Numerical and Experimental Investigation of a Miniaturized Flow Meter for High-pressure Nitrous Oxide
|關鍵字:||氧化亞氮;流量計;文氏管;多孔式孔板;混合式火箭;Nitrous oxide;flow meter;venturi tube;multi-hole orifice;hybrid rocket|
模擬結果顯示，減少回流發生的區域，較增加孔洞直徑更能有效減少壓損產生，並在兩倍管徑的長度內回復壓力。良好的多孔分佈可使流量係數(discharge coefficient)為0.84。由於多孔式孔板在流量為6kg/s時已會產生2.3bar的壓損，後來設計出壓損更小的微小型文氏管。將收縮角10.5°、擴散角5.5°、喉管直徑1mm的微小型文氏管用於內徑40 mm、管線壓力53 bar的單相液態氧化亞氮管線，當流量範圍為3 kg/s 至12 kg/s時，管路與微小型文氏管喉部間的壓差為0.136至1.807 bar，利用方程式m ̇=KA√2ρ∆P從壓差計算流量的係數為0.525。|
Recently, hybrid propulsion has been an important research subject in space technology due to its system simplicity and high operational safety. Similar to liquid propulsion system, hybrid propulsion also features the possibility of thrust profiling through the control of oxidizer flow rate. Among various choices of oxidizer, nitrous oxide is one of the oxidizers that is most frequently used in hybrid propulsion because it is self-pressurized, storable at room temperature, and almost no limit to procure from the commercial market. In addition, pressure loss induced by a flow meter reduces the inlet total pressure of the oxidizer into a hybrid propulsion motor, which indeed degrades the performance of the hybrid combustion. Thus, how to design a low pressure-loss flow meter with minimal weight and volume penalty is one of important issues in accomplishing a robust hybrid propulsion system design. In this thesis, we would like to numerically investigate two types of potential flow meters for nitrous oxide, which include a multi-hole thin orifice plate flow meter and a miniaturized streamlined venturi flow meter. In addition, limited experimental data of latter are also provided for correlating between the simulations and experiments. The simulations show a reduction of recirculation zone can reduce the pressure loss effectively than an increase of the diameter of the holes on the multi-hole orifice plate, let pressure recovery within the length about 2 times of pipe diameter. The discharge coefficient is 0.84 to the well design of the multi-hole distribution, but it still produce pressure loss 2.3 bar as the mass flow rate reached 6 kg/s. The pressure loss of a miniaturized streamlined venturi flow meter is much less than that of the multi-hole orifice plate flow meter. The optimized miniaturized venturi flow meter is found to have the conditions: convergent angle of 10.5°, divergent angle of 5.5°, and throat diameter of 1.0 mm. The simulation results show that the pressure difference between the inlet and throat of the venturi flow meter is in the range of 0.136-1.807 bar when the flow rate is 3-12 kg/s when they are installed in a pipeline with a diameter of 40 mm with a total pressure of 53 bar. Calculate the mass flow rate from the equation: m ̇=KA√2ρ∆P, the coefficient is around 0.525 for this miniaturized flow meter.