Why is CFD Modeling and Simulation important for Equipment Design?
In aerospace and many other industries, components are tested in a wind tunnel or experimented on for their performance. CFD modeling and simulation gives insights into how well a design model will perform under extreme surrounding conditions before doing it in the real world. CFD modeling and simulation tools have dramatically simplified this process by simulating a computer’s design. The Aerospace and Automobile industry has accepted CFD modeling as a part of their development and testing process. Several iterations of a component are simulated without manufacturing them. On achieving an optimum design that matches the customer requirements and market standards, the manufacturing process is initiated. It has reduced their product development cost and time drastically.
CFD simulation is also an excellent way of prototyping products. CFD modeling and simulation tools can help understand if the assumptions about product performance are valid. The CFD simulation results are helpful visual representations for in-depth research and the study of different fluid-flow phenomena.
Process equipment have seemingly simpler internals with few body parts. However, there exist a complexity of fluid flow, heat and mass transfer in the chemical process equipment. While gas-liquid, liquid-solid interactions are very common, all the three phases, gas-liquid-solid coexist in many chemical reactors and processes.
To achieve higher yield, conversion, selectivity, product quality parameters like color uniformity, right color, texture, particle size and shape, mixing/contacting of the raw material is fundamental requirement. it is important to achieve uniform solid suspension, uniform gas dispersion, liquid-liquid blending and dispersion, thermal homogenity in the process equipment. Chemical reactions are usually accompanied with heat transfer (exothermic or endothermic reactions). it is extremly critical that the thermal uniformity is achieved in the reactors for right product quality and importantly, safety. Furnaces, combustors, heat exchangers needs to be designed in compact for efficient combustion of fuel under stiochiometric air/oxidizing agent conditions.
A chemical reactor is said to optimal when it is sized optimally, operates under designed operating conditions of temperature, pressure, and with stiochiometric raw material ratios.
CFD modeling technology is best suited to give insight of the complex flow-heat-mass transfer processes occuring inside the equipment. It gives detailed, three dimensional view of mixing, thermal profiles, gas dispersion, solid suspensions, liquid blending as a function of the reactor design. CFD modeling finds its application in the entire life cycle ( ideation, conceptualization, scaleup, commercialization) in the design and operational phases.
CFD Modeling Methodology at FluiDimensions
For Equipment Retrofitting and debottlenecking, we devote our considerable amount of time in understanding customer’s problems and expectations. We understand the process and operational methodology and the constraints.
As the chemical process are complex involving slurries, multiphase flows, high temperature and pressure, understanding the underlying fundamental physics is important. The fluid properties like density, viscosity , thermal capacity and conductivity is often not known at the operating conditions and compositions. Further, the data on chemical kinetics, detailed chemical reaction mechanisms, heat of reaction are often not available. Hence, right simplification of the process is needed without losing the complexity.
At this time, in collaboration with the plant process experts, we convert the process problem and KPIs into CFD objectives and define the analysis process.
As the process and objective becomes clear, the actual CFD modeling process starts.
Domain Selection
The first step is to identify the domain, the boundary, the region of interest for the analysis. We identify all the internals in the equipment that can affect mixing process inside the domain/equipment. The engineering drawings with different views gives all the actual dimensions and details of the domain.
Using a CAD software, the actual to the scale, three dimensional CAD model of domain is created
Boundary Conditions/Operating Conditions
The flow rates, temperature, pressure, composition etc that quantifies the various streams entering and leaving the domain are measured. These conditions are also measured regularly by the operations teams and recorded.
Meshing
The selected domain and the identified boundaries are then discretized into very small volume elements called mesh/cells. This process is called meshing. In each of the cells, the governing equations of flow, heat and mass transfer, turbulence and mass conservations are solved using numerical techniques.
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| Polyhedral Mesh | Tetrahedral Mesh | Cut cell mesh |
Physics setup
This is a most important step of CFD modeling. In this step, the physics involved in the equipment is specified. For example, if heat transfer is involved in the process, then thermal models needs to be selected. Appropriate turbulence models needs to be chosen to represent the turbulence in the equipment. If chemical reaction or combustion is involved, the species involved, reactions, stoichiometry, mechanism of combustion, rates of reactions, heat of reaction etc are specified. If the problem involves multiple phases, then the volume fraction of each phase is also needed.
FluiDimensions has in-depth skills in modeling complex equipment and detailed physics.
Solve
The numerical methods to solve the non-linear second order differential equations are selected. The convergence criteria, relaxation parameters, time step size are chosen to solve the governing equations.
The automatic iterative procedure is adopted till the convergence is achieved. The solution obtained is numerically correct.
Analysis
The solution obtained is now analyzed and related to the problem being solved. The velocity, temperature, composition, volume fraction, turbulence parameters are plotted on different planes, locations of interest.
We work very closely with our customers and explain the results and our analysis in depth.
The strategy of providing the solution to the problem is now decided. A detailed discussion with the customer is done to understand the constraints of the design solutions or operating conditions. It is from these discussions few alternatives are identified that can be easily implemented at the site.
The whole above methodology is repeated till the optimal design or operating condition is arrived.
Final Delivery
A detailed report in the form of presentation or/and document is provided with all the results, analysis and the engineering drawings, optimal operating conditions for the implementation is submitted.