Fluid Mixing

[melerine24]

I am using a 2.5" diameter pipe with 60 3/16" holes and 24 feet long placed at the bottom of a 4200 gallon tank.
Is there anyway to find what pump flow rate to use to achieve the correct velocity and turnover for effective mixing?
The fluid is 25% Caustic solution.

 

[LittleInch]

Try searching on this site for tank mixing, fluid mixing, tank fluid mixing etc.

You'll find gems like this:

http://www.eng-tips.com/viewthread.cfm?qid=108085

In short thought this is a complex subject and has many variables. There are many vendors who make packages and will undertake design requirments or ask you questions that you may not know, but are required to make it work properly.

You've said the volume of the tank but what size is it?

Only you can define what "effective mixing" is? Is the fluid static? how long do you "miX2 for? What are you mixing? Why are you mixing?, what do you do now?

I think like your other thread shows, that your mixing tube is woefully undersized for any sort of effective mixing though. I don't think this thing would mix anything.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[melerine24]

Thanks for the reply LittleInch,

I am reading Perry's Chemical Engineering Handbook on Fluid mixing and perforated tube mixing. It has very general information and I understand that each problem is unique but I am just looking for what people have done in the past or "rules of thumb" to try and compare my design.

The design that I came up with above seems to work with the equations given in the handbook for a 80 gpm pump but it feels very unsettling when I hear that it is undersized because I also think the system is undersized.

I have researched Jet Nozzles but I am limited on space. I do not have much room to place nozzles or a mixer so I opted for the existing system of a perforated tube mixer but was going to make it larger as I felt it is not adequate.

The tank is approximately 28x4x5, we would like to mix for 18 hours a day, we are mixing 25-50% caustic solution that is recirculated from the vat, and we are doing it to prevent settlement build up as well to aid in cleaning the equipment.

I will be glad to answer any more questions and appreciate your time and effort.

 

[LittleInch]

It's an oblong tank?

I'll be honest here and say I don't know the answer to your questions, but what I do know is that mixing inside tanks is very difficult to achieve 100% mixing and if you have settlement of solids then it is even worse.

Jet or liquid mixing as opposed to mechanical stirrers need high velocities at the nozzles to do any good - upwards of 7-8 m/sec min. Anything else will gently stir the liquid, but if you want "mixing" then you need more power.

Mixing is often achieved using multiple nozzles on the tank or a moveable directional jet or tubes. can you fit more nozzles?

There are now any number of computational devices to model this by CFD, but not sure how detailed you want to go.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[bimr]

The capacity and number of tank mixing elements is determined by the turnover rate. The turnover rate is defined as the entire liquid contents of a tank is completely circulated through the eductors per hour. Note that the turnover rate will vary according the characteristics of the application. For example: Most plating and rinsing tanks require 3 to 20 turnovers per hour.

 

[Compositepro]

You will get much better mixing in a large tank by using one or two large nozzles (eductors) rather than a perforated pipe, which will act as a diffuser. The large flow from one nozzle will promote large circulation currents in the tank. Drawing from two or more suction nozzles will also help a lot with mixing.

 

[Artisi]

OP: you might get a better response by posting in the Water Treatment forum rather than here in the Pump engineering, there will be some overlap of people from both fora but you can't be sure of catching the eye of the right person/s to assist.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)