3 replies to this topic

I would like to know what the ratio between vertical shaft diameter and impeller diameter Or in another world how to calculate shaft diameter if you know impeller diameter , power and rpm

[kkala]

I would like to know what the ratio between vertical shaft diameter and impeller diameter Or in another world how to calculate shaft diameter if you know impeller diameter , power and rpm

This is rather a matter of "Strength of materials", so Mechanical/Civil Engineers could be consulted if it is not a preliminary estimate. General way out can be as follows.
1. Find torque from power and rotational speed, also applying some safety margin. Torque=Power/(2*π*N), N=rotations per second.
2. Estimate max bending moment on the shaft, from literature (1). Cantilever shafts can develop high bending moments close to their connection to the speed reducer.
3. Based on above, estimate moment of inertia of shaft cross section. Shaft is usually a pipe, not a full cylinder (1).
4. It is also recommended to check the system against the possibility of resonance (1).
I have followed this procedure for cost estimates in phosphoric acid tanks (with a vertical agitator each) in 1978-79, based on Reference (1) being a series of articles in "Chemical Engineering" magazine (title: Agitation...). The articles (probably dated 1977) explained the above in sufficient detail for preliminary application, using fps units.
I cannot remember more, but above procedure seems reasonable. It is noted that shaft diameter does not depend only on impeller diameter.

Edited by kkala, 04 April 2010 - 04:17 AM.

[kkala]

Relevant series of articles is titled "Liquid Agitation" and has been published in Chemical Engineering magazine from 8 Dec 1975 to 6 Dec 1976 (12 issues). The article of the series advising how to specify shaft diameter etc was in the magazine of Aug 30th, 1976, titled "How the design of shafts, seals and impellers affects agitator performance.

Edited by kkala, 08 April 2010 - 12:10 PM.

[ankur2061]

I would like to know what the ratio between vertical shaft diameter and impeller diameter Or in another world how to calculate shaft diameter if you know impeller diameter , power and rpm

anwar,

Try and get the following. This is a solved problem for calculating shaft diameter:

12.7 Shaft Design for Turbine Agitator
Chapter 12, Liquid Agitation
Handbook of Chemical Engineering Calculations, 3rd Edition, Nicholas P. Chopey

Hope this helps.

Regards,
Ankur.