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Vacuum and Gas Kinetics
Published in Eiichi Kondoh, Micro- and Nanofabrication for Beginners, 2021
Rotary pump A rotary pump or rotary vane pump is probably the most common vacuum pump. It functions from the atmospheric pressure down to about 100 Pa in the case of single-stage usage. Figure 2.14 is an example of a rotary vane pump. Two vanes attached to a rotor at the center are pressed to the inner wall of a cylinder. As the axis of the rotor is offset from the cylinder axis, the volume of the space bounded by the vanes, the rotor, and the cylinder changes as the rotor rotates. Gas enters when this space has a larger volume, gets compressed with rotation, and is finally exhausted to the outlet port thorough a gas ballast valve. The internal space, such as the cylinder, is filled with oil. The oil serves to seal the outlet valve from leaks and also lubricates the moving parts. The capacity of rotary pumps for laboratory experiments (as well as for semiconductor manufacturing) have a pumping speed of 50–2000 ℓ/min. Rotary pumps are economically affordable, irrefrangible, easy-to-use or -to-maintain, and function from the atmospheric pressure so that no roughening/backing pumps are necessary. For these reasons, rotary pumps are widely used. One serious drawback is oil emission. As the gas directly gets in contact with oil, the oil vapor is easily incorporated to the vacuum which limits the achieving pressure and leads to contamination. The oil must be exchanged regularly as the oil degrades, but usually not so often.
Parboiling of Rice
Published in B. K. Bala, Agro-Product Processing Technology, 2020
In this method, paddy is first soaked in cold water to remove impurities and lighter grains. The steeping is done in a stationary autoclave, and then a vacuum is applied first and water is injected; then high hydrostatic pressure is maintained at a controlled temperature. Steaming and drying are done in a rotary autoclave, which is also fitted with a steam jacket. The drying is done under vacuum.
Compressors and Pumps
Published in Leslie R. Rudnick, Synthetics, Mineral Oils, and Bio-Based Lubricants, 2020
Compressors and pumps, often called working machines, are used to move materials for a large variety of purposes. Compressors are machines that increase the pressure of a gas through input of mechanical work. Vacuum pumps are compressors that operate using suction pressure to create vacuum. Liquid pumps transfer liquids, or sometimes slurries of liquid–solid mixtures. Applications for these machines are in industries such as steel, petroleum, chemical, mining, food, gas, production and storage, energy conversion (refrigeration), etc. Their shutdown means loss in production. Lubricants in these applications lubricate moving parts such as bearings and gears, provide a liquid seal, and remove heat. This can be a difficult task as the lubricant often operates in a hostile environment.
Topology Optimization of Thermal Insulators considering Thermal–Structural Multi-Objective Function
Published in Engineering Optimization, 2022
Younghwan Joo, Jaeho Jung, Minho Yoon
Thermal insulation is as important as the enhancement of heat transfer in engineering fields. In nuclear engineering, particularly in designing small modular reactors, undesirable heat transfer frequently occurs because of highly integrated design features. This unwanted heat transfer causes a loss of power and sometimes results in deterioration of the system reliability. To solve this problem, state-of-the-art designs that suppress heat transfer while maintaining structural reliability have been developed through trial and error. There are various thermal insulation technologies in other fields that have similar purposes. For example, a vacuum insulation panel (Choi et al.2016) is a device that achieves a high level of thermal insulation by maintaining a near-vacuum environment inside an envelope with minimal supporting structures. The thermal protection system (TPS) (Yang et al.2019) is a thermal insulation system designed to protect hypersonic flights from the heat generated on external surfaces under a pressure load. These examples imply two competing design goals: maximizing the thermal insulation performance, which is related to minimal supporting structures, and maximizing the structural reliability, which is related to maximum supporting structures.
The Trinity High-Explosive Implosion System: The Foundation for Precision Explosive Applications
Published in Nuclear Technology, 2021
Eric N. Brown, Dan L. Borovina
From Gibbs and Popolato,34 Baratol is manufactured from finely ground barium nitrate added to molten TNT to form a castable slurry. About 0.1 wt% of nitrocellulose is added to the TNT before adding the barium nitrate to reduce the slurry viscosity. Subsequent to the addition of the barium nitrate and just before applying a vacuum to the melt, 0.05 to 0.1 wt% decylgallophenone or stearoxyacetic acid is added to prevent cracking. Before casting, a vacuum is applied to the melt to remove dissolved and occluded gas to achieve a higher and more uniform density. Nominal properties for Baratol are reported in Table II. The nominal detonation velocity is tunable by varying the percentage of barium nitrate. It is worth noting that during the Manhattan Project scientists needed to develop rate stick tests with an adequate booster to avoid anomalously low-velocity measurements from a point detonation and edge effects. They also found the refractive index between the fast and slow explosives could only be determined by experimental iteration, and the slow explosives velocity was observed to be faster in the lens configuration than measured from a rate stick test.7
Effect of ortho-para conversion on economics of liquid hydrogen tanker with pressure cargo tanks
Published in Ships and Offshore Structures, 2018
Hwalong You, Junkeon Ahn, Sangkwon Jeong, Daejun Chang
There are several representative insulation concepts that can be used to prevent external heat ingress. Multi-layer insulation (MLI) is primarily intended to protect cryogenic inventory from radiation, and it is often used in spacecraft. Vacuum insulation was designed to reduce heat ingress due to radiation, gas conduction and convection. However, it is difficult to apply MLI to complicated shapes, and it is weak to lateral conduction. In addition, vacuum insulation requires a permanently high degree of vacuum, which is easily broken by a small leak. Therefore, poly urethane foam is applied to the surface of the cargo tank. External heat ingress through the insulation and tank can be calculated using the following conditions (Table 3).