What is the optimum aspect ratio (or height/diameter ratio) is for a fermenter? The best answer is “it depends”. There is simply no universal optimum. The best design is worked on a case-by-case basis. We can list some factors that affect the optimum. Note that as aspect ratio increases, the following results are produced:
- The vessel cost usually increases, except at the transition between shop fabricated and field fabricated vessels;
- The total power (agitator + compressor) decreases at constant mass transfer rate;
- The available heat transfer area increases;
- The blend time is longer;
- The composition is less uniform, especially DO;
- The agitator gear drive becomes less expensive as there is less torque;
- More impellers are needed; and
- The shaft design often becomes more challenging.
These are but a few of the factors affecting the optimum aspect ratio. Some factors will favor a taller aspect ratio, while others will favor a shorter ratio. At Lee Enterprises Consulting, we have a number of highly qualified agitation experts available to assist you with any related matters. Feel free to call or email us for more information.