Influences of Brass Surface Morphology on Leidenfrost Effect during Liquid Nitrogen Cooling

Cooling in liquid nitrogen is a typical service condition of high-temperature superconducting wire, and the variation of boiling stages on the wire protective layers such as the brass layers could be crucial for the quench behavior of superconducting devices. In this study, the influence of brass surface morphology (parameters of surface roughness and fractal dimension) on the Leidenfrost effect (including the wall superheat at critical heat flux and the wall superheat at Leidenfrost point, which are respectively characterized by the temperatures of ΔTCHF and ΔTLP) was studied. The surfaces of brass samples were polished by sandpaper to obtain different morphologies, which were characterized by using white light interferometer images, and the boiling curves were recorded and analyzed by Matlab with lumped parameter method. The experimental results demonstrated that the surface morphology of brass samples could influence the ΔTLP significantly, but had no clear relationship with the ΔTCHF. Moreover, the multi-scaled analysis was carried out to explore the influencing mechanism of surface microstructure, the relationship between ΔTLP and scale was more clear when the scale was small, and the fractal dimension was calculated and discussed together with surface roughness. The findings of this study could be instructive for surface treatment of superconducting wires to suppress quench propagation.

Microprocesses at the brass surface after impact of scanning beam of pulse-frequency ultraviolet nanosecond laser

A mode of laser heat treatment of the brass surface prior to conducting of diffusion bonding is proposed. We used the frequency-pulse radiation of a nanosecond ultraviolet laser at a pulse energy density W = 0.15 - 0.52 J/cm2. The metal sample was moved relative to a stationary laser beam along a raster trajectory (“snake”) so that adjacent spots were overlapped with an overlap ratio of ⩾ 99 %. The impact of radiation on brass was carried out in a subthreshold mode excluding crater formation. The process took place while the metal remained in a condensed state. A regular rough structure with a height of individual uplifts of the order of 1 micron was formed on the surface of the brass. article is devoted to creation of aerosolized detergent compositions, needful for use during operation of high-precision metal mirrors, as a rule, in field conditions. The created detergent compositions with inhibitory properties allow, simultaneously with carrying out the process of physicochemical cleaning of optical surface from technological impurities, to ensure its protection from the influence of adverse climatic factors during storage, transportation, installation and exploitation of the element with the possibility of its alignment. The high climatic resilience of the protective films investigated in this article, which are formed during the cleaning of the optical surface, is shown. In this case, the optical characteristics of the processed elements after climatic tests do not get worse.

Evolution of a Superhydrophobic H59 Brass Surface by Using Laser Texturing via Post Thermal Annealing

To fabricate an industrial and highly efficient super-hydrophobic brass surface, annealed H59 brass samples have here been textured by using a 1064 nm wavelength nanosecond fiber laser. The effects of different laser parameters (such as laser fluence, scanning speed, and repetition frequency), on the translation to super-hydrophobic surfaces, have been of special interest to study. As a result of these studies, hydrophobic properties, with larger water contact angles (WCA), were observed to appear faster than for samples that had not been heat-treated (after an evolution time of 4 days). This wettability transition, as well as the evolution of surface texture and nanograins, were caused by thermal annealing treatments, in combination with laser texturing. At first, the H59 brass samples were annealed in a Muffle furnace at temperatures of 350 °C, 600 °C, and 800 °C. As a result of these treatments, there were rapid formations of coarse surface morphologies, containing particles of both micro/nano-level dimensions, as well as enlarged distances between the laser-induced grooves. A large number of nanograins were formed on the brass metal surfaces, onto which an increased number of exceedingly small nanoparticles were attached. This combination of fine nanoparticles, with a scattered distribution of nanograins, created a hierarchic Lotus leaf-like morphology containing both micro-and nanostructured material (i.e., micro/nanostructured material). Furthermore, the distances between the nano-clusters and the size of nano-grains were observed, analyzed, and strongly coupled to the wettability transition time. Hence, the formation and evolution of functional groups on the brass surfaces were influenced by the micro/nanostructure formations on the surfaces. As a direct consequence, the surface energies became reduced, which affected the speed of the wettability transition—which became enhanced. The micro/nanostructures on the H59 brass surfaces were analyzed by using Field Emission Scanning Electron Microscopy (FESEM). The chemical compositions of these surfaces were characterized by using an Energy Dispersive Analysis System (EDS). In addition to the wettability, the surface energy was thereby analyzed with respect to the different surface micro/nanostructures as well as to the roughness characteristics. This study has provided a facile method (with an experimental proof thereof) by which it is possible to construct textured H59 brass surfaces with tunable wetting behaviors. It is also expected that these results will effectively extend the industrial applications of brass material.

Mechanical bonding in cold roll-cladding of tri-layered brass/steel/brass composite

In this paper, brass/steel/brass clad-composite was fabricated using a cold roll-bonding process. Composite sheets were roll-bonded at reduction ratios between 37 and 72% at room temperature from strips of 150 mm in length and 30 mm wide, in one pass without lubrication. The threshold deformation for successful bonding was at a thickness reduction of 48% and peel strengths of the bonds were measured to be approximately 12 N cm-1, and it was found to escalate with an increase in the rolling reduction. The optimum reduction in thickness was ~66% wherein the peel strength was ~33 N cm-1. Various techniques such as optical and electron microscopy were implemented to analyze and investigate the effects of the reduction in thickness and the joining mechanism. The results showed that an increased reduction in thickness in rolling leads to an increase in the joining strength. Furthermore, increasing the brass plate thickness negatively affects the joining strength. A Cu peak on the peeled-off steel surface and the presence of Fe on the peeled-off brass surface strongly suggest that the major bonding between brass and steel was mechanically induced metallurgical bonding.

Research on erosion characteristics of a novel cavitation nozzle under nonsubmerged condition

When a cavitating jet enters the atmosphere directly, its cavitating effect weakens rapidly, and the erosion energy it produces cannot be fully utilized. Regarding the problem that existing cavitation nozzles are only used in submerged condition, methods to improve the erosion ability of cavitation jets under nonsubmerged condition are studied. The nozzle is visually simulated using Fluent software, and the results show that the dynamic submerged environment at the outlet effectively expands the nearby low-pressure cavitation area. The enhancement effect of the annular cavitation nozzle on the jet cavitation effect in the atmosphere domain is verified by measuring the impact force curve of the jet and through erosion tests on brass surface. Cleaning and derusting tests show that the annular cavitation nozzle has stronger derusting ability than the high-pressure nozzle under nonsubmerged condition and under the same pressure, demonstrating that the cleaning and derusting effect mainly comes from the collapse of cavitation bubbles.