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Since boiling is a phenomenon with high heat transfer performance, it is expected to be used in various industrial fields such as emergency cooling in nuclear power plants, power device cooling for EVs and next-generation CPU cooling in data centers. So far, various research on boiling have been carried out in the background of these trends. In particular, many studies have been conducted to improve the critical heat flux (qCHF) which is the limit of boiling heat transfer. However, since the mechanism of qCHF is a complex phenomenon, the methods of qCHF improvement are still unconstructed. Here we demonstrate the high-performance heat transfer surface using electrodeposition which fabricates copper porous plate. We found that this copper porous plate has higher qCHF (3.7 MW/m2) than the plain surface (1.3 MW/m2) in saturated pool boiling of water at atmospheric pressure. The structure of copper porous plates is investigated by X-ray CT and SEM. The copper porous plates have a honeycomb porous structure consisting of porous area and vapor escape channels extending vertically from the substrate. In addition, the diameter of the vapor escape channels increases from the substrate to the top surface. This surface structure can supply the coolant to the heat transfer surface with the reduction of pressure drop. Our results show that the mechanism of qCHF improvement using porous plate depends on the wicking phenomenon and structure. We expect that these results will help in the development of high-performance heat transfer surfaces for various industrial applications.

We developed a numerical electrodeposition (ED) model and validated its accuracy by comparing experiments and simulations using various kinds of paints and pretreated steel plates. The model was implemented in a next-generation finite element code (ES-FEM), which achieves high accuracy even with 4-node tetrahedral meshes. Besides, it was demonstrated that the difference in paint and pretreatment properties can be simulated adequately in large-scale analysis using actual paint process and car body models. [ABSTRACT FROM AUTHOR]

Dynamic behavior of electrochemical interfacial phenomena is key issue for material science. Scanning probe microscope can observe the surface on the nanoscale, however, it is difficult to discuss the reaction process due to poor temporal resolution. High-speed atomic force microscopy (HS-AFM) is one of powerful in-situ observation tools. Here, we would like to introduce the HS-AFM applications for electrochemistry, such as Cu electrodeposition, polyethylene glycol (PEG) adsorption, and nanobubble electrolytic evolution by HS-AFM. [ABSTRACT FROM AUTHOR]

Superplastic bonding was performed using electrodeposited Ni and electrodeposited Ni-B to apply to low-temperature diffusion bonding of carbon steel. Electrodeposited Ni and Ni-B were bonded at 450°C in air and at a strain rate of 1 × 10-4 s-1. The shear test measured the bond strength, and the maximum bond strength of 69 MPa was obtained. Since the obtained bonding strength at 450°C is comparable to that obtained by diffusion bonding of carbon steel at 0.5Tm, it is possible to decrease the bonding temperature to 0.4Tm by applying this boning process. The bonding strength depended on the amount of strain and increased as the strain increased in the range of strain 0.2 to 0.4. The voids at the interface shrink by superplastic deformation with grain boundary sliding, and the bonded area increases. In the superplastic bonding of electrodeposited Ni alloys, superplastic deformation effectively shrinks voids with a radius of 1-2 μm. [ABSTRACT FROM AUTHOR]

It was investigated whether the spherical electrolytic copper powder could be electrolyzed by adding polyethyleneimine (PEI) in the electrolytic solution. In order to identify the optimum electrolysis conditions for the electrodeposition of spherical copper powder, we investigated the effect of molecular weight of PEI, the amount of PEI added, the current density, and the cathode material on the morphology of electrolytic copper powder. The electrodeposited copper powder was analyzed with a scanning electron microscope, a laser diffraction scattering particle size distribution measuring device, and an X--ray diffractometer. It was found that the spherical copper powder can be obtained by electrolysis at 3000 A·m-2 scraping copper powder every 10 to 60 s in solution containing 0.126 mol·dm-3 Cu2+, 0.5 mol·dm-3 free H2SO4 and 1.0 g·dm-3 PEI with average molecular weight 10000. [ABSTRACT FROM AUTHOR]

To investigate the effect of polymer additives and chloride ions on the electrodeposition behavior and morphology of copper powder, the polarization curves were measured and constant current electrolysis of 300 A·m-2 and 500 A·m-2 was conducted in an electrolytic solution containing 0.079 mol·dm-3 of Cu2+ and 0.5 mol·dm-3 of free H2SO4 at 293K and 393K without stirring. Polyethylene glycol (PEG) and polyethyleneimine (PEI) were used as polymer additives. PEG and PEI had a suppressing effect on the electrodeposition of copper powder. The current efficiency for Cu deposition decreased with the addition of PEG and PEI. The addition of PEG decreased the average particle size of the copper powder, while PEI didn't change the average particle size. When Cl-coexisted with PEG, the suppressing effect on the electrodeposition of copper powder became even greater and the particle size of the copper powder became finer than when Cl- or PEG was added alone. [ABSTRACT FROM AUTHOR]

To investigate the effect of halide ions on the electrodeposition behavior and morphology of copper powder, the polarization curves were measured and constant current electrolysis of 300 A⋅m-2 and 500 A⋅m-2 was conducted in an electrolytic solution of 0.079 mol⋅dm-3 of Cu2+ and 0.5 mol⋅dm-3 of free H2SO4 at 293K and 303K without stirring. In the deposition of copper powder, Cl- had a promoting effect on the deposition of copper powder, while Br- and I- had a suppressing effect. The current efficiency for Cu deposition increased with the addition of Cl- and decreased with Br-. The addition of Cl- reduced the average particle size of the copper powder and grown dendrite-shaped branches and trunks, resulting in a lower tap density. On the other hand, when Br- was added, the average particle size and crystallite size of the copper powder became smaller, and the tap density also became smaller. With increasing Cl- concentration in solution, the current efficiency for Cu deposition increased, that is, copper deposition was promoted even in the diffusion rate-determining region of Cu2+ ions, showing that the deposition of copper powder was affected by the charge transfer process for Cu deposition. The change in morphology of Cu powder with halide ions is attributed to change of the charge transfer process. The deposition of Cu powder seems to proceed under a mixed rate-determining process of the diffusion of Cu2+ ions and charge transfer. [ABSTRACT FROM AUTHOR]

Electrodeposition of Zn was performed on an Fe electrode at a current density of 50-5000 A·m-2 and a charge of 4 × 104 C·m-2 in an unagitated zincate solution at 313K containing 0.62 mol·dm-3 of ZnO, 4.0 mol·dm-3 of KOH or NaOH, and organic additives. The effects of KOH and NaOH on the deposition behavior of Zn in solution containing organic additives and the microstructure of the deposits were investigated. In solution containing a quaternary ammonium cation (PQ) and a quaternary ammonium salt with a benzene ring (QA), the current efficiency for Zn deposition at high current density region of 1000 to 5000 A·m-2 to produce the glossy films was higher with KOH than that with NaOH. At high current densities above 1000 A·m-2, Zn deposition approaches the diffusion limitation of ZnO2 2- ions. With additions of PQ and QA, the diffusion of ZnO2 2- ions was significantly suppressed, and the degree of suppression was smaller with KOH than that with NaOH. The polarization resistance at 200 A·m-2 investigated by AC impedance revealed that the adsorption ability of PQ and QA onto the cathode was smaller with KOH than that with NaOH. Since the suppression effect of additives on the Zn deposition is smaller with KOH than that with NaOH, the current efficiency for Zn deposition at high current density region is larger with KOH. The upper limit of current density to produce the glossy films was smaller with KOH than that with NaOH, and the spongy thin films were partially observed on the platelets crystals obtained at high current density in KOH solution. The content of C resulting from the additives in deposited Zn was smaller with KOH. These phenomena are attributed to the adsorption ability of PQ and QA onto the cathode being smaller with KOH. [ABSTRACT FROM AUTHOR]