4 replies to this topic

[bob789]

Hi,

I am a 4th chemical engineering student. I am haveing issues designing a suitable pump that will be able to handle an extremely fibrous substance, such as alginic acid. The slurry contains 80% fibre solid, 20% water and therefore will be extremely difficult to pump. However, I am wanting validate this reasoning through design. I have selected screw or gear pump as they can handle really low flowrates. I was wandering if someone could give me some guidance on how screw pumps operate, as they will be ideal as it won't affect the integrity of the substance being pumped. Can someone direct me towards where I could find design equations for screw or gear pumps?

I have identified this list below as being key specs on the pump, am I right? diameter, flowrate, head loss, back pressure , viscosity of fluid

Capacity of Screw Pump: Diameter of screw, Speed of screw, no. Of flights mounted on screw ,Angle of inclination ,motor speed ,
efficiency of gear pump: Fluid Density, Pressure rise ,Displacement Volume (Q) , Rotational speed (n) ,Driving torque (T), Efficiency

thanks in advance.

bob

Edited by bob789, 29 January 2011 - 09:52 AM.

[Art Montemayor]

Bob:

I can’t identify what your “issues” are. Are you trying to mechanically design or process design a screw pump? I have to assume you mean the latter, since I don’t think you are a mechanical engineering student – and even those don’t mechanically design such a specialized and unique pump.

In process designing a pump all you really are doing is preparing an accurate, detailed, and correct Specification (or Data) Sheet for the subsequent estimation, tendering, and purchase of the pump.

Please refer to the attached workbook and read it carefully. I have only included two of the prime and well-established manufacturers of such pumps, but you should already have done this type of research and study on screw pumps. If you are going to specify this pump, you have to become very knowledgeable about how it works, its positive features, its negative features, key and vital components, methods of startup and shutdown, required instrumentation, alloy requirement, capacity controls, and key recognized manufacturers. That is your job as a student. There is plenty of reading and studying material out there in the library, the Internet, and in engineering journals. All you have to do to acquire that knowledge is to seek it out and study it in detail.

The final summary of all that you learn about screw pumps is boiled down in the DataSheets. You will find such a simple version of a data sheet in the workbook. There are much more detailed and standard datasheets available – as in the API standards. You can use one of the pump datasheets that I have previously uploaded in other threads in Excel format and revise it to include the main and key features of the screw pump.

You state, “I was wandering ……” (instead of wondering) – and you are correct. There is no practical or logical need for you to have “design equations for screw or gear pumps”. You are not going to fabricate a pump. You are merely intending to describe what you need in such a pump to the REAL EXPERTS: THE PUMP MANUFACTURER. And to do that, you require to communicate in an accurate, detailed, and precise manner. You use the DataSheets for that purpose.

Why do you think you need to specify:

• Diameter of screw;
• Speed of screw;
• no. Of flights mounted on screw;
• Angle of inclination;
• motor speed;
• efficiency of gear pump;
• Displacement Volume (Q);
• Rotational speed (n);
• Driving torque (T);
• Efficiency

All of the above is specified BY THE MANUFACTURER, not by you. But you need to indicate if you want or need a certain type of motor and motor speed (number of windings). The manufacturer will aim to please and if he/she can’t you will be advised of that and/or of options.

Go to:
http://www.imo-pump.com/

http://www.imo-pump.com/tech.htm

and you will find an excellent Brochure that you can download and that explains details of the screw pump, how it works, and key features. You are required to know this information before you start to specifying and describing what you need in that pump.

I hope this experience helps you out.

Attached Files

•  Screw Pumps.xls   1.89MB   149 downloads

[bob789]

Art,

Thank you for your clear response. It did clarify the issues I was having. I downloaded the screw pumps excel file that you have uploaded. However, when trying to open it, a message comes up saying "You don't have permission to open this file, contact file owner." Is there any chance you could re- upload it?

[Art Montemayor]

Bob:

I can open the Excel file that I attached to my response without any trouble. Are you sure that you don't have a protection on your computer that is keeping you from opening uploaded file? Nevertheless, I'll attached it again to this post. It is 1.9 MB big, but that should be no problem.

Let me know if you succeed in opening one of the uploaded versions so that I can come back and delete one of the files and save Server storage space.

Attached Files

•  Screw Pumps.xls   1.89MB   82 downloads

[bob789]

Art,

I tried it again, and still it doesn't open. I downloaded it on to another computer and the same thing happens. This has never happened with any of your other files.