fluid flow with chemical injection

[dragonsaver]

I haven't used my fluid dynamics in over 20 years and I can't remember how to do the calculations. What I want is probably quite easy for those of you that work with this daily.
If I have a 6" pipe with a flow of 400 USGPM (should have a velocity of 4.44 ft.sec)and I insert an injection quill into the stream it should produce turbulent flow at the point of injection. If I then inject a chemical through the quill at 1.5 USGPM the velocity from the tip of the quill should be approx 8.5 ft/sec.
My question is will I get thorough mixing of the chemical due to the turbulent flow or will the high velocity of the injected chemical put the chemical against the pipe creating a high concentration gradient which will not mix with the balance of the pipe fluid downstream.
Thanks for your assistance.

 

[koalmnr]

The turbulent flow should cause mixing. BUT! The key question is relative viscosity of the two streams, and the distance from the injection point to the discharge. Also the relative miscability of the injected chemical into the base fluid is a factor.

 

[dragonsaver]

I agree that those factors are important however we sell to a variety of end users and the chemicals etc will vary accordingly. I realize that the turbulent flow will eventually mix the chemical, given sufficient length but length is also a variable. Also, if the process pipe flow was high enough or the process fluid viscous or a slurry this would slow the injection fluid and/or keep it in the centre of the process stream.

My question is more hypothetical than specific process related. Injecting at the center of the process pipe is supposed to prevent concentration of the chemical at the edge where the velocity is low due to friction. I am concerned that with a small orifice on the quill the velocity is quite high, which could send the chemical over to the opposite side of the pipe and into an area where the effect of the turbulent flow would be minimized. This information is more for my own understanding, I need to know if this is a problem or if it won't really affect the end result.

Thanks

 

[koalmnr]

Taking your numbers as being correct, then your quill is about 3/8" diameter and you have about .45 delta p pressure differntial between the quill and the line it is being injected into. Considering that and that the quill is at the center of the line and perpendicular to the line (you have not speciefied anything else), would this be enough force to drive the injected chemical across the remaining 3" without any dispersion (ignoring viscosity, etc.)? Possibly, you really need to test it find out.

These are some of the reasons that the design of an injection point can be very critical. Options to consider:

1. Inline mixer after the injection point.

2. Injection tip not at the center of the pipe.

3. Quill tip rotated to inject parrallel to the flow at the center line.

 

[dragonsaver]

The quill has a 1/8" diam orifice, at 50 PSI it should deliver 1.5 USGPM. Using tables I got the velicity as 8.48 ft/sec. The pipe line flow for a 6" pipe was from the same table. The actual number for the pipe flow is a variable depending on the process. The quill is inserted perpendicular to the line.
We state to our customers that this quill will give maximum mixing as it is inserted at the center line of the fluid flow.
I am new to the company and was given the task to review the design and possibly recommend changes. Since the boss is the company owner and the designer (who also hates engineers), I need to have all my ducks in a row before I even try to challenge the design parameters or the mixing potential. My gut feeling without any calculations was that injecting at the center not going to put the chemical into the center of the fluid stream unless the delivery velicity was low. However, possibly bounce back off the opposite side of the pipe would aid in producing the turbulent flow and/or mixing. But, wouldn't the impingement of the chemical on the pipe cause erosion?
Another question would be will the quill cause turbulent flow just by being physically in the pipe?