Pipe/pumping question
Pipe/pumping question
(OP)
Hi,
I have design situation where I have one main pipe that receives flows from several pipes at regular intervals in length of the main pipe. So ultimately the main pipe must handle flows from all individual small pipes and pump it to the next unit in operation. The flows from several small pipes are equal. I have to calculate head loss in the main pipe.
My approach-
Size the main pipe to handle the flows coming in from every small pipe. I sized it to maintain a minimum velocity in the main pipe. Because the flow increases over the length of the main pipe (due to flows from small pipes), the diameter increases over the length. Calculate the frictional head loss for every section of the main pipe based on pipe material, velocity in that length of the pipe and diameter. And add the frictional headlosses obtained so over the total length of the main pipe. Is this correct?
The pipe does not flow through gravity. How to view this pipe network -series/parallel?
I have design situation where I have one main pipe that receives flows from several pipes at regular intervals in length of the main pipe. So ultimately the main pipe must handle flows from all individual small pipes and pump it to the next unit in operation. The flows from several small pipes are equal. I have to calculate head loss in the main pipe.
My approach-
Size the main pipe to handle the flows coming in from every small pipe. I sized it to maintain a minimum velocity in the main pipe. Because the flow increases over the length of the main pipe (due to flows from small pipes), the diameter increases over the length. Calculate the frictional head loss for every section of the main pipe based on pipe material, velocity in that length of the pipe and diameter. And add the frictional headlosses obtained so over the total length of the main pipe. Is this correct?
The pipe does not flow through gravity. How to view this pipe network -series/parallel?





RE: Pipe/pumping question
Series.
Any two or more pipes can be a network if you want to call them that.
you must get smarter than the software you're using.
RE: Pipe/pumping question
When I am sizing each section of the main pipe, the velocity is not constant (slightly decreasing and increasing) in every section due to the available pipe diameters. My question is as long as the velocity is above certain limit, the small differences in velocities between the sections of the main pipe should not matter? Or does the velocity in the main pipe must increase over the length?
What I mean by each section of a main pipe is that-length of the main pipe between the locations where small pipes discharge the flow into the main pipe.
RE: Pipe/pumping question
you must get smarter than the software you're using.
RE: Pipe/pumping question
This irregularities in Velocities between the sections is arising from choosing the diameters that are commercially available to match the flow. And the velocities calculated so are used in calculating the frictional losses.
Because I lack practical experience, I am wondering if it is ok to have irregular velocities in a pipeline such as in this example? If irregularities in velocities is ok in the pipeline, then one can further play with the diameter of the main pipe in several sections to bring down the velocities and the associated frictional losses.
I do understand that the velocity change happens suddenly and continues to remain the same along the length of the main pipe as long as there are no changes in volumetric flow rate or diameter.
RE: Pipe/pumping question
If you revisit the Bernoulli principle, you should understand that the energy in the pipeline changes form from velocity head to pressure, static head etc., but that the total energy remains the same.
RE: Pipe/pumping question
you must get smarter than the software you're using.
RE: Pipe/pumping question
Katmar Software - AioFlo Pipe Hydraulics
http://katmarsoftware.com
"An undefined problem has an infinite number of solutions"
RE: Pipe/pumping question
RE: Pipe/pumping question
Each pump must have a discharge pressure greater than the pressure in the header pipe at the connection.
You have to add the headloss in the header pipe to the headloss in each pipe from each pump.
The last segment will be the farthest pump. The last segment will also have the largest friction head loss.
Would you explain the application?
Is there a requirement for constant flow from each pump?
If you have multiple centrifugal pumps, the flow from each pump will vary slightly with the discharge pressure in the main pipe.
RE: Pipe/pumping question
RE: Pipe/pumping question
As a chem eng/metallurgist the first part of any answer I give starts with "It Depends"
RE: Pipe/pumping question
If you have multiple tanks, you need a device to control the level in each tank. Otherwise, you may have a condition where flow from one tank moves to another tank.
There is no way that you would have equal flow from each tank unless you have equal flow moving into the tanks. This is accomplished with a splitter box with overflow weirs.
Maintaining liquid level in tanks is accomplished using weirs or pipe overflows.
RE: Pipe/pumping question
In figure 1, after the flow is collected in header pipe, it must be pumped to at least 4m height.I know the frictional head losses in the individual and header pipes. Based on this total head (static head+frictional head (converting into discharge pressure) I have to select pumps. I am thinking to choose a pump at every individual pipe with a discharge pressure greater than the discharge pressure at the connection with header pipe. Is that correct?, If so, in order to pump 4 m height from header to the treatment system, where should the pump be located. Do I need to have a pump/lift station to do that? How do I develop a system curve for the pump that lifts flow from header to the treatment unit.
In figure 2, when flows from two treatment units join together and to be pumped back to the tanks through a main distribution line, do I need to have a pump station? I know the frictional losses in the entire pipe network. How does pump arrangement in this case works?
If there is any textbook, design examples one knows to understand about this, please let me know.
RE: Pipe/pumping question
If you have a tank pumping flow out of each tank into the header then you don't need a pump on the main header.
Sizing is done as follows- determine the frictional loss and head requirement to get flow through the header pipe to the treatment system. Set that pressure as the discharge pressure for the inlet feeders. Then size a pump for each inlet feeder based on its respective frictional and head loss with the extra pressure required to push flow through the header. You may need to specify individual discharge pressures if the header is long enough, or varies enough in height to impact the pressure that each feeder needs to push against.
Each individual pump needs its own flow control to (I assume) control the upstream tank level. That's why a gravity system is so much simpler. You put a sump that's low enough for all the feeders to gravity flow to and then a single pump to return the combined flow to the treatment system.
In Figure 2- A bit more complicated. I'd have a control valve on the outlet line to each tank- that would control the flow to each tank. Each treatment plant would have a discharge pump feeding the header. The pumps will need to have their own control valve or variable speed drive so that you can push more flow from treatment plant A or B depending on your needs. It's not an ideal setup but I hope you've got a decent control system/engineer. How critical is the flow split between the tanks on the discharge side?
I've designed a number of systems where I've had multiple dischage lines with a single pump controlling the header pressure but not two separate pumps from different systems where you need to control the relative inflow rates and then split it between multiple tanks- that will be fun.
As a chem eng/metallurgist the first part of any answer I give starts with "It Depends"
RE: Pipe/pumping question
Size the pump intake lines at 3 ft/sec and minimize the length of the pump intake pipes. Size the pump discharge lines at 5 ft/sec.
At these velocities, the frictional headloss will be small and insignificant as compared to the static head loss that you will be pumping against.
Calculate the total frictional headloss to the last fitting in each run of pipe. (For each pipe run.)
If you want to divide flows, use weirs or valves. It is too difficult to try to balance flows using the frictional headloss.
http://www.fao.org/docrep/field/007/af011e/AF011E0...
RE: Pipe/pumping question
http://www.aces.edu/users/davisda/classes/faciliti...
RE: Pipe/pumping question
I would think seriously about PD pumps where flow is pretty fixed and forget about trying to balance a system with pumps and pipe. Far too many variables and big changes for small changes in temperature, head etc
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Pipe/pumping question
I did basic calculations pretty much similar to that you explained. My only question is how to know the extra pressure in the header pipe.
I am right out of school. All my school experience was in classroom completely different to what I am doing now. So it is a bit challenging to imagine and feel whatever I am doing is correct.
RE: Pipe/pumping question
@Littleinch-Thank you. I considered your suggestion of PD pumps.
RE: Pipe/pumping question
For the scope of work that you have described, don't even worry about pressure drops in the piping. The pipe lengths will be small (unless you are pumping for hundreds of meters) and the major power requirement will be from moving water from tank to tank. Assume the tanks are empty and calculate the maximum head from empty tank to full tank.
For this application, most will use centrifugal pumps because they are inexpensive. Assume 60% pumping efficiency.
RE: Pipe/pumping question
Do you have a Process Flow Diagram? (which would include this information).
There's little point diving into detailed or even preliminary sizing calculations until you know where the pumps are going to go and how big they are.
As a chem eng/metallurgist the first part of any answer I give starts with "It Depends"
RE: Pipe/pumping question
RE: Pipe/pumping question
Steve