Mixing Fluids in Flow: How to Achieve a Fixed Concentration | Sanatan

In summary, the conversation discusses the mixing of two fluids, a concentrated mineral solution and an outlet from an RO filter, to achieve a fixed concentration of the mixed solution. The issue of getting the fluids well-mixed is also mentioned, and possible solutions are suggested, including accurately metering both flows, using a helical mixer tube, and considering factors such as flow rate, pressure, and viscosity. The use of peristaltic pumps to control the flow of the liquids is also proposed as a potential solution.
  • #1
sanatan
2
0
Hello,

I am trying to mix two fluids which are in flow. To be exact, I am trying to mix a concentrated mineral solution to an outlet of my RO filter.
Is there a method to mix the two fluids to get a fixed concentration of the mixed solution ?

Regards,
Sanatan
 
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  • #2
A fixed concentration just depends on how much of each you inject. Getting them well-mixed is a separate issue and has many possible solutions depending on your constraints.
 
  • #3
Thanks boneh3ad. In this case I think the pressure from the RO output would be fixed, however my concentrated solution in a separate container will have varying pressure. So what can be done to control injected volumes of each solution. I am hesitant to use a constant pressure pump for the concentrated solution, especially when its flow rate is very small.

At this point I am not thinking about getting them well mixed. I think this would not be a problem
 
  • #4
It sounds like you have two continuous flows that you want to mix, that the fluids are miscible, and that you want to do the mixing in the pipe that is conveying the fluids. If so:

1) A pipe will not mix longitudinally, so both flows need to be accurately metered. I once had a project where we conveyed a water solution through 4800 feet of 2" pipe. There was a concentration meter at each end. Step changes in concentration at the supply end came through as identical step changes at the receiving end an hour later.

2) If you have turbulent flow (Hint: calculate the Reynolds number), then you should get transverse mixing if the pipe is long enough. You can improve transverse mixing by injecting through a perpendicular nozzle sized to get reasonable velocity, adding some elbows, or by adding a static mixer.

3) Is your system open loop (set the flows, hope for the right ratio), or closed loop (measure the mixture with a concentration meter and feed back to the supply valves / pumps? If closed loop, make sure that the fluids are fully mixed before entering the concentration meter, and that the concentration meter is as close as possible to the supply valves/pumps. The flow time from the supply to the concentration meter is a delay, and delays make for really ugly control situations.

4) How to control flow is determined by viscosity, flow rate, pressures, necessary flow accuracy, line losses, and a few other variables. We need a lot more information to make recommendations on how to control flow. Start with a flow diagram that includes all available information.
 
  • #5
I only have a little experience with mixing (epoxy mixing for high-volume potted electronic products), but this combination can work well for some applications:

Use two peristaltic pumps to meter the flows of the two liquids, and feed the outputs into a helical mixer tube. Would that work for you?

Peristaltic pump: https://upload.wikimedia.org/wikipedia/commons/0/04/Peristaltic_pump_head.jpg

245486

Helical Mixing Tube: https://i.ytimg.com/vi/JYW6QDldODk/hqdefault.jpg

245485
 

What is the purpose of mixing fluids in flow?

The purpose of mixing fluids in flow is to achieve a fixed concentration of the desired substances. This is important in various industries such as pharmaceuticals, food and beverage, and water treatment, where precise concentrations are necessary for the desired outcome.

What factors affect the efficiency of mixing fluids in flow?

The efficiency of mixing fluids in flow can be affected by factors such as the flow rate, viscosity of the fluids, mixing equipment, and the properties of the fluids being mixed. These factors can impact the degree of turbulence and shear forces, which play a crucial role in achieving a homogenous mixture.

What are some common methods used for mixing fluids in flow?

Some common methods used for mixing fluids in flow include agitation, impeller mixing, jet mixing, and static mixers. Each method has its advantages and is chosen based on the specific needs of the application. For example, agitation is suitable for low-viscosity fluids, while static mixers are better for high-viscosity fluids.

How can a fixed concentration be achieved when mixing fluids in flow?

A fixed concentration can be achieved when mixing fluids in flow by controlling the flow rates of the different fluids, using appropriate mixing equipment, and ensuring proper mixing time. It is also important to consider the properties of the fluids, such as density and viscosity, to achieve a homogenous mixture.

What are some challenges involved in mixing fluids in flow?

Some challenges involved in mixing fluids in flow include maintaining a consistent flow rate, avoiding air entrapment, and achieving a homogenous mixture. Other factors such as temperature, pressure, and chemical reactions can also affect the efficiency of mixing fluids in flow. It is important to carefully consider these challenges and choose the appropriate mixing method for the desired outcome.

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