Expert ForumsMixing

Topic: Re: What is the ideal diameter-to-length ratio for a vessel?

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From a processing perspective the optimum height to diameter of a stirred vessel is almost always between L/D=1.0 and L/D=0.8, with a single impeller.  Shorter vessels (L/D less than 0.5) can have restrictive recirculation patterns and taller vessels (L/D greater than 1.5) increase the path length for recirculation.  Tall vessels with an L/D=2 have several disadvantages for a 10kl size vessel.  At least two impellers are needed for good fluid motion.  While axial flow impellers can create additive flow, the length of the pattern is longer, especially for additions made to the surface of the fluid in the tank.  At elevated viscosities, the flow pattern may result in two separate recirculation patterns, which will slow blending.  Design of a longer shaft also can be more difficult.  The cost of a mixer for a tall tank is likely to be greater than an equivalent mixer for a tank with an L/D=1.  The most common reason for choosing a vessel with an L/D equal to or greater than 2 is for a large vessel (greater than 4 m diameter), which may be difficult to transport.
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