natural convection with Darcy flow. The above MFTD method is integrated into the framework of evolutional algorithm, and the variational autoencoder is introduced to generate new offspring. Fins for accelerating the melting and solidification processes at different Grashof number (Gr) are designed. It is found that when the fin volume fraction is low, the melt designs exhibit strong heterogeneity due to the strong convection, while the solidification designs are almost isotropic. Along with the increase of the fin volume fraction, the fins are first getting longer, then having more branches or sub-branches and finally becoming thicker. The superiority of the present data-driven MFTD method to the gradient-based direct TO method for solving optimization problems with strong multimodality has been demonstrated in this work. Results find that compared with the designs from direct TO, the MFTD melt design can further reduce the melting time by at least 27 % and 20 % at Gr = 3.3 × 103 and Gr = 3.3 × 104 respectively, and the MFTD solidification design can further shorten the solidification time by at least 9 %.

Numerical simulation and analysis on melting characteristics of a solid-liquid phase change process based on hot air riveting

To improve welding efficiency, a hot air riveting technology applicable to simultaneous welding at multiple stations is proposed, with the challenge lying in clarifying the melting state of the weldment. A numerical simulation method is proposed to investigate the melting state of the tag, using the Audi airbag tag as an example. The effects of various process parameters, including the exhaust duct distance, hot air temperature, hot air velocity, and the diameter ratio β, on the melting state of the tag are discussed. The melting mass, internal contour plots of the weldment and the melting rates are compared among the different parameter settings. The results indicate that under a heating temperature of 240 °C, the increase in hot air velocity has the most significant promotional effect on the melting of the weldment. Moreover, regardless of the velocity level, an increase in hot air temperature consistently enhances the melting of the weldment. Concurrently, an increase in the exhaust duct distance has an adverse impact on melting, yet this effect diminishes as the heating temperature rises. Finally, it is observed that at lower temperatures (200 ℃), diameter ratio β = 2.0 is more conducive to melting, whereas at higher heating temperatures (240, 280 ℃), β = 2.5 is more favorable for the melting of the weldment. This method effectively grasps the melting behavior of the weldment, enabling the selection of appropriate process parameters for hot air welding in actual production based on specific requirements.

Probing the melting dynamics in a phase change Rayleigh–Bénard system under low gravity conditions

The present work aims to investigate dynamic characteristics of Rayleigh–Bénard convection during the solid–liquid phase change process under the influence of variable low-gravity conditions. Low-gravity conditions are crucial to gain physical insights into the complex convection dynamics relevant in terrestrial and space environments that feature diverse gravitational fields. The melting dynamics of a paraffin-based phase change material with Prandtl number Pr ≈ 71 in a square rigid walled enclosure is analyzed by subjecting it to a fixed temperature difference resulting in a Stefan number Ste ≈ 0.33. The enthalpy porosity method is employed to simulate the solid-liquid phase change process in Rayleigh number range 105<Ra <107 to take wide range of gravitational acceleration (0.0g, 0.1g, 0.2g, 0.4g, 0.6g, 0.8g, and g) into account. The simulation results allow detailed insights on the buoyancy-driven convective flow phenomena in a phase-change Rayleigh–Bénard system. Various characteristic flow regimes, the criteria for the onset of convective instabilities, and scaling analysis are presented under varied gravitational acceleration. The findings reveal that the critical Rayleigh number (Racr) for the onset of convection is found to vary between 1351.5 and 1810.5 under the gravity range investigated in contrast to the Racr ≈ 1707.7 for classical Rayleigh-Bénard system under the standard gravity. Furthermore, the scale analysis based on the numerical results shows that the relationship between effective Nusselt number (Nue) and effective Rayleigh number (Rae) follows a power law behavior Nue = 0.27Rae0.25 under each gravity condition, similar to the classical Rayleigh–Bénard system.

On the numerical simulation of a phase change material melting inside periodic structures: from validation to optimization

Nowadays, numerical models are considered powerful design tools, which are largely used in several engineering applications. When applied to heat transfer applications, they have already been shown to be reliable, especially in single phase systems. When considering two-phase heat transfer, and in particular solid-liquid phase change processes, the numerical tools must be carefully handled. Thus, this paper follows the critical literature on the application of numerical methods to simulate and optimize latent thermal energy storages to show how, in most cases, the common geometrical and numerical approximations should not be applied because they might lead to misleading solutions. Starting from reliable experimental results collected during melting process of a paraffin wax inside 3D periodic structures, different simulation approaches are proposed, and their advantages and disadvantages are discussed. The results show that, when dealing with certain complex 3D structures, 2D approximations cannot reliably capture the phase-change phenomenon. The validated tool also allowed to identify the optimum pore size to maximize the solid-liquid phase change. This work can be considered as a reference for future numerical studies on the solid-liquid process inside 3D structures.

Oscillatory instability of magneto-convection during the melting of non-Newtonian ferromagnetic nano-enhanced phase change materials at low Rayleigh number

This work complements mechanism of the oscillatory instability of magneto-convection in the process of melting heat transfer controlled by magnetic field at low Rayleigh number (Ra), aiming to provide a theoretical basis for improving the stability of energy storage system and melting manufacturing process. A latent heat storage cavity unit exposed in uniform magnetic field is designed to reveal the magnetic-controlled heat transfer in solid–liquid phase change process. The volume average method is used to describe porous media composite nano-enhanced phase change materials in latent heat unit. Special attentions are paid to the key parameters of Magnetic number (Mn) and Ra, and coupling flow heat transfer mechanism of magnetic force and natural convection effect is numerically studied. The evolution stages of different flow patterns are divided according to the Kelvin force, vorticity, velocity, flow field and isotherm distributions of characteristic points. Main results show that the magnetic field-modulated phase change process at low Ra can be divided into three stages, of which the second stage is characterized by periodic oscillations. Increasing Mn at fixed Ra accelerates the second stage of oscillatory convection heat transfer coming earlier and promotes melting. When Mn increase to 5 × 106, the full melting time is reduced to the greatest extent, resulting in 11.6 % reduction in heat storage but 17.4 % increase in heat storage efficiency. Three mechanisms of magnetic forced convection coupled with natural convection are found during the increase of Ra: synergistic (Ra < 2 × 103), antagonistic (2 × 103≤ Ra < 1 × 104), and natural convection-dominated (Ra = 1 × 104). Finally, the mode distribution map of Ra-Mn regulation is obtained, in which the unstable transformation mechanism of steady-state, periodic oscillation and chaotic oscillation heat transfer in the melting process under the control of magnetic field is described.

Sensitivity of an electrical impedance-based sensor for the liquid fraction estimation during melting and solidification inside a vertical rectangular enclosure

Monitoring the liquid fraction in latent thermal energy storages (LTESs) can enable the implementation of smart control strategies for improved performance and increased utilization of renewable energy sources. However, measuring the liquid fraction is challenging because solid-liquid phase change processes occur at nearly constant temperature. The present study explores an electrical impedance-based sensing technique that could become a non-intrusive and accurate alternative to determine the liquid fraction. The study examines the melting and solidification of a phase change material (PCM) inside a vertical rectangular enclosure with an isothermal wall. Two sets of electrodes are located on each of the side walls of the enclosure. Initially, numerical simulations of melting and solidification are performed to generate physically meaningful solid and liquid phase distributions. Then, these phase distributions are used as input for electrical simulations to estimate the response to changes in the liquid fraction of the electrical impedance between electrode pairs in in-line, front-facing and crosswise configurations. Also, the effect of the contrast ratios between the electrical conductivity of the solid and liquid phase on the sensitivity is assessed. The front-facing electrodes are found to have the best performance across a large range of conductivity ratios. The in-line electrodes perform the lowest because the sensitivity drastically decreases as a layer of the more conductive phase starts forming on the wall where the electrodes are located. An improvement in the performance of in-line electrodes is observed when the conductivity ratio is decreased.

Numerical Study of a Latent Heat Storage System’s Performance as a Function of the Phase Change Material’s Thermal Conductivity

The thermal conductivities of most commonly used phase change materials (PCMs) are typically fairly low (in the range of 0.2 to 0.4 W/m·K) and are an important consideration when designing latent heat energy storage systems (LHESSs). Because of that, material scientists have been asking the following question: “by how much does the thermal conductivity of a PCM needs to be increased to positively impact the design and performance of a LHESS?” The answer to this question is not straightforward as the performance of a LHESS depends on the PCM’s thermal conductivity, other PCM thermophysical properties, the type of heat exchange system geometry used, the mode of operation, and the targeted power/energy storage of the LHESS. This paper presents work related to this question through a numerical study based on a simplified 2D model of an experimental setup studied previously in the authors’ laboratory. A model created in COMSOL Multiphysics, based on conduction and accounting for the solid-liquid phase change process, was initially validated against experimental results and then used to study the impact of the PCM’s thermal conductivity (dodecanoic acid) on the discharging power of the LHESS. The results show that even increasing the thermal conductivity of the PCM by a factor of 50 only leads to a maximum instantaneous power increase by a factor of 2 or 3 depending on the LHESS configurations.

Experimental study of single-phase change material thermal diode based on calcium chloride hexahydrate

Phase change material thermal diodes designed on the basis of different heat transfer forms and coefficients caused by different phase transition degrees in opposite heat transfer directions are considered as potential thermal management devices. However, the use of a variety of materials or only relying on numerical simulation research makes its structure complex or idealized, which reduces the possibility of practical application. Therefore, in this work, a simple thermal diode structure containing only CaCl&lt;sub&gt;2&lt;/sub&gt;·6H&lt;sub&gt;2&lt;/sub&gt;O single-phase variable material is proposed in combination with changes in heat transfer form and heat transfer coefficient in solid-liquid phase change and natural convection process. The corresponding device is prepared, and a steady-state heat flux test system is set up for experimental study, the measured results are close to those recorded in the literature with good accuracy. The influence of the temperature difference between hot end and cold end and the direction of positive heat transfer and negative heat transfer on the thermal rectification effect of the thermal diode are studied experimentally. The results show that the heat flux of the thermal diode decreases with the decrease of the difference in temperature between the cold source and hot source, and the thermal rectification ratio reaches to 1.58 when the forward and reverse along the antigravity direction and gravity direction, respectively. The optimal cold source temperature range is 20–25 ℃, which is close to room temperature. The proposed phase change material thermal diode structure has a certain application potential in energy saving and thermal management of building.

Numerical investigation on rheological and thermal performances of microencapsulated phase change material suspension (MPCMS) in microchannel

Rheological and thermal performances of microencapsulated phase change material suspension (MPCMS) in microchannel are investigated with different mass fractions, Reynolds numbers and particle size distributions. The deviations of the two-phase model and the single-phase model from experiments are also examined and compared. The solid-liquid phase change process of MPCMS is described by the effective heat capacity method. The results show that as the mass fraction Cm increases up to 30%, the MPCMS flow starts to transform from the Newtonian fluid to pseudoplastic behavior (shear rate 0–110 s−1), and the resultant performance evaluation factor (PEF) increases from 1 to 1.27. As the Reynolds number is raised from 96 to 960 (Cm = 15%), the viscosity remains nearly constant (shear rate 100–1000 s−1) flowing as a Newtonian fluid, and the PEF decreases from 1.24 to 1.14. With the particle size increasing (dp = 0.1–10 μm), non-Newtonian characteristics of the suspension become more obvious (shear rate 9300–15,000 s−1), and the PEFs are all 1.15. The average deviation of the single-phase model is 12.3% compared with the experimental data, while it is only 3.65% for the two-phase model. The results provide a reference for the optimization of MPCMS application in microchannel from a rheological perspective.

Role of dielectric force and solid extraction in electrohydrodynamic flow assisted melting

A numerical study of non-isothermal solid-liquid phase change process in a differentially heated square cavity aided with an electrohydrodynamic (EHD) flow is reported. Melting of a phase change material (PCM) subjected to an electric field with different charge injection strengths is studied. The study aims to numerically demonstrate the solid extraction phenomenon and its role in accelerating the melting process. The EHD flow modifies the flow structure and notably alters the solid–liquid interface morphology. The dielectric force extracts the semi-solid PCM from the melt interface into the liquid bulk with high electric field intensity. The dielectric force causes melting-rate enhancement during the initial stages of melting. While, the later stages of melting are influenced by the combined action of Coulomb and dielectric forces. The role of the Coulomb force is weaker in the weaker charge-injection regimes. Higher electric potential and stronger charge injection generally lead to increased melting rates. Up to 62.12 % decrease in total time taken for melting is achieved within the parameters considered herein.

Passive thermal management strategy for cooling multiple portable electronic components: Hybrid nanoparticles enhanced phase change materials as an innovative solution

Modern electronics technologies have given great interest to phase change materials (PCMs). The present work is in line with this philosophy and deals with the effectiveness of a PCM-based heat sink and nanoparticles in insertion for thermal management of several electronic components. Present numerical study explores the solid-liquid phase change process of n-eicosane in an enclosure considered for cooling of electronics in the presence of one, two, and three protruding electronic components. To improve thermal management capability, four types of nanoparticles, namely, silver (Ag), magnesium oxide (MgO), multi-walled carbon nanotube (MWCNT), and silicon dioxide (SiO2), are inserted into the n-eicosane by single and hybrid ways at volume fractions ranging from 0 % to 4%, and by introducing a lateral fin playing the role of a motherboard. It should be noted that this study is interested in analysing the combined effects of the volume fraction of inserted nanoparticles ranging from 0 % to 4%, the type of inserted nanoparticles, and the number of electronic components installed at the heat sink on the overall heat transfer and flow structure of the fluid PCM. For this purpose, a mathematical model has been developed for the formulation of the governing equations of the conjugate natural convection. The enthalpy-porosity technique is applied for modelling the phase change process. Results reveal a significant relationship between the melting time and the operating temperature of the electronic component. A long phase change process is characterized by a high utilization of latent heat and subsequently the heat rejection becomes efficient. Hence, the longer melting times result in reduced operating temperatures. By insertion of SiO2-MWCNT hybrid nanoparticles, the melting time is increased by approximately 92 % compared to pure PCM, and the plateau temperature is mitigated by 11 °C by using one component in the enclosure. Furthermore, by increasing the number of electronic components, the flow structure, thermal field and melting front become more uniform. Thus, it can be recommended to use three electronic components with a lower heat generation rate instead of using one electronic component with three times higher heat dissipation in a PCM-based cooling system.

Effects of mushy-zone parameter on simulating melting and solidification phenomena inside a spherical capsule

The research on latent heat storage technology is beneficial for the large-scale popularization and application of energy storage technology. In order to solve the difficulties in the latent thermal energy storage (LTES) technology, numerical studies of the solid–liquid phase-change process of LTES units using the enthalpy-porosity method have become research hotspots. Among them, the importance of studying the mushy-zone parameter has been neglected. In this paper, a two-dimensional numerical model is created based on the enthalpy-porosity method to investigate the effects of different mushy-zone parameters within a wide range [104–108 kg/(m3·s)] on the melting and solidification processes of the spherical phase change material capsule. A comprehensive examination of the fluid flow and heat transfer characteristics during two phase-change processes is conducted. Meanwhile, the morphology of the solid–liquid phase boundary and the evolution of the mushy zone under different mushy-zone parameters are discussed in detail. It is worth mentioning that a new analytical perspective is innovated by proposing the “eccentricity phenomenon,” and the eccentricity law is further explored. The results show that the influence mechanisms of the mushy-zone parameters on the melting and solidification processes differ greatly. This paper emphasizes the significance of exploring the mushy zone and provides adequate guidance for future simulation studies to determine the mushy-zone parameter.

Numerical analysis on heat transfer and melting characteristics of a solid-liquid phase change process in a rectangular cavity inserted with bifurcated fractal fins

To improve the thermal transmission performance of latent heat thermal energy storage systems, bifurcated fractal fins inspired by leaf venation structures in nature are inserted into a typical vertical rectangular cavity. Melting thermal behaviors of lauric acid in the models with bifurcated fractal fins having different fin location ratios εd, fin length ratios εl, and fin numbers N are numerically studied. Increasing εd, εl, and N yields the enhancement of liquid fractions, and a maximum melting time reduction of 63.6% is achieved by the case with εl = 0.75 and N = 3. Raising εd is conducive to melting convection flows during the natural convection regime. Whereas, the effect of εl is primarily driven through thermal conduction area enhancement. In addition, the results imply that as εl increases, the impact of increasing N leads to a shift in flow intensity from enhancement to suppression. As against the flat fin, the bifurcated fractal fin has a superior thermal transmission efficiency thanks to the larger heat transfer surface area, and the benefit is more pronounced as the branching level changes from k = 2 to k = 3.

3D hierarchical porous expanded perlite-based composite phase-change material with superior latent heat storage capability for thermal management

The use of latent heat thermal energy storage (LHTES) technology is regarded as an effective strategy for smart heat management and building energy conservation. However, phase-change materials (PCMs), which are key components in LHTES systems, suffer from serious leakage in the solid-liquid phase-change process. In this work, 3D hierarchical porous expanded perlite (EPP)-based composite form-stable phase-change materials (FSPCMs) were successfully designed and constructed. The introduction of polyvinyl alcohol (PVA) was applied to regulate the porous framework of expanded perlite (EP) and endow the EPP with a superior ability to adsorb paraffin and inhibit its leakage. The final EPP-based composite FSPCM was obtained by impregnating paraffin into the EPP. This novel composite FSPCM exhibits excellent thermal properties and long-term cycling stability. The phase-change enthalpy of the composite FSPCM reaches up to 174.6 ± 2.20 J/g and remains at a high level even after 500 heating-cooling cycles. The mechanism by which EPP effectively inhibited paraffin leakage is attributed to the capillary action and surface tension of the hierarchical porous structure, and the electrostatic attraction between PVA and paraffin molecules. Most importantly, a novel panel fabricated by the optimal EPP-based composite FSPCM presents excellent thermal management performance and flame-retardant ability. The panel developed in this work shows great potential for building energy conservation.

A generalized thermoelastic Stefan problem with spatio-temporal nonlocal effect in picosecond pulse laser material processing

The Stefan conditions are suitable for describing the solid-liquid phase change processes with moving interface. However, the existing literature only focuses on the Stefan problem of heat conduction and does not involve the thermo-mechanical coupling effects. In this work, the generalized thermoelastic Stefan problem with spatio-temporal nonlocal effect is investigated. The solid-liquid phase change of silicon with picosecond pulse laser machining is depicted by the Stefan interface conditions. We find the solutions making use of Laplace transformation and Laplace numerical inverse transformation. The temperature distribution at the moment of surface melting is seen as the initial state of the second phase. The distributions of transient thermoelastic responses under different laser intensities, pulse widths, fractional order parameters, spatial nonlocal parameters and time are obtained and expressed graphically.

Investigation on Thermal Performance of a Novel Passive Phase Change Material-Based Fin Heat Exchanger

Abstract This work presents a numerical investigation of the thermal control performance of a phase change material (PCM) composite-filling fin heat exchanger under natural convection and transient heat flux shocks. First, the temperature control performance of the PCM-based fin heat exchanger and the fin heat exchanger without PCM is compared. Then, the influence of the PCM filling patterns, liquid phase change temperature, and the PCM filling volume fraction on the temperature control performance are studied. The results show that filling the PCM in fins could significantly improve the temperature control performance by absorbing heat during the solid–liquid phase change process. Compared with the fin heat exchangers without PCM, the temperature control performance of the designed PCM-based fin heat exchangers could be improved by up to 13%. PCM filling patterns influence the temperature control performance of fin heat exchangers to a certain extent, and the asymmetric filling pattern is better than the symmetric filling pattern. The results of different phase change temperatures of PCM show that, within a certain temperature range, the lower the liquid phase change temperature results in a better temperature control performance since more PCM would melt when suffering the heat flux shock. Besides, when the volume fraction of PCM is small, it also greatly influences the temperature control efficiency of the heat exchanger; however, when the volume fraction of PCM is larger than 75%, its influence could be neglected.

Enhanced thermal conductive lauric acid/g-C3N4/graphene composite phase change materials for efficient photo-thermal storage

Lauric acid (LA) shows much potential as one organic phase change material (PCM) for thermal energy storage, owing to its suitable melting point, relatively high thermal/chemical stability and latent heat. However, the LA-based thermal storage method invariably suffers from the big challenges of liquid leakage tendency and low thermal conductivity of single lauric acid, limiting immensely its practicality. Herein, one encapsulation and modifying strategy to fabricate high conductive and low liquid leakage composite phase change materials (CPCMs) for photo-thermal storage was proposed by constructing novel graphene doped LA/g-C3N4 CPCM. Firstly, LA is infiltrated into a novel two-dimensional porous matrix – the graphitic phase carbon nitride (g-C3N4) to prevent liquid leakage in the solid–liquid phase change process. Then it is further incorporated with a certain amount of graphite nanoplatelets to further enhance thermal conductivity. The encapsulation and modifying strategy enable the graphene doped LA/g-C3N4 to show excellent thermal storage performance for both heat and light energy, low liquid leakage, and high thermal stability. The hybrid LA/g-C3N4 with 5 wt% graphene (CPCM3) modification has a melting temperature of 45.88 °C and enthalpy of 159.19 J/g. The corresponding solidification temperature and enthalpy are 43.36 °C and 144.40 J/g, respectively. Its thermal conductivity at 50 °C is enhanced to 0.9338 W/(m·K) (one time higher than single LA), also superior to the state-of-the-art LA-based CPCMs. After 100 thermal cycles, the composite phase change material only suffers low mass loss and latent heat loss of phase change, which proves the good thermal reliability. Furthermore, TGA and DTG data indicate that CPCM3 can maintain good thermal stability in the normal operating temperature range. In the whole, the joint effect of the porous g-C3N4 matrix and graphene modification improve the thermal storage performance of LA through the improvement of liquid immobilization and thermal conductivity. This work provides a promising strategy for fabricating high conductive and low liquid-leakage CPCM toward enhanced photo-thermal storage.

Melting of phase change materials inside periodic cellular structures fabricated by additive manufacturing: Experimental results and numerical simulations

• The melting of paraffin waxes inside periodic cellular structures is studied. • The effects of heat flux, melting temperature, and cell size are discussed. • The simplified numerical model of the melting process matches the experimental data. • An analytical model previously developed for foams is applied. An experimental and numerical study of the solid–liquid phase change process of three paraffin waxes, having different characteristic melting temperatures (42, 55, and 64 °C) embedded in two different cellular periodic aluminium structures fabricated by additive manufacturing, thought of as passive heat sinks, is reported. The aluminium solid media are composed of repeating elementary cells derived from the body-centred cubic (BCC) model and have a porosity of 87%. The samples were tested in an upright position and laterally heated by applying three different heat fluxes (10, 15, and 20 kW m −2 ). The experimental results showed the effects of the heat flux, melting temperature, and size of the metal cells on the temperature of the heated surface. Numerical simulations were performed to validate a simplified model for the thermal analysis of the test modules using reduced domains. Owing to the characteristics of the experimental melting front, which is almost parallel to the heated side, suggesting a negligible effect of natural convection, the numerical simulations performed with ANSYS Fluent could be conducted on computational domains that represent only small repetitive portions of the test modules, thus allowing substantial savings in the computational time. This simplified method has been proven to yield results that are in good agreement with the experimental data. Based on the numerical results, when the metal structure is finer, the evolution is faster, and the time required to completely melt the phase change material (PCM) is shorter. This numerical model may be confidently used by thermal engineers to design PCM-based heat sinks for electronics cooling. Finally, an empirical model previously developed for paraffin embedded in metal foams was applied to the present paraffin-BCC composite structures.

Theoretical modeling of solid-liquid phase change in a phase change material protected by a multilayer Cartesian wall

Theoretical modeling of solid-liquid phase change processes is of much interest in energy storage and thermal management. While most theoretical phase change models assume that the phase change material (PCM) is in direct contact with the thermal source/sink, in most practical scenarios, the two are separated by a thick wall, which, in some cases, may comprise multiple heterogeneous layers. Accounting for thermal conduction through the multi-layer wall is important to ensure accuracy of the predicted phase change characteristics. This paper presents theoretical analysis of phase change in a system comprising a PCM and a multi-layer Cartesian wall using the eigenfunction expansion method and analysis of multi-layer thermal conduction. Thermal contact resistance between wall layers, and between the wall and PCM are accounted for. The predicted phase change front propagation is shown to agree well with past work for special case of a homogeneous wall, as well as with numerical simulations. Two distinct timescales in the solution, related to diffusion through the wall and phase change propagation in the PCM are identified. The impact of the imposed temperature, wall thermal diffusivity and thickness are presented in non-dimensional forms. Practical problems related to design of a PCM wall for energy storage are solved, showing two very different characteristics of stainless steel and polypropylene walls, as well as the impact of wall thickness on phase change propagation. The results presented here improve the fundamental understanding of phase change heat transfer processes, and are particularly relevant for relatively thick, thermally insulating walls over relatively short time periods, for which a resistance approximation for the wall is not accurate.

Pore scale simulation for melting of composite phase change materials considering interfacial thermal resistance

• Implicit-enthalpy-based LBM with interfacial thermal resistance is proposed. • Porous structure is reconstructed by randomly generation-growth method. • The effective thermal conductivity of composite PCMs is evaluated. • The effect of natural convection, porosity and interface on melting are analyzed. The convective melting process and thermal performance of phase change materials (PCMs) incorporating porous skeleton in the one-side-heated rectangular cavity are investigated numerically in this work. A pore-scale lattice Boltzmann method (LBM) with implicit scheme is developed to explore the solid–liquid phase change process. The interfacial thermal resistance between the skeleton and PCMs is considered by interfacial conditions treatment. The random porous microstructure is generated by quartet structure generation set (QSGS) which is used to compute effective thermal conductivity in LBM. The validations of the current model are employed by the two-phase series conduction model and previous numerical results. The effects of porous structure, skeleton material, and thermal interfacial conditions on heat transfer characteristics are systematically investigated. The computational results show that the melting rate and effective thermal conductivity increase with the reducing porosity and the high thermal conductivity of the skeleton material accelerate the melting process. In addition, the consideration of interactions in the LBM leads to a significant difference. When the thermal interfacial resistance is set to be 1 × 10 −4 m 2 W/K, the temperature drop is very large in two-phase conduction, the melting rate decreases remarkably in the phase change process. The present simulation is also suitable for optimizing the porous structure to prepare various composite PCM in the thermal energy storage field.