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Equipment Cleaning to Minimize Particle Deposition
Published in R. P. Donovan, Particle Control for Semiconductor Manufacturing, 2018
The frequency of major equipment cleaning may be reduced by in situ cleaning of the equipment by purging with inert gas. The object of the purging is to entrain particles into the inert gas from surfaces in the equipment and to pump them out of the system with the gas. If this procedure is done periodiccally, the system will remain clean longer and will be less likely to require major cleaning. The feasibility of this strategy has been demonstrated in experiments comparing the numbers of particles detected during slow and fast venting and pumping of a vacuum chamber (Bowling, Larrabee, and Fisher, 1988). During slow pumping and slow venting, few particles were detected by a particle monitor in the chamber. During fast pumping and fast venting, many particles were detected. The particles detected during the fast pumping and venting were dislodged from the walls of the chamber and the pumping and venting hardware by the rush of gas into and out of the chamber.
Ventilating Confined Spaces
Published in John F. Rekus, Complete Confined Spaces Handbook, 2018
Purging is the process by which a space is initially cleared of contaminants by displacing the hazardous atmosphere with air, steam or an inert gas. The choice of purging medium depends largely on the nature of the contaminant in the space. To minimize the risk of fire, inert gases such as nitrogen and carbon dioxide are often used to purge spaces of flammable atmospheres. Air, on the other hand, is used to purge spaces of toxic atmospheres and gases such as carbon dioxide, nitrogen and argon which could create an oxygen deficiency. In some cases, more than one purging cycle may be required. For example, the fire hazard posed by flammable gases and vapors may be minimized by initially purging the space with nitrogen or carbon dioxide. The atmosphere would then be made breathable by purging with air.
Sampling and Analysis of Particulate and Dissolved Matter
Published in Roger S. Wotton, The Biology of Particles in Aquatic Systems, 2020
The purging process can be speeded by improving the efficiency of the gas-transfer step. An apparatus has been devised27 which produces microbubbles having a mean radius of <100 μm. Preliminary tests have shown that purging a seawater sample with microbubbles produces a peak in VOC which returns essentially to baseline values after about 5 min. I would propose that this be considered as the definition for VOC.
Experimental investigation of a CRDI engine in terms of performance and emission under the effect of injection strategy using a moderate percentage of plastic pyrolysis oil and its blends with diesel and ethanol
Published in Biofuels, 2021
Sudershan B. G., Nagaraj R. Banapurmath, M. A. Kamoji, P. B. Rampure, Sanjeevkumar V. Khandal
The feedstock consists of composite plastic of styrene butadiene and polyester type of plastic. This feedstock is cut into small pieces of approximately 1–2 cm2. It is then transferred to a closed chamber and purging is carried out in order to remove oxygen from the chamber. Carbon dioxide gas or nitrogen gas is passed for purging as these are heavier than oxygen, and removes easily. Heating is provided from the external source, when the temperature inside the chamber reaches 420 °C, plastics are converted into wax and gas. The wax is collected separately and gas flows through the condenser. This gas gets condensed and collected in a separate chamber. This liquid is further treated to reduce the chlorine content by using catalysts such as activated bentonite, red mud, zeolites by heating to 50-60 °C for 15 minutes. This liquid was kept for 2–3 hours to settle down the impurities and finally filtered with 1 µm filter paper. The oil obtained is called PPO. Figure 1 represents the process of plastic oil production. Locally available diesel fuel was used for the study from Indian oil outlet and its properties are provided in Table 1. The readily available ethanol has been utilized for the blending purpose. Ethanol, diesel and PPO were blended on a volume basis using magnetic stirrer to homogenize the mixture.
What Limits Our Understanding of Oceans? Challenges in Marine Instrumentation
Published in IETE Journal of Education, 2020
Arathy R. Nair, S. Muthukumaravel, Tata Sudhakar
Wider temperature ranges: The oceanographic instruments should be able to work under wider temperature ranges, from 32°C to −2°C. The temperature of the ocean varies widely both horizontally and vertically. Warmer waters are observed near the equator and coldest waters are found near the poles. In contrast to the variation of pressure with respect to depth, vertical temperature variation displays a decreasing profile with increasing depth. There occurs, beneath the well-mixed isothermal layer near the surface, a thermocline layer, where the temperature decreases rapidly over a short distance. Beyond the thermocline, the decrease in temperature is gradual. The differences in temperature and salinity cause density variation and this density variation leads to deep ocean circulation known as thermohaline circulation. As the instrument descends through the ocean, the decreasing ambient temperature causes condensation of air inside the pressure vessel. These condensation droplets are detrimental to the electronic components inside. In order to avoid this, desiccant packs may also be strapped inside along with electronics to absorb any moisture developed. Another method is to use the vacuum purge system. Purging is the process of filling inert gas like nitrogen in the pressure vessel to displace the interior air so that a stable environment is established in the housing.