A passive autocatalytic hydrogen recombiner (PAR) is a self-starting device, without operator action or external power input, installed in nuclear power plants to remove hydrogen from the containment building of a nuclear reactor. A new mechanistic model of PAR has been presented and validated by experimental data and results of Computational Fluid Dynamics (CFD) simulations. The model allows to quickly and accurately predict gas temperature and composition, catalyst temperature and hydrogen recombination rate. It is assumed in the model that an exothermic recombination reaction of hydrogen and oxygen proceeds at the catalyst surface only, while processes of heat and mass transport occur by assisted natural and forced convection in non-isothermal and laminar gas flow conditions in vertical channels between catalyst plates. The model accounts for heat radiation from a hot catalyst surface and has no adjustable parameters. It can be combined with an equation of chimney draft and become a useful engineering tool for selection and optimisation of catalytic recombiner geometry.

The energetic efficiency of mixing is studied numerically in a continuous flow mixer constructed from a sequence of alternately twisted pipe bends. Counter-rotating vortices present in the curved channels and known as Dean vortices narrow the distribution of the residence time of fluid elements and accelerate the generation of a new material surface without obstructing the main flow and increasing the risk of fouling or flow stoppage. Cyclic twisting of the pipe curvature allows for quick reorientation of Dean vortices. The reorientation induces chaotic advection in a stable three-dimensional flow and speeds up mixing. The effect of computational domain discretisation for the low and medium Reynolds numbers (20 < Re < 2000º on the head loss, primary and secondary flow, residence time distribution, and the energetic efficiency of generation of the inter material surface is determined. The energetic efficiency is calculated in the time space, a standard approach in modelling reactive micromixing, and at the reactor exit. The maximum energetic efficiency is determined for Re ≈ 600 ÷ 700. It is also found that the initial orientation of the material surface to the pipe curvature has a significant impact on the energetic efficiency of mixing.

Transport properties of bronchial mucus are investigated by two-stage experimental approach focused on: (a) rheological properties and (b) mass transfer rate through the stagnant layer of solutions of mucus components (mucine, DNA, proteins) and simulated multi-component mucus. Studies were done using thermostated horizontal diffusion cells with sodium cromoglycate and carminic acid as transferred solutes. Rheological properties of tested liquids was studied by a rotational viscometer and a cone-plate rheometer (dynamic method). First part of the studies demonstrated that inter-molecular interactions in these complex liquids influence both rheological and permeability characteristics. Transfer rate is governed not only by mucus composition and concentration but also by hydrophobic/hydrophilic properties of transported molecules. Second part was focused on the properties of such a layer in presence of selected nanostructured particles (different nanoclays and graphene oxide) which may be present in lungs after inhalation. It was shown that most of such particles increase visco-elasticity of the mucus and reduce the rate of mass transfer of model drugs. Measured effects may have adverse impact on health, since they will reduce mucociliary clearance in vivo and slow down drug penetration to the bronchial epithelium during inhalation therapy.