Environmental Engineering Reference
In-Depth Information
Most common humidifier devices are used mainly for air hydration, but
sometimes also for hydrogen humidification, and are based on bubblers, water
evaporators, enthalpy wheels, membranes, or on a pump for liquid water injection
inside a mixer or directly inside the first part of the cathode side collector.
Membrane humidifiers or injection pumps have been prevalently proposed for
hydrogen humidification.
In bubblers the gas directly passes through the liquid in an external wash bottle,
but the control of relative humidity is hard to be accomplished in all operative
conditions. Furthermore, the wet stream cooled before entering the stack can form
small droplets very dangerous for cell performance maintenance.
The humidification of the reactant gases could be successfully realized by using
membrane humidifiers [
34
,
35
]. The water content of a wet stream can be trans-
ferred across a semi-permeable membrane to a dry stream (Fig.
4.8
). The mem-
brane separates the dry stream compartment from the other compartment crossed
by with liquid water or wet stream. Theoretically the dry stream could increase its
water vapor content along the entire interface area of the membranes from the inlet
up to close the saturation value at the exit of the device. The design includes a
tubular form for the humidifier and a counterflow to optimize the exchange. This
device could be more suitable for FCS management with respect not only to
bubbler humidifier but also to water vapor injection method, as the last systems
need
additional
equipments,
make
the
whole
system
complex
and
increase
Dry stream
Membrane
Wet stream
Fig. 4.8
Principle of membrane-based humidification
