Flow rate from head loss.

Travis_King

Correct, if the tank is vented, you can assume it is at atmospheric pressure, even with additional volume being added (that is, the caustic soda). The way fluids work is that the system will attempt to balace itself out.

It should be noted that, depending on how much soda is above the railcar discharge, the actual available head could be higher than the 25 psi, as the total pressure at the discharge point will be the pressure of the railcar plus the static pressure of the volume--or more correctly, the height--of soda above the discharge point.
But let's say it's 25 psi. This translates to 37.7 ft.
Your discharge pressure is atmosphere, 0 psig. Tanks that are vented to atmosphere do not put any back pressure on the system, so the pressure at the discharge is 0 psig.
However, you do have static and friction head losses due to elevation and, well, friction which it will have to overcome in order to discharge into the tank.
You say the tank is 10 ft above the tank, so that static head loss leaves us with 27.7 ft to lose by the time it discharges.

As I said, the system will balance itself, you have 25 psi at the railcar and it has to lose that pressure by the time it reaches the tank. You see that it loses some pressure due to elevation change, but the remaining must be eliminated by friction. The way a system controls this (thanks to physics) is: the caustic soda will find equilibrium at a flowrate which results in just the right amount of friction losses so that it discharges at atmospheric pressure.

You'll find that with your railcar pressurized to 25 psi, your flow will be significantly higher than 81.5 gpm.

Hazen-Williams
ANSI Sch. 80 Steel Pipe Info

EthanAnderson

Just to be sure, the tank will be filled from the top. Like filling a glass of water. So tank pressure, volume shouldn't matter?

Travis_King

Sorry, that was worded strangely. I meant exactly that. The tank is at atmospheric pressure. Feel free to ask me to clarify anything you might like elaboration on in post #18.

EthanAnderson

So how can I find the exact flow rate? The formula from engtoolbox.com is only for water with detailed properties. How did you arrive at the conclusion of being higher than 81 gpm?

Travis_King

Yea, friction losses for viscous fluids is a different process, but I figured that would help to at least show you the general viscinity you are in. A specific gravity of 1.53 is not that much more than water, relatively speaking.

Here's a link that shows you the expected losses in sch. 40 pipe for various viscous fluids. 50.97 CentiStokes is roughly 260 SSU (conversion), so bear that in mind when looking at the lines.

Viscous Fluid Friction Losses

I have a fluid dynamics program for process plants, running a quick simulation put it in the 130 gpm range. Some online calculators suggest around 100 gpm. When I said significantly higher, I didn't mean that it would be like 600 gpm, I just mean that it was a measurable and physically significant difference.

The thing to take from this, though, is that if you are going to use the method you used. What you want to do is make an initial guess (say 81.5 gpm) and figure out what the discharge pressure is. In this case you got over 7 psi. So you know your flow is too low. So you increase it to 150, you'll get a negative pressure, so it's too high. Keep doing these iterations, with logical progressions, and you will hone in on the correct answer.

Or, you can use the Darcy-Weisbach equation and do all the math:
Helpful link on that
However, because you don't know the flow, this becomes an iterative process for you anyway...
The table you are referring to likely used the D-W equations.

Unluckily for you, this scenario seems to be in the transition zone (Reynolds number in the 2000's), making an accurate calculation using the D-W equation difficult.

EthanAnderson

Thank you for your help Travis! Greatly appreciated!

jim hardy

Years ago where i worked, before computers, the "Crane Handbook" was regarded as "The Source" and was on every ME's desk.

I see it's on the web now.

http://www.craneengineering.net/prod...esFittings.pdf

hope it's some help. I downloaded one to my 'desktop'.

old jim

russ_watters

Can you attach it to the thread?

For a first pass by a co-op, that's a really good start. Adding-up all the components and then guess-and-check the flow rate vs the friction loss is the way to go if you can get accurate information on the friction loss.

Travis has given some good help -- more than I could have given. Your solution being far different from water really threw me. I probably would have used software for that.

Stupid question though: Does the railcar or tank have a sight-glass or other way to measure the volume of fluid in the tank? That plus a stop-watch equals a flow meter...