•The arrangement of metal foam flow field in PEMEC was investigated experimentally.•Metal foam is more suitable to be used in the anode side alone at RH = 1 condition.•Metal foam in the cathode side ...leads to serious performance deterioration.•Improved maximum power density is 36.2% by comparing with parallel channel.
Due to the elimination of ‘land/channel’ geometry in conventional bipolar plates, metal foam as flow distributor in proton exchange membrane fuel cell (PEMFC) has shown great potential in improving the uniformity of reactant and temperature distributions, which is beneficial to the performance enhancement of the fuel cell. However, the arrangement of metal foam which can be optimized to further enhance the performance of PEMFC has not been considered yet. In the study, nickel metal foam is used as a new type of flow field for experimental research, and compared with the performance of conventional graphite parallel flow field (case 1) in a PEMFC. With respect to the arrangement of metal foam, three cases, namely the use of metal foam either in the anode side (case 2) or cathode side (case 3), and the simultaneous use of metal foam in both sides (case 4), were designed. Experimental results showed that nickel metal foam flow field can make the temperature distribution at the membrane more uniform, which is conducive to the durability of the membrane, and improves the fuel utilization rate. By comparing with case 1 at fully humidified condition, the increase of maximal power density for case 2 is 15.67 %, which is higher than case 3 (6.36 %) and case 4 (9.09 %), indicating the importance of the arrangement of metal foam. The interpretation is that when relative humidity (RH) is high, the cathode side using nickel metal foam flow field is more prone to flooding. Furthermore, a 3-hour constant current test on case 1–4 indicated that at RH = 1, a serious voltage deterioration was observed after 105 min when nickel metal foam is used in the cathode side. With the decrease of RH, the critical flooding time was gradually postponed. This finding is especially useful for the practical applications of metal foam as flow distributor in a PEMFC.
•Modeled melting heat transfer in specialized anisotropic metal foam.•Employed tensors for permeability and thermal conductivity to elucidate foam behavior.•Evaluated the role of anisotropic angles ...and foam positioning on heat transfer.•Anisotropic foam significantly boosts charging power without added mass.•Optimal charging power achieved at 0° anisotropy in the middle layer.
Anisotropic metal foams exhibit exceptional potential for improving the efficiency of latent heat thermal energy storage (LHTES) units by enhancing heat transfer and thermal energy storage rates. This study explores the largely uncharted area of thermal behavior of anisotropic metal foams in varied configurations and enclosure designs. The research focuses on an LHTES unit with a specific channel configuration, constructed using copper and containing three layers of copper metal foam, one of which is anisotropic and infused with paraffin wax. The finite element method was utilized to manage the complexities emerging from phase change, and the anisotropic angle varied from 0 to 90° in three different placements of the AMFL: top, middle, or bottom of the enclosure. The ideal design was achieved with an AMFL in the middle with a 0°angle, resulting in a 3.7 % reduction in melting time and approximately a 2.3 % reduction in solidification time. However, AMFL designs at the middle placement with a 75° anisotropic angle were less effective, hampering the melting and solidification processes, thus potentially extending charging and discharging times. The study concludes that the placement and angle of the AMFL layer are vital for the heat transfer capabilities of phase change materials. AMFL at the middle with a 0° angle optimally leverages temperature gradients, enhancing heat transfer compared to other investigated cases. An AMFL in the middle with a 0° angle exhibits approximately 7.1 % and 6.3 % improvements for melting fractions of 0.9 and 0.95, respectively, underscoring its potential for efficient thermal energy storage.
•Effect of foam-fin structure on thermal performance of PCM is studied experimentally.•FGF module features with a better PCM performance, followed by FCF, GF, Fin, and CF.•Incorporation of fins ...enhances thermal conductivity and reduces cold recovery time.
Effective thermal management is key to ensuring the reliable operation of high power electronic equipment. In this study, the strategy of phase transition and liquid cooling coupling applied to transient high power electronic equipment has been examined. In order to improve the performance of the phase changing material (PCM) in temperature control, the effects of the coupling structure have been addressed with a consideration of fin, copper foam (CF), graphite foam (GF), fin-copper foam (FCF) and fin-graphite foam (FGF) structures in heat dissipation. In this study, pure paraffin wax (PPW) was used as phase change material to prepare heat sinks based on the above five structures. The experimental study investigates the impact of different thermal conductivity strategies on temperature control characteristics, with a focus on cold capacity recovery and the combined phase change and liquid cooling, using pure paraffin wax module as a reference. The results have revealed that the fin-foam coupling structure delivers a better PCM performance than the single fin or foam structure. Operating at a heating power of 10 W, 15 W and 20 W, the temperature control time of the FGF structure was increased by 13.6 %∼14.6 % relative to the GF structure. At 15 °C with flow rates of 1 L/min, 1.5 L/min, 2 L/min liquid cooling conditions, the cooling capacity recovery time was reduced by 18.8 %, 17.2 %, 19.7 %, respectively. In the phase-change liquid-cooling coupling temperature control experiment, the final temperature increase in the FGF system was 11.7 °C -15.2 °C lower than that of the GF system under the same water temperature and volume flow for a 50 W heat source. The incorporation of fins also enhanced the thermal conductivity strengthening capability of the copper foam and reduced the cold recovery time. Based on the comprehensive evaluation, the FGF structure demonstrates superior temperature control performance and cold recovery characteristics of PCM, making it an optimal strengthening method. Following closely are the FCF, GF, Fin and CF structures. Compared to pure paraffin modules, these five modules exhibit varying degrees of improvement in temperature control and cold capacity recovery efficiency. This study provides guidance for optimizing heat sink design based on PCM in electronic applications.
The integration of dielectric and magnetic components is a promising strategy for fabricating electromagnetic interference shielding materials with peculiar characteristics. To further promote the ...shielding capability while still maintaining the high absorption performance, rational and meticulous structural design is urgently required for their practical application as advanced shielding materials. In this work, a highly porous nickel metal foam (NF) with the macroscopic pre-constructed conductive framework is selected as the substrate. Then, the polyaniline (PANI) coating layer is successfully intertwined on NF by a facile in-situ polymerization technology. Finally, the NF/PANI composite foam (NPF) with a unique three-dimensional (3D) porous heterostructure is created. Although the thickness is only increased by 2.7% of the pristine NF, the shielding effectiveness of NPF heterostructure is significantly improved, even reaching 93.8 dB (~99.99999996% radiation can be shielded). In particular, NPF possesses superior characteristics of absorption loss per unit thickness (147.64 dB/mm) among previously reported shielding materials. Such extraordinary performance could be ascribed to the 3D porous heterostructure, the presence of abundant interfaces, and dielectric-magnetic integration in NPF. These characteristics dramatically improve the interfacial polarization, dielectric polarization, dipole relaxation, attenuation constant, and multiple reflection. Both power balance analysis and the comparison between the absorption and reflection behaviors suggest that absorption dominates the shielding mechanism. The excellent comprehensive shielding capability endows such heterostructure with great application prospects in electronic devices. Furthermore, a prototype for achieving high-performance shielding materials based on 3D porous heterostructure is also provided.
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•The conjugate free convection phase change heat transfer is addressed.•The phase change materials are embedded in a metal foam.•The effect of a transient pulse heat flux is investigated.•Melting and ...solidification heat transfer during a pulse cycle are studied.
The conjugate flow and heat transfer of phase change materials (PCMs)-metal foam confined between two annuli is addressed. A pulse heat load is employed at the inner surface of annuli, while the outer surface is subject to convection cooling. (This content of this sentence is the same as that in other sentences.) The enthalpy-porosity approach is utilized to model the phase change, and the natural convection in the porous medium is taken into account using Darcy-Brinkman model. The governing equations are transformed into non-dimensional form and solved by the finite element method. The finite element method is employed to solve the governing equations in the non-dimensional form. An automatic grid adaptation technique is employed to capture the phase change interface. The results are compared with theoretical and experimental studies available in the literature and found in good agreement. The steady-state solution and transient characteristics are addressed. The results demonstrate that the heatsink filled with PCM-metal foam can enhance the heat transfer at the hot surface, particularly at low external cooling power (Biot number < 0.2). The results reveal that the fusion temperature of phase change material is the key parameter on temperature controlling of the hot surface. Using the phase change heatsink results in a cooling power four times higher than that of pure external convection during the pulse load.
The use of partially filled high porosity graded aluminum and copper foams is explored to satisfy both heat transfer and pressure drop in a heat exchanger. Both positive and negative orientations are ...accomplished for the enhancement of heat transfer with reduction in the pressure drop. The present research includes three different configurations M1, M2 and M3 (porous layer inner diameter = 0.06 m, 0.04 m, and 0.02 m, respectively, while outer diameter = 0.10 m) partially filled with positive (i.e., increasing, 20/45 PPI) negative (i.e., decreasing, 45/20 PPI) and compound (i.e., 45 Cu/20 Al PPI) graded porous layer thickness. Each configuration involves three different graded porous layer to present the optimum graded porous layer thickness. The thermo-hydrodynamic characteristics are apprehended by using Darcy Extended Forchheimer (DEF) flow and local thermal non-equilibrium (LTNE) models for the partially filled graded porous structure and k-ω turbulence model is accomplished in open passage flow of the conduit. The decreasing graded foam located inside the models M1 and M2 performed 1.68%–12.85% and 13.42%–23.32% higher heat transfer rate compared to without graded metal foam of models M2 and M3, respectively accompanied with 55.43%–84.02% and 35.69%–50.31% lesser pumping power.
•Partially filled negative graded metal foam is suggested for heat transfer enhancement.•The negative graded foam was found superior than the positive graded foam layer.•The thinnest negative graded foam layer displayed maximum thermal performance.•The negative graded copper foam shows slightly higher performance than aluminium one.
•Metal foam should be arranged in both heat transfer fluid and phase change material;•Metal foam in phase change materials improves uniformity of temperature field;•Full melting time was maximally ...reduced by 88.548% compared with smooth tube;•j-factor was increased by 5186.91% if HTF and PCM were inserted with metal foam.
Thermal energy storage technology has attracted extensive attentions due to its remarkable energy-saving benefits. However, the low thermal conductivity of phase change materials seriously limits the energy storage efficiency, which put forward more stringent requirements for heat transfer enhancement. In this study, a two-dimensional axisymmetric simulation model with natural convection was established for the shell-and-tube thermal energy storage unit. Open-cell metal foam with a porosity of 0.94 and pore density of 15 pore per inch was employed to be arranged in either heat transfer fluid or phase change materials domains. The effects of the metal foam location and the metal foam porosity on the heat storage performance were studied. The numerical method was verified by experimental measurement, achieving good agreement. Results demonstrated that metal foam can significantly enhance heat transfer due mainly to the reduction of thermal resistance in heat transfer fluid. The case that both domains for heat transfer fluid and phase change materials were embedded in porous media can provide the best heat transfer enhancement. Compared with smooth tube without metal foam, the full melting time for this case was reduced by 88.548%; meanwhile, temperature response rate, heat flux and j-factor was increased by 834.27%, 774.90%, 5186.91% respectively. Besides, embedding metal foam into phase change materials can improve the temperature uniformity of phase change materials.
•Combines nanoparticles with metal foam in a triplex-tube PCM energy storage system.•Melting time of the PCM is modeled, validated with experiments and studied.•The combination was found to greatly ...reduce the melting time of the PCM.•Allied parameters responsible for improved performance of the system were revealed.
Phase change material (PCM) energy storage systems have relatively low thermal conductivity values which greatly reduces the systems’ performance. In this study, a compound porous-foam/nanoparticles enhancement technique was used to significantly improve melting of a phase change material (PCM) in a triplex-tube heat exchanger applicable to liquid desiccant air-conditioning systems. A mathematical model that takes into account the non-Darcy effects of porous foam and Brownian motion of nanoparticles was formulated and validated with previous related experimental studies. The influence of nanoparticle volume fraction and metal foam porosity on the instantaneous evolution of the solid-liquid interfaces, distribution of isotherms, and liquid-fraction profile under different temperatures of the heat transfer fluid (HTF) were investigated. Results show that dispersing nanoparticles in the presence of metal foams results in melting time savings of up to 90% depending on the foam structure and volumetric nanoparticle concentration. Although the melting time decreases as the porosity decreases and/or volume fraction increases, high-porosity metal foam with low volume-fraction nanoparticles is recommended. This ensures minimal PCM volume reduction and promotes positive contribution of natural convection during the melting process.
Protonic ceramic electrolysis cells (PCECs) offer significant potential for large-scale green hydrogen production. The performance of conventional PCEC stacks is notably limited due to the uneven gas ...distribution. In this research, a new stack design using metal foam as the gas distributor is proposed and numerically evaluated using a 3D Multiphysics model to improve the gas distribution uniformity. At 1.3 V and 600 °C, the current density of the newly designed PCEC with metal foam is 173 % higher than that of the conventional PCEC. Moreover, the hydrogen production capability of metal foam based PCEC is 234 % higher than that of conventional PCEC, due to the improved gas distribution uniformity and faradaic efficiency (FE) of the new PCEC. The application of metal foam increases steam distribution uniformity by 91.2 %. In a conventional PCEC, the FE under the rib is notably lower than that under the channel. In contrast, the FE distribution is more uniform in a metal foam based PCEC. The improved performance in terms of current density, FE, and distribution uniformity highlights the potential of metal foam as a beneficial component in PCEC stacks. These findings contribute to the understanding and further development of PCEC technology.
•A 3D model is proposed for PCEC stack using metal foam for gas distribution.•Metal foam based PCEC stack outperforms the conventional PCEC stack.•Effects of operating and structural parameters on the PCECs are explored.•The impact of the flow field on faradaic efficiency is explored.
•Nanoparticles in multi-PCMs with cascaded foam for energy storage were studied.•Solidification of the PCM was modeled and validated via previous experiments.•Role of nanoparticles with cascaded foam ...for improved solidification was revealed.•Cascaded foam shows better solidification enhancement potential than nanoparticles.
The thermal response of the shell-and-tube energy storage system consisting of multiple segments holding separate phase-change materials (PCMs) of different melting points was studied. Nanoparticles in PCM of 5% volume fraction with cascaded (multiple-segment) metal foam of average porosity 0.95 were applied the heat-transfer enhancement. A simulation model that accounts for the non-Darcy effects of cascaded foam and Brownian motion of nanoparticles was developed and validated with previous experimental studies. The impact of using different arrangements of multiple PCMs, multiple PCMs with nanoparticles, and multiple PCMs with cascaded foam on the time-based solidification evolution was investigated. The module that combines multiple PCMs with cascaded foam showed the best thermal response rate. Compared to the module of single PCM with no nanoparticles or cascaded foam, the full solidification time saving was up to 94% depending on the number of multiple PCMs and number of cascaded foam segments. Although solidification time decreases as the number of foam segments and/or number of multiple PCMs increases, the choice of adequate small number of multiple PCMs and foam segments is recommended. This reduces design limitations associated with cascading of the containment vessel and does not significantly affect the positive role of natural convection during the early period of the solidification.
