Research On A Micropump Based On GMA For The Application Of Cryogenic Two-phase Fluid Loop Heat Transfer

The mechanically pumped two-phase cooling loop(MPTL)technique realizes heat transfer by mechanical pump driving fluid flow through heat exchangers.As a new type of active thermal control system,MPTL meets increasing aerospace payloads high heat flux cooling needs for its fine heat transfer efficiency and high reliability,and shows good prospect in aerospace thermal management and instruments temperature control areas.As few pump developed for two phase cooling loop,in this dissertation a membrane type metal micropump driven by giant magnetostrictive actuator(GMA)is designed.Design parameters and optimization scheme of the pump are proposed through theoretical and simulation analysis.The prototype pump has been manufactured and its flow performance has been tested.Finally the heat transfer performance of MPTL system equipped with micro channel heat exchanger was tested at different temperature by using ammonia as working media,which validates the reliability of the pump.In this paper,the background and research progress of pump fluid cooling technology in recent years are investigated and summarized,and the driving methods are analyzed and compared.The driving mode of the pump used in the fluid circuit mostly relies on rotary power,such as a centrifugal pump and a gear pump,and there are few reports about a reciprocating displacement type pump used in a two-phase heat transfer circuit.Based on detailed comparison of the structure,material properties and driving methods of the micro-pump,the feasibility of the diaphragm vibrating micropump for the fluid circuit was estimated,determining magnetostrictively driven metal diaphragm pumps as the main research subject of this paper.Giant magnetostrictive material(GMM)can periodically strain in an alternating magnetic field.Its deformation law is determined by the pressure-magnetic equation.The material can be combined with a driving coil to form a giant magnetostrictive actuator.Regarding to the coupling method of the actuator and the driven-end membrane pump selected in this paper,control equation of the magnetostrictive material was linearized under low-frequency operating conditions,and an electromechanical simplified model of the entire pump was established.The magnetic circuit structure of GMA is analyzed,and the magnetic field distribution of the entire actuator is simulated based on ANSYS Maxwell's electromagnetic analysis software with actual physical properties of the material.The geometry factor is used as the criterion to optimize the structural parameters.It shows that the actuator has the lowest copper loss when the inner and outer diameters of the coil are 20 mm and 50 mm.A laser based displacement test platform was set up to test the displacement output of the actuator,which verified the magnetic circuit structure design.The displacement input achieves the design limit of over 1000 ppm,and it also has a large power consumption of 95 W.In order to reduce the power consumption of the actuator,and the permanent magnets were used as the magnetic biasing scheme.The feasible four spatial arrangements of permanent magnets were also simulated and compared on magnetic field distribution and power consumption,which shows the two-segment magnet arrangement provides the most suitable bias.With the permanent magnet biasing scheme experimentally studied.The results show that the designed magnetic circuit effectively reduce the power consumption of GMA to 41.6W with a certain degree of output displacement loss.The mechanism of the displacement loss is proved quantitatively by linearizing the magnetostrictive strain and sinusoidal field strength.According to the selected membrane pump structure,the related theoretical analysis and detailed design of the connecting rod,membrane and micro valve structure of the pump body components are carried out based on the design flow rate and driving pressure.The design parameters were checked with finite element simulation regard to the aspects of stress distribution,vibration el at the same time,the relevant material properties and sealing process were presented,and the design parameters of the entire micropump were obtained.A dynamic model was established for the mechanical coupling of the prototype from the perspective of vibration mechanics.All key elastic parameters,including GMA,were extracted and parametrically analyzed by response function.The results show that resonance of the pump structure can be achived under the condition of reducing the diaphragm stiffness and reasonably designing the connecting rod stiffness,the system can achieve a displacement amplification ratio over 100 ideally.An open system flow test platform was set up to test and analyze the flow output characteristics of the pump at different drive voltages and frequencies.The results showed that the pump with ethanol as the working fluid has a volume flow output of 2 ml/s or more,and the pressure head is higher than 0.2 MPa.The basic needs for driving a two-phase fluid circuit are achieved.In a certain range,the volumetric flow output is approximately linear with the frequency.The influence of the three different valves on the overall performance of the pump was investigated and compared,which shows that a lower the stiffness of the valve leads to a wider operating frequency range of the micropump.The designed resonance system was tested and the results show that the polyimide diaphragm can achieve a 22.6 times output displacement amplification at a contact diameter of 10 mm.With the designed metal membrane pump as a pressure source,and a stirling cryocooler as cold power source,equipped with micro-channel heat exchanger a fluid circuit is developed and tested by using ethanol as the working fluid at 0°C to-60°C,calibration of system heat leak and error analysis of experimental system under atmospheric conditions are conducted.After that,the starting characteristics of the twophase fluid heat exchange system driven by the magnetostrictive diaphragm pump,the temperature response characteristics under different external heat flow conditions,and the steady-state heat transfer characteristics were experimentally studied with ammonia as working fluid.The results showed that the system had a maximum heat transfer capacity of more than 150 W at a transmission distance of 1m with ammonia as the working medium at-30°C.Finally,this paper summarizes the design and experimental results of the magnetostrictive actuator membrane pump.And further optimization scheme of the entire pump is put forward through the analysis of the experimental data and problems in the actual operation.