Determining Line Size for very Low flows? 1

[Cee555]

How do you determine inlet Line Size for very low flows, especially for metering pumps. system needs to be able to do 82 Liters/hour. For that matter how do you size a discharge line at this low flow? Velocity is certainly not an issue, what is the rule of thumb?

 

[TD2K]

As a starting point, I'd go back to a pressure drop criteria to come up with a range.

Are you planning on using piping or tubing? Small bore piping has to be supported pretty frequently, tubing is installed often in raceway, both for support and protection or it can be supported off existing piping (I've seen this especially for preinsulated tubing).

 

[MortenA]

Unless growth (bacterial or whatever) is an issue i dont see any problems in low fluid velocities.

You engineering standards may have a minimum size to be used in plants. Check this first.

Best regards

Morten

 

[PAN]

Cee555,
Velocity should be concerned. Too low velocity may be a cause of plug in the line.

What is your intended pipe size for flow rate 82 litres/hr?

 

[MortenA]

Pan: Do you mean depositions?

Again this will depend on whats in the pipe. If it does not contain solids then i dont believe this is a concern.

Best regards

Morten

 

[JLSeagull]

Select the piping size for the ability to support itself. As the pipe size drops the distance between supports also drops. Provide tubing track to support tubing; or run 1.5-inch pipe with normal support spacing.

 

[Jankog]

Try to keep the flow / Reynolds number in the Turbulent range with regard to the velocity.

A high velocity does give a high dP over the line though.

Are there plans for placing Flow meters in the pipeline? If this is so, scale the pipe according the type of flowmeter that would be best suited for the application.

 

[MortenA]

Jankog

Just had a little look at your suggestion.

In order to Re high enough to get into turbulent flow (>10000) the ID would need to be <3 mm! Not very realistic.

I will maintain my position that he should just get on with it and select the smallest diameter that they usually use! Depending on the installation this could be quite large if e.g. operators on occation may grab hold of the line or even step upon it.

Best regards

Morteb

 

[katmar]

I assume the 82 liter/hour rate is continuous.

An item to consider is the length and layout of the line. If you are pumping a short distance (<10 ft) then it is reasonable to use 1/4 inch instrument tubing supported on a dropper or rack. If it plugs or gets crushed then replacing it is quick and easy.

If you are pumping longer distances, and the pipe needs to be self supporting then I would use at least 1" pipe. This would give you a velocity in the region of 0.13 ft/sec. If the pipe is 50 ft long that is a residence time of approx 6 minutes. Sounds OK to me.

I had a similar application a few years ago adding anti-foam to 10 fermenters. We used 1" piping with a total length of about 100 ft. Worked fine.

Harvey

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[Artisi]

your flow of 82l/hr equates to 0.3 GPM / 0.36USGPM.
If you check your friction loss tables 3/8" tube gives a friction loss of round 2.15ft / 100 ft or in metric terms 2.15m / 100 m.

If you use 1/2" tube the losses amount to nothing.

What size are the in / outlet ports on the pump?

Naresuan University
Phitsanulok
Thailand

 

[Cee555]

Thanks guys!!
Yes the flows are too small to apply the standard velocity principles, so it's nice to get some experienced input. My biggest concern was not being able to fill the pipe up on horizontal flow as I would have to maintain a "set" pressure. I based my size on the pump size which in some of the pumps selected were 1/2". Flow Meters will be used, the pumps are diaphragm metering pumps, in some cases the pumps will be pumping 13 strokes a minute!!!

 

[chicopee]

One issue that was not mentioned is the viscocity of the media being pumped as you did not state what it was. High viscocity can create high back pressures even under low flow condition.

 

[MortenA]

Look really nice!

Best regards

Morten

 

[chicopee]

I missed you reply MortenA

 

[itdepends]

Regarding target velocities- it really depends on what your pumping. If it is a clean service (no solids, or non settling solids) then go for a reasonable size at a low velocity (<1m/s).

If it's not a clean service then it's worth considering a ring main with very short off takes to your consumption/dose points.

Cheers

 

[Cee555]

This is an incredble site.
The suggestions just keep pouring in!!!
Thanks to all who responded, your advice is very very very much appreciated!!!
(PS made me look smart in the boardroom!!!)


Look for my thread regarding CRN- Numbers and how they apply to pumps or do they?

 

[FACS]

Here is a "rule of thumb" that I started using in 1986. It's an old formula that's good for a starting point; as a rule of thumb....since you asked.

Pd=(.0273)LVG/D^4

where:
Pd=Pressure Drop
.0273 is a constant
G= (Gallons Per Minute)
V= (Viscosity in Centipoise)
L= (Length of tubing in feet)
D^4= Diameter of pipe in inches, to the 4th power





So, you can pick a desired pressure drop, then plug and chug.

Charlie

http://www.facsco.com

 

[Artisi]

Just a quick question -- why is pipe diameter to the 4th power, friction loss varies as the 5th power of diameter.

Naresuan University
Phitsanulok
Thailand

 

[ChristopherFehr]

I just went through a similar exercise in our plant and we wound up using a presurized loop so the fluid didn't have a chance to plug the line. It doesn't carry solids but has a tendency to create a build up on the inside of the pipe if it sits too long or slowely.

We used about 300 ft of 1" pipe and went down to 1/2" for the off takes. Can't remember the flow rate but it was also very low.