Research On The Chemical-electric Integrated Micro-propulsion System Based On MEMS Technologies

With the advantages of low-cost,small size,light weight,and high integration,micro/nanosatellites are quite suitable for the fast response launch and constellation network,which show great potential in the future development of aerospace.Also,with the limitation of size and power supply,most micro/nanosatellites do not equip propulsion system,which lead to the diversity of the space mission reducing.In order to meet the mission requirements of micro/nanosatellites including attitude control,orbit transfer and other flight attitude changes,nanosized propulsion system has received extensive attention and in-depth development.However,there are still great difficulties in the design and application of low power consumption,thrust up to 10 m N and high integration micro-propulsion systems which are suitable for formation flight of micro-nano satellites.In this article,to meet the demand of micro/nanosatellites formation flying,the chemical-electric integrated micro-propulsion system combined with the micro-scale machining of MEMS（Micro-Electro-Mechanical System,MEMS）technology are studied throuth theory research and engineering implementation.The key reasearch points are the pinch-off mechanism of bubbles in the microchannel,the two-phase flow high efficient reaction and instability,microchannel high performance thin film heating and optimization design of micro-scale two-dimensional thruster.Firstly,the dynamic model of bubble pinch-off and its applicable scope in microchannel as well as the influencing factors are studied.Under the of unconstrained condition,a dynamic model of bubble pinch-off based on the Laplace equation,the generalized Bernoulli equation and the free interface motion equation is established.Then,through theoretical derivation and experimental analysis of bubble pinch-off in the cross junction microchannel flow focusing device,three advances are made:（1）The gas inertia force is introduced into the equation to improve the solution accuracy.（2）The relationship amont the liquid inertia force,surface tension and liquid viscosity force in the process of bubble pinch-off in the microchannel is analyzed.And the liquid inertia force and surface tension are determined to be the dominant roles.（3）The time ceriatirans between the free pinch-off stage and the liquid squeezing stage during the microchannel bubble pinch-off process are determined,which determine the applicable scope of the unconstrained equation.Secondly,the efficiency and instability suppression of hydrogen peroxide catalytic reaction in the microchannel reactor are studied.To solve the low-efficient problem of hydrogen peroxide decomposition in micro-scale,which is caused by the adhesion of bubbles to catalysts,two kinds of high cross section ratio rectangular microchannel reactors are designed by using the analysis results of bubble pinch-off and the main effect of liquid inertia force on bubble pinch-off.At the same time,in order to suppress the instability of two-phase flow,four different pin-fin configurations are designed in the microchannel.The designed microchannel reactors and pin-fin are manufactured by MEMS processing.The experimental system is also designed.Based on the time-frequency analysis（wavelet transform）,the effect of the flow rate and different pin-fin configurations on the reaction efficiency and flow instability are studied.The switching process of annular flow and bubble-annular flow in the inlet microchannel reactor is revealed.And the stable conversion rate of hydrogen peroxide reaction which is independent of the flow rate is obtained because of the corresponding relationship between the voidage and the critical pressure.The conversion rate of outlet reactor is 700%higher than those of H₂O₂ decomposition in microchannel reactors ever reported in the literature,which proved the advance of the design.Then,the simulation and performance test of the submicron multilayer thin film heater are studied.A simulation model of the micro heater coupled with structural mechanics field,solid heat transfer field and thin film current field is constructed.The model is verified by temperature and stress distribution using finite element simulation method in COMSOL.According to the requirement of maximum temperature,the optimization scheme of heater geometry and titanium substrate double layer thin film heater are determined.The optimized thin film heater is manufactured by MEMS processing and the experimental system is designed for testing.In terms of steady-state performance,the maximum temperature of the thin film heater can reach 557.2k under the input voltage of 30V.The maximum difference between simulation and experiment at the maximum temperature value of the heater is less than 10%and the average difference is less than 5%,which verifies the accuracy and effectiveness of the multi-physical field coupling simulation.Through the performance test,it shows that the optimized Aluminum-Titanium double-layer thin film heater has excellent heating performance and can meet the demand of electric heating in the micro-propulsion system.Finally,the simulation and optimization of two-dimensional expanded MEMS micronozzle and the micro-thrust testing system are studied.One-dimensional isentropic flow is used to estimate the parameters of the micronozzle.Combined with MEMS processing compatibility,the nozzle structure design is completed and the finite element simulation model is established.In the simulation,linear approximation constrained optimization algorithm（COby LA）is used to obtain the optimal expansion ratio and half expansion angle in the two-dimensional expanded micronozzle,aiming at the optimal specific impulse.In order to solve the high-precision and high-efficiency micro-thrust testing problem,a micro-thrust testing system based on high-precision balance is designed and built.Compared with the C-type torsion pendulum micro-thrust testing system,this micro-thrust testing system based on high-precision balance has the characteristics of small error and high experimental efficiency.By comparing the results of experiment and simulation,an optimization method based on the expanded friction area is proposed to solve the problem of parameter coupling in the expanded section.By using this method,the optimal half expansion angle of 15°and the expansion ratio of 6.22are optimized in the experiment,which are very close to the simulation optimization results.In conclusion,this paper has carried out in-depth research and engineering test on the four key technologies in the chemical-electric integrated micro-propulsion system based on MEMS technology,and formed research methods of model calculation,simulation optimization,prototype processing and experimental testing of each subsystem.This paper is of great significance to the design of micro-propulsion system and the application of MEMS technology.