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Summary: Gas foil bearings are crucial to guarantee stable operation and oil‐free for centrifugal air compressors that pressure the air to the stack in hydrogen fuel cell vehicles. However, the load is smaller and the friction torque is larger. In this study, multi‐objective optimization considering simultaneously both the higher load and lower friction torque is firstly performed to improve the reliability and decrease the energy consumption of the air compressor. The effects and contributions of the factors including rotation speed, nominal clearance, bump foil thickness, and bump pitch on two bearing performances are investigated by the Taguchi method and analysis of variance. The contributions of nominal clearance and rotation speed on the load are 68.82% and 18.62%, while the two factors on the contributions of friction torque are 66.48% and 17.62%, respectively. The optimal combination with the highest grey relational grade value of 0.7736 is obtained based on grey relational analysis. These findings can be used to guide the efficient operation and selection of the centrifugal air compressor in hydrogen energy vehicles. [ABSTRACT FROM AUTHOR]

Summary: Claw‐type pump is one of the most promising candidates in the circulating system of the hydrogen fuel cell because of its compact structure and high reliability. In this paper, claw‐type hydrogen circulating pump with a rated flowrate of 0.4 Nm3·min−1 was designed and fabricated. An internal flow model of the claw pump was established to investigate the thermodynamic performances with air. Then, a test rig was carried out to validate the feasibility of the numerical model with air. Finally, the numerical model was used to predict the thermodynamic performance with the fluid medium of hydrogen mixtures. Moreover, the effects of axial clearance and the content of water vapor and nitrogen were examined. The results showed that decreasing the axial clearance contributed to the increase in volumetric efficiency, hydrogen mass flow rate, power consumption, and the decrease in specific power. Meanwhile, increasing the contents of water vapor and nitrogen helped to increase the volumetric efficiency and decrease the specific power. However, it had a negative influence on increasing power consumption and decreasing hydrogen flow rate. The specific powers of all the hydrogen mixtures decreased much slower at the smaller axial clearances. [ABSTRACT FROM AUTHOR]

Summary: Centrifugal air compressors are promising due to their zero emissions, long driving range, and wide fuel sources. The gas foil thrust bearing (GFTB) is considered as one of the key components in the centrifugal air compressor to guarantee the system is oil‐free and reliable due to there is self‐acting and high speed. However, the gas foil thrust bearings were all of lower capacity in previous research. In this study, the effects of each foil and nominal clearance on the static performance are developed experimentally. The optimal GFTB with higher capacity is obtained. The feasibility study of the proposed GFTB is carried out, which is installed on the ultra‐high‐speed centrifugal air compressor. The result shows that the proposed GFTB can run stably and efficiently in the full speed ring, and the high‐pressure ratio and large flow rate of the air compressor also can be ensured. The results play an important role in guiding the stable operation of centrifugal air compressors applied in hydrogen fuel cell vehicles (HFCVs). [ABSTRACT FROM AUTHOR]

Summary: The gas foil bearings (GFBs) are one of the vital components of the air compressor applied in fuel cell vehicles. The design and operating parameters have an impact on the static and dynamic performances of GFBs, the properties of which need to be tailored to match the specific application demands. The influence of excitation frequency, nominal clearance, loading direction, and elastic structure on the performances is experimentally studied in this article. The results show that the displacement increased while the stiffness decreased with the increase in the nominal clearance. The recommended loading position is provided based on the analysis. The largest stiffness is obtained in the GFBs with the radial trisection foil. Considering the high stiffness and low damping, the best GFB aimed at anti‐vibration is obtained. The results can be used as guidelines for component matching in the design and operation of the polymer electrolyte membrane fuel cell system. [ABSTRACT FROM AUTHOR]

The air compressor is a key component in the polymer electrolyte membrane (PEM) fuel cell system and its performance has great impact on the electric power output from the system. Here, analysis was conducted firstly on the Roots-type compressor with fixed internal compression based on the volume reduction created by helical rotors. The built-in volume ratio variations with the wrap angle and the lobe numbers were calculated and discussed. Then a prototype of the Roots-type air compressor with 6 lobes was developed according to the outcomes of the research. The volumetric and isentropic efficiency of the prototype were measured under the discharge pressures from 0.11 MPa to 0.25 MPa while the rotation speeds from 10000 to 14000 rpm. Under the design conditions, the volumetric efficiency and isentropic efficiency of the Roots-type air compressor were 75.8% and 53.9% respectively. It was concluded that this kind of Roots-type air compressor is especially suitable for the fuel cell systems applied in the range extended electric vehicles. [ABSTRACT FROM AUTHOR]

In this paper, the development and testing of a Roots pump with a new rotor profile for hydrogen recirculation in the fuel cell system are presented. The design method of the rotor profile, port position, and structure of the pump is presented. A prototype of a three-lobe Roots pump with helical rotors was fabricated, and its performance was experimentally tested. The measured data show that the effect of the pressure difference on the flow rate and volumetric efficiency of the Roots pump is the most significant, while the effect of suction pressure is limited. It is concluded that the leakage rather than flow resistance is the key factor, which has a major influence on volumetric and isentropic efficiency. The comparison of the performance is also given by the measured results of the same Roots pump working with air, helium, and hydrogen. Finally, the successful integration of the Roots pumps into three PEM fuel cell systems is reported and the optimal operating parameters of the Roots pump in the systems under various loads are also presented. It is found that the performance of the Roots pump integrated into the fuel cell system is better than that measured with pure hydrogen on the test rig. The performance maps composed of all the measured data of the Roots pump are very helpful for the optimal design and operation of the fuel cell system. [ABSTRACT FROM AUTHOR]

The hydrogen recirculation ejector, known for its low cost and simple structure, has garnered widespread attention in PEM fuel cell applications. As a fluid-driven passive component, the fluid dynamics inside the ejector play a pivotal role in determining its entrainment performance. This study explores the impact of the primary flow temperature on phase change characteristics based on the Euler-Lagrange model. Results indicate that at a primary flow temperature of −40 °C, the mass flow rate of droplets at the outlet reaches 285.2 mg/s, representing a condensation efficiency of 24.1%. Concurrently, condensation elevates the outlet temperature by 31.2 °C, resulting in an 8.8% reduction in the entrainment ratio. The mass flow rate of droplets decreases significantly as the primary flow temperature increases. As the temperature rises to 60 °C, homogeneous droplets vanish entirely. Simultaneously, foreign heterogeneous droplets evaporate by 42.0%, attributed to the negative subcooling degree at the diffuser and outlet pipe. This study emphasizes the significance of controlling the primary flow temperature for the hydrogen recirculation ejector. [Display omitted] • Condensation efficiency increases with decreasing primary flow temperature. • 24.1% of the water vapor condenses at a primary flow temperature of −40 °C. • Condensation reduces the entrainment ratio and enhances outlet temperature. • Evaporation occurs when the primary flow temperature rises to 60 °C. [ABSTRACT FROM AUTHOR]

The startup-shutdown behavior of the gas foil bearings-rotor system is vital for proton exchange membrane fuel cells due to the inherently frequent start-stop of hydrogen fuel cell vehicles, which significantly affects the sustainable power generation and efficiency of the fuel cells. In this paper, the effects of three systematic factors including bump foil structure, nominal clearance, and coating on the dynamic response of the bearings-rotor system are first investigated based on startup-shutdown experiments. The mathematical model considering both gas film and thermo-hydrodynamic characteristics is presented to investigate the startup-shutdown behavior further. The influencing mechanisms of the factors on performance are analyzed. The energetic results demonstrate that the bearing structure parameters have a significant influence on the startup-shutdown performance and energy consumption. Considering optimal startup-shutdown performance, a better bearings-rotor system is proposed. Compared to the average values in all cases, the take-off speed, temperature rise, and average energy consumption of the system are decreased by 51.3%, 16.2%, and 60.7%, respectively. This indicates that the startup-shutdown improvement of the bearing-rotor system has great significance for enhancing the energy efficiency of the fuel cell. [ABSTRACT FROM AUTHOR]

The hydrogen pump is an important component in the hydrogen circulation system of fuel cells. Excessive pulsation at the outlet of the pump is challenging when the Roots hydrogen pump is used, which has a negative impact on the operation performance. To reduce the impact of excessive fluctuations in the hydrogen circulation system, a new structure of reflow grooves is proposed in this paper, which connects the different chambers and adjusts the pressure using a diversion method. The internal flow of the two pumps was studied for comparison, using a three-dimensional simulation model established by Computational Fluid Dynamics (CFD) method. Results showed that the reflow grooves reduce the exhaust pressure and mass flow pulsations, which has a positive effect on the pressure stabilization of the hydrogen circulation system and the anode inlet pressure of the fuel cell stack, contributing to the long durability and stability of the fuel cell stack. [Display omitted] • A novel reflow structure is proposed for the Roots hydrogen pump. • The internal flow of the pump is simulated by the dynamic grid method. • The gas pressure variation in one compression in the Roots pump was analysed. • The reductions in flow fluctuations at different rotational speeds are compared. • Pressure fluctuation is supressed at high rotation speed by the reflow structure. [ABSTRACT FROM AUTHOR]

The start-stop performance of gas foil bearings (GFBs)-rotor system directly affects the operation range and energy consumption of the air compressor for hydrogen fuel cell vehicles which has the inherent characteristic of frequent start and stop. In this paper, the effects of three factors including cooling gas flow, cooling gas pressure, and cooling gas type on the start-stop performance of the GFBs-rotor system are experimentally investigated for the first time. Based on the start-stop response analysis, the take-off speed of 6576 rpm and power consumption of 0.61 kW for the optimum GFBs-rotor system are obtained. The performance of the proposed system for the centrifugal air compressor is compared with the commercial products. The comparison shows that the lowest speed can be decreased by 34.2% while the operating range is expanded by 8.6%, which can in turn improve the performance of the centrifugal air compressors in hydrogen fuel cell vehicles. [Display omitted] • Effects of cooling gas on the start-stop performance were considered. • Start-stop response of the GFBs-rotor system in start-stop processes was studied. • Optimal operating parameters of the GFBs-rotor system were proposed. • Optimal system with minimum takeoff speed and power consumed was identified. • Verification of the optimum GFBs-rotor system was carried out. [ABSTRACT FROM AUTHOR]

Centrifugal air compressor is critical to hydrogen fuel cell vehicles due to it guarantees the air provided to the stack is higher pressure ratios and a larger flow rate. However, the compressor has low efficiency and high energy consumption. In this paper, the multi-objective optimization was performed based on experimental data, which considered both the maximum isentropic efficiency and minimum total power consumption. The effects of the factors on the performance of the compressor were obtained by mean S/N ratios. The contributions of the factors to the optimization objectives of the compressor were investigated by analysis of variance. The optimal parameters combination providing the larger isentropic efficiency and lower total power consumption was found by grey relational analysis. The isentropic efficiency increased by 34.5% and total power consumption decreased by 48.5% in comparison with the average value in all Taguchi cases for the optimal compressor. [Display omitted] • Optimal operating parameters of the centrifugal air compressor were proposed. • Effects of operating parameters on performance of compressor were analyzed. • The contributions of operating parameters to the optimal objectives were found. • Grey relational analysis was used for performance analysis for the first time. [ABSTRACT FROM AUTHOR]

As hydrogen circulation pump is one of the key components for hydrogen circulation in Fuel Cell Vehicles (FCVs), the optimization of a hydrogen circulation pump is critical for the performance improvement of a FCV. This study focuses on six factors that have impacts on the performance of a claw-type hydrogen pump, including the rotating speed, pressure ratio, inlet pressure, the radial clearance between the rotor and the casing (RC1), the radial clearance between the rotors (RC2), and the axial clearance (AC). By using the Taguchi method, a series of CFD simulation cases with different levels of the six factors were carried out to determine the optimum conditions for the volumetric efficiency and the shaft power. With the analysis of variance (ANOVA) method, the quantitative contribution of these six factors to volumetric efficiency and shaft power were obtained separately. According to the results, pressure ratio (36.2%), AC (29.4%) and rotating speed (21.5%) had the greatest impact on volumetric efficiency, while shaft power was more sensitive to the pressure ratio (64.6%), rotating speed (23.0%) and inlet pressure (5.2%). Based on the analysis of the ANOVA method, the most significant factors on volumetric efficiency and shaft power were chosen to be input factors of the Neural Network and the data of simulation were adopted to train the Neural Network to predict the performance of a claw pump. The accuracy of the Neural Network was tested and validated. The results can be used as guidelines for the design and selection of claw pumps used for fuel cell systems. • The quantitative effect of 6 main factors was illustrated. • Optimum combinations of the 6 main factors were presented. • Performance prediction model with ANN was established. [ABSTRACT FROM AUTHOR]

The startup performance is crucial to the high-efficient operation of the sustainable power generation system. Current literature usually focuses on catalysts and startup strategy to improve startup performance of the proton exchange membrane fuel cell, which ignores the gas foil bearings-rotor system that directly affects startup response. Therefore, in this paper, the effects of bump foil structure, coating, and nominal clearance on the startup response of the bearings-rotor system are first investigated experimentally. Multi-objectives optimization mathematical model considering simultaneously lower power consumption, takeoff speed, and vibration is presented based on grey relational analysis. The optimal bearings-rotor system with radial trisection bump foil, coating MoS 2 , and nominal clearance of 50 μm is identified. Compared to average values, the power consumption of the optimal system is diminished by 27.2% while the takeoff speed and nonlinear vibration are reduced by 16.2% and 47.3%, respectively. These findings can be used to improve energy efficiency and startup performance for fuel cells. The systematic methodology proposed in this study can be extended to other investigations about the startup. • Bump foil type, coating, and nominal clearance are first considered in PEMFCs. • Multi-objective optimization mathematical model is presented. • Optimal gas foil bearings-rotor system is proposed and verified. • Startup performance of the proposed system is improved. • Power consumption of the proposed system is diminished by 27.2%. [ABSTRACT FROM AUTHOR]