Ian Jakupca

Unitized Regenerative Fuel Cell System Gas Storage/Radiator Development

High energy density regenerative fuel cell systems that are used for energy storage require novel approaches to integrating components in order to preserve mass and volume. A lightweight Unitized Regenerative Fuel Cell (URFC) Energy Storage System concept is being developed at the NASA Glenn Research Center (GRC). This Unitized Regenerative Fuel Cell System (URFCS) minimizes mass by using the surface area of the hydrogen and oxygen storage tanks as radiating heat surfaces for overall thermal control of the system. The waste heat generated by the URFC stack during charging and discharging is transferred from the cell stack to the surface of each tank by loop heat pipes, which are coiled around each tank and covered with a thin layer of thermally conductive carbon composite. The thin layer of carbon composite acts as a fin structure that spreads the heat away from the heat pipe and across the entire tank surface. Two different sized commercial grade composite tanks were constructed with integral heat pipes and tested in a thermal vacuum chamber to examine the feasibility of using the storage tanks as system radiators. The storage tank/radiators were subjected to different steady-state heat loads and varying heat load profiles. The surface emissivity and specific heat capacity of each tank were calculated. The results will be incorporated into a model that simulates the performance of similar radiators using lightweight, space rated carbon composite tanks.

Unitized Regenerative Fuel Cell System Gas Dryer/Humidifier Analytical Model Development

A lightweight Unitized Regenerative Fuel Cell (URFC) Energy Storage System concept is being developed at the NASA Glenn Research Center (GRC). This Unitized Regenerative Fuel Cell System (URFCS) is unique in that it uses Regenerative Gas Dryers/Humidifiers (RGD/H) that are mounted on the surface of the gas storage tanks that act as the radiators for thermal control of the Unitized Regenerative Fuel Cell System (URFCS). As the gas storage tanks cool down during URFCS charging the RGD/H dry the hydrogen and oxygen gases produced by electrolysis. As the gas storage tanks heat up during URFCS discharging, the RGD/H humidify the hydrogen and oxygen gases used by the fuel cell. An analytical model was developed to simulate the URFCS RGD/H. The model is in the form of an Excel® worksheet that allows the investigation of the RGD/H performance. Finite Element Analysis (FEA) modeling of the RGD/H and the gas storage tank wall was also done to analyze spatial temperature distribution within the RGD/H and the localized tank wall. Test results obtained from the testing of the RGD/H in a thermal vacuum environment were used to corroborate the analyses.

Development of Passive Fuel Cell Thermal Management Technology

The NASA Glenn Research Center is developing advanced passive thermal management technology to reduce the mass and improve the reliability of space fuel cell systems for the NASA exploration program. The passive thermal management system relies on heat conduction within the cooling plate to move the heat from the central portion of the cell stack out to the edges of the f uel cell stack rather than using a pumped loop cool ing system to convectively remove the heat. Using the passive app roach eliminates the need for a coolant pump and ot her cooling loop components which reduces fuel cell system mass and improves overall system reliability. Previous analysis had identified that low density, ultra-high thermal con ductivity materials would be needed for the cooling plates in order to achieve the desired reductions in mass and the h ighly uniform thermal heat sink for each cell withi n a fuel cell stack [1] . A pyrolytic graphite material was ident ified and fabricated into a thin plate using differ ent methods. Also a development project with Thermacore, Inc resulted in a planar heat pipe. Thermal conductivity tests were done using these materials. The results indicated that l ightweight passive fuel cell cooling is feasible. I. Introduction The purpose of this work was to test sample potenti al cooling plates for NASA’s fuel cells. The key pa rameters used to screen these samples were thermal conductivity, material density, and compatibility with the a nticipated fuel cell stack environment. Materials that demonstrated sufficient promise as passive cooling plates would continue to be studied and further optimized with the goal of d eveloping a light weight fuel cell cooling plate.

Bi-Directional Pressure Regulation for Regenerative Fuel Cells in Aerospace Applications

To achieve the potential energy density of 790 wh/kg, the unitized regenerative fuel cell system (URFCS), in development at Glenn Research Center (GRC) in Cleveland, Ohio, needs to maintain pressure control during the multiple modes of fuel cell operation using a low-mass component. The most effective means to reduce the system mass changes the process streams from mono-directional to bi-directional flow within the fluid lines. Unifying each process stream inlet and outlet lines require system components that function independently of fluid flow direction. A software model performed a preliminary evaluation of the bi-directional pressure regulation potential and was used to develop the resulting control algorithm. The bi-directional pressure regulator (BiPR), a software controlled stepping motor connected to a needle valve, is situated between the supply/vent port and a gas storage tank within the physical test stand. The BiPR controls the orifice size according to both the pressure on the supply/vent side of the valve and the pressure within the gas storage tank. Conducted between November 2002 and March 2003, the results from multiple charge/discharge cycles of the gas storage tank through the BiPR encourage further development of bidirectional flow systems.