3 replies to this topic

[nick_tri]

Goodady all,
I am a final yr student designing a centrifugal pump to recycle acetone and water from a column back to a reactor.
For Pump. Design Flowrate: 0.0073 m3/h
Total System Head: 75.25 m
Inlet Pressure: 150 kPa
Outlet Pressure: 600 kPa
Pipe Internal Diameter: 5.461 mm

Using Coulson & Richardson vol6 I found that a multistage pump was needed...however due to the ridiculously low flowrate, I can't even get an efficiency for this. I assumed the impeller would be operating at 3500 rpm.

I was advised to use a bypass (recirculation) loop to increase the flowrate to the suction part. However I have no idea how to design a multistage centrifugal pump with a bypass loop. Can anyone please advise?

Nick
PS: I've attached my excel sheet incase anyone wants to look through it and tell me where i might be going wrong with this. Thank you in advance.

Attached Files

•  Pump_Design.xls   44.5KB   83 downloads

[djack77494]

I found that a multistage pump was needed

Nick,
Not having your reference book handy, I'm not sure what led you to the idea that you need a multistage centrifugal pump. This seems to be well within the realm of positive displacement pumps, which excel at lower volumetric flowrates against high or low discharge pressures. Have a look at what's offered and I think you'll find what you need.
Doug

[Art Montemayor]

Nick:

I really like your style. I wish all Chemical Engineering students were as straight-forward, prepared, and not shy to put all their data out in front when they are seeking help and advice. Your candor has allowed Doug to come immediately forward with a professional engineer’s response: you really don’t have a difficult problem at all! A simple, conventional positive displacement piston pump will do this application very nicely, indeed!

Your 600 kPa (gauge?) is a very common and relatively low pressure – as pumps go. A single-stage, common overhanging impeller design will handle this size of head very easily. I think you might have been looking at the wrong reference, although this wouldn’t be the first time that Coulson & Richardson “missed the boat” on the correct answer. A Total Developed Head (TDH) of 450 kPa (65 psi = 150 ft of water) is a rather benign TDH. Were it not for the ridiculously low flow rate, you could be using a conventional centrifugal pump found at nearly any hardware store.

Clearly, as Doug states, the K.I.S.S. (“Keep It Simple, Stupid”) answer is to use a conventional piston pump. This works out very well in your favor because it is a lot easier to control the capacity of a piston pump than it is of a centrifugal model. You can vary the speed as well as the stroke of the pump. You don’t need a by-pass loop. The bad feature in a piston pump is the resultant pulsations – but you can lessen these by installing a surge drum on the discharge to absorb the pulsating flow before measuring it.

I like the up-front work you did on the required calculations. Good job! All students should turn in their work like this. You guys are giving Trinidad & Tobago something to standup and brag about. Keep up the good work.

Good Luck.

[nick_tri]

Thank you very much Djack and Art, your insight was very much appreciated, i was really fearing having to design a multistage. It was Coulson & Richardson that led me to this. I will do my calculations and give an update on how it worked out. Again thank you.


Nick