Vaporizing Liquid Microthruster Research Articles

Towards an optimized heat transfer process in vaporizing liquid microthrusters using pulsed heating control

The Institute for Microelectronics and Microsystems of the Italian National Research Council (Italy) has designed and fabricated a water-fed MEMS vaporizing liquid microthruster (VLM) in collaboration with the University of Salento (Italy) and KU Leuven (Belgium). Previous studies have demonstrated the device’s functioning and highlighted the presence of a strong thermoelectric-hydraulic coupling that severely affects the heating and propulsive efficiencies and reliability of the device. In this regard, the current work provides a preliminary experimental investigation of a pulsed heating system actively controlled by temperature using PI-D logic (proportional and integrative actions applied to the error; derivative action applied to the output). The overall performance assessment focuses on evaluating power consumption during steady-state operation and analyzing the dynamic response of the VLM undergoing such an actively controlled pulsed heating, which has been built using both manual and data-driven offline adaptive tuning of the PID parameters. Concerning the steady-state operation, results highlight a promising enhancement of the heating efficiency to values above 0.9. The dynamic response analysis shows that operating with a single set of fixed PID parameters is not feasible and that the manual tuning is a trial-and-error approach highly dependent on the operator’s experience, operating conditions, and reference temperature profile. Furthermore, shorter rise and response times require a higher proportional gain, and the overshoot experienced when crossing the saturation temperature cannot be avoided. In this paper, we show that the response of the data-driven adaptive controller solves these issues, exhibiting a reduced maximum settling time from around 59 s to less than 10 s, while the overshoot is avoided thanks to the temporal adjustment of the PID parameters.

Additively manufactured vaporizing liquid microthruster with micro pin fins for enhanced heat transfer

Vaporizing liquid microthruster is a relatively new concept for evaporation based propulsive system. The research interest in vaporizing liquid microthruster mainly comes from its simplicity and the use of green propellant: water. This paper presents the study of a highly compact additively manufactured vaporizing liquid microthruster of 38 × 22 × 8 mm in dimension. The heat transfer enhancement effect of micro pin fins for vaporizing process has been investigated using modeling and computational fluid dynamics simulation, followed by experiments to validate the results. It has been shown that all micro pin fins (square, diamond, circular) with different array arrangements (staggered and inline) can enhance heat transfer. Square shaped pin fin exhibited the best heat enhancement performance with an increase in dimensionless total thermal resistance of 14.65% (as compared to blank vaporizing liquid microthruster) due to its large contacting area, while the circular shape was least effective. Meanwhile, the inline arrangement was found to induce a significant fluctuation in transverse flow velocity between the columns, which promotes heat convection. The vaporizing liquid microthruster prototype was produced using a specialty resin of good heat resistance up to 350 °C as confirmed by the thermogravimetric analysis. Thrust performance of the prototype was measured using a torsional thrust stand in a vacuum chamber. The vaporizing liquid microthruster with square micro pin fins and in inline configuration has produced the highest thrust of 740.2 μN at 2 μl/s flow rate, giving a specific impulse of 37.7s. The developed prototype could be implemented as micropropulsion system for nanosatellites, such as CubeSat and PocketQube.

Flow regime characterization of a silicon-based vaporizing liquid microthruster

The present work discusses an experimental investigation of the flow into a silicon-based vaporizing liquid microthruster equipped with sensing capabilities and low-power on-channel secondary heaters. The sensing capabilities (resistance temperature detectors and capacitive void fraction sensors) are used to investigate the flow instability and to evaluate its performances. The device has a sandwich structure composed of a silicon substrate and a glass substrate. This last one allows optical access into the device. The main heating of the propellant is provided using a platinum resistive heater placed on the bottom of the silicon layer. By varying the electrical power supplied to the main heater at fixed mass flow rate, three flow regimes have been observed and investigated: fully liquid flow, two-phase flow, and fully vaporized flow. Their dynamics have been captured through high-speed micro-flow visualizations under rough vacuum conditions (about 29 kPa). Furthermore, the expansion of the exhaust vapor plume exiting from the micronozzle has been analyzed via Schlieren visualizations. Results highlighted the occurrence of a cyclic flow behavior during the two-phase flow regime. In contrast, the flow exhibits the presence of both liquid and vapor phases at the micronozzle exit. Once the fully vaporized flow regime is established, the two-phase flow dynamics into the inlet chamber become more stable with complete filling and more uniform distribution of the flow at the microchannels entrance. Schlieren imaging captured the increase of the exhaust plume spreading half-angle when moving from ambient condition towards rough vacuum.

A new vaporizing liquid microthruster with planar induction heating

This paper presents a new vaporizing liquid microthruster (VLM), which is driven by the vaporizing liquid with planar induction heating. The developed microthruster mainly consists of an inlet, a microchannel, a vaporizing chamber, a micronozzle, a microheating plate and an external excitation coil. Experiments of the apparent power required to achieve a complete vaporization of the propellant with different flow rates were carried out. Thrust forces of the new VLM were characterized with water as the propellant. A maximum thrust of 970 μN was obtained with 5.30 mg/s propellant consumption and an apparent power of 9.31 VA.

A tubular vaporizing liquid micro-thruster with induction heating

This paper presents a study of a new tubular vaporizing liquid micro-thruster (VLM) with induction heating. The developed micro-thruster consists of a micro-heater core, an excitation coil, a vaporizing chamber, a nozzle and a micro-channel, all integrated in a glass tube with a dimension of 3 mm (outer diameter) × 18 mm (length). The temperature of the micro-heater core is tested with experiments and an optimal AC frequency is selected for the VLM based on the experimental tests. Vaporization of water-propellant feeding with different flow rates range of 0.1 ml/min − 0.3 ml/min is demonstrated. A maximum thrust force of 680 μN at 0.3 ml/min propellant consumption rate is realized measured with a pendulum thrust stand. Comparing with other VLMs, one merit of the new VLM is that there is no physical connection between the micro-heater core and the power supply. Other merits of the new VLM proposed by this paper is that it can work with a larger input power, provide more heat energy and generate a relative larger thrust force.

Design and testing of a microelectromechanical-system-based high heat flux vaporizing liquid microthruster

This paper presents the design of a low power (8 W) water-fed vaporizing liquid microthruster that operates in the Leidenfrost boiling regime. The direct thrust measurements show the proposed design is able to produce one of the best specific impulse amongst all similar microthrusters reported in the literature. One of the important features that enables the superior performance is the high heat flux miniature molybdenum heating elements fabricated inside the vaporization chamber in a single silicon device package of dimensions 35 mm ✕ 35 mm ✕ 1.05 mm. The molybdenum heating elements are capable of producing a heat flux output of 370 kW/m2 resulting in a sustained operational pressure of 2 bar and temperature of 446 K. The specific design details, such as choice of configurations and sizing, are given in this paper. In particular, the choice of material and the fabrication process carried out at the in-house nanosystem fabrication facility are described. The experimental setup and uncertainty analysis of the mN-range hanging pendulum direct thrust measurement stand are presented. Then, the evaporation of liquid water propellant is investigated in detail. The occurrence of Leidenfrost effect inside the vaporization chamber is captured with a high-speed camera at a frame rate of 5000 Hz. It can be seen that the rapid vaporization of propellant in the Leidenfrost boiling regime results in a high specific impulse amongst other microelectromechanical-system-scale vaporizing liquid microthrusters. The direct thrust measurements show the current design is capable of producing a specific impulse ranging between 25.9–51.1 s at a continuous thrust level of 1.00–2.00 mN; considering contemporary energy storage technologies, the estimated thrust per device dry mass and specific impulse per device dry mass levels are 4.0–8.0 mN/kg and 103.6–204.0 s/kg respectively.

PPG buys Dexmet, Whitford & Hemmelrath

The data presented in this data article were on the basis of the study reported in the research articles entitled “A novel quasi-one-dimensional model for performance estimation of a Vaporizing Liquid Microthruster” (De Giorgi and Fontanarosa, 2018). The reference study presented a numerical analysis of the performance of the Vaporizing Liquid Microthruster (VLM) experimentally investigated in the data article entitled “Performance evaluation and flow visualization of a MEMS based Vaporizing Liquid Microthruster” (Cen and Xu, 2010). For the purpose, a novel quasi one-dimensional model was proposed, and results were compared with the numerical predictions provided by 2D and 3D CFD computations.Due to the scarcity of experimental data concerning the flow characterization inside a Vaporizing Liquid Microthruster, the present Data in Brief aims to provide the entire dataset coming from the numerical predictions for benchmark purposes and comparisons with different numerical approach.

A novel quasi-one-dimensional model for performance estimation of a Vaporizing Liquid Microthruster

The present work aims to propose a novel quasi-one-dimensional model for the performance estimation of a Vaporizing Liquid Microthruster (VLM). The analytical model was applied to the analysis of a MEMS-based VLM composed of a rectangular inlet chamber, a set of parallel microchannels as heating chamber, and a planar convergent–divergent micronozzle. It combines a steady-state boiling model for the analysis of the heater with a real nozzle flow model for the evaluation of actual thrust force and specific impulse, based on iterative procedure aiming at the convergence of the actual mass flow rate and the heat flux. For the purpose, a set of semi-empirical formulas found among both theoretical and experimental scientific works have been introduced for the estimation of the critical heat flux condition and the local heat transfer coefficient. In addition, the real nozzle flow model predicts the performance and the viscous losses due to the boundary layer growth inside the micronozzle. The last ones are estimated by introducing analytical expressions for the discharge coefficient and the Isp-efficiency into the isentropic nozzle flow theory. The resulting performance predictions of the 1D model referred to the on-design operating conditions. They well agreed with the experimental data, with a maximum estimated error of 7.3% on the thrust and the specific impulse. Furthermore, the analytical model of the micronozzle predicted a reduction of the mass flow rate up to about 8%, as well as thrust losses up to 15% due to the contraction of the cross sectional area.In addition, 2D and 3D computational fluid dynamics (CFD) simulations were performed in order to enforce the analysis of the viscous effects. Predictions of 2D computations overestimated the performances of the microthruster with respect to experiments, up to about 19% of the thrust and 20% of the specific impulse. On the other hand, the 3D predicted thrust approached to the experimental one with an error of about 9.2% below. In addition, a severe reduction of jet thrust in favor of the pressure thrust was observed at the nozzle exit. Furthermore, 3D computations pointed out the influence of the micronozzle depth on the boundary layer growth and the viscous losses. In particular, they revealed the establishment of the nozzle blockage and the thermal chocking of the supersonic flow owing to the subsequent viscous heating.

Torsional thrust stand for characterization of microthrusters

This paper describes the setup of a precise thrust stand based on torsional pendulum design for characterizing the performance of microthrusters. Calibration has been carried out by using an improved version of electrostatic calibrator, which produces a wide range of accurate and repeatable calibration force. After the calibration, the thrust stand can resolve constant force from 40μN to 3.4mN and impulse bit from 7μNs to 340μNs. The usefulness of the thrust stand has been demonstrated by measuring the performance of two different microthrusters: a pulsed plasma thruster that produces impulse bit of 23.15μNs and a vaporizing liquid microthruster that produces steady state thrust of 633.5μN.

Fabrication and performance evaluation of a high temperature co-fired ceramic vaporizing liquid microthruster

This paper presents the study of a microelectromechanical system (MEMS)-scaled microthruster using ceramic as the structural material. A vaporizing liquid microthruster (VLM) has been fabricated using the high temperature co-fired ceramic (HTCC) technology. The developed microthruster consists of five components, i.e. inlet, injector, vaporizing chamber, micronozzle and microheater, all integrated in a chip with a dimension of 30 mm × 26 mm × 8 mm. In the dry test, the newly developed microheater which is deposited on zirconia substrate consumes 21% less electrical power than those deposited on silicon substrate to achieve a temperature of 100 °C. Heating temperature as high as 409.1 °C can be achieved using just 5 W of electrical power. For simplicity and safety, a functional test of the VLM with water as propellant has been conducted in the laboratory. Full vaporization of water propellant feeding at different flow rates has been successfully demonstrated. A maximum thrust of 633.5 µN at 1 µl s−1 propellant consumption rate was measured using a torsional thrust stand.

Design, fabrication and performance evaluation of a vaporizing liquid microthruster

A recent application domain of MEMS technology is in the development of microthrusters for micro-/nanosatellites. Among the various types of MEMS microthruster developed so far, the vaporizing liquid microthruster (VLM) has been widely explored for its capability to produce continuously variable thrust in the micro-Newton (µN) to mili-Newton (mN) range. This paper reports the design and experimental validation of silicon MEMS VLM consisting of a microcavity, inlet channel and converging–diverging (C-D) in-plane exit nozzle integrated in two micromachined bonded chips and sandwiched between two p-diffused microheaters, located at the top and bottom surface of the device. Structural configuration was designed using simple analytical equations to achieve maximum thrust force by controlling the inlet propellant flow and heater power of VLM in an efficient way. In addition, a 3D model using a computational fluid dynamics technique was constructed to simulate the aft section of VLM for the investigation of its aerodynamic behavior. The device fabrication and testing have been briefly described. The fabricated VLM is capable to produce 1 mN thrust using maximum heater power of 3.6 W at a water flow rate of 2.04 mg s−1 using an in-plane C-D exit nozzle of throat area 130 µm × 100 µm. A detailed thrust force measurement was carried out with the variation of input heater power for different mass flow conditions and exit to throat area ratio of the exit nozzle, and the results were interpreted with the theoretical model. The model gives considerable physical insight in the operation of the VLM. Finally, a performance comparison with other published VLM results indicates that the present design can yield comparatively more thrust force with much less input power. A performance comparison with other published VLM results indicates that the present design can achieve improved performance by integrating two heaters with appropriate chamber volume in respect of propellant flow rate and input power for obtaining a supersaturated dry stream.

Low temperature co-fired ceramic vaporizing liquid microthruster for microspacecraft applications

Low temperature co-fired ceramic (LTCC) technology is successfully employed for the first time to develop a vaporizing liquid propellant microthruster (VLM). The VLM has potential applications as micropropulsion system for attitude control of microsatellites. The design, fabrication and testing of the LTCC based VLM are presented. Preliminary testing is done by using water as liquid propellant. The VLM of nozzle throat size 220μm×200μm produces an average thrust in the range of 34–68μN for a flow rate of 1mgs−1 with an input heater power varying from 7.1–9.2W. An average specific impulse of 3.4–6.9s is measured. An average impulse bit of 0.67–1.4mNs, 3.40–6.70mNs is measured for thruster firing time of 20s and 100s during VLM stable mode operation at sea level conditions.

Performance evaluation and flow visualization of a MEMS based vaporizing liquid micro-thruster

MEMS micro-thruster is promising for future applications in precision formation flying missions. This paper presents performance evaluation and two-phase flow pattern visualization of a vaporized liquid micro-thruster (VLM). Micro-thrust force of several milli-Newtons was measured by a test rig with a lever. Flow patterns in the micro-thruster chip were visualized by a high speed camera bonded with a microscope. We found that flow patterns influenced its specific impulse and there were several types of flow boiling patterns in the thruster chip. Thrust instability was discussed as well. The results are helpful to understand flow characteristics of a VLM and improve its performance.

Simulation and experiment research on vaporizing liquid micro-thruster

In the present work, a micro-thruster chip with dimension of 19.5 mm × 9.5 mm was fabricated with MEMS technologies for the experiment study of vaporizing liquid micro-thruster. In addition, a full 3D computational model was constructed to simulate the aft section of a vaporizing liquid micro-thruster for investigating flow characteristics. The results show that there were four distinct flow patterns observed in this study including snake flow, vapor-droplet flow, vapor-droplet-jet flow, and vapor flow. To prevent the failure of micro-thruster chip from generating of snake flow, the heating treatment of an empty micro-thruster chip at 300 °C for 2 h was the key factor. The generation of vapor flow preliminarily proved that the concept of vaporizing liquid micro-thruster chip was feasible. Furthermore, the numerical model in this study successfully provided the thrust estimation. The channel cross-section of 1 mm × 100 μm designed in this study was fit for developing a micro-thruster of O(mN) (ranging from 1 to 6 mN approximately). The numerical simulation could match better with the experiment results for the vapor flow cases if the flow oscillation was taken into consideration, and the heating channel of micro-thruster was lengthened to completely vaporize the liquid water.

Characterization of Dryout Point in the Vaporizing Liquid Microthruster

A specially designed vaporizing liquid microthruster (VLM) with a Pyrex cover glass to provide optical access has been used to investigate the two-phase flow of water through the heated channel, which is approximately 700 μm wide and 300 μm deep. The design and calibration of a feed system to control mass flow to the VLM in the range of 75-250 μg/s is described along with the video microscopy system used for optical imaging of the phase transition within the channel. Images are presented showing the flow structure during the initial vapor formation, a pulsing mode of operation, and unsteady interaction between individual vapor packets within the channel. As the flow rate is increased from 135-175 μg/s at a heater power of 0.85 W, the location of phase boundary (dryout point) is found to move downstream by approximately 1 mm. Two candidate flow instabilities that could account for the observed unsteady behavior are discussed as well.

An analytical model of a silicon MEMS vaporizing liquid microthruster and some experimental studies

A recent application of the MEMS technology is in the field of microthrusters for micro/nano satellites. A silicon MEMS vaporizing liquid microthruster (VLM) produces continuously variable thrust in the range from μN to mN. The theoretical simulation of a VLM involves complex numerical 3D micro-fluidic, thermodynamic and electro-thermal solutions. A fast analytical method is, however, desirable in the initial phase of development of a VLM. In this paper, a simple analytical model of a VLM is presented. The model is based on one-dimensional approximations for fluid-dynamical and heat-flow equations. VLMs are fabricated by bonding two micromachined silicon chips. The device consists of a microcavity, an inlet nozzle, an exit nozzle, a microchannel and an internal p-diffused resistor for heating. The thrust is measured by a sensitive cantilever and a laser based lamp-and-scale arrangement. The experimental results on the variation of thrust with heater power are interpreted with the help of the theoretical model. A novel iterative computation is performed to extract the chamber temperature and other important parameters corresponding to the measured values of thrust for different values of heater power. The model gives some physical insight into the operation of the VLM.

Silicon MEMS vaporizing liquid microthruster with internal microheater

This paper reports a silicon MEMS vaporizing liquid microthruster (VLM) with an internal p-diffused microheater. The device fabrication and testing have been briefly described. The VLM consisting of two micromachined, bonded silicon chips produces thrusts in the range of 5 µN to 120 µN with a heater power of 1 W to 2.4 W at a water flow rate of 1.6 µl s−1 using an exit nozzle of throat size 30 µm × 30 µm. A maximum thrust of 120 µN was produced with a heater power of 2 W at a water flow rate of 0.7 µl s−1 with exit nozzle of throat size 50 µm × 50 µm. The measurement has been carried out using a sensitive cantilever and a laser based lamp-and-scale arrangement. The internal microheater is expected to yield a higher efficiency compared with the external microheater.

AN OVERVIEW OF MEMS-BASED MICROPROPULSION DEVELOPMENTS AT JPL

Development of MEMS (Microelectromechanical Systems) micropropulsion at the Jet Propulsion Laboratory (JPL) is reviewed. This includes a vaporizing liquid micro-thruster for microspacecraft attitude control, a micro-ion emgine for microspacecraft primary propulsion or large spacecraft fine attitude control, as well as several valve studies, including a solenoid valve studied in collaboration with Moog Space Products Division, and a piezoelectric micro-valve.