Geonhui Gwak

Effects of porous properties on cold-start behavior of polymer electrolyte fuel cells from sub-zero to normal operating temperatures

In this investigation, a parametric study was performed using the transient cold-start model presented in our previous paper, in which the ice melting process and additional constitutive relations were newly included for transient cold-start simulations of polymer electrolyte fuel cells (PEFCs) from a sub-zero temperature (−20°C) to a normal operating temperature (80°C). The focus is placed on exploring the transient cold-start behavior of a PEFC for different porous properties of the catalyst layer (CL) and gas diffusion layer (GDL). This work elucidates the detailed effects of these properties on key cold-start phenomena such as ice freezing/melting and membrane hydration/dehydration processes. In particular, the simulation results highlight that designing a cathode CL with a high ionomer fraction helps to retard the rate of ice growth whereas a high ionomer fraction in the anode CL is not effective to mitigate the anode dry-out and membrane dehydration issues during PEFC cold-start.

A Numerical Investigation of Effects of Methanol Concentration Fluctuation in Active-type Direct Methanol Fuel Cell (DMFC) Systems

In this study, we develop a one-dimensional (1-D), two-phase, transient-thermal DMFC　model to investigate the effect of methanol concentration fluctuation that usually occurs in active-type direct methanol fuel cell (DMFC) systems. 1-D transient simulations are conducted and time-dependent behaviors of DMFCs are analyzed under various DMFC operating conditions such as anode/cathode stoichiometry, cell temperature, and cathode inlet humidification. The simulation results indicate that the effect of methanol concentration fluctuation on DMFC performance can be mitigated by proper control of anode/cathode stoichiometry, providing a guideline to optimize operating conditions of active DMFC systems.

A Numerical Investigation of Hydrogen Desorption Reaction for Tritium Delivery from Tritium Storage Based on ZrCo

In this paper, a three-dimensional hydrogen desorption model is applied to a thin double-layered annulus ZrCo hydride bed and validated against the temperature evolution data measured by Kang et al. 1) The present model reasonably captures the bed temperature evolution behavior and the 90% hydrogen discharging time. In addition, the performance of thin double-layered annulus bed is evaluated by comparing with a simple cylindrical bed using hydrogen desorption model. This study provides multi-dimensional contours such as temperature and H/M atomic ratio in the metal hydride region. This numerical study provides fundamental understanding during hydrogen desorption process and indicates that efficient design of the metal hydride bed is critical to achieve rapid hydrogen discharging performance. The present three-dimensional hydrogen desorption model is a useful tool for the optimization of bed design and operating conditions.

Development of a Lightweight 200W Direct Methanol Fuel Cell Stack for UAV Applications and Study of its Operating Characteristics (II)

Abstract >> A lightweight 200W direct methanol fuel cell (DMFC) stack is designed and fabricated to powera small scale Unmanned Aerial Vehicle (UAV). The DMFC stack consists of 33-cells in which membrane-electrodeassemblies (MEAs) having an active area of 88 cm 2 are sandwiched with lightweight composite bipolar plates.The total stack weight is around 3.485 kg and stack performance is tested under various methanol feed concentrations. The DMFC stack delivers a maximum power of 248 W at 13.2 V and 71.3℃ under methanol feed concentrationof 1.2 M. In addition, the voltage of individual cell in the 33-cell stack is measured at various current levelsto ensure the stability of DMFC stack operations. The cell voltage distribution data exhibit the maximum cell voltage deviation of 28 mV at 15 A and hence the uniformity of cell voltages is acceptable. These results clearlydemonstrate that DMFC technology becomes a potential candidate for small-scale UAV applications. Key words : Direct methanol fuel cell, DMFC(직접메탄올연료전지), Unmanned aerial vehicle, UAV(무인비행기),Fuel cell stack(연료전지 스택), Methanol crossover(메탄올 크로스오버)