Conductivity Of Phase Change Materials Research Articles

Improving thermal conductivity of styrene ethylene butylene styrene/paraffin/boron nitride phase change composite via the sacrificial template method for battery thermal management

To address the bottleneck of easy leakage and low thermal conductivity of phase change materials (PCMs) for battery thermal management. Phase change composite (PCCs) with paraffin (PA) as the PCM, styrene ethylene butylene styrene (SEBS) as the supporting skeleton, and boron nitride (BN) as the thermally conductive filler were fabricated by the sacrificial template method. Compared with the composite prepared by melt-blending method, the thermal conductivity of PCC was improved by 27.6 % and the leakage rate was reduced by 82.4 % because the BN was rubbed with Na2SO4 under the shear provided by internal mixer. As a result, the maximum temperature and maximum temperature difference of the battery pack with PCC cooling were 35.8 % and 62.5 % lower than those without PCC cooling at 2C discharge rate. In total, this work offers a strategy for improving the thermal conductivity and the leakage-proof ability of PCCs as well as for large-scale fabrication.

Analysis and comparative assessment of charging dynamics in vertical multi-channel latent heat storage system with corrugated wavy channels

Latent heat thermal energy storage (LHTES) is a promising technology, but thermal response limitations caused by the relatively poor thermal conductivity of phase change materials (PCMs) remains an issue. In recent years, computational fluid dynamics (CFD) has proven to be a powerful and reliable tool in design optimization of different systems and problems in the energy sector. Building on that, the present work will use CFD to investigate the thermal performance enhancements achieved using vertical double-tube LHTES systems with multi-channel sinusoidal wavy geometries. The main parameters investigated here are the wavy channel height (H), pitch (P) and the number of channels (N) and the results are assessed in terms of melting rates and heat transfer coefficients. The analysis found that increasing the height from 1 mm to 3 mm, accelerated the phase change by 21 %, while reducing the pitch from 12.5 mm to 5 mm, enhanced the heat storage rates by 28 %. In addition, increasing the number of channels from 3 to 7 improved the charging rate by 64 %. Compared to a conventional straight channel, the enhanced wavy channel (N = 7, H = 3 mm, P = 5 mm) achieved 80 % higher thermal storage rate and 42 % faster charging time. The above findings provide new insight into the potential of utilizing compact vertical LHTES systems via customized wavy channels, with significant impact towards enhancing the existing thermal energy storage systems.

Performance evaluation and optimization of compact tube-fin latent heat storage system in phase change nanoemulsion discharge mode

The low thermal conductivity of phase change materials (PCMs) and the reduced heat transfer temperature difference along a tube both limit the thermal performance of latent heat thermal energy storage (LHTES). Herein, a compact tube-fin LHTES system based on phase change nanoemulsions was developed and the heat transfer process of nanoemulsion and PCM was numerically investigated. The effects of the heat transfer structure of the heat exchanger and the thermophysical parameters of the heat transfer fluid (HTF) on the cold energy discharge performance of the system were quantified. The optimized model reduced the discharge time by 24.4 % in nanoemulsion mode relative to water. Heat transfer improvement on the PCM side could be achieved by decreasing the fin spacing and tube spacing and by increasing the fin thickness. Such improvement reinforced the heat transfer enhancement of the nanoemulsion. The heat transfer mechanism was explained by the temperature distributions of the HTF and PCM along the tube. The phase-change thermostatic properties of the nanoemulsion and PCM contributed to the formation of dual-phase-change coupled heat transfer (i.e., the heat transfer process when the fluid inside the tube and the PCM filled outside the tube undergo a simultaneous phase change) within the LHTES, increasing the heat transfer temperature difference and the magnitude of the driving force. Increasing the phase change temperature difference accelerated the onset of dual-phase-change heat transfer, while increasing the PCM content prolonged the process. Briefly, this study provided operational and design assistance for LHTES systems in nanoemulsion mode with the intention to accelerate heat transfer rates.

A graphene-CuNWs@PAMPS mixed aerogel for composite phase change materials with high thermal conductivity and excellent solar-thermal to electrical conversion

Phase change materials could store and release heat energy through phase change. However, the shortcomings of low thermal conductivity in the photothermal conversion process and easy leakage in the solid-liquid conversion seriously hinder the application of heat energy utilization. Graphene had high thermal conductivity, and it was an ideal material for improving the solar absorption, solar energy conversion and thermal conductivity of phase change materials. In this paper, a graphene aerogel composed of copper nanowires (CuNWs)/2-acrylamide-2-methylpropanesulfonic acid (AMPS) was designed. The thermal conductivity and shape stability of phase change materials for solar-thermal-electrical conversion applications were enhanced by composite CuNWs. Furthermore, PAMPS was coated on the surface of copper nanowires to avoid the oxidation of copper nanowires, and the sulfonic acid group of PAMPS was used to induce CuNWs to disperse uniformLy on the graphene sheets, which further constructed a good conductive network. After vacuum impregnation of PW, the best thermal conductivity phase change composite (PW-CuNWs@PAMPS-GA(1:1)) was obtained. The PCC loaded with CuNWs with the same graphene content achieved a thermal conductivity of 1.46 W/(m·K) and a high latent heat of 206.8 J/g. The latent heat retention rate was as high as 99.57 %. The photothermal conversion efficiency of PW-CuNWs@PAMPS-GA(1:1) was remarkable at 96.4 %. Due to its excellent solar-thermal-electrical conversion efficiency, the output voltage and output current were 800.8 mV and 85.8 mA, respectively, at a solar analog intensity of 5 kW/m2. Even after the sunlight was stopped, the voltage output could be maintained for a while by releasing the heat energy stored in the phase change composite.

Heat transfer study of metal foam with partial filling method to strengthen phase change material

The advancement of ice-ball thermal energy storage systems is limited by the poor thermal conductivity of phase change materials(PCM). This paper presents a numerical investigation into enhancing heat transfer in ice balls by partially filling them with metal foam. Dynamic temperature changes, solid phase fraction, and cold storage capacity are analyzed for various filling radius ratios (2/13, 4/13, 6/13, 8/13, and 13/13). We quantitatively assess the specific impact of metal foam filling on heat transfer by calculating changes in the comprehensive thermal conductivity coefficient. Our findings reveal that the comprehensive thermal conductivity coefficient increases nonlinearly with the growing metal foam filling radius ratio, indicating that full filling may not the most optimal configuration. Furthermore, the energy storage capacity per unit time, per unit weight and per unit cost of the ice ball filled with metal foam under different radius ratios was evaluated by comprehensive evaluation criteria, and the optimal filling radius ratio was determined to be 6/13. Contrary to prior findings, this research highlights the efficacy of partial filling strategies, offering valuable insights for optimizing ice ball performance in thermal energy storage applications.

Enhanced study of phase change thermal storage using active rotating tank wall coupled fins combined with eccentric design

To address the low thermal conductivity of phase change materials and e improve heat storage, a novel rotating T-LHTESU structure is proposed. Numerical simulations systematically analyze the effects of rotation speed, various eccentricities and wall temperature on the performance of phase change heat storage. The results show that the introduction of rotation in the intermediate sleeve shortens the melting time with increasing rotation speed, reaching a maximum reduction of 61.66 % at 2 rps. Furthermore, the melting rate at 1 rps and 2rps first decreases and then increases with increasing eccentricity. At an eccentricity of 10 mm and 2 rps, the melting time is reduced by 7.23 % compared to the non-eccentric model. In addition, a higher wall temperature accelerates the change in the liquid phase fraction and increases the energy input. At a wall temperature of 371.15 K, the melting time is reduced by 73.56 % compared to the stationary model, with an increase in total heat by 2.52 %. This study provides theoretical guidelines for subsequent research on phase change heat transfer.

Effect of local mechanical oscillation on the performance of PCM thermal energy storage with various unit configurations

The low thermal conductivity of phase change materials is an essential restriction to their usage in thermal energy storage units. In this research, applying local oscillation by an oscillator on the portion of a side wall of RT35 enclosure is presented as a novel method to enhance the charging rate. The finite volume method is conducted for the numerical study on the effect of different configuration parameters including enclosure aspect ratios in the range of 1: 6, 1:2, 1:1, and 2:1, various oscillator lengths of 5, 10, 15, and 20 mm, as well as different oscillation frequencies of 10, 100 and 1000 Hz on the melting performance. Results indicate that applying local oscillation enhances the melting rate by more than 50 % as compared to without using oscillator because of enhancing convection heat transfer originating from vorticity intensification. The improvement of required time for melting the PCM is 91.55 %, 54.66 %, 67.7 % and 71.4 % for aspect ratios of 1:6, 1:2, 1:1 and 2:1, respectively.Results show that the melting performance is enhanced as the length of the oscillator increases. The required time for complete melting is obtained equal to 24, 26, 28, and 33 min at the oscillator length of 20, 15, 10, and 5 mm, respectively. The finding on the effect of oscillation frequency reveals that the liquid fraction, mean temperature, and heat flux at a specified time of melting process becomes higher as the oscillation frequency increases with significant enhancement of vorticity around the oscillator. At the frequency of 1000 Hz, the required time for melting is reduced by 9.5 % and 20.8 % as compared to frequencies of 100 Hz and 10 Hz, respectively. Other results also indicate that the higher Nusselt number is obtained for a higher enclosure aspect ratio.

Efficient preparation of polydimethylsiloxane‐based phase change composites with sandwich structure

AbstractWith the rapid development of portable electronic devices, there is an urgent need for the multifunctional composites like excellent electromagnetic interference (EMI) shielding performance, mechanical property, and thermal management capabilities. Here, due to the low thermal conductivity of phase change materials (PCMs), a sandwich structure carbon nanotube/phase change microcapsule/carbon nanotube (CNT/PMC/CNT (CPC)) film was prepared by vacuum‐assisted filtration (VAF) method. CNT, PMC, and cellulose nanocrystal (CNC) were used as functional fillers. The addition of CNCs was used to improve the mechanical performance of CPC film. Compared with PMC‐CNC (PC) film, CPC film with sandwich structure prevented leakage phenomenon efficiently. Subsequently, the use of ultrasonic‐assisted forced infiltration (UAFI) successfully infiltrated polydimethylsiloxane (PDMS) matrix in the filler skeleton to obtain CNT/PMC/CNT/PDMS (CPCP) composites. When filler mass ratio (CNT: CNC and PMC: CNC) reached 10:1, the thermal conductivity of CPCP composites was 2.32 W/(m·K) and total EMI shielding effectiveness (EMI SET) of it with 0.38 mm thickness reached 37.46 dB at 12.4 GHz. Besides, these sandwich composites exhibited the good mechanical properties and heat storage capacity. And we systematically observed the impact of different addition amounts of PC homogeneous dispersing solution on phase change ability of CPCP10:1 composites. In summary, CPCP phase change composites with sandwich structure shows potential application prospect in thermal management materials with EMI shielding of electronic devices.Highlight The sandwich structure CPCP composites prepared by the combination of VAF and UAFI method, showing superior thermal conductivity and phase change ability. CPCP has excellent EMI shielding performance, which can meet the need of TMMs with EMI shielding performance. Compared with same thickness PC film, sandwich CPC film can prevent leakage phenomenon efficiently.

Equivariant graph neural network interatomic potential for Green-Kubo thermal conductivity in phase change materials

Equivariant graph neural network interatomic potential for Green-Kubo thermal conductivity in phase change materials

Optimization design of a hybrid thermal runaway propagation mitigation system for power battery module using high-dimensional surrogate models

The demand for high energy density in lithium-ion battery packs for electric vehicles poses a challenge to maintaining its optimum operating temperature while reducing the risk of thermal runaway (TR) propagation. This study proposes a novel hybrid TR propagation mitigation system that balances heat transfer and thermal insulation requirements using low and high thermal conductivity phase change materials (PCM), heat pipes (HP), and air-cooling. The design and optimization of such a mitigation system are complex due to the many design parameters involved. The Adaptive-Kriging-High dimensional model representation (Adaptive-Kriging-HDMR) is used to establish a surrogate model of the system, and the sensitivity of the system's design parameters is evaluated with the maximum battery temperature and the system weight as the targets, thereby improving the efficiency of model calculation and reducing the dimension of optimization parameters. Then, the design of the sensitive parameters is optimized using an extended elitist non‐dominated sorting genetic algorithm (E-NSGA-II) multi-objective optimization algorithm. The results show that the modeling difficulty and optimization calculation time are significantly reduced by using a surrogate model. The calculation time for a single surrogate model only takes a few seconds instead of several hours for the original three-dimensional heat transfer and flow calculation. The thermal conductivity of high thermal conductivity-PCM, the distance between battery and low thermal conductivity-PCM, the battery spacing, and the HP length significantly affect the system. The optimized system substantially reduces the overall weight of the battery system while ensuring its good heat dissipation capability. In the case of TR in a single battery, the system succeeds in limiting the TR propagation to the same row, with the maximum battery temperature in the second row being only 64.3 °C, well below the battery TR trigger point. Under more severe conditions, such as TR occurring in two batteries simultaneously, the maximum battery temperature in the second row is 155.5 °C, and no TR spreads to the adjacent row. This study provides a rapid and effective method for designing a TR propagation mitigation system. It can serve as a reference for the engineering design and optimization of battery thermal management systems.

Experimental comparative study on thermal performance of latent heat storage tanks with pin, perforated, and rectangular fins at different orientations

The low thermal conductivity of phase change materials (PCMs) has limited their widespread use in practical applications. In the present study, different fin structures, namely, rectangular, perforated, and pin were examined to analyze the thermal performance of the melting process in rectangular latent heat storage tanks. Experiments were performed at both horizontal and vertical orientations to evaluate the effectiveness of different fin configurations. Visual observation of the phase change evolution at different time intervals was enabled through a transparent plexiglass shell. Instantaneous heat transfer rate and energy storage were measured using thermocouple readings and melting photographs. The results show that the maximum heat transfer coefficient between the heated wall and PCM is obtained by the pin-finned tank followed by perforated and rectangular-finned tanks. This thermal behavior is justified by the intensification of the upward convection flows through the voids provided by pin fins or perforated fins. Although the rectangular fin structure has the lowest convective heat transfer coefficient, its heat transfer rate is slightly higher than the other structures due to its larger heat transfer area. At a wall temperature of 70℃, the convective heat transfer coefficient and heat transfer rate obtained by the pin fin configuration are respectively 25% higher and 4% less than those of the rectangular fin. It reveals that the pin fin structure provides the most effective heat transfer area compared to its counterparts which have a significantly larger fin volume. In addition, it was found that regardless of the fin configuration, the melting rate in the horizontal tank was significantly higher than in the vertical tank due to the formation of more vortical flow structures within the molten PCM. The melting time in the unfinned horizontal tank was less than those of the vertical finned tanks implying that the tank orientation should be well-chosen to minimize the melting time along with adding fins of various configurations.

Polypyrrole-modified flax fiber sponge impregnated with fatty acids as bio-based form-stable phase change materials for enhanced thermal energy storage and conversion

In this study, we integrated organic phase change materials, decanoic acid (DA) and palmitic acid (PA), into bio-based samples made from sodium alginate (SA) and flax fiber (FF). We also synthesized conductive polypyrrole (PPy) coating through in situ polymerization to create two thermal energy storage and conversion systems with distinct phase change temperatures (32 °C and 63 °C). The PPy coating exhibited uniform polymerization, resulting in electrical conductivity (1.52 ± 0.07 S/m) and thermal conductivity (0.453 ± 0.02 W/mK). The conductive sponge, similar to the plain sponge, had a porous microstructure (85 % porosity) that allowed successful impregnation of 60 % and 74 % of DA and PA, resulting in outstanding energy storage and conversion properties. Specifically, the conductive sponges with DA and PA achieved phase change enthalpies of 100.98 J/g and 154.52 J/g, respectively. DA/PPy@Sponge demonstrated exceptional durability after thermal cycling tests. Furthermore, the conductive sample efficiently converted electrical energy into thermal energy along the conductive path, making it suitable for storing generated heat as both sensible and latent heat, as well as capturing and storing solar energy. Overall, the developed conductive phase change materials offer shape stabilization, high thermal energy storage capacity, and efficient electric/photo-to-thermal conversion properties. These attributes make them promising candidates for diverse applications in energy harvesting, storage, and management in electronics, buildings, transportation, and other relevant fields.

Charging and discharging performances investigation for a vertical triplex-tube heat exchanger with a tapered configuration and reverse layout

Given the inherent low thermal conductivity of phase change materials, the majority of previous research has focused on heat transfer intensification for the double-tube heat exchanger. However, a triplex-tube heat exchanger (TTHX) delivers a larger heat transfer area. To further elevate the heat transfer properties, a TTHX with a tapered configuration is proposed. How the tapered structure boosts heat transfer and the impact of cone angles on the charging and discharging performances of TTHX are investigated. Results demonstrate that employing the tapered structure significantly elevates the charging rate, and the charging time exhibits a trend of first declining and subsequently rising as θ increases from 3° to 8°, where the optimal cone angle (θ = 6°) shortens the charging time by 40.41% compared to θ = 0°. However, the heat transfer during solidifying is inhibited, and the inhibition becomes more pronounced as θ increases. This negative effect can be remarkably improved by imposing a reverse layout, which reduces the discharging time by a maximum of 32.54% compared to devices without reverse layout. This study offers a new perspective for the optimization research of the charging and discharging performances of TTHX and can provide guidelines for the optimization design of TTHX.

A novel topology optimization of fin structure in shell-tube phase change accumulator considering the double objective functions and natural convection

Shell-tube phase change accumulator (STPCA) has been widely applied in renewable energy generation and energy-saving building field. However, due to the low thermal conductivity of phase change material (PCM), its structure needs to be carefully designed to obtain the best heat release and storage rate. Most of the traditional design schemes are trial and error method, which has long design cycle, low efficiency, and difficulty in obtaining the optimal structure. In this contribution, we firstly adopt the topology optimization methods to obtain novel fins in STPCA considering natural convection. Then, we compared the difference between different objective functions and demonstrated the superiority of topology optimization. In addition, we have further studied fin design under double objective functions with different weight ratios and analyzed the synergistic effects on the objective functions. The results have shown that after natural convection has been considered in the topological optimization process, it can help obtain a better structure, and the generated fins can better enhance the performance of STPCA. For the case of single objective function, the conclusions are as follows: the maximum average temperature can be used to obtain the faster melting speed, while the minimum temperature difference can be used to obtain the best temperature uniformity. The conclusions of using double objective function are as follows: when the weight ratio of the maximum average temperature and the minimum temperature difference is 0.6: 0.4, the field synergy angle is smallest, and the performance of STPCA is further improved. This contribution can provide a guidance for STPCA design and enhance its thermal storage performance.

Experimental and numerical analysis of the thermal performance of PCM-impregnated reticular structures obtained by additive manufacturing

This paper proposes a combined experimental and numerical analysis of the melting of three different paraffin waxes embedded in reticular structures fabricated by additive manufacturing. The parent material of the reticular structures is AlSi10Mg. Metal structures, having a 100 mm square base and a thickness of 20 mm, were printed between two 10 mm thick plates. Samples were positioned in an upright position and laterally heated applying different heat fluxes. Three different paraffins were tested, with different characteristic melting temperatures (42 °C, 55 °C, and 64 °C), which are suitable for electronics cooling applications. Four different structures were tested, having a cell length of 5 mm and 10 mm, and porosities of 0.87 and 0.93. Besides the experimental tests, numerical simulations of the melting phenomenon were carried out using a purely conductive model implemented in ANSYS Fluent. The discretized numerical domains represented just small repetitive portions of the test modules, thus allowing substantial computational time savings. This simplified method has been proven to yield results that are in good agreement with the experimental data. The main outcome of this work is the setup of the simplified numerical procedure, which was then validated and used to investigate the effectiveness of the considered structures in diffusing heat into the low thermal conductivity phase change materials. It was concluded that the best overall thermal performance can be obtained with low porosity and low cell size since this enables faster melting processes and better surface temperature control.

Study on the effect of partial filling of foam metal on the solidification performance of ice storage spheres

Ice storage sphere systems are favored in the field of energy storage, however, the poor thermal conductivity of phase change materials (PCM) seriously weakens their wide application. Metal foam has been shown to enhance its heat transfer. In this paper, we investigate the impact of varying the filling radius ratio of foam metal to further improve energy storage performance and reduce costs in ice storage spheres. Computational fluid dynamics are employed to analyze the heat transfer and solidification processes. The enthalpy-porosity method is used to describe PCM solidification, while the local equilibrium thermal (LET) model characterizes heat transfer between the PCM and foam metal. The study explores temperature field variations, solid phase fraction changes, solidification times, and cold storage volumes, accounting for natural convection. By comparing solidification rates and other relevant parameters, the effect of foam metal filling on the solidification process is explored. Moreover, a new evaluation index is proposed, which can assess the overall performance of ice storage systems in real-time, considering market prices. The results show that natural convection is the primary heat transfer mode in pure PCM-ffild ice storage spheres, whereas smaller foam metal filling radii significantly inhibit natural convection, resulting in heat conduction as the dominant mode. Without specific requirements, an optimal fill radius ratio of 9/13 is determined. This paper offers a comprehensive understanding of cold storage employing various foam metal filling radios, contributing to advancements in efficient thermal energy storage systems.

Combined passive enhancement techniques improve the thermal performance of latent heat storage system: A design anomaly?

Poor heat transfer rate due to low thermal conductivity of phase change material limits the wide application of latent heat storage (LHS) systems. Thermal performance enhancement techniques can be potential methods to address this major limitation of LHS systems. In this context, the present numerical study examines the individual and cumulative impact of two passive heat transfer enhancement techniques (the orientation of the domain and position of the heat transfer fluid (HTF) tube) on the thermal performance of the latent heat storage (LHS) system consisting of high-temperature (HT) phase change medium (PCM). The individual effect of orientation decreases the charging duration of θ = 0° (horizontal configuration) by 10.5 %, 15 %, and 19.04 % than θ = 30°, θ = 60° and θ = 90° (vertical configuration), respectively. However, the discharging duration remains unchanged for all inclinations (11.5–12 h). The individual effect of eccentricity decreases the charging duration of horizontal (θ = 0⁰, ey = −5 mm,-10 mm,-20 mm) system by 6.25 %,12.8 %, and 18.75 % than concentric horizontal (θ = 0°, ex = ey = 0) system. Moreover, the combined effect of orientation and eccentricity (θ = 0⁰,ey = −5 mm,-10 mm,-20 mm) reduces charging duration by 28.75 %, 33.33 %, and 38.1 % than vertical concentric domain (θ = 90°, ex = ey = 0), respectively. However, eccentricity in vertically upward and downward directions increases the discharging duration compared to the concentric domain. Hence, the combined effect results in a design anomaly for HT-LHS system. The charging and discharging performances are observed to be predominantly sensitive to the Rayleigh number than the Reynolds number.

Uncertainty assessment method for thermal runaway propagation of lithium-ion battery pack

To some extent, the thermal runaway issue pertaining to lithium-ion battery still present challenging problems, to put the safety-related issue under control in high-power and high-energy applications. One of these challenging issues relates to the underpinning stochastic uncertainties associated with thermal runaway propagation. Therefore, this study proposes a methodology to evaluate the uncertainty of thermal runaway propagation in Li-ion battery modules. Firstly, a numerical thermal runaway propagation model is developed for phase change material-based thermal management system and verified by experiments. Subsequently, the Adaptive Kriging High-dimensional model representation method is employed to construct a surrogate model, followed by global sensitivity analysis to evaluate the impact of six different influencing factors on thermal runaway propagation. Finally, the random fluctuation of the critical factors affecting thermal runaway propagation is integrated to analyze and quantify the uncertainty. The results show that the state of charge, the thermal conductivity of phase change material, and inter-cell spacing are critical factors affecting thermal runaway propagation. With the system parameters proposed in this paper, the critical state of charge range that significantly impacts the uncertainty of thermal runaway propagation is approximately 40% to 55%. The analysis of the propagation results and the cell temperature indicates that the highest level of uncertainty occurs at around 45% state of charge. In this case, the thermal runaway propagation is significantly impacted by changes in key factors, and the battery temperature exhibits high fluctuation levels. Furthermore, although there is a 59% likelihood of no propagation, the potential damage to all batteries becomes exceedingly significant once thermal runaway propagation occurs. The method proposed in this study effectively evaluates the uncertainty of thermal runaway propagation in battery systems. It identifies the causes of the uncertainty, which can be used to implement effective suppression measures to enhance safety.

Thermal energy storage control using phase change materials in a rectangular energy storage chamber with metal foam gradient and magnetic field

Considering the low thermal conductivity of phase change materials (PCM) and the slowness of the melting process in the thermal energy storage chamber (TESC), a comprehensive study on the use of magnetic field and porous foam gradient in the phase change process of PCM in a rectangular chamber with a cylinder is presented. The numerical solution is done using the finite volume method. PCM, metal foam and nanoparticles are respectively lauric acids, aluminum and iron oxide. Porosity coefficient changes have been examined in the positive and negative directions of the coordinate axes during melting and compared to a uniform porosity coefficient in the common case. As a result of a constant magnetic field, melting does not take place as much, but when a non-uniform magnetic field is used, the process of melting in the TESC increases by about 35 times, and the intensity of the magnetic field can be used between 0.025 and 0.05 mT. The average thawing fraction of the PCM has augmented by 5.046, 6.86, 7.66 and 7.819 %, respectively, compared to the no-field. The metal foam gradient has an imperative efficacy in enhancing the process of melting and up to about 97 % reduces melting time. When the porosity coefficient is higher near the active wall, the heat transfer and liquifying are quicker. In the chamber, temperature changes of the cylinder can have a momentous efficacy on the thawing process. The greatest effect is observed when the changes of cylinder temperature with time are stepwise. The sensitivity analysis was done based on the Sobol method, which shows that the porosity coefficient has the greatest effect on the melting rate.

Effect of pore density and filling ratio of metal foam on melting performance in a heat storage tank

Thermal energy storage through solid–liquid phase change is an efficient method for mitigating solar energy intermittency by providing continuous energy supply for the end-users. However, the low thermal conductivity of phase change material, which serves as the heat transfer medium in the thermal energy storage systems, severely undermines the heat charging/discharging rates. Metal foam can significantly strengthen the heat storage performance via increasing the thermal conduction capability of phase change material and metal foam composite, mainly due to the large extension surface area and highly-conducting metallic ligaments of the metal foam. To squarely explore the influence of the two vital parameters (filling ratio and pore density) for the metal foam upon the phase change process, numerical models for describing the phase change process in a tank filled with phase change material and metal foam are established, and the experimental validations of the corresponding models are performed. Melting time, temperature uniformity, and heat storage capacity are selected as the targeted indexes for assessing and evaluating the impacts of filling ratio and pore density on the phase change process. The results show that the full melting time of heat storage decreases first and then increases with the decrease of filling ratio under any PPI. The smaller the PPI, the smaller the overall heat storage time. And the larger the PPI, the greater effect of the filling ratio on the heat storage time. The melting time of the PCM under the optimal filling ratio of 10 PPI and 100 PPI is shortened by 8.06% and 18.06%, and the temperature uniformity is reduced by 5.48% and 10.11%, respectively, compared with that of the complete filling.