Potential uses include regenerative and primary fuel cell power systems.
An advanced reactant pressure regulator
with an internal ejector reactant circulation
pump has been developed to
support NASA’s future fuel cell power
systems needs. These needs include reliable
and safe operation in variable-gravity
environments, and for exploration
activities with both manned and
unmanned vehicles. This product was
developed for use in Proton Exchange
Membrane Fuel Cell (PEMFC) power
plant reactant circulation systems, but
the design could also be applied to other
fuel cell system types, (e.g., solid-oxide
or alkaline) or for other gas pressure
regulation and circulation needs. The
regulator design includes porting for
measurement of flow and pressure at key
points in the system, and also includes
several fuel cell system integration
NASA has recognized ejectors as a
viable alternative to mechanical pumps
for use in spacecraft fuel cell power systems.
The ejector motive force is provided
by a variable, high-pressure supply gas
that travels through the ejector’s jet nozzle,
whereby the pressure energy of the
fluid stream is converted to kinetic energy
in the gas jet. The ejector can produce
that are relatively high (2-3 times), and
this phenomenon can potentially (with
proper consideration of the remainder
of the fuel cell system’s design) be used
to provide completely for reactant prehumidification
and product water
removal in a fuel cell system.
Specifically, a custom pressure regulator has been developed that includes: (1) an ejector reactant circulation pump (with interchangeable jet nozzles and mixer sections, gas-tight sliding and static seals in required locations, and internal fluid porting for pressure-sensing at the regulator’s control elements) and (2) internal fluid porting to allow for flow rate and system pressure measurements. The fluid porting also allows for inclusion of purge, relief, and vacuum-breaker check valves on the regulator assembly. In addition, this regulator could also be used with NASA’s advanced non-flow-through fuel cell power systems by simply incorporating a jet nozzle with an appropriate nozzle diameter.
For this advanced regulator and ejector concept, ejector flow and outlet pressure are controlled in a manner similar to an “external-sense” regulator. This control method senses the pressure downstream of the ejector mixer outlet, and uses that signal as the feedback to its internal control valve. As changes in ejector mixer outlet pressure occur as a result of consumption of gases in the fuel cell stack (or system), the regulator’s control elements quickly respond with the variable supply of high-pressure gas to the inlet of the ejector jet nozzle to match the real-time flow needs of the fuel cell stack (or system).
In earlier tests of the regulator and ejector assembly at NASA’s test facilities, purposefully selected geometry (ejector jet nozzle and mixer internal diameters), pressure, and flow ranges were tested to gather useful performance data to support the development of design guidelines for fuel cell systems utilizing ejectors for reactant circulation. The results of these tests (and with the particular ranges tested) showed that approximate 10:1 ejector-mixer-tojet diameter ratios could produce performance (scalable over the range of fuel cell power output of 0.7 to 20 kW) that matched the presumed closed fuel cell circulation requirements of total-to-motive flow ratios of 2.5 to 4.5 at the higher motive flow ranges, and with pressure differences developed as high as about 2.5 psid (≈17.2 kPa) with reactant gas circulation.
This work was done by Arturo Vasquez of Johnson Space Center. MSC-24731-1