The Ultimate Guide to Chemical Reactor Scale-Up Software

There are a lot of possibilities in the market to calculate any mathematical required system with
mathematical tools. More than this, there are many software programs that are trying to solve
these systems with empirical data and specific models regarding chemical reactors. However,
the main assumption behind these models is that we are talking about well-mixed equipment.
Because of this assumption, all the true influence of the mixing in the reactor and reaction
systems is not taken into consideration.
In reality, mixing is a complex unit operation that cannot be fully captured by a simple set of
empirical equations or assumptions. To accurately calculate and simulate reactions with
simulators, there are two main different approaches you can take.
The Two Main Simulation Approaches
1. Computation of Flow Dynamics (CFD)
The first approach is the computation of flow dynamics, which encompasses all fluid flow
capabilities. One common method within this category is finite elements. This method tries to
solve complex, nonlinear differential equations through approximation to determine the
velocity of the flow based on typical models like the Reynolds stress approximation.
While these programs perform numerical solutions of basic flow dynamics equations, standard
CFD tools can generally only be used by professionals with deep expertise in mathematical
modeling, requiring the user to spend significant time creating and formalizing the model.
2. Semi-Empirical Physical Modeling (VisiMix)
The other kind of software that you can find in the literature for stirred vessels is VisiMix. The
model used here is a semi-empirical model. On one hand, it goes more deeply into the physics
that actually happen inside the tank, reducing the complex non-linear equations down to a
simple non-linear differential equation. This simplified equation is then solved by numerical
methods within the software.
On the other hand, in order to be completely sure that the results are relevant and
representative of a realistic industrial situation, this semi-empirical model utilizes a huge
database collected over many, many years by VisiMix. This allows the software to calculate key
parameters in a matter of seconds on a standard PC, rather than requiring days of high-
performance computing.
Beyond Hydrodynamics: The Level of Specific Chemical Processes
Calculating the fluid flow and hydrodynamics that happen inside the tank is vital, but we have
another level after that. Once the hydrodynamics are known, we must take the specific
chemical process into consideration.
In a specific process, we have reactions. This means we have reagents or molecules that, when
placed in interaction with each other and in a good proximity, will generate a product (or
different products depending on the complexity of the reactions involved). In order to be truly
realistic when simulating this process, we encounter another deep level of complexity that
must be solved:
 The Fluid Element Size: The smallest eddy or fluid element that can be generated in the
physics world is on the order of magnitude of a micrometer.
 The Molecular Size: The actual order of magnitude of the molecular size we are
managing and trying to react is on the scale of nanometers.
Because of this, we have a two or three order of magnitude gap between the group of

molecules that will be in the same place to interact. This physical gap generates a very high
deviation in standard calculations. If a simulator ignores it, you cannot get results that will be
representative of your actual plant scale.
How VisiMix-Can Solves the Scale Gap
This critical gap is solved only with VisiMix software, specifically VisiMix-Can software, which
takes this physical scale gap into consideration as a core part of its calculations.
Inside VisiMix-Can, you will find a multi-level calculation approach that explicitly separates what
is happening at the macro-level from what is happening at the molecular level:
Level 1: Perfect Macro-Mixing
First, the software generates a calculation taking into consideration only the velocity of the
flow. This is a model of perfect macro-mixing (not a "well-mixed" equipment assumption, but
perfect macro-mixing). This calculation looks at how long it takes for the material to be sprayed
and distributed across the tank. These fluid elements move in the tank and generate macro-
homogeneity. The size of these fluid elements depends entirely on the mixing energies that we
have inside the tank.
Level 2: Actual Mixing Results
The lower level in constraint is the physical gap between the fluid element size and the
molecule size. To solve this, VisiMix applies molecular diffusivity inside these fluid elements as
they move into different zones of the tank with varying sizes.
When you provide a solution using this software, VisiMix displays the results transparently
across two distinct columns:
1. The Perfect Macro-Mixing Column: Taking into consideration only the distribution of
the fluid elements in the tank.
2. The Actual Results Column: Taking into consideration the lower level—the real-world
gap between the molecule level and the fluid element.
The Ultimate Guideline for Reactor Scale-Up
This unique capability to connect these two distinct scales together gives us the actual mixing
results that happen in VisiMix. This is why VisiMix represents the ultimate guide and innovation
in the industry; it is the only way to accurately describe a chemical reaction in a stirred vessel
for the liquid phase.
Furthermore, where other phases are involved—such as a gas phase or a solid phase—VisiMix
is fully able to calculate the mass transfer first, and after that, calculate the exact reaction that
happens in the local interaction between the molecules.
This main innovation is fully represented in our software guidelines. Rather than dealing with
unvalidated, model-dependent outputs, VisiMix provides a clear visual representation showing
exactly how "Actual Reactor" performance can differ significantly from an ideal "Reactor with
Perfect Macromixing."
To learn more about how these physical principles apply to different regimes, read our
comprehensive guide on What are the processes of mixing? or explore how our Industrial
Process Simulation Software provides direct scaling across lab, pilot, and production scales.
You can also check out our dedicated pages on VisiMix Turbulent and VisiMix Laminar to find
the right mathematical modeling tools for your specific media viscosity.
Contact us today to get a full representation of the software and take your chemical reactor
scale-up to the next level.