混合式火箭內N2O 流體供應系統實驗及模擬之研究

Abstract

混合式火箭近年來受到高度關切，不僅僅因為其得以控制推力的優點，更因為環保無汙染，並且操作較為安全。為了善用推力控制，最容易的方法為控制進入燃燒室之氧化劑之質量流率。本論文旨在探討一利用文氏管校正及量測之流量系統，能使用氧化亞氮或二氧化碳作為操作流體，並且可以HBMS真實流體模擬，與實驗結果相互比較。並且利用白努利定律假設流體為不可壓縮流體導出經驗公式，探討文氏管入口及喉管壓力差及質量流率之關係，求得一經驗係數(Cv)。 此一使用氧化亞氮之文氏管校正及量測之流量系統，包含可使用氮氣加壓之儲存槽，可調整壓力範圍目前為63至85大氣壓，能使用氧化亞氮或二氧化碳作為操作流體，並且在出口處安置一直徑7毫米之孔板(orifice)，藉由孔板之背壓控制文氏管下游壓力。此論文使用二氧化碳取代氧化亞氮為實驗流體，因為兩者熱力學性質相似，且二氧化氮價格便宜甚多。最後完成三種文氏管設計，入口內徑分別為10、28及28毫米，喉管直徑分別為8、16及20毫米，量測質量流率範圍分別在1~2、3~8、6~12公斤/每秒。壓力計及熱電偶安置其內分別量測即時壓力及溫度。實驗平台使用荷重元量測儲存槽內流體即時重量變化，用以推斷各時間點之質量流率。 現階段結果顯示模擬與實驗量測得之數據非常接近，並且根據前段描述之三種不同流量範圍量測用之文氏管，以白努利定律推導出之不可壓縮流之經驗係數(Cv)分別為0.96、0.97及0.91。建議及未來展望也會在此論文結尾作討論。

Hybrid rocket propulsion has attracted much attention recently mainly because of its capability of thrust profiling, in addition to its safe and green operation. To realize thrust control, the easiest way is to accurately control the flow rate of oxidizer flowing into the combustion chamber. In this thesis, a venturi flow meter calibration/measurement system for pressurized nitrous oxide or carbon dioxide is developed and validated by comparing between experiments and flow simulations using real-fluid HMBS model. An incompressible Bernoulli type empirical correlation that links between pressure difference (inlet and throat) and mass flow rate is also proposed with an empirical coefficient. This venturi flow meter calibration/measurement system for nitrous oxide includes a nitrogen pressurized source tank with adjustable pressure (63-85 bars), a venturi flow tube and an orifice (7 mm in diameter) for controlling the back pressure in the downstream of flow meter. CO2 is used as the working gas in this thesis instead of N2O because of their similarity in thermodynamic behavior and also large cost saving. Three different venturi flow tubes, including 10, 28 and 28 mm in inlet diameter with 8, 16 and 20 mm in throat diameter, respectively, were designed to cover different ranges of mass flow rates, including 1~2, 3~8, 6~12 kg/s, respectively. Pressure transducers and themocouples were used to measure instantaneous pressure and temperature, respectively, wherever is necessary. A load cell is used to measure the instantaneous weight of the pressurized tank during experiment that can be used to deduce the instantaneous mass flow rate. Results show that the simulations agree very well with the measurements performed in the current study. An empirical correlation based on the incompressible Bernoulli type equation is proposed with velocity coefficients of 0.96, 0.97, and 0.91, respectively, for the three ranges of flow rates as mentioned in the above. Recommendations for future work are also outlined at the end of the thesis.