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Practical Course Course 2 Find a plan to improve the productivity of the mixing tank on the existing production line! (Part 1)

In the previous lecture, it was explained that it's possible to determine the basic specifications of the mixing tank with a simple procedure using only limited information such as "operating liquid volume, viscosity, density".
While at the same time, it's emphasized "how to mix (HOW)" is important in determining the specifications suitable for "the purpose of mixing (WHAT)".

The theme this time is Simulation ! Skills to understand the characteristics of various IT tools and use them properly are becoming more demanding than ever.
Here, we will talk about the basics of simulation in a mixing tank and how to use it correctly.

Case Study:
At a certain agitator manufacturer's office

This is the office of an agitator manufacturer. The sales manager, Ueda, and the young engineer, Blendy, talk about something.

Mr. Ueda

In the previous request for quotation, we received a compliment from the customer that they submitted the specifications and quotation speedily and accurately !
Thank you Blendy for working hard, and this time the same customer asked me to do a simulation, so I'm asking you !


Director Ueda, what kind of simulation?

Simulation of a mixing tank!

What is the purpose of simulation for?

Eh! Don't you understand by simulation?

There are various simulations.
If we understand the simulation as CAE (computer simulation), it's much wider meanings.

What is CAE?

It seems that Director Ueda and Blendy don't understand each other's story.
In order to know the cause, it is first necessary to understand the whole picture of simulation.
Then, we will explain in order.

What is CAE ?

CAE is a technical term stands for Computer-Aided Engineering.
In dictionaries, it is said that "supports for product development, design, manufacturing, process design, etc. using computer technology. CAD (Computer-Aided Design), CAM (Computer-Aided Manufacturing), CAT (Computer-Aided Testing), etc. are also included."
In other words, CAE is "to evaluate (simulate) objects and movements that are virtually modelized or simulated on a computer" and is a word that means the work and supporting tools in general.

Since the range shown by CAE is very wide, we will proceed here with CAE as a technology for numerical calculation using a computer in development and design.
Numerical calculations using a computer is utilized not only for the analysis in a mechanical design such as strength/vibration analysis of products and parts (structural analysis) but also, gas, liquid, and solid flows analysis outside and inside the product (fluid analysis) and heat transfer analysis(heat transfer analysis).
There are many CAE tools are available for these analyses, one of which is shown in Figure 1.
I suppose it also includes the ones that you use every day.

Figure 1. CAE tool (software)

CAE tool (software)
CAD Structural
Fluid Analysis
CAM Acoustic
Field Analsis
CAT Press Forming

Oh, CAD is included in CAE.

As you can understand that the range is very wide, even if it is called just a simulation.
Fluid analysis (CFD) and structural analysis, which are often used in mixing tank design, are positioned as one of so-called CAE. That's why Mr. Blendy repeatedly asked "What kind of simulation?" to Director Ueda.

Next, let's discuss CFD, which is often used in mixing operations.

What is CFD ?

CFD is an abbreviation for Computational Fluid Dynamics.
The behavior of a fluid can be predicted by discretizing the continuous equation that governs fluid motion and the basic equation of the Navier-Stokes equation, approximating it with an algebraic equation, and numerically solving it with a computer. With the birth of this CFD, it has become possible to visualize the mixing state and flow pattern in the mixing tank.

In CFD, various physical phenomena are modeled (formulated) as needed and discretized into algebraic equations, but since assumptions and approximate values are used in modeling and discretization, errors will always occur. In addition, there are errors due to the nature of the computer. Therefore, it is important to keep in mind that numerical solutions include these errors.

The turbulence model is an example of a well-known model for modeling in CFD.
Turbulence occurs when the Reynolds number, which is the ratio of inertial force to viscous force, is large. Therefore, turbulence must be considered when solving high Reynolds number flows in CFD. Various turbulence models such as k-ε model and LES (Large Eddy Simulation) exist by modeling various kinds of eddy motions that make up turbulence. Therefore, the selection of this model is extremely important when solving fluid motions using software such as CFD.

Advantages and disadvantages of fluid simulation

By the way, what are the advantages of conducting a simulation?
The biggest advantage of numerical simulation, especially fluid simulation, is that you can visualize invisible phenomena. Furthermore, there are merits such as verification in unrealistic extreme conditions in experiments, reduction of labor for prototypes and experiments, and analysis under actual conditions.

However, fluid simulation has not only advantages but also disadvantages.
In fluid simulation, it is not possible to calculate unless the phenomenon is formulated, and since the assumptions and approximate values are used when formulating, it is not possible to know if it will be the same as the actual value unless it is calculated is.

For example, in the case of a gas entrainment phenomenon from the liquid surface to the liquid, it is difficult to formulate the mechanism such as how much gas is entrained from the liquid surface under what conditions and what is the diameter of bubbles entrapped in the liquid. Therefore, analysis with general-purpose CFD software becomes difficult.

Even if it is possible to simulate the entrainment of gas from the liquid surface, the consistency between the calculation results and the actual phenomenon could be shown for the whole system by using overall evaluation factor such as kLa (gas-liquid mass transfer coefficient), and difficult to evaluate for the local condition.

Therefore, even if the gas entrainment conditions and entrained bubble diameters are analyzed by simulation, the final evaluation will be the overall evaluation, so verification by a scale-down test is the most effective and reliable means.

That is why the fluid simulation should be used after conducting experiments to verify the consistency with actual phenomena and understanding the disadvantages. However, it goes without saying that it can be a very effective tool if you understand and use it.


  • You can see the invisible condition.(Flow field, Pressure distribution, Shear stress distribution, etc.)
  • Can be analyzed safely for unrealistic extreme conditions with actual experiments.
  • Experimental conditions can be focused by relative evaluation of analysis results.


  • Difficult to analyze unformulated system. (For example, entrainment of bubbles from the liquid surface)
  • Difficult to know if the analyzed results match the actual condition without verification.(Analysis solution = not always the actual value)
  • Depends on the skill of the analyst.

Advantages and disadvantages of fluid simulation

So, Mr. Ueda.
What kind of simulation for the mixing tank does the customer want?

Well, I feel that the customer said the flow in the mixing tank and there are many deposits, but I do not remember it well.

So that's it. Is it a countermeasure for the adhesion in the tank?
If so, the point first is wherein the mixing tank the adhesion occurs.
Mr.Ueda, let's ask our customers again ! I will accompany you too !

I see. I'll take the appointment immediately. (It's kind of reliable this time)

This time, Blendy's face has become dignified, doesn't he?
By the way, the point we wanted to tell you this time is that it's necessary to clarify the purpose of the simulation and then select a simulation tool suitable for it. And simulation is not an almighty engineering tool.

When improving the mixing operation, it can be said that it is almost difficult to solve it only by simulation. It may be possible if you can tolerate a great deal of time and money, but there are limits to the time and money that a company engineer can be given.
Improving the production efficiency of existing mixing tanks within this limitation is a permanent challenge for process engineers.
So, it's essential that work is to thoroughly examine past cases and expert know-how, make a hypothesis that "this is probably the case", and then carry out total verification by appropriately combining simulations and experiments.

We will introduce the idea about this in the next "Find a plan to improve the productivity of the mixing tank on the existing production line ! (Part 2)".
What is the thinking step of the engineer of the mixing tank manufacturer who received the request for the adhesion countermeasure?
looking forward to it.