Speaker
Description
Normally cryogenic liquids such as oxygen or hydrogen are used as propellants of the launch vehicle. Densification of propellants means the density of propellants are increased by decreasing the cryogenic fluid temperature. Compared to common incompressible liquids, the density of cryogenic fluids changes more sensitively according to the temperature. Therefore, this densification technology is actually used in current launch vehicle, and it increases the fuel efficiency of launch vehicle since the more propellant could be stored in the same propellant tank volume. There are several kinds of method to densify the propellants by cooling down the temperature of liquid propellants. One of the densification methods is decreasing the pressure of propellant tank under the atmospheric pressure by using a vacuum pump. In fact, ejector could be used instead of the vacuum pump. Ejector is a simple device and has no moving parts, so it is clean and highly reliable which is more appropriate to use in launch vehicle. In this study, an ejector is designed and its performance is tested to cool down the liquid nitrogen temperature below 77 K. The ejector is installed at the top of the liquid nitrogen tank, and high-pressure nitrogen gas is used as the primary fluid of ejector. Then saturated vapor of nitrogen in the tank is suctioned to the secondary fluid of the ejector. The test result showed that the entrainment ratio decreased over time. The reason is that both the secondary flow rate and the tank pressure decrease during the subcooling process. The optimum ejector geometry such as the nozzle diameter and the mixing throat is determined from the operating condition of the ejector like the primary and secondary flow inlet pressures, temperature, and mass flow rate. Therefore, the optimum size of each ejector component should be different at different subcooling pressure. This means multiple ejectors rather than a single ejector would be a more effective way for a subcooling system with ejector. Optimum ejector geometries at different secondary flow inlet pressures were calculated by 1-dimensional ejector model, and the performance of subcooling system with multiple ejectors is investigated.
| Submitters Country | Republic of Korea |
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