Suppose a large amount of CO2 is pumped deep into the ground so that it is kept out of the atmosphere and does not harm the climate. How will the CO2 behave together with the groundwater in the rock? This is a typical example of a question that pushes the known theory of fluid dynamics to its limits: How do currents behave in porous materials? What chemical effects take place? How does the rock morphology vary due to the flow and how does this change in turn affect the flow?
Marco De Paoli from the Institute of Fluid Mechanics and Heat Transfer is working on such complex questions. He is developing ways to describe the flow of liquids through porous materials - especially when this flow shapes the porous material. The European Research Council (ERC) has now awarded him an ERC Starting Grant worth around 1.5 million euros. The research project is scheduled to run for five years.
From heat reservoirs to ice on the ocean
"Flow through porous materials is something we encounter in many different areas, both in nature and in industry," says Marco De Paoli. However, many questions in this field are still unsolved. One particular challenge is that you often have to keep an eye on different size scales at the same time: Perhaps the flow behaviour is determined by microscopic details of the material, on a lenght scale of less than a millimetre. Ultimately, however, you want to be able to explain a macroscopic situation - such as the transport of material through a layer of rock hundreds of metres thick.There are many important technical applications for this research. For example, thermal energy can be stored by working with phase transitions: Energy is provided to a solid material until it melts. Later, when the liquid solidifies again, the energy is released. "If you want to employ this energy storage technique on a large scale, however, you have to accurately design your storage system. This is challenging because you have to understand how solids and liquids interact during this process, and here again you are dealing with a flow through porous structures that are constantly evolving," explains Marco De Paoli.
Something similar happens in nature, for example, when ice forms on the ocean. Cold air causes the first ice crystals to form on the surface, while the water underneath is warmer. The ice does not form as a perfectly solid block, but as a porous structure made up of countless small crystals. However, because the salt in the seawater is not incorporated into the ice crystals, the salt concentration in the water directly beneath the fresh layer of ice increases. Water with a higher salt content has a higher density and therefore sinks - and again, a complicated system emerges, which can only be understood if several different effects that are closely interlinked are considered together.
