In this article we cover how gas flow is managed within Simcenter Amesim and provide a brief overview on how the different gas library work.
In Simcenter Amesim, flow in the gaseous phase is covered by several libraries, all catering to the various needs a user may have. The Pneumatic library deals with gas flow in the compressible flow regime and may be used to simulate gas containing a single species or multiple species at the same time. The library is made up of common components often found within a pneumatic systems, such as compressors, heat exchangers and pneumatic valves, and may be used to predict pressurized gas flow within a system.
To extend the capabilities of the Pneumatic library, the Pneumatic Component Design library exists to make it possible to create new and more detailed pneumatic components by using smaller building blocks. An example of this could be creating a more detailed compressor model made up of different smaller parts describing the pistons, internal volumes, internal orifices and valves. The purpose of the Pneumatic Component Design is similar to its liquid counterpart, the Hydraulic Component Design library.
Both the Pneumatic and Pneumatic Component Design libraries deal with single, or constant mixture of different gases, and do not change concentrations throughout the system during a simulation. This is in many cases the desired outcome of a simulation and is adequate to describe what is happening in the system. However, in other situations we want to explore how concentrations evolve over time when different species are introduced to the system. For these purposes the Gas Mixture library is used and the library is able to handle a large number of different applications, from fuel cells found in the automotive domain to environmental control systems in Aeronautics. In addition to be able to simulate entire pneumatic systems containing pipes, valves and heat exchangers, the library also allows users to predict phenomena such as diffusion between species and take into account behavior of porous media in a model. The Gas Mixture library may also be combined with the Moist Air library to capture phenomena relating to liquid condensate within the mixture.
Below, a simple mixing example is given where two streams of pure oxygen and hydrogen are allowed to enter a tank filled with air (O2, N2, Ar). By doing so it is possible to study how the concentration within the tank will evolve over time.
On the left-hand side in the image above, the model’s overall gas mixture is set and defined by accounting for each individual species. In this example four species make up the mixture (H2, O2,..). The properties of each individual species may be set by selecting from the material library or as a user defined gas. Additionally, the selection of Equation of State (EOS) to use during the simulation may be done from the drop-down list under “properties definition”. The equation of state defines which equations to use to describe the state of the gas mixture under different conditions, e.g. temperature, pressure and volume. Depening on the purpose of the simulation the gas mixture may be treated as a perfect gas or by using real gas formulations, such as Soave-Redlich-Kwong (SRK).
Below, an example where the Moist Air library has been introduced to account for liquid droplets within the mixture is shown.
Now, suppose that we not only what to investigate how concentrations evolve within our system, but also would like to manipulate the mixture by subtracting or adding completely new species during a simulation, such as during a chemical reaction. This can be achieved in a functional way by sensing the composition of the flow, calculating the appropriate conversion using a set of functions, and then feeding back a new mixture to the system. This approach is outlined in the image below, where a process involving steam reforming to convert methan to hydrogen and carbon monoxide is carried out by sensing temperature and concentration for the stream, and then removing species (reactants) and adding new species (products) to the same stream. The equations and functions used may be dependent on any sensed property for its calculation, temperature in the case below, and may influence other parts of the system as well, such as the removal of heat.
Hopefully this post provides a good starting point for navigating between the different Gas libraries within Simcenter Amesim. If you have any questions or comments, please feel free to reach out to us at support@volupe.com
Author
Fabian Hasselby, M.sc.
