Flow rate of nitrogen-rich air and influence factors for onboard air separation unit

The flow rate of a certain type onboard air separation unit to produce the nitrogen-rich air related with the flight height, inlet pressure, temperature and the nitrogen concentration was experimentally studied on a test apparatus. An empirical correlation to predict the flow rate of the nitrogen-rich air was obtained and verified via the polynomial fitting method and experimental data. In addition, the influence factors affecting the flow rate were investigated and the variation of the flow rate along the entire flight profile was calculated. Results indicate that, the obtained empirical correlation has high prediction accuracy; the flow rate of the nitrogen-rich air along the flight profile could be calculated based on the present mathematical model; under a constant pressure, temperature, flow rate of the nitrogen-rich air is reversely proportional to the nitrogen concentration, so when nitrogen concentration increases, the flow rate decreases; especially, the effect will be larger under the higher inlet temperature and pressure; the flight height, pressure, temperature are proportional to the flow rate, and the lower nitrogen concentration, higher flight height, temperature and pressure will bring larger impact on the flow rate. The research results could be beneficial to the design of fuel tank inert system.