Posted by admin on Oct 22, 2009 in Alex Heltzel, Publications, Thermal Systems | 0 comments

A. Heltzel, PC Krause and Associates, Inc; Liangti Qu, Liming Dai, University of Dayton Research Institute A three-dimensional (3D) electrodynamic model is built using the finite-difference time-domain (FDTD) method to investigate the optical response of carbon nanotubes grafted with gold nanoparticles. Theoretical characterizations suggest an anisotropic response, in line with previously observed absorption peaks of such systems in the optical range. An investigation of geometric and wavelength dependences is conducted, predicting the ability to tune the sub-wavelength intensity enhancement for efficient localization and propagation. The support of electric field enhancement along the nanotube walls raises the possibility of utilizing such systems as plasmon generators and waveguides for optical signal propagation. Online at...

Posted by admin on Oct 22, 2009 in Alex Heltzel, Publications, Thermal Systems | 0 comments

N. P. Malcolm, Department of Mechanical Engineering, University of Texas at Austin; A. Heltzel, PC Krause and Associates, Inc;  A. Shi, J. R. Howell, Department of Mechanical Engineering, University of Texas at Austin A Finite Difference Time Domain (FDTD) simulation is employed to calculate electromagnetic field and charge density distributions at the junction between a gold nanoparticle (NP) tip of a scanning ZnO nanowire and gold NP bio-markers. This three-dimensional simulation calculates the magnetic and electric field components in a large matrix of Yee cells by solving Maxwell’s curl equations. An absorbing boundary condition is included to eliminate reflection back into the simulation chamber. In the specific simulations considered here, a laser pulse of single wavelength is incident on the backside of a transparent silicon dioxide micro-cantilever, and coupled into a ZnO nanowire grown from an opening on a metal coating of the front side of the cantilever. The simulation results reveal local field enhancement between the gold NP tip of the nanowire and only one of three 20 nm gold NPs with a 28 nm empty spacing between two adjacent NPs. The charge density distributions in the gold tip and the gold NP are calculated and correlated with the local field enhancement, which makes the gold tip of the scanning nanowire waveguide attractive for use in imaging gold NP bio-labels on cell membranes. Proceedings of 9th International Conference on Heat Transfer, 2009, San Francisco...

Posted by admin on Oct 22, 2009 in Alex Heltzel, Publications, Thermal Systems | 0 comments

Alex  Heltzel, PC Krause and Associates, Inc. Book Chapter in Nanomanufacturing American Scientific Publishers, 2009. A. Heltzel, PC Krause and Associates, Inc. Book Chapter in...

Posted by admin on Oct 22, 2009 in Alex Heltzel, Publications, Thermal Systems | 0 comments

A. Heltzel, PC Krause and Associates, Inc. Three-dimensional conjugate heat transfer models are built to predict the steady-state performance of microscale pin-fin and cross-flow heat exchangers with hydraulic diameters on the order of 100 μm. Modeling, meshing, and segmentation techniques are presented to allow for macroscale simulation of the microstructured devices. The effect of variation in geometric and flow parameters is investigated. Hydraulic and thermal predictions are compared to published experimental and extended beyond the limited range of test data to provide performance within a wide parametric range. A discussion of the dominating and relevant thermal transport mechanisms in both fluids and solid clarifies the routes to optimizing heat transfer in these small scale heat exchangers. Journal of Aerospace, in press...