Definition of efficiency criteria for a fuel cell humidifier: Application to a low power proton exchange membrane fuel cell system for negative surrounding temperatures

The humidifier plays a key role in fuel cells system by ensuring good hydration of membranes and transferring part of the exhaust heat to the cells. To characterise this device and evaluate its performance at negative ambient temperatures, several methods from different fields of engineering can be adopted. In our investigation, we first tested the performance criteria applicable to a heat exchanger since the humidifier can be considered a heat and mass exchanger. To estimate mass exchange, i.e., moisture transfer, the criteria used in industrial drying were tested. Eventually, to consider irreversibilities involved in the humidification process, exergetic criteria were defined. Following the design of experiments (DOE) method, we fit all performance criteria into a linear model. An analysis of variance showed that only the exergy yield ζ model is robust and reliable. A study of this model helps us present several recommendations for optimizing humidifier performance. The DOE results reveal that between −20 °C and 0 °C, the ambient temperature does not have a significant impact on the exergy yield. This indicates that humidifier sizing and optimisation made at a given ambient temperature would be applicable for other ambient temperatures.