MEMS Based Paraffin-actuated Gas Flow Regulating Microvalve

The continuous maturity of micro-nano satellite technology and developments of its application has placed an urgent need for the micro-nano satellite micro-propulsion system.Among the electrothermal MEMS thrusters,the resistojet has a simple structure and high reliability.At the same time,the solid gas generator can be used instead of the high-pressure tank to increase the integration and reduce the volume.To fulfill the wide thrust range of the micro-nano satellite propulsion system,the micro-proportional valve was used to regulate the gas flow to control the thrust of the micro-thruster.Considering the working voltage,response time,actuator stroke,regulation precision,process feasibility and mutual integration with electrothermal MEMS thrusters,the paraffin actuated valve which is one of the phase change material actuated valve has the best fit.Therefore,it is necessary to carry out research on paraffin-actuated microvalve based on MEMS technology.This research is very important for the wide range regulation of thrust of electrothermal MEMS thruster,and it is also of great significance for the development of micro-nano satellite micro-propulsion system in China.In this paper,the paraffin wax is used as a functional material.The static pressure generated during the expansion process drives the silicon material diaphragm to elastically deform.The deformation varies with the temperature of the paraffin.By adjusting the input power of the heater,the temperature of the paraffin material can be adjusted,thereby changing the volume expansion ratio of the paraffin wax and the deformation of the silicon material regulating diaphragm,and finally changing the cross-sectional area of the gas passage and the mass flow rate of the gas.Among the components of the paraffin actuated MEMS microvalve,the exit substrate and the adjustment diaphragm use conventional silicon wafers because the silicon material is a commonly used material for MEMS micromachining,which has high process maturity and is easy to integrate with other micromachining processes.The micro-heater material selects the metal Pt for the reason that the preparation process of the metal Pt heater is mature and reliable,the temperature increase is fast,and the thermal stability is fine.The heater part material was selected from BF33 glass sheets because of the electrical insulation,temperature stability,reasonable cost,and potential anodic bonding process integration of the BF33 glass sheets.Through the MEMS manufacturing process,the regulating part and the heating part are successively obtained,and then the paraffin micro-actuator is prepared by heating the paraffin,the thermal conductive adhesive laminating regulating film and the heating film,the conductive tape connecting wire and the plate electrode through a silicone heater.On the basis of above,the outlet glass piece and the micro-actuator are bonded together by perforated double-sided tape to obtain a paraffin micro-valve,and the use of the perforated double-sided tape for bonding can form a displacement interval between the adjustment diaphragm and the valve seat,and can ensure the reliability of the gas seal between the perforated glass sheet and the micro-driver mating surface.The relationship between diaphragm deflection of micro actuator and input current was obtained through test of micro actuator.At the same time,the flow rate curve corresponding to different inlet pressures under full-open state and the curve corresponding to the fixed inlet pressure under regulating state was obtained by measuring the mass flow rate of microvalve.Then,compare the mass flow result of Fluent simulation and experimental test,which verified the reliability of fluid simulation result.Finally,assume that the microvalve and micro actuator has the same deflection under the same input current and perform fluid simulation under regulating state.After comparing simulation results and experimental results,it was found that the convective heat transfer generated by the directional gas flow around the diaphragm has a more significant effect on the diaphragm deflection than the natural convection heat transfer of the air around the diaphragm.