Spark conditioning is an effective method to increase the dielectric strength in vacuum by melting and removing micro-protrusions on the cathode surface. We aim to optimize the conditioning effect in ...vacuum for the application of vacuum circuit breakers (VCBs) to higher voltage levels. To obtain high breakdown (BD) voltage, the control of BD charge in the conditioning process is required. When a BD occurs, we have suggested that micro-protrusions can be generated on the cathode surface by particles from the anode. For the suitable control of BD charge, the meltability of generated micro-protrusions and their size are important. In this article, we focus on the generation of micro-protrusions on the cathode surface in conditioning process. First, we conduct spark conditioning by repetitive impulse voltages of rod-plane electrodes made of OFHC Cu in a vacuum chamber with different BD charges. Later, we observe the surface of rod cathode with a digital microscope in order to count the number of visible protrusions and measure their radii. By considering the meltability of micro-protrusions, we quantitatively reveal the existence of residual protrusions that cannot be completely melted by BD. Next, we estimate the maximum size of generated micro-protrusions by BD charge. In consideration of the collision of ions into the anode accelerated by the anode sheath voltage, we estimate the meltable amount of anode material by the BD charge. We confirm that the radii of experimentally measured protrusions are close to the estimated ones. Moreover, we consider the difference in dielectric strength due to the difference in the initial surface condition of the electrodes. We clarify that the dielectric strength is improved by applying acid wash and heat treatment to the electrodes before conditioning, which can be optimized by the BD charge and the initial surface condition of the electrode.
•Vacuum Flat Plate Enclosures were fabricated involving Ultrasonic Soldering techniques.•Heat transfer in vacuum space was theoretically studied.•Thermal properties of the fabricated enclosures were ...tested using a hot box calorimeter.•Heat flow through the individual components of the vacuum enclosures were theoretically predicted.•Infrared thermography was undertaken on the vacuum enclosures with different internal vacuum pressures.
Non-concentrating solar thermal collectors are generally available in two forms, flat plate or evacuated tube. Recently a third configuration, the evacuated flat plate, has attracted interest due to enhanced performance and aesthetic characteristics. By isolating a solar absorber in a vacuum space (<1 Pa) heat loss from the absorber can be minimized resulting in improved efficiency. In addition the improved thermal insulation performance of evacuated panels over conventional glazing systems makes them attractive solutions for integration into energy efficient building facades.
This two part paper describes the design, construction techniques and thermal performance of two vacuum enclosures, fabricated at Ulster University, as prototype components for evacuated flat solar collectors. The first enclosure consists of two glass panes sealed to an edge spacer and separated by an array of support pillars on a regular square grid to form a narrow evacuated space. The second enclosure incorporates an uncooled copper sheet to represent a solar thermal absorber. The enclosures were tested at three conditions i.e. with an internal pressure of high vacuum (0.0021 Pa), low vacuum (8.4 Pa) and no vacuum (atmospheric pressure).
Part 1 of this paper describes the fabrication process for the vacuum enclosures and the measurement of their thermal insulation properties using a hot box calorimeter. The theory of heat transfer through an enclosure with support pillars is discussed; experimental results are compared with mathematical models predictions. A fabrication methodology has been successfully established and a U-value of 1.35 W/m2 K for an enclosure with an internal pressure of 0.0021 Pa has been demonstrated. The experimental results are in good agreement with the predictions.
Part 2 of this paper describes solar simulator testing of the enclosure containing a copper plate. The highest stagnation temperature (121.8 °C) was reached under steady-state conditions in the high vacuum test and was in good agreement with predictions. The transient plate and glass surface temperatures were measured and found to be consistent with the predicted curves.
The vacuum chamber is an important part of microparticle optical levitation technology. The traditional vacuum chamber has a large volume and many peripheral components, which cannot meet the ...requirements of miniaturization and on-chip optical levitation technology. Therefore, this study proposes a novel microparticle vacuum chamber based on the micro-electro-mechanical system (MEMS) process. This MEMS microparticle vacuum chamber adopts a “glass-silicon-glass” three-layer vacuum bonding process, with a volume of only 15 mm × 12 mm × 1.2 mm, including particle chamber, cantilever resonator chamber, and getter chamber, which can encapsulate microparticles in a tiny vacuum environment and realize optical levitation of microparticles. At the same time, the air pressure in the micro vacuum chamber is monitored by the cantilever resonator, which can provide a miniaturized microparticle chamber with a more accurate vacuum environment for microparticle optical levitation. The research of this paper has significance for promoting the development of miniaturized optical levitation technology.
Traditional vacuum system designs often rely on a 100% reserve, lacking precision for accurate petrochemical computations under vacuum. This study addresses this gap by proposing an innovative ...modeling methodology through the deconstruction of a typical vacuum-enabled process. Emphasizing non-prescriptive pressure assignment, the approach ensures optimal alignment within the vacuum system. Utilizing process simulation software, each component was systematically evaluated following a proposed algorithm. The methodology was applied to simulate vacuum-driven separation in phenol and acetone production. Quantifying the vacuum system’s load involved constructing mathematical models in Unisim Design R451 to determine the mixture’s volume flow rate entering the vacuum pump. A standard-sized vacuum pump was then selected with a 40% performance margin. Post-reconstruction, the outcomes revealed a 22.5 mm Hg suction pressure within the liquid-ring vacuum pump, validating the efficacy of the devised design at a designated residual pressure of 40 mm Hg. This study enhances precision in vacuum system design, offering insights that are applicable to diverse petrochemical processes.
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•Vacuum application provides enhanced quality characteristics in dough-based products.•Vacuum mixing/kneading improves the dough quality by affecting the gluten network.•Baking under ...vacuum conditions could inhibit the formation of HMF and acrylamide.•Vacuum is an effective approach for rapid cooling of dough based products.
Cereal-based foods have been essential elements in nutrition throughout history. Recently, there has been an increasing interest in the application of innovative strategies to improve technological and nutritional properties of dough-based cereal products. Literature studies indicate that the integration of vacuum technology into baking and noodle industry can significantly enhance the quality and feasibility of final products. The vacuum has direct impact on gluten network, gas distribution and interaction of components in food matrix, especially due to aerated structure of dough systems. In this respect, this review for the first time presents a comprehensive evaluation regarding to use of vacuum technology in processing steps (i.e., mixing, baking, and cooling) of dough-based products in light of recent studies. The implementation of vacuum in the processes provide desired impacts on productivity and profitability for manufacturing industries. Vacuum application provides many advantages including improved product quality, nutritive value, extended shelf life, and reduced energy consumption.
Spark conditioning is an effective method of increasing the dielectric strength in vacuum. In this article, we discuss the breakdown (BD) charge dependence of counter electrode material adhesion and ...dielectric strength after spark conditioning. We have applied a negative impulse voltage to a rod-plane electrode configuration with a cathode and an anode made of stainless steel (SUS) that is defined as SUS304 by JIS G 4303 or oxygen-free high-conductivity copper (Cu). The electrode system of cathode SUS and anode Cu is called SUS-Cu electrode system, and the electrode system of cathode Cu and anode SUS is called Cu-SUS electrode system. We have changed BD charge (<inline-formula> <tex-math notation="LaTeX">{Q}_{\text {BD}} </tex-math></inline-formula>) in conditioning by changing the limiting resistance in the experimental circuit. As a result, in both cases of SUS-Cu and Cu-SUS electrode systems, the larger the <inline-formula> <tex-math notation="LaTeX">{Q}_{\text {BD}} </tex-math></inline-formula>, the smaller the amount of the anode material adhered to the cathode surface. When <inline-formula> <tex-math notation="LaTeX">{Q}_{\text {BD}} </tex-math></inline-formula> is large, the dielectric strength increases in SUS-Cu electrode system and decreases in Cu-SUS electrode system. From these results, when <inline-formula> <tex-math notation="LaTeX">{Q}_{\text {BD}} </tex-math></inline-formula> is large, we consider that the conditioning characteristics are less likely to be dominated by the anode material, i.e., Cu in the case of SUS-Cu electrode system and SUS in the case of Cu-SUS electrode system. In other words, the decisive parameters, such as <inline-formula> <tex-math notation="LaTeX">{Q}_{\text {BD}} </tex-math></inline-formula> to maximize the dielectric strength, may depend on the combination of electrode materials.
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