Hybrid gPROMS-CFD Multitubular Interface

High-fidelity modelling of multitubular fixed-bed catalytic reactors

The Hybrid gPROMS-CFD Multitubular interface links reactor tube models created in PSE’s AML for Fixed Bed Catalytic Reactors (AML:FBCR) to an ANSYS FLUENT® computational fluid dynamics (CFD) model of the shell side.

This provides an unprecedented degree of predictive accuracy for design and operational troubleshooting of externally-cooled tubular and multitubular (MTR) reactors.


Multitubular reactors are very difficult to model accurately, because of their complex geometry and operation (a typical reactor contains about 20,000 tubes, each with a wall temperature profile that depends strongly on local conditions).

High-accuracy modelling brings significant design and operational benefits to fixed-bed reactor design – for example, in eliminating hotspots and ensuring a more uniform distribution of temperature through the reactor. This enables higher overall operating temperatures and greater selectivity, throughput and catalyst life.

Accurate quantification is particularly important where the fluid mechanics and heat transfer on the shell side have a major effect on the operability and safety of the reactor with respect to thermal runaway.

The proprietary solution techniques embodied in Hybrid Multitubular ensure a high degree of accuracy within reasonable solution times for this complex problem.

How Hybrid Multitubular works

Hybrid Multitubular links a relatively small number of “representative” tubes implemented in gPROMS®, to a FLUENT® model of the shell-side fluid dynamics and heat transfer.

The model of an individual tube is constructed using the gPROMS Advanced Model Library for Fixed-Bed Catalytic Reactors (AML:FBCR).

Any number of tubes can be used (typically 20 to 100), each representing a much larger number of neighbouring tubes within the tube bundle. The FLUENT model can contain any internal shell configuration.

Hybrid Multitubular automatically maps corresponding tube-surface points, performs validity checks on supplied data, co-ordinates the execution of gPROMS and FLUENT, and manages all the required information flows.

Using the Hybrid gPROMS-CFD Multitubular interface – a simple step-by-step guide

A. Prepare the CFD model of the shell side

Step 1: Create a FLUENT model for the shell, representing the tube-bundle as a porous medium.

Define boundaries in the geometry and declare the entire zone of the tube bank as a single thread of cells.

B. Prepare the gPROMS model of the tube side

Step 2: Using the gPROMS Advanced Model Library for Fixed Bed Catalytic Reactors (AML:FBCR), configure a single tube model within gPROMS ModelBuilder®.

You can use gPROMS ModelBuilder’s model validation facilities to determine accurate reaction kinetic parameters and bed-to-wall heat transfer coefficients from laboratory and/or pilot plant data.

C. Execute the combined simulation

Step 3: Specify the number of representative tubes and their x and y co-ordinates within a horizontal cross-section of the CFD model of the shell in a simple text file, together with other relevant information.

Step 4: Execute a FLUENT simulation of the shell model. The Hybrid Multizonal automatically acts as a FLUENT User Defined Function that computes a heat source and a body force acting on the heat transfer medium in the shell.

View the results using FLUENT’s and gPROMS’ results management facilities. typical results are shown below:


Licensing, supported platforms and pre-requisites

The Hybrid gPROMS-CFD Multitubular interface is available for ANSYS’s FLUENT® CFD software. It is licensed as an option within the gPROMS Advanced Model Library for Fixed Bed Catalytic Reactors (AML:FBCR).

See supported platforms for the latest details on supported platforms.

More Information
The gPROMS AML:FBCR allows us to improve the performance of industrial reactors using our catalysts significantly

Combining FLUENT and gPROMS models provides unprecedented accuracy for MTR design

Mechanical design geometry

Accurate quantification supports geometry / mechanical design of multitubular reactors


High-fidelity multitubular reactor modelling enables you to:

  • identify and eliminate hotspots
  • ensure uniform temperature distribution
  • understand catalyst degradation
  • enhance selectivity, increase throughput and product quality
  • optimize economic operation.


  • provides unprecedented accuracy in predicting the behaviour of multitubular fixed-bed catalytic reactors
  • allows any level of complexity in the reactions taking place within the tubes
  • allows virtually any shell geometry (e.g. baffles, compartments)
  • combines gPROMS and FLUENT® in a unique tool that leverages the best of each of these two technologies in a seamless, easy-to-use and computationally efficient manner.