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The requirements for performance by planetary exploration missions are increasing. Landing at a single location to take data is no longer sufficient. Due to the increasing cost, the missions that provide mobile platforms that can acquire data at displaced locations are becoming more attractive. Landers have also had limited range due to power limitations, limited lifetime of subsystems and the inability to negotiate rough terrain. The Center for Space Nuclear Research has designed an instrumented platform that can acquire detailed data at hundreds of locations during its lifetime—a Mars...
This paper describes the updating of the sub-cooled boiling model with the more recent and better sub-models. The improved sub-models include: Hibiki and Ishii correlation for nucleation site density, Kocamustafaogullari correlation for bubble departure diameter and the S-gamma model of Lo and Rao for bubble size distribution in the flow. The new model has been tested against measured data from Debora and Bartolomei . The results show that improvement in the bubble size prediction has the most significant impact on the accuracy of the model.
Distributions in reactant species concentration in a PEMFC due to local consumption of fuel and local transport of water through the membrane cause distributions in current density, temperature, and water concentration in three dimensions in a PEMFC. These distributions can lead to flooding or drying of the membrane that may shorten the life of an MEA. Changing the cell's flow-field pattern to distribute the gas more evenly is one method of minimizing these stresses. This paper investigates how 200 cm 2 serpentine flow-fields with different number of gas paths, and thus different gas path...
To reduce diesel engine emissions, a split injection strategy with PHCCI combustion in a diesel engine was investigated with simulation. A multidimensional CFD application, Star-CD coupled with a modified 2-D flamelet was used to simulate multiple injection combustion. Several mass ratios of the first injection and second injection conditions compared to the conventional pilot and main injection strategy were evaluated. The injection angle and the injection timing of the first injection were fixed to 150° and 55° BTDC, respectively. Because of the early injection, the in-cylinder pressure and...
Computational fluid dynamics (CFD) simulations were performed for four 10cm2 serpentine flow-fields with single channel, double channel, cyclic-single channel, and symmetric-single channel patterns to investigate the effect of flow-field design. High and low inlet humidity operating conditions were studied by calculating the distributions of overpotentials, current density distribution, and membrane water content at different cell voltages. At high inlet humidity, the double channel flow-field was predicted to have better polarization performance and uniform current density distribution,...
Many mechanisms of colloid retention in porous media under unfavorable conditions have been identified from experiments or theory, such as attachment at surface heterogeneities, wedging at grain to grain contacts, retention via secondary energy minimum association in zones of low flow drag, and straining in pore throats too small to pass.However, no previously published model is capable of representing all of these mechanisms of colloid retention. In this work, we demonstrate that incorporation of surface heterogeneity into our hemispheres-in-cell model yields all experimentally observed non-...

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