476218 Understanding and Optimizing Energy and Mass Transport in Porous Materials for Water, Energy, and Thermal Management Applications

Sunday, November 13, 2016
Continental 4 & 5 (Hilton San Francisco Union Square)
James W. Palko, Mehdi Asheghi, Kenneth E. Goodson and Juan G. Santiago, Mechanical Engineering, Stanford University, Stanford, CA

Research Interests:

Porous materials are ubiquitous and vital in a wide range of applications. Transport of energy, mass, and charge to the large fluid/solid interfacial area provided by these materials often controls the behavior of such systems. My research examines these transport phenomena as well as the functionalization of the surfaces themselves to optimize performance in several applications including toxin removal from water, energy storage in electrochemical capacitors, and dissipation of extreme heat fluxes from next generation electronic systems.

Part of my ongoing research addresses the challenge of water purification via capacitive deionization (CDI), an emerging technology which removes ionic contaminants from water via electrostatic interactions with the porous electrodes of a capacitor. Specifically, we focus on inverted CDI approaches using surface functionalization of porous electrodes to produce enhanced affinity for a variety of toxins. The porous electrodes act as adsorbents with selectivity for certain toxins. These adsorbents may then be regenerated by the action of an applied electric potential, which drives off the charged toxin species (as compared to traditional CDI where ions are attracted to the electrode surface by an applied potential). We have shown the ability to remove common contaminants from impaired input water streams to levels well below safe drinking water limits and to later expel these contaminants from the porous media without the need for the attendant waste disposal and cost concerns of chemical regeneration. My future research aims toward developing novel materials for better selectivity of difficult to treat impurities and the design of cells to maximize throughput and efficiency.

Another application closely related to CDI is energy storage in electrochemical capacitors. Recent advances in electrode materials provide great potential to enhance the energy density of these systems based on increases in material capacitance and pseudo-capacitance. However, due to the resulting potential for electrolyte depletion based on intrinsic solubility limits or desired operational regimes, the response of these systems involves a complex interplay of electromigration and diffusive transport of electrolyte species throughout the porous structures of the electrodes and spacer. We have developed parametric transport models including electrolyte depletion, capable of accounting for variations in cell geometry, electrolyte composition, and electrode material capacitance, resistivity, and structure. I will extend these models to provide guidance for cell design, electrode material choice, and electrolyte composition leading to electrochemical capacitors capable of addressing arising demands in grid energy storage and electric vehicle applications.

Beyond their use in electrochemical systems, porous materials have great potential in thermal management systems, such as heat pipes. We have studied energy and mass transport in two-phase cooling systems allowing dissipation of extreme heat fluxes, which is key to enabling dramatic performance improvements in a wide variety of electronic components including microwave amplifiers, power transistors in inverters for renewable power generation and electric vehicle applications, and 3D integrated microelectronics. We have produced thin conformal porous copper films with precisely defined microstructure using templated electrodeposition techniques. These structures with high surface area and thermal conductivity support heat dissipation via boiling of fluxes in excess of 1200 W/cm2 at superheats less than 10 K from hot spots in electronic devices. We have also integrated these films with extended surfaces formed from laser micromachined diamond to create heat sinks capable of extending this performance to large areas. In future, I will focus on improving the mechanistic understanding of two phase mass and energy transport during boiling in porous media and using this knowledge to design two-phase cooling systems employing porous media to solve current and emerging thermal management challenges.

Teaching Interests:

I am prepared to teach a variety of courses in the chemical and mechanical engineering and materials science curriculums. I would be excited to teach materials related courses as well as thermodynamics, heat and mass transfer, and fluid dynamics. I am also interested in developing a new graduate course or seminar providing an integrated treatment of fluid, thermal, charge, and chemical transport in porous media along with relevant surface science.

Extended Abstract: File Uploaded