Solid-liquid Phase Change Process Research Articles

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.

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.

Development of temperature-responsive transmission switch film (TRTSF) using phase change material for self-adaptive radiative cooling

To overcome the problem of unable automatic turn on and off response to the ambient temperature of current static radiative cooling systems, we prepared a series of temperature-responsive transmission switch film (TRTSF) samples using n-octadecane as phase change material (PCM) and polydimethylsiloxane (PDMS) as carrier material. The phase change cycle permeability analysis showed that the TRTSF samples with PCM content above 30.0 w.t.% exhibit a serious leakage problem due to a large number of holes on surface. The TRTSF samples with 10.0–30.0 w.t.% PCM content were further analysed by Differential scanning calorimetry (DSC) and Thermogravimetry (TG), and compared with the theoretical PCM contents, which verified the reliability of the curing results of PCM in TRTSF from various aspects. The ultraviolet–visible light-near-infrared (UV–VIS-NIR) and mid-infrared (MIR) transmittance characterization of TRTSF revealed that the switching effect was obvious during solid–liquid phase change process. TRTSF microstructure analysis revealed that the particle size distribution of PCM microspheres was between 1 μm and 6 μm. The UV–VIS-NIR band (wavelength at 0.25–1.1 μm) transmittance of PCM decreased to less than 3.7% after solidification due to the interfacial reflectance of solid PCM particles increased to more than 66.8% even in monolayer, thus the solid PCM particles would produce Mie scattering and isolate the internal and external radiation heat transfer. However, the TRTSF can be used as the radiative cooling emission layer since its optical properties were similar to the PDMS when the PCM is in liquid phase. Overall, the TRTSF film prepared in this study successfully adapted the temperature switching properties, also, is expected to be further used for the development of self-adaptive radiative cooling systems.

Mussel-inspired strategy to construct 3D silver nanoparticle network in flexible phase change composites with excellent thermal energy management and electromagnetic interference shielding capabilities

Nowadays, efficient thermal management and electromagnetic interference shielding as effective measures for maintaining the normal operation of electronic devices are extremely significant. However, composites with both thermal management and electromagnetic interference shielding performance are rarely reported. In this study, a kind of flexible polydopamine (PDA) and silver nanoparticles (AgNPs) wrapped melamine foam (MF) constructed by adopting the mussel-inspired strategy was used to fabricate MPAχ-PEG phase change materials (PCMs) via encapsulating polyethylene glycol (PEG). PDA was selected to enhance the interface bonding between MF and AgNPs due to its strong adhesion based on mussel-inspired surface chemistry. Continuous AgNPs wrapped on skeleton of MF construct the three-dimensional (3D) thermal/electrical-conductive porous network. MPAχ-PEG PCMs exhibit a relatively high phase change enthalpy of 148.9 J/g and a high thermal conductivity enhancement of 1400% in comparison with that of MF-PEG. Moreover, MPAχ-PEG PCMs are provided with electromagnetic interference (EMI) shielding performance with the mean SET of 82.02 dB and electro-to-thermal energy conversion efficiency (86.3% under the voltage of 1.2 V) due to the 3D conductive AgNPs network. Combining the elasticity of MPAχ foams and the phase change feature of PEG, the MPAχ-PEG PCMs show good solar-induced shape memory performance. The flexible PCMs could avoid the sharp temperature increase of smartphone by the solid-liquid phase change process of PEG. Therefore, this study provides a promising strategy to prepare flexible PCMs, which can achieve various forms of energy conversion, as well as thermal management and EMI shielding performance, can definitely broaden their application prospect in electronic devices.

Modeling of Multi-Layer Phase Change Material in a Triplex Tube under Various Thermal Boundary Conditions

Nowadays, limited energy resources face ever-growing demands of the modern world. One engineering approach to mitigate this problem which has received considerable attention in recent years is using latent heat thermal storage (LHTS) systems, a significant opportunity which is provided by phase change materials (PCMs). In the present study, a numerical investigation was devoted to estimate the simultaneous freezing and melting processes of a double-layer PCM in terms of heat transfer and fluid flow phenomena. A double-pipe cylindrical channel with two compartments, A and B, was considered for locating two PCMs of RT28 and RT35 in various arrangements. The inner and outer walls were exposed to both hot and cold heat transfer fluids (HHTFs and CHTFs, respectively) beginning with solid or liquid initial state, which led to solid–liquid phase change process through PCMs. The numerical simulation was handled by a two-dimensional finite volume method (FVM) with a fixed Rayleigh number of 106 in which conduction and convection heat transfer mechanisms are taken into account. The effects of employing double-layer PCM and their arrangements, inner and outer walls’ boundary conditions, and initial statuses of PCMs are discussed, and the details of the compared results are shown in the form of temperature and liquid fraction variations over time.

Isotherm-evolution-based interface tracking algorithm for modelling temperature-driven solid-liquid phase-change in multiphase flows

In this paper, an isotherm-evolution-based algorithm is proposed for effective tracking of the phase-change interface in temperature-driven solid-liquid phase-change process in multiphase flows (e.g., droplet freezing in the air). To fulfill the temperature condition on the interface, an interface indicator φ is defined, whose variation between specified maxima and minima marks the passing through the melting temperature. Previous approaches directly generate φ from the temperature field with explicit function and an artificial phase-change temperature interval, which could be affected by uneven temperature gradient and thus loses interfacial sharpness. The new algorithm devices an isotherm evolution equation to fulfill thermodynamic principles on the phase-change interface and maintain interface sharpness. Specifically, diffusive terms with explicit parameter are used to analytically ensure a finite interfacial width; and the migration term is introduced to cope with the phase-change temperature condition. The consistency of the proposed algorithm with the sharp interface limit is verified by comparing with analytical solutions of the Stefan problem. In numerical tests of the freezing droplet on substrate, the new algorithm presents better consistency of interfacial width throughout the computational domain and during the whole evolution process, as compared with the previous approach. The accuracy, convergence and robustness of the method as well as its capability in three-dimensional simulations are also validated through quantitative comparisons with reference results in the literature.

Simulation of solid-liquid phase change at pore scale using lattice Boltzmann method with central moments in thermal energy storage

The solid-liquid phase change process is of significant importance to the thermal energy storage and electronics cooling using phase change material. In this paper, the central moments multiple-relaxation time (CM-MRT) collision model has been introduced into the solid-liquid phase change lattice Boltzmann model, in order to solve the solid-liquid phase change problem in porous medium at pore scale. To evaluate the influences of different collision functions, the problems of one-region phase change and natural convection with phase change at pore scale have been investigated. The results have showed that the CM-MRT model possessed higher accuracy in revealing temperature and liquid fraction distribution. Compared with mesh system of 256 × 256, the CM-MRT model with 64 × 64 possess the minimum error, 0.014%. Besides, in the case of high Rayleigh number (5 × 107) and low Prandtl number (0.005), the CM-MRT model presented extraordinary stability and the clear phase interface when investigating the heat transfer of porous medium composite phase change materials at the pore scale.