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Coagulation and Mixing
Published in Paul N. Cheremisinoff, Handbook of Water and Wastewater Treatment Technology, 2019
Paddle mixers are devices consisting of two or more blades mounted on a vertical or inclined shaft. The basic paddle impeller configurations are shown in Figure 14, and a description of each is given in Table 3. The main advantages of paddle mixers are their simplicity and low cost. A disadvantage is their small pumping capacity (a slow axial flow), which does not provide a thorough mixing of the tank volume. Perfect mixing is attained only in a relatively thin stratum of liquid in the immediate vicinity of the blades. The turbulence spreads outward very slowly and imperfectly into the entire contents of the tanks; hence, circulation of the liquid is slow. Therefore, paddle mixers are used for liquids with viscosities only up to about 1000 cp. Because of a concentration gradient that often is created in the liquid when these type mixers are used, they are unsuitable for continuous operation. This can be remedied by tilting the paddle blades 30–45 degrees to the axis of the shaft, which results in an increase in axial flow and, consequently, a decrease in concentration gradients. Such a mixer can maintain particles suspended provided settling velocities are not high. Mixers with tilted blades are used for processing slow chemical reactions, which are not limited by diffusion.
Mixing Practices
Published in Nicholas P. Cheremisinoff, Polymer Mixing and Extrusion Technology, 2017
Paddle mixers are devices consisting of two or more blades mounted on a vertical or inclined shaft. The basic paddle impeller configurations are shown in Figure 32, and a description of each is given in Table 7. The main advantages of paddle mixers are simplicity and low cost. A disadvantage is their small pumping capacity (a slow axial flow), which does not provide a thorough mixing of the tank volume. Perfect mixing is attained only in a relatively thin stratum of liquid in the immediate vicinity of the blades. The turbulence spreads outward very slowly and imperfectly into the entire contents of the tanks; hence, circulation of the liquid is slow. Therefore, paddle mixers are used for liquids with viscosities only up to about 1000 cP. Because of a concentration gradient often created in the liquid when these mixers are used, they are unsuitable for continuous operation. This can be remedied by tilting the paddle blades by 30 to 45° to the axis of the shaft, resulting in an increase in axial flow and consequently a decrease in concentration gradients. Such a mixer is capable of maintaining particles suspended, provided settling velocities are not high. Mixers with tilted blades are used for processing slow chemical reactions which are not limited by diffusion.
M2(CHOO)4 paddlewheel of metal organic frameworks (M = Co, Mo, Ir) with open metal sites as anode materials of Na/K ion batteries: a theoretical study
Published in Molecular Physics, 2022
Bui Thi Hoa, Fateme Parsapour, Mohammad Amin Asgari, Morteza Moradi, Bui Xuan Vuong
Metal ions in the frameworks can sometimes create open metal sites, which are coordinative unsaturated sites (OMSs). These OMSs can function as gas molecule interaction sites and Lewis acidic sites. A typical OMS is the MOF-74 (or CPO-27) family [52], and experimental and theoretical research suggests that it is essential to the considerable adsorption energies of gas molecules [53]. A paddle-wheel (PW) structure comprising two metal ions and four carboxylate ligands, is another characteristic of OMS seen in MOFs. Agusta et al. demonstrate that an open metal site in a PW system has higher adsorption energy than a typical octahedral system due to hydrogen’s significant affinity for unsaturated metal atoms [54]. From a theoretical standpoint, the performance of metal-paddlewheel clusters with metal ion batteries has not yet been proven. Based on DFT calculations, these findings might shed more light on how Na/Na+ and K/K+ interact on the metal core.
A scale-up evaluation of a semicontinuous culture of Scenedesmus sp. in a raceway under greenhouse conditions using a commercial fertilizer as culture medium
Published in Biofuels, 2021
Luis Fernández-Linares, Enrique Durán-Páramo, Claudia Guerrero-Barajas
Two different volumes of open-channel RW reactors were used for cultivation. Five 200-L RW were used, consisting of 2.05 m channels, each channel 0.25 m wide and connected by 180° bends at both ends to provide a total surface area of 1.2 m2. Four 2000-L RW were used, consisting of 3.1 m channels, each channel 0.72 m wide and connected by 180° bends at both ends to provide a total area of 6.3 m2. The RWs were constructed with fiberglass, and in each case the culture was circulated and mixed by a four-paddle wheel system at a superficial flow velocity of 0.30 m s-1. The effective working volumes were 150 and 1100 L, with a culture medium depth of 0.15 and 0.18 m, for the 200- and the 2000-L RW, respectively. The paddle wheel was driven by a 0.5-hp Baldor brand electric geared motor. The experiments were conducted under greenhouse conditions (under diurnal and seasonal cycles) in Mexico City, Mexico (19.513°N, 99.126°W). Light irradiance, culture temperature and greenhouse temperature were recorded with a T&D RTR-500 data logger. The harvesting cycles were carried out in most cases every 2 weeks. During harvesting, half of the culture volume was removed and replaced with the same volume of fresh medium. Water losses due to evaporation were determined and replaced periodically with treated tap water.
Performance analysis of vortex flow through a swirler by computational fluid dynamics technique
Published in International Journal of Ambient Energy, 2020
Swirl motion can be defined as the uniform and predictable rotational flow of the charge about the direction of flowing or entrapped fluid in a chamber. Swirl is created in the internal combustion engine at the beginning of intake stroke into the engine cylinder with an initial angular momentum (Heywood 1988). This swirl ratio can be determined by a simple experimental arrangement. According to the experiment, a simple paddle wheel having vertical plane projections on its circumference will be set in the path of the flowing fluid. If the flow is rotational, then due to the tangential velocity component of fluid, the paddle wheel will rotate. This rotation can directly measure swirl number by the following basic formula (Figure 4) (Heywood 1988), Here swirl number of the fluid flow.ωp = angular velocity of paddle wheel in rad/s.B = Bore diameter in metrev0 = Characteristics velocity in m/s.