A pseudo two-phase model to study effects of non-condensable gases on the water autonomy of a direct methanol fuel cell system

摘要

In a direct methanol fuel cell (DMFC) system, water at the condenser outlet is recirculated into the mixing chamber where it mixes with pure methanol and anode outlet stream. The selection of condenser design and operating conditions plays a key role in the successful operation of the system with water autonomy. In this study, a novel pseudo two-phase computational fluid dynamics (CFD) model is proposed to investigate the condensation capability of the condenser under the operating conditions of a DMFC system. The condenser model is simplified by implementing an iterative multi-domain approach where continuity at the decoupled domain interfaces is satisfied by the convergence of boundary conditions. The proposed thermofluids model is validated with experimental data. Through the model, the performance of the condenser is investigated for DMFC operating conditions. The results show that the amount of non-condensable gases, the velocity and the saturation level of cathode exhaust gas (CEG) are the key parameters in these scenarios. The highest condensation effectiveness is calculated for the saturated CEG flow scenario with lower velocity and lower content of non-condensable gases, while the lowest condensation effectiveness is calculated as for the under saturated CEG flow scenario. Another important result is that the increment of the amount of the non-condensable gases throughout the downstream distance is found as 4% which results in the decrement of the saturation and film temperature by 8 K and 4 K, respectively. In addition, it is found that when the inlet velocity of CEG decreases from 0.82 m•s~(-1) to 0.18 m•s~(-1), the overall condensation rate decreases by 55%.