Improvement of degradation with non-condensable gas in micro steam injector

Effect of non-condensable gas on a micro steam injector (MSI) to obtain a vacuum was experimentally studied. The MSI used in this study had a nozzle of approximately 3 mm in diameter to inject a water jet in the mixing with a supersonic steam flow. When a pure steam was used in the MSI, the high vacuum condition was obtained. However when the mass fraction of air included in the steam was larger than a certain value, the MSI became unstable and the vacuum condition could not be obtained. It is considered that the malfunction of MSI is due to the instability triggered with the uncondensed steam at the throat in downstream of the mixing region resulted with the degraded condensation behavior. The water nozzle was considered to be a key component to mitigate the effect of non-condensing gas. Three kinds of water nozzle whose flow area were round and screw shapes were used in the present experiment. The screw nozzle expected to drive air away outside the condensing surface could mitigate the effect of non-condensing gas. (author)