The decontamination of porous materials that have been contaminated with hazardous chemical agents is a difficult and important problem, with critical implications for the environment and for public health. One decontamination method employed by government agencies is to apply a cleanser at the surface of the contaminated porous material, which reacts into the contaminated porespace, neutralizing the hazardous chemical. The agent and cleanser fluids are usually immiscible, so that the neutralisation reaction occurs at the interface between the fluids.
One difficulty of simulating this process is that the pore-space in the porous material forms an intricate, complicated domain through which to simulate chemical transport and reactions. Using homogenization and boundary layer methods, we have developed averaged models for the reactive decontamination of these porous materials, which hold over the much simpler domain of the entire porous material, but rigorously take into account the effect of the microstructure. Analysis and simulation of these models is much more computationally efficient than of the original models, and we can be used to understand and optimise the decontamination protocols.
See our paper for more detail, and a case study on problems in cleaning and decontamination. You can play around with simulating these models online using our Story on decontamination in VisualPDE here.
How does a porous material dry out? In situations where an evaporation front moves into the porous material, we have used a combined homogenisation and boundary-layer approach to understand how the microstructure of a porous material affects the motion of the evaporation front. It turns out that this depends on the "chemistry" of the evaporation: we might either assume (i) that there's an evaporation rate (that depends on how humid the air is next to the evaporation front) or alternatively (ii) that the water vapour is at its saturation point adjacent to the evaporation front. In case (i) the shape of the evaporation interface within the microscale pores is crucial, and there is an effective evaporation rate which depends on the average surface area. In case (ii) however, it doesn't matter what shape the evaporating surface is in the pores: the evaporation is purely driven by the transport of water vapour out of the porous material.
Take a look at our paper for more details.
Building on this, current work is focused on what happens if there is dirt in the water: where might that dirt go when the water evaporates? Answering this question will help to understand contaminant build-up within filters, enabling the prediction of product lifetimes and the identification of appropriate cleaning processes.
