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Forecast of the gas supersaturation in Gezhou Dam under multiple flows and discharge patterns
Published in Airong Chen, Xin Ruan, Dan M. Frangopol, Life-Cycle Civil Engineering: Innovation, Theory and Practice, 2021
In order to study the influencing factors of supersaturated gas in the discharge process of Gezhou Dam and to provide guidance for reducing the concentration of saturated gas, a three-dimensional two-phase flow model was used. Firstly, the model was calibrated with Grand Coulee Dam on the Columbia River in the United States, and the saturation gas concentration of Grand Coulee Dam under different water levels, discharge flows, discharge patterns, and fore pond concentrations was compared with field observation data. The comparison results revealed that the model used in this paper had high reliability and the relative error was within 4%. Furthermore, based on the discharge data of Gezhou Dam in typical years, the simulated three-dimensional mathematical model was used to simulate and analyze the saturated gas concentration under different discharge patterns and discharge flows. Taking the simultaneous discharge of the three areas of spillway as an example, the distribution law of saturated gas concentration and the variation of the number of bubbles were analyzed. Finally, by fitting the simulation data, the empirical formula of saturated gas pressure under these four flood discharge patterns was obtained, which could provide a reference for future engineering scheduling optimization.
Equilibrium Partitioning
Published in J. Mark Parnis, Donald Mackay, Multimedia Environmental Models, 2020
It transpires that two approaches can be used to develop equations relating equilibrium concentrations to each other as shown in Figure 2.1. The simpler and most widely used is Nernst’s Distribution law, which postulates that the concentration ratio C1/C2 is relatively constant and is equal to a partition or distribution ratio K12. Thus, C2 can be calculated as C1/K12. Ideally, K12 is expressed as a function of temperature and, if necessary, of concentration. To determine K12 by measurement, mixtures are equilibrated, both concentrations measured, and plotted as in Figure 2.1. Linear or nonlinear equations then can be fitted to the data.
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Published in Carl W. Hall, Laws and Models, 2018
NERNST DISTRIBUTION LAW The simple distribution law is modified to use the concentration of the given contents instead of total concentration. Keywords: chemistry, concentration, distribution NERNST, Walther Hermann, 1864-1941, Polish German physical chemist; Nobel prize, 1920, chemistry Source: Mandel, S. 1972. NERNST EFFECT OR LAW (1886) When heat flows across lines of magnetic force, an electromotive force is produced in the mutually perpendicular direction. Keywords: electromotive, heat magnetic NERNST, Walther Hermann, 1864-1941, Polish German physical chemist; Nobel prize, 1920, chemistry Sources: Besancon, R. M. 1974; Considine, D. M. 1976; Landau, S. I. 1986. See also ETTINGSHAUSEN; HALL NERNST EQUATION Represents the concentration dependence of the reversible equilibrium potential of a working electrode and electropotential represented by one of many forms of the equation: Erev = EO - {[0.059/n] log[Aacid/Areduc]} where Erev = reversible potential EO = value of amperage when substances in standard state n = change in valence Aacid, Areduc = activities of oxidized and reduced reactants
Numerical investigation on replacement depth of black cotton soil for controlling cracking of highway embankment
Published in European Journal of Environmental and Civil Engineering, 2022
Yongzhen Cheng, Xiaoming Huang
The long-term water losing shrinkage will lead to cracking of BCS specimen. Figure 9 presents the distribution of major principal stress on specimen surface and at the layer 4 mm away from surface after drying for 1, 3 and 7 days. After water losing shrinkage of BCS, the tensile stress first appears at the center of the cylindrical specimen and increases rapidly. Then the distribution of the tensile stress gradually expands to the surrounding areas. Finally, the tensile stress concentration region without obvious distribution law appears on the surface of the specimen. Therefore, when the tensile stress induced by water losing shrinkage of BCS is greater than its tensile strength, multiple tensile cracks appear successively on the surface of specimen and expand around, instead of the single crack along a certain path. This finding is verified by the cracking law of BCS specimen in the free shrinkage test (Figure 10). In different evaporation stages, the tensile stress at the depth of 4 mm is less than that on the surface. Hence cracks appear firstly on the surface and gradually expand to the inside of the BCS specimen.
Experimental verification of permeability and inertial resistance coefficient model in the goaf
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2022
Qian Liu, Baiquan Lin, Yan Zhou, Yanjun Li, Liu Ting
The distribution law of methane concentration in the goaf is obtained by numerical simulation. 60 min, 120 min and 180 min durations, and the cloud diagram of methane concentration at 5 cm, 10 cm and 15 cm above the coal seam floor are shown in Figure 8 and Figures 10-12. It can be observed that with increasing distance from the working face, the methane concentration increases gradually, with the highest methane concentration appearing in the deepest part of the goaf, on the return roadway side. At the same time, as distance from the coal seam floor increases, the methane concentration shows a downward trend, because the coal seam floor is the source of methane emission, and concentration shows a gradient change.
Influence of refrigerant charge volume on the flammability risk of an R32 rotary compressor
Published in Science and Technology for the Built Environment, 2023
Wufeng Jin, Yi Wang, Lizhi Jia, Shuo Liu, Deokkyu Moon, Sungwoo Song
The aim of this study is to fill this gap by combining experimental observations and simulated modeling by assessing the influence of different refrigerant charge amounts on the degree of flammability risk of R32 rotor compressors under specific air intrusion conditions. The high-risk flammable area inside the compressor is obtained by analyzing the compressor exhaust pressure, internal temperature distribution, dynamic volume change, and duration of the R32 flammable concentration area. Then the flammable volume time (FVT) is used to evaluate the degree of R32 flammability risk inside the compressor under different refrigerant charge volumes (Okamoto et al. 2014). The FVT is calculated as follows: where is the flammable volume (× 10−3 m3) and is the duration. Therefore, FVT comprehensively reflects the volume and duration of the flammable area through their product integral. The larger is the flammable volume, the longer the flammable volume duration, the greater the FVT, and the greater the flammability risk. This study combines FVT with the dynamic distribution law of the R32 flammable concentration area in the compressor to assess the flammability risk more accurately. Optimization or development of a unique compressor for R32 refrigeration systems is suggested, and the minimum allowable charging standard of R32 is determined, thus ensuring the internal safety of the system (compressor) in the event of air intrusion during the maintenance and recovery process. This is crucial for improving the safety of R32 refrigeration systems in the entire life cycle. In addition, the study guides the popularization and application of R32 as a refrigerant.