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| CSIRO | SOLVE | Issue 8 | Aug 06 | |
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ARTICLE
FLUID DYNAMICS:
Going With the Flow By Youna Angevin-Castro
Predicting the flow of a fluid in an industrial, mining or medical setting can have far-reaching effects – from the bottom line to patients’ healthA modelling technology that has its roots in weather prediction and the aerospace industry could have far-reaching applications in industries such as minerals, biomedicine and computer animation. Computational fluid dynamics (CFD) is a complex software tool that uses advanced computational techniques to model the flow of fluids. Used across a wide range of fields in the process industries, its major application by CSIRO has been in the minerals industry. By predicting outcomes of variations in physical design or parameters, it allows for practical and cost-effective solutions to plant and processing problems. Dr Phil Schwarz of CSIRO Minerals says the minerals industry has been an early adopter of CFD technology because its processes are typically very complex, multiphase systems, and may be conducted in a hot or corrosive environment. “Because there is limited scope to make accurate measurements within many systems, computer modelling is often the only practical way to gain a better understanding of how to improve the system – and CFD is one of the most advanced of these computer modelling systems available at the present,” Dr Schwarz says. New uses for CFD are opening up. Key research into biomedical applications is being undertaken by Dr Murray Rudman and his group at CSIRO Manufacturing and Materials Technology (CMMT). Dr Rudman says CSIRO’s ongoing commitment to developing its own internal fluids technologies – which it has a view to marketing – has helped develop these new uses. “We use CFD to look at quite fundamental issues of fluid mechanics, which later have applications in places we might not have expected to begin with – more blue sky stuff,” Dr Rudman says. “One of the key things we’re keen to look at in the biomedical field is the flow of blood throughout the body as a result of the heart beating and how that interacts with arteries, in particular with arterial implants and aneurysms.” One of Dr Rudman’s colleagues, Dr Ilija Sutalo, is working on an analysis of the possible effects on blood flow in the treatment of aortic aneurysms. Aneurysms result from a ballooning of the arterial wall. Typically, as you get older, artery walls weaken, causing a balloon to form through the pressure of blood flow. If they balloon out too far, the artery wall may rupture and death follows in a matter of minutes. The current treatment for this type of aneurysm is surgery, where an endoluminal graft is inserted inside the artery. This graft is designed to alleviate pressure on the arterial wall, giving it a chance to heal. “One of the questions we have been investigating is once you’ve inserted these grafts, what are the fluid forces that the blood flow exerts on the graft wall,” Dr Sutalo says. “Are they going to stay in place? Or are they going to move down the artery, allowing blood to leak around the outside of the graft and repressurise the aneurysm? “CFD allows us to determine the kinds of forces you can expect to be applied to these grafts and to determine if a patient will continue to have the same problem after surgery.” Beyond the biomedical, Dr Rudman has seen tremendous savings in both time and money for industry through the use of CFD. For example, the Rotated Arc Mixer (or RAM) – a CSIRO technology used for mixing very viscous materials such as polymers or food products with low energy inputs – relied heavily on CFD in its design. “We had a basic idea of how the design would work, but the way we actually went about it was to use computational fluid dynamics to search through the huge range of parameters that were possible and find the ones that were actually going to work,” Dr Rudman says. “Once we found suitable parameters, we then built the experiment to validate the CFD predictions. The experiment we ran gave us exactly the results that we predicted using CFD. “Rather than building hundreds of different potential mixers, we were able to do some computational simulations, predict which designs would work and then construct them, saving huge amounts of time, money and effort.” As an early adopter of the technology, the minerals industry has also benefited from CFD. Dr Schwarz says CFD is very valuable for improving designs – such as increasing throughput. “This is very valuable for industry because without spending much capital they can increase the return on the existing equipment. It may be improving the product quality, or it may be increasing recovery – such as increasing the recovery of nickel or copper in the flotation process.
A recent example is a project developed by CSIRO Minerals for BP. Seeking to improve plant operations, CSIRO used CFD to enhance the operation of BP’s fluidised bed catalytic cracker (FCC) stripper and regenerator. The work used CFD to identify the best design modifications to improve oxygen use, obtain a more uniform temperature distribution in the regenerator unit and to optimise the stripper to maximise stripping of hydrocarbons from the catalyst, while avoiding flooding. “CFD modelling enabled us to understand what was occurring within an area of the refinery, and to assess modifications prior to upgrading,” says John Lee of BP. “Subsequently, unit capacity was increased and feedstock costs reduced significantly, saving us millions of dollars per annum. “CSIRO’s outstanding expertise in CFD was crucial in achieving these savings.” In a project to improve gravity thickeners, the use of CFD and other research tools, has led to efficiency gains worth an estimated $295 million. In the longer term these figures are expected to exceed $500 million. “Australia is a very technically advanced nation with regards to the minerals industry, and there is no doubt that the continued investment in this research will continue to provide many gains to the industry,” Dr Schwarz says. Dr Rudman says that one of the requirements when undertaking a reliable CFD analysis is the ability to validate predictions using available data and matching experiments. “Validation is an extremely important part of CFD – you need to be able to compare it to some sort of concrete data, to check whether what you predict has a good correspondence to reality. Without a good level of understanding of how your model compares, it is possible to make predictions that look realistic but are not correct.” Beyond this, CFD’s uses are endless, Dr Rudman says. “All the things we do stem from problems related to fluid flow and the fluid mechanics are essentially the same across a range of industries – from mining, to biomedical industries, to oil and gas. “Although there may be additional physics to consider in different processes (such as heat transfer, chemical reaction or multiple phases) fluids are fluids, and while they each have different properties, the underlying equations and the underlying techniques for solving the equations are similar across all of these fields. “So once you have experience in applying CFD in one industry, it does open up the possibilities of looking at other industries and applying knowledge and models across a range of scenarios.”
APPLICATION Computational fluid dynamics (CFD) is a complex software tool that uses advanced computational techniques to model the flow of fluids BENEFIT Industries as diverse as mining, oil, gas, food processing, animation and biomedicine are taking advantage of CFD modelling
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“All of that can save a lot of money, because in the minerals industry the throughput rates are so high that a small percentage improvement in recovery can make a very large impact on the bottom line.” 
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