Daniel W. Crunkleton

Phase transformations of nano-sized cubic boron nitride to white graphene and white graphite

We report quantum-mechanical investigations that predict the formation of white graphene and nano-sized white graphite from the first-order phase transformations of nano-sized boron nitride thin-films. The phase transformations from the nano-sized diamond-like structure, when the thickness d > 1.4 nm, to the energetically more stable nano-sized white graphite involve low activation energies of less than 1.0 eV. On the other hand, the diamond-like structure transforms spontaneously to white graphite when d ≤ 1.4 nm. In particular, the two-dimensional structure with single-layer boron nitride, the so-called white graphene, could be formed as a result of such transformation.

CFD-Based Optimization of a Flooded Bed Bioreactor for Algae Production

Abstract Algae show great potential for use as a feedstock for energy applications, but the cost of production must be reduced to compete with traditional feedstocks. One method of doing so is to optimize the algae production photobioreactor. This study presents the method of obtaining, and results of, such an optimization using a model derived from computational fluid dynamics simulations.

Natural convection of low Prandtl-number fluids in rectangular enclosures

A three-dimensional, finite volume algorithm was developed to calculate the velocity and temperature profiles of liquid tin heated from below in rectangular enclosures. These calculations are performed for a variety of Rayleigh numbers as a function of the two aspect ratios. The predicted first critical Rayleigh number and flow patterns are in good agreement with previous calculations conducted by other techniques.

Fuel Economy and Emission Performance of Fuel Cell-Based Diesel HEVs

The fuel economy and emission advantages of diesel-electric hybrid powertrain modifications and an auxiliary fuel cell subsystem over those of a conventional midsize crossover SUV are discussed. The vehicle architecture is representative of one selected for the multiyear ChallengeX intercollegiate student design contest. To analyze the fuel economy, a simple “top-level” approach is used to estimate the fuel economy characteristics and performance potential to illustrate the advantages of the hybrid-electric powertrain configuration and the auxiliary fuel cells. Chained energy efficiency assumptions for the powertrain components lead to gasoline equivalent fuel mileage estimates. In the emission analysis, the greenhouse gases, regulated emissions, and energy use in transportation model is used to track the environmental impact of the powertrain on a well-to-wheels basis.

Periodic oscillations of low Prandtl-number fluids in rectangular enclosures

Periodic oscillatory flows in low Prandtl-number fluids are numerically characterized in this study. A mathematical model is developed to solve the three-dimensional mass and momentum conservation equations using a control-volume algorithm. For various aspect ratios, the second critical Rayleigh number is determined. For an aspect ratio (length/height) of 0.25, macroscopic oscillations are unmistakably observed; while as the aspect ratio is increased, oscillations tend to dampen.