•This work describes pore-scale two-phase simulations for open-cell metal foams.•The dispersed oil-phase was tracked using a Lagrangian approach: discrete phase model.•Foams of pore densities ...10–50 ppi and porosities 75, 85 and 95% were investigated.•The fractions of non-captured oil droplets of the investigated foams were evaluated.
Oil/air separation is a critical process in aero engines since a two-phase flow is created in bearing chambers with closed-loop oil systems. This work describes an application of a two-phase pore-scale modeling method to open-cell metal foams, which are used in secondary oil separation in aero-engine separators. The dispersed oil-phase flow through open-cell foams was studied using a Lagrangian approach: discrete phase model (DPM) and investigated on foam structures of pore densities 10–50 ppi and porosities 75, 85 and 95%. The simulations were performed over flow velocities ranging from 5 m/s to 50 m/s, and for separate uniform droplets of diameters ranging from 0.5 to 15 μm, with the commercial CFD analysis package Ansys Fluent. Results indicated that the fraction of non-captured droplets decreased when the flow velocity rose, and the higher the foam porosity, the higher the number of non-captured oil droplets. The flow velocity had a significant impact on the oil capture for intermediate droplet diameters of 1–3 μm. The fraction of non-captured oil droplets increased as the pore density of the open-cell foam increased at the normalized position of x/dp = 5. Foams with a larger pore size and smaller specific surface area showed an increased oil capture when compared with foams with smaller pore sizes and larger specific surface area. For Stokes numbers below 0.1, the oil capture efficiency was small and remained rather constant independent of the Stokes number. However, for 0.1 < Stokes numbers < 1.0, the oil capture efficiency increased substantially with increasing Stokes numbers. Stokes number values above 1.0 were associated with a high capture efficiency, which remained stable with increasing Stokes numbers.
The widespread use of plastics, especially polyolefin including polyethylene and polypropylene, has led to severe environmental crises. Chemical recycling, a promising solution for extracting value ...from plastic waste, however, is underutilized due to its complexity. Here, a simple approach, silicone-assisted direct laser writing (SA-DLW) is developed, to upgrade polyolefin plastic waste into multifunctional porous graphene, called laser-induced graphene (LIG). This method involves infiltrating polyolefins with silicone, which retards ablation during the DLW process and supplies additional carbon atoms, as confirmed by experimental and molecular dynamic results. A remarkable conversion yield of 38.3% is achieved. The upgraded LIG exhibited a porous structure and high conductivity, which is utilized for the fabrication of diverse energy and electronic devices with commendable performance. Furthermore, the SA-DLW technique is versatile for upgrading plastic waste in various types and forms. Upgrading plastic waste in the form of fabric has significantly simplified pre-treatment. Finally, a wearable flex sensor is fabricated on the non-woven fabric of a discarded medical mask, which is applied for gesture monitoring. This work offers a simple but effective solution to upgrade plastic waste into valuable products, contributing to the mitigation of environmental challenges posed by plastic pollution.
•Five types of open-cell copper foams with different porosities were selected.•The flow and heat transfer performance were studied experimentally and numerically.•The numerical simulation considered ...local thermal non-equilibrium.•Experiments and simulations agreed on thermal resistance and pressure drop.
A metal foam with an open-cell structure is a type of material with low flow resistance, high specific surface area, and strong fluid mixing ability. Open-cell metal foams have broad application prospects in electronic component cooling, multiphase heat exchangers, and compact heat exchangers for aerospace applications. This paper presented experimental and numerical analyses of the flow and heat transfer characteristics of five different copper foams under forced air convection. The pores per inch (PPI) of selected foams were 10, 20, 30, 40, and 60, with porosities ranging from 0.968 to 0.973. Analysis of the collected heat transfer and pressure drop data yielded the overall heat transfer coefficient, unit pressure drop, normalized average wall temperature, inertia coefficient, and resistance coefficient. The influence mechanisms of the porosity and flow velocity on heat transfer were analyzed and discussed. The numerical simulation and experiment fitted well. The results showed that increasing porosity led to a significant increase in heat transfer coefficient and unit pressure drop. The 60 PPI foam brought the maximum pressure drop while achieved the minimum thermal resistance.
Polyacrylonitrile (PAN)-based carbon fibers have high strength, high elongation, and low volume fraction of voids. The precursors of PAN-based carbon fibers are produced by wet or dry jet spinning ...techniques. To obtain high-quality PAN precursors, the flow field inside a redesigned rectangular spinneret was investigated in this work. The influence of the perforated area ratio of outer holes to inner holes and the fillet diameter of corner holes on the axial velocity distribution before the spinneret plate was discussed. An orthogonal experiment was carried out to acquire optimized structural parameters of the rectangular distributor. After the optimization, the CV of the axial velocity on the observation cross-section decreases from 62.26% to 47.61%.
To preserve characteristics of triangles in random order, with high repetition between the adjacent layers in STL files, a uniform thickness algorithm is proposed to improve the slicing efficiency, ...which deletes the triangles below the slicing plane gradually to decrease the number of searches for intersecting triangles and establish the dynamic topology based on intersecting triangles to obtain orderly intersections and closed profiles. A slicing program is developed based on a VC++ platform and an OpenGL interface. This slicing program is validated by comparing the slicing efficiency of different slicing methods for three ASCII STL models. The results show that the slicing program developed in this work can significantly improve the slicing efficiency of STL models.
Water–solid interactions are crucial for many fundamental phenomena and technological processes. Here, we report a scanning tunneling microscopy study about the charge density wave (CDW) transition ...in 1T-TaS2 driven by a single water dipole layer. At low temperature, pristine 1T-TaS2 is a prototypical CDW compound with 13 × 13 charge order. After growing a highly ordered water adlayer, a new charge order with 3 × 3 periodicity emerges on water-covered 1T-TaS2. After water desorption, the entire 1T-TaS2 surface appears as localized 13 × 13 CDW domains that are separated by residual-water-cluster-pinned CDW domain walls. First-principles calculations show that the electric dipole moments in the water adlayer attract electrons to the top layer of 1T-TaS2, which shifts the phonon softening mode and induces the 13 × 13 to 3 × 3 charge order transition. Our results pave the way for creating new collective quantum states of matter with a molecular dipole layer.
Hydrogen storage technology is a critical segment for solving future energy problems and is currently an escalating issue for developing our energy economy. In the past two decades, numerous ...theoretical works and hydrogen storage experiments have been carried out to explore hydrogen storage through the hydrogen spillover method. Hydrogen spillover was found to be an effective method to improve the hydrogen storage performance of carbon - based materials at room temperature. This review mainly addressed the principles of hydrogen spillover, evidence for improving hydrogen storage efficiency, and theoretical studies on the spillover method. In an effort to find some ideas on which materials could be used to store hydrogen at room temperature, we summarized the influencing components of spillover for hydrogen storage from three perspectives: hydrogen storage materials, efficient catalysts, and other factors. Finally, we outlined the current problems and future research directions for hydrogen storage at room temperature and proposed some strategies to address them.
The unexpected chiral order observed in 1T-TiSe_{2} represents an exciting area to explore chirality in condensed matter, while its microscopic mechanism remains elusive. Here, we have identified ...three metastable collective modes-the so-called single-q modes-in single layer TiSe_{2}, which originate from the unstable phonon eigenvectors at the zone boundary and break the threefold rotational symmetry. We show that polarized laser pulse is a unique and efficient tool to reconstruct the transient potential energy surface, so as to drive phase transitions between these states. By designing sequent layers with chiral stacking order, we propose a practical means to realize chiral charge density waves in 1T-TiSe_{2}. Further, the constructed chiral structure is predicted to exhibit circular dichroism as observed in recent experiments. These facts strongly indicate the chirality transfer from photons to the electron subsystem, meanwhile being strongly coupled to the lattice degree of freedom. Our work provides new insights into understanding and modulating chirality in quantum materials that we hope will spark further experimental investigation.
