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Metallic foam composite phase change materials (MF-PCMs) have a high thermal energy storage capacity. However, obtaining a high heat transfer coefficient and a consistent temperature distribution remains challenging. Here, we present a novel double-gradient void metallic foam construction. Furthermore, we build a three-dimensional numerical model to study how pore size, porosity, and diameters affect heat transport and thermal storage performance. The results show that the homogeneity of the cooled wall temperature distribution is well improved by the enhancement of thermal conductivity produced by this double-gradient design. With a graded gradient, the maximum deviation between the individual temperature and the average temperature of the cooled wall is within 15 K, as the total thermal storage capacity is close to 75.5 % of the pure PCMs. Meanwhile, for pure PCMs, this deviation can reach 67 K. These characteristics hold promise for lithium-ion battery thermal management because the spaces between neighboring individual cell units must absorb and retain the heat emitted. Our novel composite structure offers a significant method for designing battery temperature control.

Virus filtration membranes contribute to the virus safety of biopharmaceutical drugs due to their capability to retain virus particles mainly based on size-exclusion mechanisms. Typical product molecules like monoclonal antibodies with 9–12 nm in hydrodynamic diameter have to be transmitted by >95% while small viruses, e.g. parvoviridae (B19, MVM, PPV) with a diameter of 18–26 nm, have to be retained by at least 99.99%. Therefore, membrane fouling caused by product aggregates, which are similar in size compared to the viruses that have to be retained, is a common observation. Minimal membrane fouling is a requirement for economical processes and is influenced by both the membrane surface chemistry and the membrane structure, particularly with regard to the pore size gradient (PSG). In this work, virus filtration membranes were challenged with gold nanoparticles (GNPs) in order to determine PSGs for a wide range of different commercial and non-commercial parvovirus retentive membranes differing in structure, material and surface chemistry. GNP adsorption to the membrane material was suppressed by the use of an anionic surfactant, allowing to gain insights into size-exclusion properties of the membranes. Membrane performance with regard to fouling was further investigated by determination of protein mass throughputs up-to a defined membrane flux decay using solutions containing intravenous immunoglobulin (IVIG) as model protein. Additionally, the fouling mechanism of IVIG was investigated and confirmed to be caused by trace amounts of species larger than IVIG monomers and dimers, which were already present in the feed. The fouling results are discussed in relationship to the determined PSGs, since the porous support structure of virus filtration membranes can act as a depth pre-filter protecting the separation-active layer from particulate foulants. [ABSTRACT FROM AUTHOR]

A gas diffusion layer (GDL) is the primary component of proton exchange membrane fuel cells (PEMFCs) that aid in supplying reactant gases from the flow channel to the catalyst layer. It improves the discharge of water generated by the electrochemical reaction from the catalyst layer to the flow channel. Since the GDL is composed of pores that range from nanometer to micrometer in size, it is susceptible to water flooding. Thus, water discharge capability should be enhanced by increasing the capillary pressure gradient. In this study, the porosity and average pore size of the GDL are varied in the planar direction by varying the gasket thickness in the in-plane direction. Furthermore, the effects of the disposition of perforations in the GDL on PEMFC performance are investigated by forming perforations by mechanical processing. A total of three types of GDLs were fabricated, with the same number of perforations on the inlet, outlet, and the entire area of the GDL. Performance tendencies of the GDL were confirmed in both the porous flow channel mimicking the flow channel currently used in fuel-cell electric vehicles and the serpentine flow channels. • Effects of the compression ratio of gas diffusion layer. • Effects of the gradient of porosity in the in-plane direction. • Effects of the gradient of average pore size in the in-plane direction. • Effects of disposition of perforations in gas diffusion layer. [ABSTRACT FROM AUTHOR]

The proton exchange membrane fuel cell (PEMFC) is one of the up-and-coming power sources for automotive vehicles. To generate a stable performance during driving, the PEMFC needs to achieve an optimized water management under various humidity conditions. Being the path for the two-phase flow of fuel, air, and water, the gas diffusion layer (GDL) is a critical component, which influences water balance. In this study, a pore size gradient structure is introduced in the substrate of a GDL to control the local capillary pressure gradient, which is the driving force of the water flux inside the PEMFC. Through measurements of steady-state performance, transient response, voltage instability and electrochemical impedance spectroscopy, it was found that the pore size gradient structure improves the cell performance regardless of the relative humidity conditions used (50% and 100%). Furthermore, it is possible to hold the water on the membrane for higher ion conductivity and drain it toward the channel to secure gas supply toward the catalyst layer. In addition, it was also confirmed that the structural change enhances the bending stiffness of the GDL. [ABSTRACT FROM AUTHOR]

Abstract: We describe the manufacture of track-etch membranes with controlled gradients of pore size and density along the length of the membrane. Gradient of track density is obtained by controlled motion of a screen between the swift ion beam and the polymer material. Linear gradient of pore size is obtained by a dipping process at constant velocity in alkali solution. The two steps are linked by the desired characteristics of the membrane. Membranes were characterized by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Examples are given with pore radius gradient of 3nm/cm and a theoretical model of flow in a channel with such kind of porous wall is presented. This two-step process is rather simple and presents numerous variants at will. The method could be extended easily to produce any desired parameter variation, or to maintain some characteristics constant along the membrane, as for instance porosity, pore internal area or hydraulic resistance. [Copyright &y& Elsevier]

Thin self-supporting ceramic TiO2-layers with a graded pore structure were prepared by using centrifugal deposition of powders and sols with different particle size distributions from mixed, diluted suspensions. During the evaporation drying step the layers have a strong tendency to warping and crack-formation because of the resulting difference in the capillary pressure in the upper and the bottom side pores. Four drying methods were investigated concerning their suitability for diminishing or eliminating capillary forces and for the production of planar, crack-free dried specimens. The drying techniques used in the experiments are briefly introduced. It should be emphasized that the most successful drying method for the layers mentioned above is a combination of microwave drying and subsequent critical point drying. [ABSTRACT FROM AUTHOR]