A study on intermittency phenomena in the impeller stream via digital particle image velocimetry (DPIV)
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Intermittency
Rushton turbine
Slip factor
Isolated mixing region often appears in the high-viscosity fluid with laminar flow in a stirred vessel,reducing fluid mixing efficiency.Diminishing or eliminating isolated mixing region improves the mixing efficiency and reduces mixing energy consumption.Experimental and computational studies were carried out to compare the flow field structures with rigid Rushton turbine impeller(rigid RT impeller) and rigid-flexible Rushton turbine impeller(combination RT impeller).Analyses were carried out on axial,radial and tangential velocity vector plots,velocity contours and velocity distribution scatter plots at the same time power consumption(3 kW·m-3)with these two impellers.Results show that the energy concentrates at the tip of rigid RT impeller and the fluid velocity away from the impeller is small,even at 0 m·s-1,while for combination RT impeller,the energy distributes well in the stirred tank so that the fluid gains certain velocity everywhere.The numerical simulation results agree with experimental results.The combination RT impeller improves mixing efficiency by eliminating isolated mixing regions,while rigid RT impeller presents a poor mixing efficiency since isolated mixing regions always exist.
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This paper presents the results of an experimental investigation of the power input of pitched blade impellers and standard Rushton turbine impellers in a cylindrical vessel provided with four radial baffles at its wall under a turbulent regime of flow of an agitated liquid. The influence of the geometry of the pitched blade impellers (pitch angle, number of blades) and the off-bottom impeller clearance of both high-speed impellers tested on the impeller power input is determined in two sizes of the cylindrical vessel (0.3 m and 0.8 m diameter of vessel). A strain gauge torquemeter is used in the small vessel and a phase shift mechanical torquemeter is used in the large vessel. All results of the experiments correspond to the condition that the Reynolds number modified for the impeller exceeds ten thousand. The results of this study show that the significant influence of the separating disk thickness of the turbine impeller corresponds fairly well to the empirical equations presented in the literature. Both the influence of the number of impeller blades and the blade pitch angle of the pitched blade impeller were expressed quantitatively by means of the power dependence of the recently published correlations: the higher the pitch angle and the number of blades, the higher the values of the impeller power input. Finally, it follows from results of this study that the impeller off-bottom clearance has a weak influence on the power input of the Rushton turbine impeller, but with decreasing impeller off-bottom clearance the power input of the pitched blade impeller increases significantly.
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Abstract Both the numerical and experimental approaches were used to study the effects of the gas recirculation and non‐uniform gas loading on the mass transfer rate for each impeller in a multiple impeller system. By combining the calculated gas velocity and local gas holdup, the gas recirculation rate around each impeller was estimated. The local mass transfer coefficients for systems equipped with various combinations of the Rushton turbine impeller ( R ) and pitched blade impeller ( P ) were determined by using the dynamic gassing out method. It is found that the Rushton turbine impeller has to be served as the lowest impeller in order to have a better gas dispersion and to give a higher overall K L a for a multiple impeller gas‐liquid contactor. The upper pitched blade impeller always enforces the circulating flow around the Rushton turbine impeller just beneath it and gives a higher overall average mass transfer rate. However, the system equipped with only the pitched blade impellers results in a much lower mass transfer rate than the other systems owing to the poor gas dispersion performance of the pitched blade impeller.
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Abstract A characterisation of three commonly used impellers was made in this study by measuring local mean velocities and the fluctuations of these velocities with the LDV technique. The data was used to estimate volumetric flow, velocity fluctuations and turbulent intensity in the impeller region of the tank. The impellers investigated were a high flow impeller, a pitched blade turbine and a Rushton turbine. The cylindrical vessel used was made of Perspex, had a dished bottom (DIN 28013), was equipped with four baffles and had an inner diameter of 0.45 m. It was found that the bulk velocities could be scaled with the tip‐speed of the impeller ( ND ). The flow rate at constant impeller speed increased in the order high flow impeller — Rushton turbine — pitched blade turbine. The corresponding order for the turbulence fluctuation is: high flow impeller — pitched blade turbine — Rushton turbine. The velocity profile of the flow out from the high flow impeller was furthermore, not as smooth as could be expected.
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然而，双片泵广泛地在污水处理工业被使用关于有技术是的粒子图象 velocimetry (PIV ) 的双片泵的内部流动特征的研究很很少目前。为了在离开设计和设计下面在两倍片泵 impeller 揭示内部流动特征，调节，在双片的内部流动抽 impeller，其特定的速度是 111，在五个离开设计条件下面被测量并且设计由使用 3D PIV 测试技术的状况。为了保证 3D PIV 测试，使用眼的纤维的外部扳机同步系统和等价物的精确性，刻度方法被使用。3D PIV 相对速度合成过程被使用 Visual C++ 2005 编。在双片泵 impeller 的然后绝对的速度分发和相对速度分发被获得。旋涡核心的旋涡处于每个条件存在的测试结果表演，而是地点，尺寸和速度是不同的。impeller 插头的平均绝对速度价值起初随流动率的增加再增加，然后减少，然后增加。在 0.4， 0.8，和 1.2 设计状况下面的再次平均的相对速度价值在 1.0 设计状况下面比那高，当不到 0.6 和 1.4 设计状况时它更低。在低流动率条件下面，在 impeller 插头和片入口的绝对速度的光线的向量随流动率的增加接近泵柄减少，当在泵柄附近的吸方面的相对速度的减少时。绝对速度和相对速度的光线的向量在二个大流动率条件下面稍微变化。研究结果能被使用指示两倍片泵的水力的优化设计。
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