OT: Fluid Dynamics for Idiots

[bce123]

use the orfice plates, add diff press xmiters(for flow rate). get the ball valves add actuators to them I suggest 40 to 20 ma control for these. A compact or even a micro logix should work nice for the PID. Get a nice HMI to display your HARD work on. sounds like a justifiable project kick it upstairs for budget attach your bosses name to it so he thinks its his Idea, that should help speed up the approval process. Good luck!!

 

[Tom Jenkins]

Congrats on the new job. Hopefully they don't make a policy of hiring executives who FAIL the IQ test!

Shawn 75's method is correct. However, don't forget the velocity head regain - when fluid slows down the static pressure goes up (Bernoulli's Law). Also, remember that +/- 10% is excellent accuracy when doing pressure drop calculations. Don't expect dead nuts results no matter what.

Has anyone asked ho much the time for analysis and drilling holes is going to cost, vs. the cost of screwing a valve to the end of a pipe? And again, don't forget that power waste from pump backpressure increases.

Oh well, you know what they say about trying to teach a pig to sing; it frustrates you and annoys the pig!

 

[OkiePC]

They decided to go with 5/8" holes to start.

 

[leitmotif]

Okie

Since you are in a meat processing plant I assume
The tanks and pump systeme sound like a solid sepearator and grease trap set up. You will need to maintain a steady flow to handle the waste water yet ensure a minimal flow in tanks to allow for settling time. I am not sure if you can do this with three tanks in parallel.

I believe series tanks is better way to go but each must be sized to allow for retention time at a set flow rate.

Dan Bentler

 

[GlennA]

pressure washer ?

275 gallons per minute x 231 in^3 per gallon x 1 min/60 sec = 1,058 in^3 per second.
5/8 orifice x 3 is about 1 in^2 total.
Sounds like a pressure washer.
What head pressure can the pump deliver ?
Or are my calculations off ?

 

[Peter Nachtwey]

The flow through the orifice depends on how it is shaped and the pressure drop across the orifice. What is funny is that the density will probably change from time to time making accurate calculations impossible but you can get close.
http://en.wikipedia.org/wiki/Orifice_plate
There is lots of info in the web if you look.

How did someone come up with 5/8th of an inch? Is that for all three? That won't work.

This is not a simple problem. It isn't that the math can't be done it is the fact that one can't get values or specifications from the component manufacturers with which one can do calculations.

I would look at how the people that design lawn sprinkler systems make their calculations.
Keep us informed on how this is working out. It should be a good story.
I think trial an error will be the method used in the end.

 

[tommy23t]

Jumping in a little late, but many years ago I was a fireman, and attended many courses on pressure and flow. We used different sized holes in a round plate clamped between the hose and the nozzle to simulate different pressure and flows. Some of these formulas may be what you are looking for, my memory (long time ago) tells me the 5/8 dia hole is way too big for water, but may work for you.

http://www.fireengineeriq.com/Hydraulics Formulas.htm

Good Luck on the new job.

tommy23t

 

[Saffa]

If this is indeed a high solids content wastewater with entrained fat, little holes in a steel plate are soon going to find themselves blocked. Someone (who is probably not at work that day, or any other day) will have to remove said orifice and clean them. If it blocks regularly, it'll need monitoring. It amazes me how people never consider operating cost when planning systems.

I also love projects like this where people buy the parts before they've even worked out the design - here's a buncha **** some salesman told me would work, so... make it work.

Orifice plates are very tricky. I've only ever had to size one, and I got it completely wrong - hole way too big. After a few re-tries we got the flow correct - 30m3/hr through a 20mm hole I think it was, from a gravity intake in the hills. There will be a hole scoured through the downstream 90 degree bend in the next couple of years I bet!

 

[GlennA]

when the purge cycle ends

Air at 275 gallons per minute should go through those orifices easily.
I wonder how fast water at 275 gallons per minute runs through 3 inch pipe ?
And what will happen when it hits the orifices ?
I would be tempted to stand back a ways.

 

[OkiePC]

I have no intention of getting involved now. They didn't directly ask me to solve this problem. One of the good "floor techs" has been asking the bosses for help. After over hearing him for two days bugging them for an answer, I told him, if they can't help you, I will see what I can do to help.

I am sure he told them something like 'Paul said he would try to help if you guys can't figure it out.' Then they told him, 'Let's try 5/8" and go from there'...

Which is another way of saying, "suggestion box closed".

Nah, I was volunteering to apply effort outside my area of responsibility (again). Since it is also outside my area of expertise, I came straight here with the puzzle and will take no ownership of the results.

They did that whole project their way including the refusal of all of my advice for the controls. I washed my hands of it months ago, except at the last minute (a few weeks ago) I was forced to wire up the push button panel for all the pumps (exactly like the old rusty one they pulled out). All my schtuff (their 1960's design, my wiring) works perfectly, so I will stay out of the room until the plumbing is done unless they call me for an electrical issue...

 

[OkiePC]

The part which I find most humorous is the fact I'm told there are no pipe couplings or flanges between the header and the tank inlets. It's all threaded iron pipe. And, it's 13' off the floor. So, for each trial, they will have to get several guys on ladders to try to flex the lines away while one guy with a pipe wrench completely disassembles the whole mess.

Yep, now that's funny (since I have no pipe wrench duties)...

Why no couplings? I dunno, maybe the $2000 for selector switches and buttons put them over budget.

 

[ndzied1]

Air at 275 gallons per minute should go through those orifices easily.
I wonder how fast water at 275 gallons per minute runs through 3 inch pipe ?
And what will happen when it hits the orifices ?
I would be tempted to stand back a ways.

I'd call it about 12 ft/s
(((275 * 231) / (pi * (1.5 * 1.5))) / 60) / 12 = 12.4818738

For the 5/8 orifice about 66 ft/s
((((275 / 3) * 231) / (pi * (.375 * .375))) / 60) / 12 = 66.5699935
If I am right that only about 1/3 of the 275 gpm hits the 5/8 hole.

As an aside, did you know that you can type equations like above into google and it will do the calculations. Furthermore, you can type in equations of x to get a plot or, I think, even equations of x and y to get a surface plot (it complained I don't have WebGL

 

[GlennA]

no couplings ?

I was installing a machine at a stone shop when they put in a process water pump = no foot valve, no pipe couplings, no flexible connections, no flow bypass, no purge valve.
After several problems and several re-fits they had all been added.
There is never enough time to do it right the first time, but there is always enough time to do it over.

 

[leitmotif]

I was installing a machine at a stone shop when they put in a process water pump = no foot valve, no pipe couplings, no flexible connections, no flow bypass, no purge valve.
After several problems and several re-fits they had all been added.
There is never enough time to do it right the first time, but there is always enough time to do it over.

Design in haste
Repent at leisure

Okie
How many days till Emancipation Day?
Started counting minutes yet?

Dan Bentler

 

[Tom Jenkins]

Aargh

I couldn't stand it any more. Not only did the "designer" flunk out of Fluids for Dummies, he skipped Common Sense 101.

This system is not only uneconomical, it is unlikely to work. I assume that your Gormann Rupp is a centrifugal pump. Therefore it will only deliver 275 gpm at a specific head. I doubt they allowed for an extra 400 ft. of head!

I just found this site:
http://www.pumpcalcs.com/calculators/view/103/