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Phase change material (PCM) based heat sink has the potential to be applied for the thermal management of electronic devices. Whereas, PCM suffers from a low thermal conductivity, which results in local overheating at the base of heat sink. To enhance thermal performance of heat sink, a structured porous material (SPM) used as thermal conductivity enhancer (TCE) is designed and fabricated, where 3D printing technique is adopted to achieve the fast and precise manufacture of SPM. The thermal response of heat sink using SPM with different porosities (80%, 85%, 90%, and 95%) is experimentally investigated at various heating power levels (8 W, 10 W, and 12 W). Results show that the use of SPM has a significant effect on thermal response of heat sink for electronic cooling system. Furthermore, the thermal behavior of heat sink can be further heightened by reducing the porosity of SPM, e.g., the heat sink using SPM with 80% porosity shows the highest enhancement ratio in all cases of present study. The increase of power level can result in the reduction of operation time of PCM-based heat sink. This study is of great significance for the design and application of SPM used in thermal management unit.

The present article investigates the melting process of aluminum foam/paraffin composite with low porosity by using experimental and numerical methods. Three composites with porosities 67%, 75%, an...

International audience; Phase change material (PCM) is a promising candidate for application to thermal energy storage. However, low thermal conductivity hinders its wide application. In this paper, a porous metal structure (PMS) with cubic cell is used to enhance the thermal performance of PCM, in which additive manufacturing (AM) as advanced manufacturing technology enables the fast and precise fabrication of PMS with a controlled structure and material. A visualized experiment setup is built to investigate the thermal performance of PCM with and without PMS, including solid-liquid interface, temperature variation, and total melting time. To examine the heat transfer characteristics and clarify the role of PMS in the melting process, a three-dimensional numerical model is developed based on the pore-scale numerical simulation method. The experimental results illustrate that embedding PMS can significantly improve the thermal performance of PCM, e.g., the total melting time can be shortened by 38% compared with that for PCM without PMS. The numerical results are in good agreement with experimental results, which indicates that heat transfer characteristics can be predicted using pore-scale numerical simulation. The numerical results show that the temperature field of PCM with PMS is more uniform and heat transfer mechanics is different for PCM with and without PMS. In addition, PMS made of highly thermally conductive materials significantly enhances the thermal performance of PCM. Due to structure and material controllability of porous material fabricated by AM, this study highlights the capacity and potential of PMS as a heat transfer enhancer.

International audience; In this paper, a comprehensive experimental and numerical investigation is conducted to study the thermal behavior of phase change material (PCM) infiltrated in low porosity metal foam (LPMF). A visible experiment is designed to trace the temperature field and solid-liquid melting evolvement of PCM with and without metal foam. The experimental method and pore-scale numerical simulation are employed to extract temperature histories at different location during the melting process. Besides, the effective thermal conductivity of composite PCM is calculated by numerical simulation and compared with the theoretical models. Experimental results indicate that the thermal behavior of PCM can be visibly enhanced by embedding LPMF, e.g., by comparing with pure paraffin, the melting time of composite PCM is reduced by 45% and the maximum temperature difference is decreased by 83.3%. The porosity has influences on the thermal characteristics of composite PCMs. Numerical results exhibit good agreement with experimental data, which indicates that modified Kelvin model can be employed to predict the thermal performance of composite PCM. Also it can be found from numerical results that effective thermal conductivities of composite PCMs are distinctly heightened, e.g., the effective thermal conductivities of composite PCM with 67% porosity is about 108 times as much as that of paraffin. Numerical model is of great significance for study and design of thermal management system using composite PCM.

International audience; Pore-scale numerical simulation is conducted to study the thermal performance of composite change phase material (PCM). The low melting point paraffin wax R56 is selected as PCM. Aluminum foam with cubic periodic cell structure is designed, which not only possesses high thermal conductivity, high porous structure and low relative density but also can be rapidly manufactured by the new manufacturing technology. Hence it is an excellent candidate used as metal matrix of composites. The pore-scale numerical method is used to calculate the temperature variation and trace the melting evolution of composite PCM. The effects of geometrical parameters of metal foam such as porosities and pore densities on the thermal behavior of composite PCM are numerically investigated. It is observed from numerical results that the effects of aluminum foam on the thermal performance of composite PCM are very pronounced. Compared with the pure paraffin, the melting time for composite PCM is greatly shortened to 24.1% of that of pure paraffin. Also the effective thermal conductivity of composite PCM is drastically improved, e.g., the effective thermal conductivity can be enhanced about 123 times as much as that of pure paraffin. By comparing with the different porosities and pore densities composite PCMs, the geometrical parameters of aluminum foam have the distinct effects on the thermal performance of composite PCMs, e.g., the melting rate for composite PCMs with the low porosity or high pore density is higher as compared to the composite PCMs with the high porosity or low pore density. By analyzing the temperature-time history, it is demonstrated that there is local thermal non-equilibrium phenomenon between aluminum skeleton and paraffin during the melting process and local thermal non-equilibrium gradually weakens as the reduction of temperature difference between aluminum skeleton and paraffin.

International audience; Since the past five decades, the study of new materials has become attractive in both scientific research and industrial applications. For purpose of enhancing mechanical properties of metallic foam, a new composite entitled “Metal-Porous-Polymer-Composite (MPPC)” consisting of open-cell metallic foam and filling polymers was developed by infiltrating the filling polymers throughout the connected pores in open-cell metallic foam. Based on a three-dimensional (3D) structural modeling, microscopic structural models of Al metallic foam and MPPCs with spherical pores and Kelvin’s pores are established in the finite element code. Introducing the elastoplastic mechanical properties, the polymer–metal interfacial behaviors and the proper loads and boundary conditions on these structural models of Al metallic foam and MPPCs, the numerical compressive behaviors of Al metallic foam and PA6/Al & LDPE/Al MPPCs are successfully performed. The results show that the mechanical properties of PA6/Al & LDPE/Al MPPCs are mainly influenced by the filling polymers, the kind of pores, the pore size, the polymer–metal interface, the polymer volume fraction and the distribution of pores, respectively. It means that a good understanding can be provided concerning the deformation mechanism and engineering applications of both Al metallic foam and MPPCs.

This study focuses on the thermal analysis and comparing a lattice model and an optimized model of open-cell metal foams manufactured thanks to a metal casting process. The topological optimization defines the complex geometry through thermal criteria and a plaster mold reproduces it in 3D printing to be used in casting. The study of the thermal behavior conducted on the two open foam metal structures is performed based on several measurements, as well as numerical simulations. It is observed that the optimized metal foam presented less and non-homogenous local temperature than the lattice model with the gap of about 10 °C between both models. The pore size and porosity significantly affect the heat transfer through the metal foam. The comparison between numerical simulations and experimental results regarding the temperature fields shows a good agreement allowing the validation of the developed three-dimensional model based on the finite element method.

International audience; The metal foam/phase change material (PCM) composite is a promising material in the thermal energy storage system. In the present study, a modified structure of metal foam, finned metal foam with graded porosity (FFGP), is proposed to further accelerate the melting process of the composite. The finite volume method and two equations model are applied in the modeling of FFGP. The average power of energy storage is defined to evaluate the energy storage efficiency of the composite. The effects of the structural parameters of FFGP on the average power of energy storage are investigated, including thickness of metal fin, porosity gradient of metal foam and pore per inch (PPI). The results indicate that FFGP structure could reduce the total melting time and enhance greatly the energy storage performance. This is because the metal fin changes the melting sequence of PCM and the gradient metal foam contributes to the heat transfer between the heat source and the composite. Besides, the value of PPI has a great impact on natural convection in the composite. Through combining the proper metal fin, gradient metal foam and PPI, the FFGP structure with the good performance could be obtained.

International audience; Three methods to further enhance thermal performance of the metal foam/phase change material (PCM) composite are investigated and compared. These three methods include changing the pores per inch (PPI) of metal foam, modifying the shape of the cold wall and using the discrete heat sources. In this study, the composite consists of two materials: aluminum foam with 90% porosity as metal foam and paraffin wax as PCM. The numerical model based on finite volume method is developed, and the non-equilibrium equation is applied to study the melting process of the paraffin embedded in aluminum foam. The heat loss, the liquid average velocity and the efficiency of latent heat storage are analyzed and discussed. The results show that adopting the aluminum foam with high PPI value or modifying the shape of the cold wall could improve the thermal response of composite. Besides, the discrete heat sources could lead to a large average velocity in the liquid region. Combining the advantages of these methods, an optimization method is also proposed, which could improve the efficiency to 83.32% comparing with the pure paraffin.

International audience; The acoustic properties of an air-saturated macroscopically inhomogeneous aluminum foam in the equivalent fluid approximation are studied. A reference sample built by forcing a highly compressible melamine foam with conical shape inside a constant diameter rigid tube is studied first. In this process, a radial compression varying with depth is applied. With the help of an assumption on the compressed pore geometry, properties of the reference sample can be modelled everywhere in the thickness and it is possible to use the classical transfer matrix method as theoretical reference. In the mixture approach, the material is viewed as a mixture of two known materials placed in a patchwork configuration and with proportions of each varying with depth. The properties are derived from the use of a mixing law. For the reference sample, the classical transfer matrix method is used to validate the experimental results. These results are used to validate the mixture approach. The mixture approach is then used to characterize a porous aluminium for which only the properties of the external faces are known. A porosity profile is needed and is obtained from the simulated annealing optimization process.

Hierarchical porous wood-templated ZnO has been successfully synthesized using Lauan and Fir woods as template through a simple hydrothermal bioinspired approach. The template type and calcination temperature in the preparation process have a large effect on the morphologies and porous structures of ZnO according to FESEM, TEM, mercury porosimetry and N 2 adsorption investigations. The gas sensing performances of wood-templated and non-templated ZnO were investigated using H 2 , CO, H 2 S, NH 3 , Formaldehyde, Methanol, Ethanol, Acetone, and Isobutene. The article studies the effects of wood template, calcination temperature, and working temperature of gas flow on the gas sensitivity and selectivity in detail. It is revealed that wood-templated ZnO has excellent sensitivity and selectivity to H 2 S due to inheritance of wood's hierarchical porous structure. The sensing response to H 2 S of Fir-templated ZnO is about 5.1 times higher than that of non-templated ZnO. Fir-templated ZnO calcined at 600 °C, has the best sensing properties including the highest gas sensing response, the highest selectivity coefficients of H 2 S and the shortest response and recovery time. The selective sensing mechanism has been discussed from some key aspects, such as gas properties, gas–solid reactions, grain size and hierarchical porous microstructures.

Porous iron with woodlike microstructures was prepared from two kinds of wood templates through a developed biotemplating method in the present work. The biomorphic iron oxide was first produced through infiltration and sintering procedures, and was then reduced to the biomorphic iron in a hydrogen atmosphere at high temperatures (600C and 1000C). The morphologies of iron and iron oxide products were observed using SEM and FESEM, and their crystal structures were identified using X-ray diffraction. The results indicate that the pure iron phase can be obtained after the reduction process and the products faithfully retained the microstructures of the corresponding wood templates. [doi:10.2320/matertrans.48.878]

The compression characteristics of open-cell aluminum foams were experimentally and numerically investigated. It is found that the mechanical parameters, such as collapse stress and absorbed energy, are dependent on the porosity of aluminum foams material. During simulation of metal foam compression, the finite elements distort severely at the local regions with high gradient of physical field. The procedure integrates Explicit solver of Abaqus FEA, 3D Optiformmesher and Python script program transfer to execute step by step the incremental deformation of deformable body.

International audience; Pressure infiltration casting technique is widely used to manufacture open-cell metal foam and it has been well performed in manufacture practice in our research group. In the present study, an attempt is made to highlight the influence of the infiltration casting process on the physical structure of metal foam. According to the production practice, several parameters: the pressure difference, the temperature condition, the particle size and the mould dimension, need to be well considered. A 2D model coupling porous zone and multiphase is created with a fixed grid. The cooling and solidifying process of molten metal are as well carried out with enthalpy method. Reasonable convergence rules are used to proceed high quality calculations. This work provides excellent experimental and numerical comprehension of pressure infiltration casing process to manufacture open-cell metal foam. These understandings can well guide and optimize the product manufacture, the physical structure and the mechanical behaviors of open-cell metal foams within their industrial application.

A novel porous ZnFe2O4/SiO2 composite product has been generated with a template-directed assembly method from porous diatomite under different synthesis conditions, such as precursor concentrations (metallic nitrates), calcination temperature and diatomite type. The phase composition and morphology of all the materials were examined by x-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The results indicated that an inherited hierarchical porous structure from the diatomite template can be obtained, and the synthesis conditions were found to have clear effects on the formation of the ZnFe2O4/SiO2 composite. The ideal composite of ZnFe2O4/SiO2 can be obtained through optimization of diatomite template type, precursor solution and calcination temperature. Furthermore, the adsorption abilities of two types of diatomites were analyzed in detail using FTIR spectra and nitrogen adsorption measurements etc, which proved that A-diatomite (Shengzhou-diatomite) is better than B-diatomite (Changbai-diatomite) on the aspect of adsorbing Zn and Fe ions, and of forming the ZnFe2O4.