In the present study, a cylindrical solid state hydrogen storage device embedded with finned heat exchanger is numerically investigated. The finned heat exchanger consists of two ‘U’ shaped tube and ...circular fins brazed on the periphery of the tubes. 1 kg of LaNi5 alloy is filled inside the device and 80 g of copper flakes is evenly distributed in between the fins to increase the overall thermal conductivity of the metal hydride. Water is used as heat transfer fluid. Absorption performance of the storage device is investigated at constant hydrogen supply pressure of 15 bar and cooling fluid temperature and velocity of 298 K and 1 m/s respectively. At these operating conditions, the required charging time is found to be around 610 s for a storage capacity of 12 g (1.2 wt%). The study is extended to examine the influence of different heat exchanger configurations based on number of fins, thickness of the fins, diameter of tubes, holes in fins, amount of copper flakes etc. An analysis for the same weight of the heat exchanger assembly has also been carried out by changing the number of fins at different thickness and pitch.
•LaNi5 based hydrogen storage device embedded with a heat exchanger is numerically investigated.•Copper flakes are used to enhance the effective thermal conductivity of metal hydride.•Numerical results are validated against the experimental results.•Effects of different heat exchanger design on absorption performance are examined.
The combination of polymer and copper (Cu) is common and economical in thermal interface materials (TIMs). However, it is remains challenging for traditional polymer-Cu composites to obtain high ...thermal conductivity (TC) (>10 Wm−1K−1) due to the poor filler connection. Herein, we introduced small amount of 2D-structured graphite nanoplatelets (GNPs) into bulk Cu flakes/epoxy composites via the thermal molding method. Surprisingly, we found an extraordinary synergistic effect, revealed highly thermally conductive percolation network through intercalation of GNPs between Cu flakes. A high isotropic TC 13.4 Wm−1K−1 is achieved with 5 wt% GNPs and 80 wt% Cu flakes, which superior than most reported Cu/polymer composites. Although a high electrical conductivity of 34000 S/m was obtained, a phonon-dominated thermal transport mechanism was observed due to the existence of GNPs bridges between Cu flakes. The resulting composite also demonstrate excellent thermal management ability, superior acid resistance and good mechanical property, which offers a promising composite in thermal management application.
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•An epoxy/Cu/graphite-nanoplates composite (GNPs) was fabricated via a simple hot-pressing method.•The GNPs bridged between Cu flakes and realized pronounced thermal conductivity at 13.4 Wm−1K−1.•The composite possessed outstanding thermal management and self-warming ability.•The composite showed satisfied comprehensive properties.
This study reports about the enhanced thermal conductivity of epoxy composites fabricated by introducing relatively aligned structure of cellulose fibers with copper flakes embedded in their ...surface-layer. The obtained composite shows anisotropic thermal conductivity; in the parallel direction being higher than that in the perpendicular direction. With varying preparation conditions, a thermal conductivity of as high as 1.4 W m−1 K−1 has been achieved at a low filler concentration of 36.4 wt%. A theory available in literature is modified by the introduction of resistivity factor to account for the loose connectivity at the flake-flake junctions and the effective thermal conductivity of epoxy composites filled by copper flakes coated cellulose fiber has been investigated. The theoretical prediction shows that the heat conduction along the fiber direction is mostly influenced by the thermal conductivities of cellulose fibers and copper flakes. Meanwhile, the thermal conductivity of polymer matrix and packing fraction of fiber affect strongly on the perpendicular thermal conductivity of the composites. The contact resistivity factor of at the flake-flake junction has been estimated to be 0.07 m K W−1. This report gives potential guidance exploiting recyclable cellulose fiber for further study in designing high thermal conductive composites for heat management applications.
Copper (Cu) is an attractive low‐cost alternative to silver or gold. However, it is susceptible to oxidation in air. Here, facile in situ regeneration of oxidized Cu flakes (CuFLs) for the synthesis ...of highly conductive non‐oxidized nanocomposites is reported. The oxidized CuFLs are regenerated into non‐oxidized CuFLs and Cu nanosatellite (CuNS) particles by formic acid‐aided in situ etching and reduction reaction in soft epoxy matrix. The average particle size of CuNS particles is only 3.3 nm with an interparticle distance of 2.7 nm. Furthermore, the negligible potential barrier height between Cu and epoxy dramatically increases the electrical conductivity (66 893 S cm−1) of the nanocomposite (Cu = 46 vol%) by more than three orders of magnitude. The thermal conductivity is also highest (85.1 W m−1 K−1), compared with Cu‐based nanocomposites in literature. The conductivities are invariant in air for more than 95 days. The simple scalable in situ regeneration of oxidized CuFLs may find immediate industrial applications.
Oxidized copper flakes (CuFLs) are regenerated into non‐oxidized CuFLs and nanosatellite particles (3.3 nm) by formic acid‐aided in situ etching and reduction in epoxy . The negligible potential barrier between copper and epoxy dramatically increases air‐stable electrical conductivity (66 893 S cm−1) by more than three orders of magnitude. Thermal conductivity is also highest (85.1 W m−1 K−1) for copper‐based nanocomposites.
Paper-based electronics have been attracting significant attention because of their inexpensive, renewable, and eco-friendly substrates. In this study, Cu-based composite inks composed of a ...copper-based metal-organic decomposition (MOD) ink and Cu flakes were prepared as precursors to obtain conductive Cu films on untreated cellulose paper. Copper-based MOD inks have not been explored for the production of conductive Cu films on cellulose paper because the properties of the paper, such as high porosity, high permeability, and surface roughness, are not favorable to obtain continuous conductive Cu films. However, using our method, we have obtained Cu films on paper with resistivities that are ∼10 times lower than those of films on polyimide or glass substrates. Importantly, the Cu films on paper exhibited better mechanical resistance than those on a polyimide substrate, without any pre-treatment of the paper surface.
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•Cu-based composite inks of self-reductive Cu complex with Cu flakes were prepared.•Cu film resistivity on paper was ∼10 times lower than that on polyimide or glass.•Higher bending stability of Cu film on paper than that on polyimide.
The physical properties as well as thermal and electrical stability of copper particles can be improved by surface protection, which mainly depends on the coating material. Our study was, therefore, ...focused on the rheological, thermal, mechanical and electrical characterization of polymer composites by comparing uncoated (Cu), silver-coated (Cu@Ag) and silica-coated (Cu@Si) copper flakes in low-density polyethylene at various volume concentrations (up to 40%). Interactions among particles were investigated by rheological properties, as these indicate network formation (geometrical entanglement), which is important for mechanical reinforcement as well as establishing an electric pathway (electrical percolation). The results showed that geometrical and electrical percolation were the same for Cu and Cu@Si, ~15%, while, surprisingly, Cu@Ag exhibited much lower percolation, ~7.5%, indicating the fusion of the Ag coating material, which also decreased crystal growth (degree of crystallinity). Furthermore, the magnitude of the rheological and mechanical response remained the same for all investigated materials, indicating that the coating materials do not provide any load transfer capabilities. However, they profoundly affect electron transfer, in that, Cu@Ag exhibited superior conductivity (74.4 S/m) compared to Cu (1.7 × 10−4 S/m) and Cu@Si (1.5 × 10−10 S/m). The results obtained are important for the design of advanced polymer composites for various applications, particularly in electronics where enhanced electrical conductivity is desired.
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Continuous silver shells were deposited on copper flakes using a two-stage precipitation process. A tightly packed layer of silver nanoparticles was first formed on the surface of the ...base metal by galvanic displacement. The size of the noble metal particles and their distribution on the substrate were controlled using complexing agents and dispersants. A continuous Ag deposit was subsequently grown by reducing slowly Ag(NH3)2+ ions with glucose. The final shell thickness was controlled by varying the amount of metal deposited in the second step. The electrical properties of resulting silver coated copper flakes are comparable to those measured for silver flakes of similar size and aspect ratio. By preventing the oxidation of copper cores up to 400°C, the hermetic noble metal shell dramatically extends the temperature range in which Ag/Cu flakes can successfully replace pure silver.
Micro-copper flakes were coated with nano-TiO2 in an ethanol-based colloid sol by chemical deposition, in order to improve their oxidation resistance. The as-prepared composites were characterized by ...field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). Results showed that TiO2 nanocrystals (predominantly anatase) of approximate 10nm in size were successfully deposited on the surface of Cu flakes, forming a granular coating. The growth of titania on the copper flakes seems to be implemented by anchoring TiO2 through Ti-O-Cu bonds. The thermal stability of the composites was tested by thermogravimetric analysis (TGA) in an air atmosphere. The results showed that TiO2-coated copper flakes acquired better oxidation resistance compared to the pure copper flakes. Oxidation in air of pure copper flakes began at 190°C, whereas the composites did not oxidize until 360°C.
The easy oxidation of copper is one critical obstacle to high-performance copper-filled isotropically conductive adhesives (ICAs). In this paper, a facile method to prepare highly reliable, highly ...conductive, and low-cost ICAs is reported. The copper fillers were treated by organic acids for oxidation prevention. Compared with ICA filled with untreated copper flakes, the ICA filled with copper flakes treated by different organic acids exhibited much lower bulk resistivity. The lowest bulk resistivity achieved was 4.5 × 10
−5
Ω cm, which is comparable to that of commercially available Ag-filled ICA. After 500 h of 85°C/85% relative humidity (RH) aging, the treated ICAs showed quite stable bulk resistivity and relatively stable contact resistance. Through analyzing the results of x-ray diffraction, x-ray photoelectron spectroscopy, and thermogravimetric analysis, we found that, with the assistance of organic acids, the treated copper flakes exhibited resistance to oxidation, thus guaranteeing good performance.
