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Treatment of Ground Water
Published in Larry W. Canter, Robert C. Knox, Ground Water Pollution Control, 2020
The design of an air stripping process for stripping volatile organics from contaminated ground water is accomplished in two steps. The cross-sectional area of the column is determined and then the height of the packing is determined. The cross-sectional area of the column is determined by using the physical properties of the air flowing through the column, the characteristics of the packing, and the air-to-water flow ratio. A key factor is the establishment of an acceptable air velocity. A general rule of thumb used for establishing the air velocity is that an acceptable air velocity is 60% of the air velocity at flooding. Flooding is the condition in which the air velocity is so high that it holds up the water in the column to the point where the water becomes the continuous phase rather than the air. If the air-to-water ratio is held constant, the air velocity determines the flooding condition. For a selected air-to-water ratio, the cross-sectional area is determined by dividing the air flow rate by the air velocity. The selection of the design air-to-water ratio must be based upon experience or pilot-scale treatability studies. Treatability studies are particularly important for developing design information for contaminated ground water.
Design method for efficient cross-flooding arrangements on passenger ships
Published in Pentti Kujala, Liangliang Lu, Marine Design XIII, 2018
If the flooding is equalized to a condition, where sfinal = 1.0, in practice meaning that the heel angle is less than 7°, in all cases within 60 s, then the cross-flooding arrangement is confirmed to be efficient enough. Consequently, the cross-flooded rooms can be considered as instantly flooded. If the condition of instant flooding is not met, the design of the cross-flooding arrangement can be improved, e.g. by increasing the area of the device, or the number of air pipes. Alternatively, the particular devices can be included in the SOLAS damage stability calculations.
Particle Characterization and Dynamics
Published in Wen-Ching Yang, Handbook of Fluidization and Fluid-Particle Systems, 2003
Flooding occurs when the solids flow into the dipleg is greater than the solids discharge through the valve. This causes solids to back up into the cyclone. Flooding is generally caused by extremely high solids flow rates or excessive leakage or aeration.
Analysis of compression in uniform and non-uniform GDL microstructures on water transport
Published in International Journal of Green Energy, 2022
Ikechukwu S. Anyanwu, Zhiqiang Niu, Shaohui Jin, Kui Jiao, Zhengwei Gong, Zhi Liu
In PEMFCs, the membrane electrolyte assembly (MEA), which is the combination of the gas diffusion layer (GDL), catalyst layer (CL) and the proton exchange membrane (PEM), is sandwiched between two bipolar plates (BP). This tri-layer forms the basic building block and heart of the PEMFC. To a great extent, the effectiveness of the cell depends on the overall kinetics of the electrochemical process and the performances of MEA and BP. Hydrogen-rich fuel and oxidant are supplied to the cathode and anode sides of the MEA via the flow channels of the BP. As a result of the cell electrochemical reaction, product water and heat are released as the by-product. The GDL is the kernel of the MEA which serves as a link between the MEA and the BP. The GDL is a porous medium generally made of woven carbon fabric, woven carbon paper or non-woven carbon paper. This porous material is designed to allow gas, water heat and charge transport. The product water generated as a result of the electrochemical reaction must be effectively transported from the CL into the channel. As the main bridge of water transportation, the effective water transport through the GDL is very crucial. Excessive accumulation or ineffective water transport can lead to flooding, which will limit the overall cell performance, as well as lead to component damage. The GDL is also saddled with the responsibility of supplying sufficient conductivity to convey the electrons between the CL and the BP, while serving to provide the needed mechanical support for the MEA against compressive loads imposed by the BP. Normally, during assembly the clamping pressure on the BP can lead to deformation of the GDL. This compression of the GDL is inevitable, because the essence of applying some clamping force during assembly is to prevent leakages. However, this exposes the porous GDL to some degree of deformation as a result of the compressive load, which generally affects its performance.
Removal of odorous compounds emitted from a food-waste composting facility in Korea using a pilot-scale scrubber
Published in Journal of Environmental Science and Health, Part A, 2018
Kris Niño G. Valdehuesa, Grace M. Nisola, Seong-Poong Lee, Alex V. Anonas, Enkhdul Tuuguu, Melvin M. Galera, Eulsaeng Cho, Wook-Jin Chung
An important packed column design parameter to be considered is the optimum L/G ratio, due to its role in assessing the economics of the absorption equipment.[18] The main parameter set for calculating L/G is at > 95% removal of ammonia and methylamine. Experimental runs were performed with the L/G ratio varying from 2 to 11, while maintaining the scrubbing solution pH below 6.5. The results show that a minimum L/G ratio of 4.5 and 2.0 (L per m3) were required for 95% removal of ammonia and methylamine, respectively (Fig. 2b). The observed high removal efficiencies of methylamine at low L/G values were due to its higher solubility at 108 g per 100 g water, compared to ammonia at 48 g per 100 g water at 25 °C.[19] Consequently, the removal efficiency for ammonia and methylamine was reduced upon increasing the gas flow rate, while holding the scrubber liquid loading rate at 3 m3/m3-hr (Fig. 3a). The loss of removal efficiency was more pronounced with ammonia, achieving ∼84% removal at ∼4000 m3/m3-hr gas loading rate. This may be due to factors such as reduced gas-liquid contact time and increased column pressure drop leading to flooding and liquid holdup.[18] To achieve 95% removal efficiency, the gas loading rate for ammonia and methylamine should not exceed 1750 and 3819 m3/m3-hr, respectively. In the case of liquid loading rate, a slight increase in removal efficiencies for both ammonia and methylamine were observed when the loading rate was varied from 3 to 8 m3/m3-hr (Fig. 3b). The increased removal efficiency even at a higher liquid loading rate of 8 m3/m3-hr shows that the system has not reached its “loading point” wherein severe channeling starts to occur. Usually, increasing the liquid loading rate (i.e. approaching “flooding velocity”) leads to better packing surface wetting/liquid distribution of the packed bed, thus providing higher interfacial area for mass transfer.[18]