A simulation tool for mass transfer inside compressed air vessel for water networks pressurisation

Feeding a water distribution network with the correct pressure is a fundamental requirement for its proper operation; to this end, a simple and reliable solution commonly adopted in small and medium industrial plants is the adoption of a pressure vessel. For small systems, a membrane seals the system water from the gas compartment, anyway, as the size of the vessel increases, the adoption of sealing diaphragm or bladder is no longer feasible, and thus there is a direct contact between air and water. The high pressure of the vessel, combined with the cyclic loading and unloading phases, which replace the water inside the tank, leads to a considerable mass transfer phenomenon of air inside water. The loss of air mass cannot be monitored and detected by simply controlling system pressures; to this extent, water level measurement and reference analytical models are required. Since there is a lack in scientific literature of these models, the present study presents a model for mass transfer estimate in the systems described, starting from a real pilot plant. The main results of the model implementation in a spreadsheet, in terms of the trend of the key model parameters in time, are also reported and discussed.