The Boussignac valve: Experimental and numerical study of the working principle and thermofluid behavior

Devices that generate Continuous Positive Airway Pressure (CPAP) allow to increase respiration pressure in patients and enable an easier oxygenation. Despite advances in device size and noise reduction, many of them are still found cumbersome by patients. The Boussignac valve is a device without moving parts and reduced noise, able to generate CPAP by the coalescence of four high-speed-air jets. When connected to a face mask and an oxygen source, it may help in non-invasive ventilation procedures without disturbing patients. Due to its working principle, the generated pressure becomes a function of the valve flowrate, so its characterization becomes of vital importance to ensure patients receive adequate treatment. In this work, experimental tests and numerical Computer Fluid Dynamics (CFD) simulations were combined and compared with the manufacturer curve. It was possible to identify the main mechanisms responsible for pressure generation and flow amplification. – jet coalescence and viscous shearing. In contrast to the initial assumption of turbulence generating a one-directional valve, bidirectional flow was observed in the simulations, allowing exhaled air to leave the valve in the opposite direction. Pressure generation was found at between 20 and 60 % of the valve length. In addition, compressible effects arise as the flow rate increased above 10 L/min, leading to supersonic conditions at more than 25 L/min and the corresponding local temperature drop at the jet passages. The numerical procedure used may serve as a guideline for developing new valve models, ensuring mesh-independent results.