Mass environmental control

Shen C-C, Edwards RL, Cheng H, Dorale JA, Thomas RB, Moran SB, Weinstein S, Edmonds HN (2002) Uranium and thorium isotopic and concentration measurements by magnetic sector inductively coupled plasma mass spectrometry. Chem Geol 185 165-178 Shen GT, Dunbar RB (1995) Environmental controls on uranium in reef corals. Geochim Cosmochim Acta 59 2009-2024... 

Environmental control in respect of determining concentrations and isotope ratios, e.g. of U, Pu and other actinides, is also required in routine measurements near to nuclear power plants, uranium enrichment facilities or nuclear waste recycling companies. Groundwater samples are analyzed after dilution directly by ICP-MS for soils a digestion step before mass spectrometric measurement is necessary. If isobaric interferences are observed a trace matrix separation and/or a careful analyte separation (e.g. of U and Pu) is recommended. 

With ex situ treatment of contaminated soils, a controlled environment for soil treatment can be maintained- With mixing, nutrient addition, aeration, and other environmental controls, mass transfer rates that typically limit in situ bioremediation can be greatly increased. Of course, the disadvantages of ex situ bioremediation are the costs of soil excavation and reactor operation. Thus, ex situ bioremediation is favored by localized, shallow soil contamination. 

For a solid sulfur product, the sulfur layer is pumped to large outside vats where it is allowed to cool. The simplest containment for this method consists of a vertical sheet metal rim which is used to hold the molten sulfur until it solidifies. Once the product is solid, the metal rim is moved upward ready to receive the next layer of molten sulfur. The large, compact dense masses of product thus formed represent one of the least expensive and best environmentally controlled forms of storage of excess sulfur inventory. For delivery, the large mass is broken up using small explosive charges or mechanical means. 

Gas-to-liquid mass transfer is a transport phenomenon that involves the transfer of a component (or multiple components) between gas and liquid phases. Gas-liquid contactors, such as gas-liquid absorption/ stripping columns, gas-liquid-solid fluidized beds, airlift reactors, gas bubble reactors, and trickle-bed reactors (TBRs) are frequently encountered in chemical industry. Gas-to-liquid mass transfer is also applied in environmental control systems, e.g., aeration in wastewater treatment where oxygen is transferred from air to water, trickle-bed filters, and scrubbers for the removal of volatile organic compounds. In addition, gas-to-liquid mass transfer is an important factor in gas-liquid emulsion polymerization, and the rate of polymerization could, thus, be enhanced significantly by mechanical agitation. 

Aggregation of fine particulate solids also takes place in liquids. In environmental control, the removal of particulate solids from liquid process effiuents is of great importance. As for gas/solid separations, when the size of the solids diminishes and reaches the micron or submicron (nano) range, the mass of individual particles becomes so small that they remain in suspension and carmot be removed by setding. Because of the fineness, membranes would be required to retain particles on a diaphragm, which is uneconomical for the cleaning of large volumes of contaminated liquids from industrial plants or waste-water treatment facilities. 

The constmction of a gas manifold incorporating four mass flow controllers allowed the mixing of water saturated air with dry air to produce test streams of gas with accurate RH. Measured amounts of hydrogen were then added to the test stream. An environmental test chamber was also constructed from an insulated cooler. A heating element on the test chamber and a proportional temperature controller allowed control of the gas temperature and thus the thin film temperature to within 0. PC. 

Second The size (mass) of a cell at division is under genetic and environmental control, but the critical mass for fission shows small random variations about the mean value. The concept that cell division results when cells have attained a critical mass is not new its history is reviewed by Koch and Schaechter. Random variations of cell size at division may be due to (i) the critical mass varying slightly from cell to cell or (ii) appearance of visible evidence of fission in individual cells may be premature or delayed. In either case the observed variation is supposed to be due to the accumulation of small effects of a large number of random influences. Hence, as a subpostulate, Koch and Schaechter assume that the distribution of sizes at fission is nearly Gaussian. 

The space shuttle environmental control system handles excess CO2 (which the astronauts breathe out it is 4.0% by mass of exhaled air) by reacting it with lithium hydroxide, LiOH, pellets to form lithium carbonate, Li2C03, and water. If there are 7 astronauts on board the shuttle, and each exhales 20. L of air per minute, how long could clean air be generated if there were 25,000 g of LiOH pellets available for each shuttle mission Assume the density of air is 0.0010 g/mL. 

Bennett CJ, Kolaczkowski ST, Thomas WJ. Determination of heterogeneous reaction kinetics and reaction rates under mass transfer controlled conditions for a monohth reactor. Process Safety and Environmental Protection Transactions of the Institution of Chemical Engineers, Part B 1991 69 209-220. 

The chapter authors feel that the sessile drop technique represents a more precise and versatile tool for quantifying wetting, particularly in high-temperature systems where environmental control is imperative. For solderability assessment, the technique involves placing a solder alloy on a preheated substrate either as a molten (Uquid) drop or as a solid mass that subsequently melts. Wetting in the sessile drop method is spontaneous rather than forced. Therefore, it shares a strong similarity with the conditions that prevail in many commercial soldering processes. 

Like its earlier editions, this book has two purposes. First, it presents a clear description of diffusion, the mixing process caused by molecular motion. Second, it explains mass transfer, which controls the cost of processes like chemical purification and environmental control. The first of these purposes is scientific, explaining how nature works. The second purpose is more practical, basic to the engineering of chemical processes. 

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