Applying hot-wire anemometry to directly measure the water balance in a proton exchange membrane fuel cell – Part 2: Experimental

• Simple and useful method for the ad-hoc and real-time determination of the fuel cell water balance.
• Relative voltage signal E/E0 is independent of fuel cell stack current.
• The power–law equation has to be used to calculate the Nusselt number for heat transfer around the hot wire.
• Method determines the fuel cell water balance with very good accuracy.

In order to better understand and more accurately measure the water balance in a proton exchange membrane fuel cell our group has recently proposed to apply hot wire anemometry in the fuel cell's anode outlet. It was theoretically shown that the electrical signal obtained from the hot wire sensor can be directly converted into the fuel cell water balance. In this work an ex-situ experimental investigation is performed to examine the effect of the wire diameter and the outlet pipe diameter on the voltage signal. For a laboratory fuel cell where the mass flow rate the anode outlet is small, it is found important to use a small output pipe diameter to obtain a sufficiently strong convection effect and hence clear voltage readings. Depending on the hot wire diameter and the inner pipe diameter, the resulting values for the exponent of the Reynolds number Re in the determination of the Nusselt number Nu range between m = 0.267 and m = 0.329. In general, it is shown that applying hot wire anemometry yields in fact very clear voltage readings with high frequency, and it can be used as a diagnosis tool in various fuel cell applications.