Air dehumidification with hydrogels: the combined effect of temperature and pressure on adsorption

Industrial environments require precise air humidity control for the well-being of individuals, product storage and the adequate functioning of machineries. The latter goal, focus of experimental and theoretical activities of this thesis, presents critical issues especially when pressurized air plays an active role. In pneumatic circuits, where pressurized air runs in conducts and components, humidity and the consequent water condensation are responsible for rust and damage of pipes, moving parts and components like valves, flowmeters, motors. In addition, water drops formation affects the final product quality of industrial manufacturing processes. The reduction of the condensation risks can involve passive and active solutions. Mechanical filtration is an example of a passive approach usually applied just before each individual component to locally lower air water content. Active solution as well, like cooling-based or adsorption-based dehumidifiers, are often used when higher levels of humidity reduction are required. This work focuses on an innovative approach for adsorption-based solutions, investigating the behaviours of a composite biopolymer derived from alginate salts and providing a mathematical tool for system design and performance estimations. The first part explores, through an experimental campaign, the water vapor affinity of the polymeric composite under the influence of different positive or negative relative pressure conditions. In particular, the advantage of high pressures on adsorption cinematics, and the reciprocal improvement given by depressurization in enhancing the regeneration of the material, are investigated. The second part focuses on the design of a steam exchanger which will exploit the positive pressure available in a pneumatic circuit for the air dehumidification treatment. The physical modelling of material properties, formalized in a set of equations describing the dynamic of dehumidification and regeneration process happening in the steam exchanger, provides a mathematical tool for the component design. A one-dimensional and not stationary mathematical model correlates the size of the component and operational time with absolute pressure, temperature and relative humidity of inlet air, in order to guarantee the required water content specifics before entering the actual pneumatic circuit. The mathematical modelling, validated through experimental testing, is used as a tool to estimate absorbed power and dehumidification capacity of such system in order to compare and classify the proposed innovative design against other existing machines and solutions to dehumidify air in industrial contexts.