CFD Analysis

Mixing and agitation can be interesting for various reasons. The objective may be uniform mixing of two or more phases. Mixtures’ components might all be fluids (gas or liquid) or also solid phase might be present. Sometimes agitation of just one phase is important for cooling or heating purposes.

CFD can provide a vast amount of information about the mixing process with only one simulation. Depending of the application, the information of interest may be

• Flow fields
  e.g. impeller power number, flow fields close to critical areas (such as heating/cooling coil)
• Pressure fields
  e.g. at the impeller blade and baffle surfaces
• Other interesting phenomena
  e.g. chemical reactions, mixing time, temperatures

In addition, process optimization is relatively simple compared to experimental work when comparing different process parameters, such as impeller blade shape, does not require building a new, expensive prototype.

Heat transfer processes

Heat transfer has a significant role in several applications. Applications for CFD are various, such as

• Estimation of average heat transfer coefficient of a heating/cooling equipment
• Estimation of maximum and minimum temperatures (reactors, furnaces, etc.)
• Estimation of temperature distributions at wall, thermal stresses
• Dynamic estimation of heating / cooling efficiency

Production process optimization

CFD was used to examine the solid surface temperature of a production process cast mold. The cooling agent was liquid nitrogen. The process required for the solid surface temperature to be in a specific range and CFD was used to examine the effect of different feed arrangements and nitrogen flow rates.

Heat exchangers

In case of heat exchangers CFD can be utilized to estimate the local surface temperatures, which are rarely uniform. Local cold or hot spots can cause unwanted condensation or liquid overheating. Also uneven flow distribution on the pipe side can unnecessarily decrease the heater efficiency.

Pressure analysis

CFD can provide information about the pressure fields inside the equipment. Structure-wise, interesting could be flow induced pressure impulses or pressure fields at surfaces, or pressure at specific locations. Too low local pressure, for example, is a common pumping related problem resulting in cavitation. Structure related pressure fields can be used in structural optimization to ensure durability of the design.

Flow-Structure Interaction (FSI) analysis is also possible and by combining ANSYS product family’s fluid dynamics (ANSYS Fluent) and structural analysis (ANSYS Professional) software in a common user environment (ANSYS workbench), the problem set up and information transfer is straightforward.

Flow resistances

Packed beds, filters, sieves, nozzles and equipment related pipe lines and connections in general cause pressure drop.

Pressure drop can be compensated with, for example, a pump or compressor. CFD allows to analyze how the equipment design, operation and pipe lines affect the produced pressure drop, thus ensuring optimal operation of the equipment and avoiding unnecessary power consumption.

Pipe connection shape

Perforated plate

CFD can be used as:

• Part of the product development process
  CFD offers versatile possibilities as a part of the product development process. Stressfield Oy is your competent, reliable and motivated partner in product development. Read more: Product development services
• Part of a problem solving procedure
  The root cause for equipment malfunction or lower than expected performance is not always obvious. Here, CFD provides detailed information from inside equipment that is often unavailable for measurements. Whereas measurement data offer insight on what is happening, CFD simulations can provide a deeper understanding on why. When the underlaying phenomena behind the problems are understood, it is possible to take corrective action.
• Optimization tool for equipment and process line sizing
  CFD is a useful tool also in equipment and process line sizing and optimization. Although there are very good tools in various process design handbooks for equipment sizing (e.g. balance calculations), computational fluid dynamics can be a useful tool to ensure, for example, even distribution of heat transfer.

CFD results can be presented as illustrative temperature, pressure, velocity and phase/particle distributions. Vector fields and streamlines offer also a clear visual demonstration of the simulated phenomena. Results can also be translated into numerical values to help result comparison. For example average flow rate, pressure or temperature, total pressure loss, local flow resistances, impeller power number and reaction/burning rate. In addition, CFD can be used to evaluate dynamic phenomena such as how long mixing, heating/cooling or a tank emptying sequence takes. And, above all, how the planned innovation affects the functionality of the equipment.

Our suite of software includes the CFD tools Ansys Fluent and CFX as well as the modelling/post-processing tools FEMAP, NX6, Ansys Workbench, SpaceClaim and MSC Patran.

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