Numerical and experimental analysis of cold gas microthruster geometric parameters by univariate and orthogonal method

Microthruster has been playing significant role in micropropulsion system, of which micronozzle is the key component. In the present work, the geometric parameters of a typical micronozzle on a cold gas microthruster are first optimized using numerical univariate and orthogonal analysis combined with confirmation of thrust experiments. A 2 Dimension (2D) univariate numerical simulation, with only one geometric parameter varying within a large range during a simulation, is used to fully discuss the eight structural parameters of the proposed micronozzle. According to the effect of each parameter on the micronozzle performance, five critical factors, including half expansion angle θ _out , expansion ratio W _out /W _t , throat width W _t , throat radius of curvature R _t , Inlet width W _in and their corresponding proper levels range are selected. Then, a 2D orthogonal numerical simulation analysis is conducted utilizing an L ₁₆(4⁵) orthogonal table with the selected factors and levels. By analyzing the selected factors and levels simultaneously by range analysis method, the orders of significance of different factors are sorted and the optimum structural parameters are selected. The optimum result achieved in this study is identified as θ _out of 15°, W _t of 200 μm, W _out /W _t of 7, R _t of 20 μm and W _in of 4000 μm. Then, a 3 Dimension (3D) numerical simulation is conducted to predict and analyze the performance of the optimum microthruster when inlet pressure varies in three different values. When inlet pressure is 0.918 bar and temperature is 300 K, 3D simulation result shows that the microthruster using nitrogen as propellant can generate a thrust of 2.23 mN and efficiency of 72.14%. At last, an optimum cold gas microthruster adopting nitrogen gas as propellant is fabricated and tested. Experiment is conducted in three different inlet pressure. Results show that experimental values and simulation values are in agreement, which verifies the correctness of the simulation model. Under the inlet pressure of 0.918 bar and temperature of 300 K, the optimum microthruster can produce a thrust of 1.41 mN and efficiency of 52.84% when outlet pressure is set as 1000 Pa.