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The dynamic performance is a very important evaluation index of proton exchange membrane (PEM) fuel cells used for real application, which is mostly related with water, heat and gas management. A commercial PEM fuel cell system of Nexa module is employed to experimentally investigate the dynamic behavior and transient response of a PEM fuel cell stack and reveal involved influential factors. Five groups of dynamic tests are conducted and divided into different stage such as start-up, shut-down, step-up load, regular load variation and irregular load variation. It is observed that the external load changes the current output proportionally and reverses stack voltage accordingly. The purge operation benefits performance recovery and enhancement during a constant load and its time strongly depends on the operational current level. Overshoot and undershoot behaviors are observed during transience. But the current undershoot does not appear due to charge double-layer effect. Additionally, magnitudes of the peaks of the voltage overshoot and undershoot vary at different current levels. The operating temperature responds fast to current load but changes slowly showing an arc-like profile without any overshoot and undershoot events. The air flow rate changes directly following the dynamic load demand. But the increased amount of air flow rate during different step-change is not identical, which depends on the requirement of internal reaction and flooding intensity. The results can be utilized for validation of dynamic fuel cell models, and regarded as reference for effective control and management strategies.

The dynamic performance is a very important evaluation index of proton exchange membrane (PEM) fuel cells used for real application, which is mostly related with water, heat and gas management. A commercial PEM fuel cell system of Nexa module is employed to experimentally investigate the dynamic behavior and transient response of a PEM fuel cell stack and reveal involved influential factors. Five groups of dynamic tests are conducted and divided into different stage such as start-up, shut-down, step-up load, regular load variation and irregular load variation. It is observed that the external load changes the current output proportionally and reverses stack voltage accordingly. The purge operation benefits performance recovery and enhancement during a constant load and its time strongly depends on the operational current level. Overshoot and undershoot behaviors are observed during transience. But the current undershoot does not appear due to charge double-layer effect. Additionally, magnitudes of the peaks of the voltage overshoot and undershoot vary at different current levels. The operating temperature responds fast to current load but changes slowly showing an arc-like profile without any overshoot and undershoot events. The air flow rate changes directly following the dynamic load demand. But the increased amount of air flow rate during different step-change is not identical, which depends on the requirement of internal reaction and flooding intensity. The results can be utilized for validation of dynamic fuel cell models, and regarded as reference for effective control and management strategies.

Abstract The development of miniaturization and high-density packaging of electronic components demands heat dissipation components that are compact and exhibit high performance. An ultra-thin micro heat pipe (UTHP), as a novel heat pipe with a flat shape that is highly suitable for application with high power and limited heat dissipation space, has been extensively investigated and widely used in mobile electronics. Understanding the influence of the manufacturing processes, capillary wick structures and flattened thickness on the thermal performance of UTHPs has been the aim of numerous studies. This paper presents a comprehensive review of the recent developments and applications of UTHPs for thermal management of electronics. The different types and applications of UTHPs are introduced, and the packaging technologies of UTHPs are summarized and compared. Furthermore, the fabrication methodology and heat transfer characteristics of various wick structures used for UTHPs are reviewed and analysed in detail. Finally, the challenges affecting the development and application of UTHPs are outlined, and recommendations for future research are presented.

Abstract The development of miniaturization and high-density packaging of electronic components demands heat dissipation components that are compact and exhibit high performance. An ultra-thin micro heat pipe (UTHP), as a novel heat pipe with a flat shape that is highly suitable for application with high power and limited heat dissipation space, has been extensively investigated and widely used in mobile electronics. Understanding the influence of the manufacturing processes, capillary wick structures and flattened thickness on the thermal performance of UTHPs has been the aim of numerous studies. This paper presents a comprehensive review of the recent developments and applications of UTHPs for thermal management of electronics. The different types and applications of UTHPs are introduced, and the packaging technologies of UTHPs are summarized and compared. Furthermore, the fabrication methodology and heat transfer characteristics of various wick structures used for UTHPs are reviewed and analysed in detail. Finally, the challenges affecting the development and application of UTHPs are outlined, and recommendations for future research are presented.