共查询到20条相似文献,搜索用时 31 毫秒
1.
Constantinos Xanthopoulos Michael Stamatoudis 《Chemical Engineering Communications》1986,46(1):123-128
Impeller power numbers in closed square vessels with/or without baffles and in closed cylindrical vessels with baffles were studied for impeller Reynolds numbers in the range between 75000 and 300000. A flat vertical blade disk style, a vertical blade open style and a 45° pitched blade open style impellers were used. A substantial reduction of power number is observed for all three impellers inside the square vessels without baffles in comparison with baffled cylindrical and square ones reaching up to 61 %. 相似文献
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Donald J. Gray 《Chemical Engineering Communications》1987,61(1):151-158
The effect of impeller off bottom clearance on the power input requirement for off bottom solid suspension was examined for 45° pitched blade impellers in flat and round bottom fully baffled agitated vessels. Results showed a similar dependence as obtained for radial flow impellers when similar flow patterns were observed. The dependence appears to be independent of the impeller diameter to tank diameter ratio and vessel shape. 相似文献
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比较了挡板和蛇管对搅拌功率的影响关系,并在Ф476和Ф784两台几何相似的有蛇管釜中,采用六直叶圆盘涡轮,详细研究了不同液体中搅拌功率与通气量,桨径,桨层数,液位等因素的关系,由回归分析法得不通气时桨的功率准数Np为Np=2.4(D/T)-0.32.n0.51.(H/T)0.57通过时的搅拌功率计算式为Pa=1.66(P0^2.N.D^3/QG^0^.^5^6)0.41当在Ф1000釜中安置三层圆 相似文献
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Mixing in a completely filled vessel, designed as a pressure vessel, has been investigated. The power demand of two pitched blade turbines of different sizes, and one high flow impeller was studied. The influence of side-mounted and bottom-mounted baffles, as well as the clearance between the bottom and the impeller was investigated. The experiments were carried out in a plexiglass vessel with a diameter of 288 mm. The Power number was calculated from measured data on the power demand and the impeller speed. Furthermore, preliminary studies on the critical impeller speed and power demand at the off-bottom suspension point for one set of glass particles were carried out. The Power number was mainly influenced by the impeller type, while the power demand at the off-bottom suspension point was more dependent of the impeller size and clearance. For bottom-mounted baffles a minimum in the Power number was noticed with increased clearance. It was found the minimum was located at the transition point between two different How patterns. This study shows that the configuration with the lowest Power number is not necessary the most efficient for suspending solid particles. 相似文献
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Masanori Yoshida Yuma Wakura Kazuaki Yamagiwa Akira Ohkawa Shuichi Tezura 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2010,85(7):1017-1022
Liquid‐phase mixing is a common operation, often performed in vessels using mechanically rotating impellers. To enhance axial mixing the vessels are generally equipped with baffles; however, in industries where cleaning the vessel interior is a major concern, i.e. food and pharmaceuticals, and crystallization, where baffles can disturb particle growth, unbaffled vessels are preferred. One method of agitation in unbaffled vessels is an impeller that periodically changes either the direction or rate of rotation: so‐called unsteady rotation. For use in an enhanced agitation vessel, an agitation technology using an unsteady forward–reverse rotating impeller in an unbaffled vessel was investigated. Such unsteady agitation is expected to enhance mixing. However, knowledge of the liquid flows in such an apparatus remains elusive. Thus an aim of this work was to characterize the circulation flow in such a system. Circulation by a disk turbine impeller with six flat blades was studied through examination of tracer particle trajectories. Images showing flow patterns with the forward–reverse rotating impeller resembled those obtained with a unidirectionally rotating impeller in a baffled vessel. The pattern was characterized by a circulation loop whose pathway exits from the impeller rotational region and returns to that region past the wall and bottom of the vessel. Time‐series particle tracking velocimetry (PTV) images obtained during one forward–reverse rotation of the impeller showed that the flow near the vessel wall reduced the periodic fluctuation downstream and that a flow that was almost independent of time was induced near the vessel bottom. For the flow from the bottom to the impeller, unsteadiness was provided by proximity to the impeller. Based on the intensity distribution of the unsteady flow produced by this type of forward–reverse rotating impeller within the vessel, the unsteady flow was shown to have the potential to reach the region near the vessel wall. Copyright © 2010 Society of Chemical Industry 相似文献
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Yung-Chien Hsu Chyuan-Jih Huang Wen-Hsin Yen Robert Y. Peng 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1998,71(3):187-196
The onset speed of gas induction and the power consumption after gas induction were studied in a gas-induced type agitated tank. In such an agitated tank, four unique baffles which were shorter and narrower than the conventional ones were adopted. Two 45° downward pitched blade turbines (PBT) in series were used as impellers. Gas induction could be formed by the dual impellers operated above the onset impeller speed. Several geometric factors and operation parameters were considered by theoretical aspects and the dimensionless analysis to study the onset of gas induction and the power consumption. In all experiments, air and tap water were used as working fluids. Results revealed that a lower agitation speed and less power consumption were needed for the present tank than a narrower full-length baffled agitated tank. In the present tank, the least specific power consumption was found when the liquid level was about 1·9 times the tank diameter. Two correlation equations were obtained to predict, respectively, the onset speed of gas induction and the power consumption after gas induction. Comparison between the present type and various other gas-inducing type agitated tanks were also discussed. © 1998 SCI 相似文献
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V. B. Rewatkar K.S.M.S. Raghava Rao J. B. Joshi 《Chemical Engineering Communications》1990,88(1):69-90
Power consumption was measured in mechanically agitated contactors of internal diameter 0.3 m, 0.57 m, 1.0 m and 1.5 m. Tap water was used as a liquid in all the experiments. The impeller speed was varied in the range of 0.3-13.33 r/s. Three types of impellers, namely disc turbine (DT), pitched-blade downflow turbine (PTD) and pitched blade upflow turbine (PTU) were employed. The ratio of the impeller diameter to vessel diameter (D/T) and the ratio of impeller blade width to impeller diameter (W/D) were varied over a wide range. The effects of impeller clearance from the tank bottom (C), blade angle (φ), total liquid height (H/T), number of impeller blades (nb) and blade thickness (tb) were studied in detail. Power consumption was measured using a torque table
Power number was found to have a strong dependence on the flow pattern generated by the impeller. Unlike, DT and PTU, the power number of PTD was found to increase with a decrease in clearance. The PTD (T/3) was found to have the lowest power number in all the vessels and the power number increased with either a decrease or an increase in the impeller diameter from T/3. The dependence of power number on impeller diameter was found to be more prominent when the D/T ratio was more than 0.3. In general, the power number was found to increase with an increase in blade angle and blade width. The effect of blade width was found to be more prominent in larger diameter vessels. A correlation has been developed for power number in the case of PTD impellers. 相似文献
Power number was found to have a strong dependence on the flow pattern generated by the impeller. Unlike, DT and PTU, the power number of PTD was found to increase with a decrease in clearance. The PTD (T/3) was found to have the lowest power number in all the vessels and the power number increased with either a decrease or an increase in the impeller diameter from T/3. The dependence of power number on impeller diameter was found to be more prominent when the D/T ratio was more than 0.3. In general, the power number was found to increase with an increase in blade angle and blade width. The effect of blade width was found to be more prominent in larger diameter vessels. A correlation has been developed for power number in the case of PTD impellers. 相似文献
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Hans Theliander 《Chemical Engineering Communications》1995,132(1):169-186
The suspension of solid material in a closed vessel has been studied. The vessel was designed as a pressure vessel having dished ends. Both the impeller speed at the off-bottom suspension point as well as the power demand related to this speed have been determined. In the study, emphasis was placed on studying the influence of both form and position of the baffles
It was found that a new dimensionless number, designed to describe the phenomena related to the suspension of particles, is a function of the impeller Reynolds number at the off-bottom suspension point. The impeller Reynolds number was varied between 10000 and 800000
Based on the results of this study, it can be stated that the design and position of the baffles are of great importance in minimizing the power demand in the suspension of particles. At the off-bottom suspension point, the power demand was lower for solid baffles when compared with baffles constructed of rods. 相似文献
It was found that a new dimensionless number, designed to describe the phenomena related to the suspension of particles, is a function of the impeller Reynolds number at the off-bottom suspension point. The impeller Reynolds number was varied between 10000 and 800000
Based on the results of this study, it can be stated that the design and position of the baffles are of great importance in minimizing the power demand in the suspension of particles. At the off-bottom suspension point, the power demand was lower for solid baffles when compared with baffles constructed of rods. 相似文献
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翼形轴流桨用于液液分散的冷模研究 总被引:3,自引:0,他引:3
翼形桨是新一代高效轴向流叶轮。本文将这类叶轮用于液液分散的冷模试验,测定了基本流型及其造成的液滴大小分布,研究了分散特性与搅拌功率的关系,并与传统叶轮比较了搅拌混合的综合性能。 相似文献
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Mixing of Newtonian fluids in a stirred tank at low Reynolds numbers was investigated experimentally by means of a visual decolourization technique and shaft power measurements. The research was focused on the Isolated Mixing Regions (IMRs), which are “doughnut-shaped” structures in a stirred tank exhibiting little mixing with bulk of the fluids. The effect of Reynolds number on the IMRs was determined. The critical Reynolds numbers beyond which IMRs are destroyed were presented. The study was focused on agitation design which consumes less power input to destroy the IMRs. A pitch-bladed impeller with an alternating pitch was found more energy efficient than other test impellers in eliminating IMRs in both baffled and unbaffled configurations. It was also found that dramatic reduction in the power consumption could be achieved with installation of baffles to eliminate IMRs at typically low Reynolds numbers. The improved energy efficiency was thought related to generation of more chaotic mixing from the disturbance generated by the baffles, or impeller blade asymmetry such as alternating pitch. An energy parameter was introduced to account for the mixing time scale and the power required in regimes above the critical Reynolds number, in order to evaluate the energy efficiency when IMRs are non-existent. 相似文献
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A. D. Raidoo K.S.M.S. Raghav Rao S. B. Sawant J. B. Joshi 《Chemical Engineering Communications》1987,54(1):241-264
Rate of gas induction, static pressure, mixing time and power consumption have been measured in 0.57 m i.d. vessel. Different types of impellers namely shrouded disc turbine, shrouded curved blade turbine and pitched blade turbine were used. The impeller diameter was varied from 0.15-0.25 m and the impeller speed was varied from 3 to 20 r/s.
The pitched blade turbine was found to give 30-60 per cent higher rates of gas induction as compared with the best design reported in the literature. The mixing time was found to be lower by a similar magnitude. Moreover in the case of pitched blade turbine it was found that the gas was getting induced radially as well as axially. This eliminates the necessity of the diffuser and hence reducing the complexities in the mechanical structure. 相似文献
The pitched blade turbine was found to give 30-60 per cent higher rates of gas induction as compared with the best design reported in the literature. The mixing time was found to be lower by a similar magnitude. Moreover in the case of pitched blade turbine it was found that the gas was getting induced radially as well as axially. This eliminates the necessity of the diffuser and hence reducing the complexities in the mechanical structure. 相似文献
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The radial and axial distribution of mean 1iquid velocity were measured by a.hot-filmanemometer at the impeller region in an aerated and stirred tank 0.287m in diameter.The tangentialjet model for impeller discharge flow used for single phase flow was modified to conform with thecharacteristics of gas-liquid flow.The radial and axial velocity profiles at the impeller region in thegas-liquid stirred tank were calculated by the model The results predicted by the model were in goodagreement with those obtained in experiment. 相似文献
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基于搅拌桨旋转扭矩和搅拌槽内所有壁面的平均扭矩近似相等的关系,引入流况系数,提出了计算非牛顿流体表观粘度的剪切速率模型.并对内蛇管、外蛇管和直管以及不同几何尺寸的MIG、透平、三叶后掠式、板式、锚和半椭圆片桨组成的多种搅拌体系,用该模型关联夹套侧和冷却管侧的给热系数,分别得到了统一不同几何尺寸搅拌桨的给热系数关联式.该模型适用于不同冷却构件.不同类型、不同几何尺寸的搅拌桨、过渡域和湍流域以及夹套侧和冷却管侧的非牛顿流体给热系数关联.另外,对多种剪切速率模型进行了比较和讨论. 相似文献
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Masanori Yoshida Masahiro Shigeyama Tomoko Hiura Kazuaki Yamagiwa Akira Ohkawa Shuichi Tezura 《Chemical Engineering Communications》2007,194(9):1229-1240
For an unbaffled agitated vessel with an unsteadily forward-reverse rotating impeller whose rotation proceeds with repeated acceleration, deceleration, and stop-reverse processes, the liquid flow in the impeller region was studied based on photographs showing path lines of tracer particles. An image series taken during one cycle of the forward-reverse rotation was analyzed to characterize the internal stream inside the impeller rotational region and the discharge stream outside its region when a disk turbine impeller with six flat blades was rotated unsteadily. Because of the unsteady flow generated inside the impeller rotational region, the velocity vector of outflow from its region fluctuated periodically with the change of the impeller rotation rate. The circumferential velocity was almost in phase with the impeller rotation rate, oscillating periodically. The radial velocity exhibited larger values in the process for the impeller from decelerating to stopping and reversal. The radial flow, whose velocity decreased downstream outside the impeller rotational region, was clarified to be transformed into upward and downward axial flows that are almost uniform in the circumferential direction throughout the region near the vessel wall. 相似文献
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Masanori Yoshida Masahiro Shigeyama Tomoko Hiura Kazuaki Yamagiwa Akira Ohkawa Shuichi Tezura 《Chemical Engineering Communications》2013,200(9):1229-1240
For an unbaffled agitated vessel with an unsteadily forward-reverse rotating impeller whose rotation proceeds with repeated acceleration, deceleration, and stop-reverse processes, the liquid flow in the impeller region was studied based on photographs showing path lines of tracer particles. An image series taken during one cycle of the forward-reverse rotation was analyzed to characterize the internal stream inside the impeller rotational region and the discharge stream outside its region when a disk turbine impeller with six flat blades was rotated unsteadily. Because of the unsteady flow generated inside the impeller rotational region, the velocity vector of outflow from its region fluctuated periodically with the change of the impeller rotation rate. The circumferential velocity was almost in phase with the impeller rotation rate, oscillating periodically. The radial velocity exhibited larger values in the process for the impeller from decelerating to stopping and reversal. The radial flow, whose velocity decreased downstream outside the impeller rotational region, was clarified to be transformed into upward and downward axial flows that are almost uniform in the circumferential direction throughout the region near the vessel wall. 相似文献