Experimental measurements in a flat‐bottom tank with narrow‐blade hydrofoil and pitched‐blade impellers are used to develop guidelines for off‐centre, or eccentric, placement of vertical agitators in unbaffled tanks. The guidelines are based on providing a turbulent blend time that is no more than 20% longer than that of the same impeller operating at the same rotational speed on the centreline of a baffled tank. In addition to investigating the effect of impeller type, impeller diameter and off‐bottom clearance are also considered. The results support the commonly noted rule of thumb that as off‐centre distance is increased, performance in an unbaffled vessel approaches that in a baffled tank. A notable exception to this axiom occurs when a large impeller is located close to the tank base (specifically, D/T = 0.40, C/T = 0.10, and O/T = 0.25). In this case, a stable impeller tip vortex forms with both impeller types, with slow exchange of material between the vortex and bulk liquid leading to long blend times. Besides blend time decreasing with increasing off‐centre distance, the uncertainty or run‐to‐run variation in blend time also decreases dramatically. In most cases, the pitched‐blade turbine requires a smaller off‐centre distance than the hydrofoil impeller to approximate the blending performance provided during baffled operation.

中文翻译：

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偏心V型搅拌器的湍流混合时间

在带有窄叶片水翼和斜叶片叶轮的平底水箱中进行实验测量，可用于为在无挡板水箱中偏心或偏心放置垂直搅拌器制定指南。该指导原则是基于提供的湍流混合时间不超过在带挡板的水箱中心线上以相同转速运行的相同叶轮的湍流混合时间。除了研究叶轮类型的影响外，还应考虑叶轮直径和底部间隙。结果支持通常的经验法则，即随着偏心距离的增加，在无挡板容器中的性能接近在有挡板容器中的性能。当大叶轮靠近罐底放置时（特别是D / T = 0.40，C / T = 0.10和O / T = 0.25），会出现这种公理的明显例外。在这种情况下，两种类型的叶轮都会形成一个稳定的叶轮尖端涡流，涡流和散装液体之间的材料交换缓慢，导致混合时间长。除了混合时间随着离中心距离的增加而减少之外，混合时间的不确定性或逐次运行变化也显着降低。在大多数情况下，桨叶式涡轮机需要比水翼式叶轮更小的偏心距离，以接近折流板运行期间提供的混合性能。