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ABSTRACT
Ejectors are used for anode hydrogen recirculation in proton exchange membrane fuel cell (PEMFC) systems, and the geometric parameters of the primary nozzle of ejectors have essential effects on the ejector performance. A 3D numerical model was established to investigate ejectors, and the reliability of the numerical model was verified by experiments. The operating characteristics of ejectors in the PEMFC system were analyzed by numerical simulation. Moreover, the effects of four geometry parameters (throat diameter, convergent angle, divergent angle, and length) on entrainment performance were studied. The results showed that the angle and length of the divergent zone have a significant influence on entrainment performance. A larger divergent angle may cause over-expanded under low power conditions, resulting in lower entrainment performance. For PEMFC systems with stable operating conditions or high entrainment requirements, a supersonic ejector with an appropriate divergent angle and length is recommended. Conversely, a convergent primary nozzle is suggested to be employed for the PEMFC systems with the wide operating power range. This study may provide a helpful reference for the design of ejectors used in fuel cell systems.
Nomenclature
| A | = | area, m2 |
| Dt | = | throat diameter of the primary nozzle, m |
| ERH2 | = | entrainment ratio of hydrogen |
| Lnd | = | length of the nozzle divergent region, m |
| Ma | = | Mach number |
| m | = | mass flow rate, kg/s |
| mp | = | primary mass flow rate, kg/s |
| ms | = | secondary mass flow rate, kg/s |
| mo | = | outlet mass flow rate, kg/s |
| P | = | operating power of the fuel cell stack, kW |
| p | = | pressure, bar |
| pp | = | primary flow pressure, bar |
| ps | = | secondary flow pressure, bar |
| SR | = | stoichiometric ratio of the fuel cell stack |
| T | = | temperature, K |
Greek Symbol
| αnd | = | divergent angle, ° |
| αnc | = | convergent angle, ° |
| ρ | = | density, kg/s |
Subscripts
| cell | = | single fuel cell |
| e | = | nozzle exit section |
| n | = | primary nozzle |
| nc | = | convergent portion of the nozzle |
| nd | = | divergent portion of the nozzle |
| o | = | outlet flow |
| p | = | primary flow |
| s | = | secondary flow |
| t | = | throat of the primary nozzle |
| H2 | = | hydrogen |
Abbreviations
| CFD | = | computational fluid dynamics |
| EXP | = | experimental |
| SIM | = | simulation |
| PEMFC | = | proton exchange membrane fuel cell |
Acknowledgments
This research was supported by the National Key Research and Development Program of China [Grant No. 2018YFB0105303], and Supported by state key laboratory of compressor technology (An hui laboratory of compressor technology).
Additional information
Funding
Notes on contributors
Jianmei Feng
Jianmei Feng is currently an associate professor with the School of Energy and Power Engineering, Xi'an Jiaotong University, Xi'an, China. Her research interests include PEM fuel cell vehicle systems, numerical simulation methods about compressors, and separation technology related to multiphase flow.
Jiquan Han
Jiquan Han is currently a Ph.D. student in School of Energy and Power Engineering, Xi'an Jiaotong University. His research interests include anode hydrogen recirculation in PEM fuel cell systems, especially the study of the ejector used in PEMFC systems.
Tianfang Hou
Tianfang Hou is currently a M.Sc. student in School of Energy and Power Engineering, Xi'an Jiaotong University. His research interests include experimental test methods about anode hydrogen recirculation systems and research on hydrogen scroll pump.
Xueyuan Peng
Xueyuan Peng is currently a professor with the School of Energy and Power Engineering, Xi'an Jiaotong University. His research interests include the research on the transcritical CO2 refrigeration cycle, hydrogen pumps and air compressors used in PEM fuel cell vehicles, process reciprocating compressor airflow pulsation and pipeline vibration, and energy saving of compressor system.