微小化高壓氧化亞氮流量計模擬設計及實驗研究

Abstract

近年來，混合式火箭(Hybrid Rocket)因其推進系統簡單及操作安全高的特性，已成為國內外在太空科技上的研究目標，混合式火箭的推進系統與液態火箭一樣，可藉由調整氧化劑流量來控制推力。氧化亞氮因為具有自我增壓特性(self-pressurized)，可在室溫下儲存，且容易於市面上取得，常作為混合式火箭的氧化劑。流量計產生的壓損會降低氧化劑流進燃燒室的入口壓力，降低燃燒時的推力表現。因此，如何設計出輕量化低壓損的流量計成為發展混合式火箭的重點之一，本論文透過數值模擬對可能適用於氧化亞氮的流量計進行研究，包括多孔式孔板流量計以及微小型文氏管流量計，並與受限的實驗結果共同探討。 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.