Engineering Model to Calculate Mass Flow Rate of a Two-Phase Saturated Fluid Through An Injector Orifice

An engineering model is developed to calculate mass flow rate of nitrous oxide, a self-pressurizing saturated oxidizer commonly used in hybrid rocket motors. While use of N_{2}0 cannot be accurately modeled using traditional ideal gas, compressible, or incompressible flow assumptions. To obtain accurate mass flow rate this one-dimensional analysis includes both incompressible fluid and homogeneous equilibrium mass flow rate models. Mass flow calculations from the two models are independently weighted and summed to obtain representative two-phase mass flow rate. Fluid properties are iterated in time by keeping track of fluid enthalpy and are propagated across the injector using either isentropic or adiabatic assumptions. The model excellently predicts mass flow rates as verified by comparison to experimental cold flow data. The experimental conditions resulting from the test apparatus set-up produces fluid stratification and mixing effects that cannot be modeled by the algorithm as developed. Thus the run tank and temperature drops as predicted by the model are significantly larger than measured