Anode Flow Rate Research Articles

Thrust estimate method of an on-orbit Hall thruster using Hall drift current

In order to realize the thrust estimation of the Hall thruster during its flight mission, this study establishes an estimation method based on measurement of the Hall drift current. In this method, the Hall drift current is calculated from an inverse magnetostatic problem, which is formulated according to its induced magnetic flux density detected by sensors, and then the thrust is estimated by multiplying the Hall drift current with the characteristic magnetic flux density of the thruster itself. In addition, a three-wire torsion pendulum micro-thrust measurement system is utilized to verify the estimate values obtained from the proposed method. The errors were found to be less than 8% when the discharge voltage ranged from 250 V to 350 V and the anode flow rate ranged from 30 sccm to 50 sccm, indicating the possibility that the proposed thrust estimate method could be practically applied. Moreover, the measurement accuracy of the magnetic flux density is suggested to be lower than 0.015 mT and improvement on the inverse problem solution is required in the future.

Analysis and control of Hall effect thruster using optical emission spectroscopy and artificial neural network

This study presents a proof-of-principle for using optical emission spectroscopy and artificial neural networks for real-time monitoring and control of the operational parameters of a Hall effect thruster: the anode voltage, the anode xenon injection, the discharge current, and the coil current. In that regard, we build an optical database of 26 spectral lines across 6469 operating conditions to train and test the neural network. We then reduced the learning lines from 26 to 15 based on their statistical correlation with the target parameters. After tuning the hyperparameters of the network, the network predicted the thruster’s parameters with notable accuracies: 95% for the anode voltage, 84% for the coil current, and 99% for both the anode flow rate and the discharge current. The estimated uncertainty of predictions, at 3σ, is ±51V for voltage, ±1A for coil current, ±0.15A for discharge current, and ±0.15mgs−1 for anode flow rate. The prediction calculations were within milliseconds and enabled real-time monitoring of the thruster parameters. Therefore, a proportional-integrator-derivative controller (PID) controller was implemented to regulate the anode voltage and flow rate based on the optical emission of the plume. The PID showcased short settling times from 0.1 to 0.4 s and overshoot levels up to 3% of the target value for the voltage and 10% of the target value for the flow rate. These results were for a fixed coil current at 4A. The study showed that changing the coil current may necessitate more sophisticated prediction models and control strategies. Future work will expand the model’s generalizability to different thruster types, propellants, and magnetic field configurations.

An experimental investigation on the performance of direct methanol fuel cell using new anode and cathode flow field designs

This is a comprehensive study of the DMFC through the introduction of new channel designs. A traditional serpentine design with a rib and channel width of 0.8mm on an area of 50mm×50mm is designated as design-1 and used as the reference channel design. Three other new designs are fabricated and tested in comparison with design-1. A 4-outlet, 1-inlet, 4-zone serpentine with 0.8mm of rib and channel width, is designated as design-2. A 4-outlet, 1-inlet, 4-zone serpentine with a converging channel width is designated as design-3. A 4-outlet, 1-inlet, 4-zone zigzag serpentine with a converging channel width is designated as design-4. The study was done in three stages. The first stage investigates the effect of anode channel designs by fixing the cathode design to design-1 and varying the anode designs from design-1 to design-4. The second stage investigates the effect of cathode designs by fixing the anode design to design-1 and varying the cathode designs from design −1 to −4. The third stage investigates the effect of using the same designs at both the anode and cathode sides. All the stages were tested using three anode flowrates (2,5, and 8mL/min) and three methanol concentrations (1, 2, and 3mol/L). Higher concentrations perform better than lower concentrations while lower flowrates perform better than higher flowrates. The percentage improvement by the new designs in comparison to the reference design is: 142%, 94%, and 136% for the first stage; 74%, 125%, and 40% for the second stage; and 16%, -33% and -45% for the third stage, and the order being design −2, −3 and −4 respectively. Design −3 and −4 underperform in the third stage due to the availability of direct paths that boost methanol crossover when using the same design of anode and cathode. The new designs evacuate the CO2 bubbles and byproduct water faster and more efficiently than the reference design.

Indicator of abnormal cathode electron emission state with gas flow in Hall thrusters

The accurate diagnosis of abnormal electron emission state in hollow cathodes is crucial for the stable operation of Hall electric propulsion systems. In this study, a method of reducing the cathode working gas flow rate was used to simulate abnormal working conditions in which the cathode electron emission state (CEES) was deteriorating. By analyzing and comparing the oscillation signals under abnormal and steady-state working conditions, it was found that as the CEES deteriorated, the power content of the breathing oscillation decreased in the 1–40 kHz frequency band, and the main frequency decreased; in contrast, the power content of the transit-time oscillation increased in the 100–500 kHz range, and the main frequency was on the rise. Combined with the current growth rate analysis of breathing and transit-time oscillations, when the cathode gas flow rate decreases, the CEES deteriorates, the coupling voltage drop increases, and the potential drop in the channel decreases. The electron temperature and nonlinear power absorption of the electrons decrease, leading to a decrease in the growth rate of breathing oscillations and the breathing oscillation weakens; however, the time-averaged ion velocity and ion sound velocity in the channel decrease simultaneously, but the ion velocity decreases significantly faster than the ion sound velocity, leading to an increase in the growth rate of the transit-time oscillation, and the transit-time oscillation strengthen. Through comparison of the oscillation signals under different working conditions, such as varied anode flow rate, anode voltage, magnetic induction, it was proven to be a unique feature of CEES deteriorates, and can be used as an indicator of CEES deteriorates during the on-orbit operation of the Hall-effect thrusters.

Machine learning optimization of operating parameters to achieve high power density and efficiency of polymer electrolyte membrane fuel cell

The performance of PEMFCs is significantly influenced by operating conditions, including temperature, pressure, and flow rates. To optimize the complicated nonlinearity of operational conditions such as anode pressure (AP), cathode pressure (CP), cell temperature (Temp), anode flow rate (HFL), cathode stoichiometry (CS), and current density (CD) in experiments, this study employs five machine learning (ML) regression models: Artificial Neural Network, Decision Tree, Random Forest, Gradient Boosting, and Extreme Gradient Boosting to predict key performance indicators: voltage, power density, and efficiency, thereby optimizing the fuel cell’s operational parameters. Among these, the Gradient Boosting regressor demonstrated superior performance when validated with experimental data and was subsequently employed to fine-tune the operating parameters. Leveraging the prediction model, the performance of PEMFC in terms of power density and efficiency was further assessed by varying AP, CP and CS. The optimal conditions were identified with AP, CP at 2 bar, and CS at 2.50–2.75.

Multi-physics field modeling and electrochemical performance analysis of medium-temperature methanol-fueled proton-conducting solid oxide fuel cell

ABSTRACT A two-dimensional axisymmetric multi-physics field simulation for a methanol-fueled proton-conducting solid oxide fuel cell (CH3OH-SOFC-H) was created in this work. The influence of structural and operating parameters on the performance of the cell was analyzed. Moreover, the cell performance was compared with that of a methanol-oxygen ion-conducting SOFC (CH3OH-SOFC-O) under the same operating conditions. It was found that the anode support enables CH3OH-SOFC-H to exhibit higher performance, with the highest power density being 1493.3 W‧m−2 at 973 K. As the anode flow rate rises, the current density rises and subsequently falls, with a peak of 7623.6 A‧m−2. Meanwhile, as the methanol content in the gas composition and the cathode flow rate increase, so does the current density. CH3OH-SOFC-H has better electrochemical performance at low and medium temperatures, reaching 562.64 W‧m−2 at 773K (66% higher than that of CH3OH-SOFC-O at the same operating conditions). Meanwhile, CH3OH-SOFC-O has better performance at high temperatures. This study provides a theoretical reference for the subsequent application and promotion of CH3OH-SOFC-H.

Experimental evaluation of proton exchange membrane fuel cell performance with sinusoidal flow channel designs

Proton Exchange Membrane Fuel Cells (PEMFCs) with three distinct flow field designs were investigated: sinusoidal with a diffuser at the intake, sinusoidal serpentine, and serpentine flow fields. The sinusoidal flow field with a diffuser at the intake has been found to be the best flow field design. Following that, parametric experiments were performed on PEMFCs equipped with a sinusoidal flow field with a diffuser at the intake. Operating pressures (1–3 bar), back pressures (0–3 bar), anode humidification temperatures (40 °C–80 °C), cathode humidification temperatures (40 °C–70 °C), anode flow rates (250 sccm to 350 sccm) and cathode flow rates (250 sccm to 400 sccm) and cell operating temperatures (COT) ranging from 40 °C to 70 °C were all adjusted. The experimental findings showed that a COT of 60 °C, a 3-bar back pressure, a 3-bar working pressure, cathode humidification at 70 °C, anode humidification at 60 °C, and flow rates of 300 sccm for the anode and 350 sccm for the cathode resulted in the best PEMFC performance.

Magnetic focusing of low-power Hall thruster with a center-mounted hollow cathode

Magnetic focusing with xenon propellant has been verified in orbit from medium-to high-power Hall thrusters but has yet to be achieved in low-power Hall thrusters. A magnetically focused Hall thruster was designed to solve the common issue of large plume divergence angle in low-power Hall thrusters, which realizes the plasma lens magnetic field topography with permanent magnet excitation on the wide channel and adopts the center-mounted cathode layout. Experimental results indicate that the HEP-300CHC thruster exhibits an optimal magnetic focusing mode when operated at 288W with plume divergence half-angle approximately 11.7°. The magnetic focusing range is relatively narrow, concentrated within discharge voltage between 210V and 230V, and anode flowrate between 18sccm and 20sccm.The anode efficiency is higher than 40% at the nominal power, and the maximum anode efficiency reach 52% at the discharge power of 300W. This study provides a reference basis for ion beam control of low-power Hall thrusters.

Perturbation indicator for Hall effect thruster operating state based on statistical characteristics of breathing oscillation time scale signals

The failure of Hall effect thruster (HET) is usually the result of the accumulation of several tiny abnormal disturbances during operation. Timely and accurate early warning of perturbations is an important guarantee for the normal operation of thrusters. In this study, when the perturbation rate of HET signal (anode voltage or anode flow rate) is −4% to 4%, the time scale signal of breathing oscillation (BO) in the frequency range of 10 kHz to 100 kHz is statistically analyzed. Experiments show that when the signal is perturbed, the balance between ionization and acceleration of plasma in the discharge channel is destroyed, resulting in the dwell time of the wave peaks and valleys of BO in the far-zero region with the perturbation law, which visually shows that the number of scattered points at the corresponding current value changes regularly. According to the above statistical characteristics, this paper proposes a new condition monitoring index, namely the number of scattered points in the wave peaks side of the far-zero point area, and designs a perturbation indicator for the operating condition of the HET. Compared with direct monitoring of discharge current in engineering, this indicator can amplify the influence of the perturbation signal on BO, and has better identification and accuracy. Meanwhile, the indicator does not use invasive measurement and complex equipment, and is promising to be applied to the monitoring and diagnosis of the perturbation operation state of the on-orbit thruster.

Assessment of innovative graphene oxide composite membranes for the improvement of direct methanol fuel cells performance

The main objective of the study was to verify potential of GO-PEM and its best effective usage in a Direct Methanol Fuel Cells (DMFC) application so investigating the effect of this filler on cell performance, varying several operating conditions, without affecting the mechanical and electric properties of the baseline PEM. In this work, GO was added to the Nafion polymer using a weight percentage varying from 0.5 to 1.5%. The present analysis showed that the GO-membranes have higher tensile strength, greater water, and methanol uptake. It was also demonstrated that the presence of carbon compounds slightly reduced the proton conductivity suggesting that an optimal GO-content must be determined. Comparing several physical and electrochemical properties, we concluded that the 1 wt. %GO-loading PEM represents the most effective solution. Later, the advantages of adopting GO-PEMs in DMFCs were also assessed. A comparative analysis of a GO-DMFC and a standard DMFC was carried out by changing the relevant control parameters, such as anode flow rate, temperature, and methanol concentration obtaining that: a) the GO-DMFC performance enhanced when increasing the temperature and the anode flow rate; b) an increase in methanol concentration had a beneficial effect on DMFC performance only up to a peak value after that a rapid reduction was noticed. Optimal conditions were obtained for an anode flow rate of 7 µl min−1, a temperature of 60 °C and a 1 M methanol concentration.

Modelling of an integrated protonic ceramic electrolyzer cell (PCEC) for methanol synthesis

In this study, a novel reactor model is developed by combining protonic ceramic electrolyzer cell (PCEC) electrolysis for hydrogen production and CO2 recycling for methanol synthesis. The problem of temperature mismatch between PCEC and methanol synthesis is solved by supplying low-temperature gas intermediately, so as to realize the integrated direct synthesis of methanol. After model validation, a study of the effects of key operating parameters on the methanol production and temperature distribution of the system is conducted. It is found that increasing the operating voltage and electrolysis operating temperature, or decreasing the supplemental gas temperature enhances methanol production, while the carrier gas flow rate, supplemental gas flow rate and anode flow rate all have the optimal values (QN2 = 10–35 SCCM, QCO2 = 20–50 SCCM and Qan = 250–300 SCCM). Meanwhile, the temperature distribution of the system is also significantly affected by the above operating parameters, and it is possible to achieve a precise control of the operating conditions of the coupled system by adjusting the above operating parameters to ensure an efficient and long-term operation. This study provides an insight and a new approach for the recycling of CO2 and the green synthesis of methanol.

A study into Proton Exchange Membrane Fuel Cell power and voltage prediction using Artificial Neural Network

Polymer Electrolyte Membrane fuel cell (PEMFC) uses hydrogen as fuel to generate electricity and by-product water at relatively low operating temperatures, which is environmentally friendly. Since PEMFC performance characteristics are inherently nonlinear and related, predicting the best performance for the different operating conditions is essential to improve the system’s efficiency. Thus, modeling using artificial neural networks (ANN) to predict its performance can significantly improve the capabilities of handling multi-variable nonlinear performance of the PEMFC. This paper predicts the electrical performance of a PEMFC stack under various operating conditions. The four input terms for the 5 W PEMFC include anode and cathode pressures and flow rates. The model performances are based on ANN using two different learning algorithms to estimate the stack voltage and power. The models have shown consistently to be comparable to the experimental data. All models with at least five hidden neurons have coefficients of determination of 0.95 or higher. Meanwhile, the PEMFC voltage and power models have mean squared errors of less than 1 × 10−3 V and 1 × 10−3 W, respectively. Therefore, the model results demonstrate the potential use of ANN into the implementation of such models to predict the steady state behavior of the PEMFC system (not limited to polarization curves) for different operating conditions and help in the optimization process for achieving the best performance of the system.

A kinetics-mass transport model for CO2 electroreduction reactor to investigate performance limitation factors

Modeling of CO2 electroreduction reactor (CO2ECR) is highly demanded for rapid design of industrial processes, while facing challenges in practical applications. Herein, a kinetics-mass transport model is proposed, which can well balance the competition between HCOO– produce and H2 evolution, and be easily integrated into Aspen HYSYS as a user defined module for CO2ECR process design. By considering both cathode potential and CO2 concentration in flow channel, optimal regions of the key parameters can be simulated to achieve high efficiency of CO2 electroreduction, i.e., about 80 % for both HCOO– Faraday efficiency and CO2 conversion with slightly compressed pure CO2 feedstock of 300 kPa. By increasing anode flow rates, the lean streams with H2 concentration of around 50% achieve nearly the maximum H2 utilization, which is attractive due to the possible reduction of purification cost.

Power and Voltage Modelling of a Proton-Exchange Membrane Fuel Cell Using Artificial Neural Networks

A proton exchange membrane fuel cell (PEMFC) is a more environmentally friendly alternative to deliver electric power in various applications, including in the transportation industry. As PEMFC performance characteristics are inherently nonlinear and involved, the prediction of the performance in a given application for different operating conditions is important in order to optimize the efficiency of the system. Thus, modelling using artificial neural networks (ANNs) to predict its performance can significantly improve the capabilities of handling the multi-variable nonlinear performance of the PEMFC. However, further investigation is needed to develop a dynamic model using ANNs to predict the transient behavior of a PEMFC. This paper predicts the dynamic electrical and thermal performance of a PEMFC stack under various operating conditions. The input variables of the PEMFC stack for the analysis consist of the cathode inlet temperature, anode inlet pressure, anode and cathode inlet flow rates, and stack current. The performances of the ANN models using three different learning algorithms are determined based on the stack voltage and temperature, which have been shown to be consistently predicted by most of these models. Almost all models with varying hidden neurons have coefficients of determination of 0.9 or higher and mean squared errors of less than 5. Thus, the results show promise for dynamic modelling approaches using ANNs for the development of optimal operation of a PEMFC in various system applications.

The effect of anode axial position on the performance of a miniaturized cylindrical Hall thruster with a cusp-type magnetic field

A 200 W cylindrical Hall thruster with a cusp-type magnetic field was proposed, manifesting convergent plume and high specific impulse. In this paper, a series of ring-shaped anodes are designed and the influence of anode axial position on the performance of CHT with a cusp-type magnetic field is studied. The experimental results indicate that the thruster keeps stable operation at the condition of 140–270 W discharge power. When the anode moves axially towards the upstream cusp field, the thrust enhances from 6.5 mN to 7.6 mN and specific impulse enhances from 1658 s to 1939 s significantly. These improvements of thruster performance should be attributed to the enhancement of current utilization, propellant utilization and acceleration efficiency. According to the analyses on the discharge characteristics, it is revealed that as the anode moves upstream, the electron transport path could be extended, the magnetic field in this extended path could impede electron cross-field transport and facilitate the ionization intensity, yielding to the enhancement of current utilization and propellant utilization efficiency. Moreover, along with this enhancement of upstream ionization at the given anode flow rate, the main ionization region is thought to move upstream and then separate more apparently from the acceleration region, which has been demonstrated by the narrowing of ion energy distribution function shape. This change in acceleration region could decrease the ion energy loss and enhance acceleration efficiency. This work is beneficial for optimizing the electrode structure of thruster and recognize the ionization and acceleration process under the cusp magnetic field.

Scaled up on direct methanol fuel cell under different operating conditions

A direct methanol fuel cell with an active area of 100 cm2 was tested experimentally under a variety of operating situations to determine its overall performance. Different operational parameters, such as anode flow rate (1–5 ml/min), cathode reactant (Air/Oxygen) and cathode flow rate (100–2000 ml/min) are the most influencing parameter, and the performance output of each parameter are compared. In addition, different cathode flow channels, such as serpentine and sinuous, are used to improve reactant supply, and their performance is compared with one another. Using sinuous flow field at the cathode and 3 ml/min of methanol and 500 ml/min of oxygen, the maximum power density of 24 mW/cm2 has been achieved.

Influence of acceleration grid voltage and anode flow rate on performance of ion thruster

In order to achieve the optimal performance and reliability of the ion thruster in a wide power range, the influence of acceleration grid voltage and anode flow rate on the performance of ion thruster are studied experimentally and theoretically. The results show that in a certain range the ion beam current decreases continuously with the decrease of the absolute value of the accelerating voltage, and then increases suddenly. The electron backstreaming limited voltages in large and small thrust modes are –140 and –115 V, respectively. When the anode flow rate increases, the discharge voltage and discharge loss increase monotonically, and the deceleration current decreases monotonously. Under the power of 300−4850 W, the thrust is 11−188 mN, the specific impulse is 1800−3567 s, and the efficiency ranges from 34% to 67% by adjusting the anode current, grid voltage and working fluid gas flow. The maximum efficiency of thruster reaches 67% at 3000 W. This turning point is critical for thruster design and on-orbit applications. Choosing a reasonable range of working parameters can improve the performance and life of the thruster in application.

Investigation of gas purging and cold storage impact on PEM fuel cell system performance for aeronautical applications

Durability of proton exchange membrane fuel cell systems under cold weather conditions is essential and a critical challenge for transportation applications. During cold storage the water remaining in the cells can freeze causing damage to the cell components. In order to avoid this degradation, fuel cells are commonly purged with dried gases during shutdown prior to its storage at subzero temperatures. This work investigates cold storage of PEMFC systems at temperatures down to -40°C with the aim of developing a shutdown procedure that leads to minimal degradation due to cold storage, while meets energy efficient and time requirements of aeronautical applications. To that end, several experiments were carried out with two different stacks (a 4 kW liquid cooled and a 100 W air cooled) under a wide range of operating parameters: cathode gas, purge temperature, anode and cathode gas purge flow rates, purge time and cold storage temperature. The fuel cell performance degradation due to ice formation was measured by the polarization curves conducted prior and after every F/T cycle. The effects of these operating parameters on the durability of the PEMFC systems under cold storage are evaluated. The obtained experimental results showed that very long purge process lead to further performance degradation at -10°C than shorter process at -40°C, which indicates that eliminating all remained water in the cells is not only inefficient, but also lead to degradation due to the drying process. Moreover, guidelines to improve shutdown procedure for cold storage of proton exchange membrane fuel cell systems for aeronautical applications are discussed.

Experimental analysis of internal leakage current using a 100 cm2 class planar solid oxide fuel cell

This work studies the effect of the electronic conductivity of a commercially used yttria-stabilised zirconia (YSZ) electrolyte on solid oxide fuel cell performance. For the first time, an experimental method is used to measure the electronic conductivity of YSZ in commercially manufactured and operated single cells. An inert-gas step addition (ISA) method is employed to measure the electronic conductivity in the form of voltage changes at the open-circuit state. Since the electronic conductivity allows oxide ion transfer and water generation at the anode, a reduction in open-circuit voltage (EOCV) occurs due to the increased water partial pressure. The step increase in the anode flow rate in the ISA method reduces water partial pressure and raises EOCV. The EOCV change is then converted into internal leakage currents and electronic resistivities. The YSZ's electronic resistivity obtained in this work is comparable to the results obtained using the Hebb-Wagner polarisation technique and the oxygen permeation method.

A Non-Intrusive Signal-Based Fault Diagnosis Method for Proton Exchange Membrane Water Electrolyzer Using Empirical Mode Decomposition

This work focuses on a signal-based diagnosis approach dedicated to proton exchange membrane water electrolyzer (PEM WE) anode pump fault. The PEM WE cell measurements are performed with an experimental test bench to highlight the impact of water flow rate in the anode compartment. This approach is non-intrusive, and it can detect anode flow rate variation during the electrolysis and is designed to fulfill online diagnosis requirements. Contrary to electrochemical impedance spectroscopy-based approaches (EIS), this method stands out from existing procedures as a result of its few requirements, excluding any signal with perturbing amplitude. Therefore, the electrolyzer remains continuously available, even while the analysis is performed. The empirical mode decomposition (EMD) is used to decompose the signal variation into a sum of amplitude modulation and frequency modulation (AM-FM) components, called intrinsic mode functions (IMFs). In this work, the PEM WE current signal is decomposed into several IMFs using EMD. Then, the energetic contribution of each IMF is calculated. Experimental results exhibited that the energetic contribution of IMFs can be used as relevant criteria for fault diagnosis in PEM WE systems. This process only requires monitoring of the PEM WE current and has a low computational cost, which is a significant economic and technical advantage.