I am in my third year as a PhD student at Oregon State University. My advisor is Todd Palmer and my co-advisor is Alex Greaney1; I am also a member of the Computational Materials Group at UC Riverside.
We are interested in simulating deterministic phonon transport using the code Rattlesnake (written in the MOOSE framework) to predict thermal conductivity in nuclear fuels operating at high temperatures with isotopic defects and evolving microstructures. We are developing a framework to bridge the gap between the atomistic and engineering scale, and collaborate with Dr. Alex Greaney and his research group at UC Riverside.
We have shown Rattlesnake to be an effective and efficient engine for simulating homogeneous phonon transport; it solves the frequency independent equation of phonon radiative transfer in the Self-Adjoint Angular Flux formulation using the single mode relaxation time approximation. We are interested in phonon transport at high temperatures and therefore must implement multifrequency transport to model these physics effectively, in addition to considering contributions from anharmonic three- and four-phonon processes.
Phonons crossing a material interface experience a phenomenon known as thermal boundary resistance (TBR), unlike neutrons which rely on a cross section of interaction to dictate their scattering behavior in materials. TBR occurs when phonons cross an interface; phonons are either transmitted or reflected based on probabilities which are dependent on internal energy, phonon velocity and density of states. We apply the diffuse mismatch model (DMM) to quantify the behavior of phonons at interfaces, which generates probabilities of transmission or reflection through that interface. We have implemented this method for 3D heterogeneous structures with quantized defects. These physics are necessary to include due to the highly mismatched interfaces (such as an interface between a xenon bubble and a surrounding UO lattice).
We have previously developed the capability of phonon transport in the gray approximation – analogous to one-speed thermal radiation transport. This approach is beneficial in the rapid development of methodologies but falls short in highly resolved predictions of heat flux and thermal conductivity. We leverage the multi-group capability present in Rattlesnake to simulate multi-frequency phonon transport. We take data generated through ab-initio density functional theory (DFT) simulations by our colleagues at the UC Riverside campus and integrate it into our Boltzmann phonon transport simulations. While this capability is still in development, we have simulated temperature gradients, heat flux and thermal conductivity in silicon. We can show the contribution to overall thermal conductivity from each phonon polarization, mode, frequency and predict an average value of in the material.
S. Nimmala, S. Hosseini, J. Harter, T. Palmer, E. Lenz, and P.A. Greaney, “Characterizing Macroscopic Thermal Resistance Across Contacting Interfaces Through Local Understanding of Thermal Transport”, MRS Advances, 1-7 (2018). doi: 10.1557/adv.2018.485.
J. Harter, L. de Sousa Oliveira, A. Truszkowska, T. Palmer, and P.A. Greaney, “Deterministic Phonon Transport Predictions of Thermal Conductivity in Uranium Dioxide with Xenon Impurities”, ASME. J. Heat Transfer, 140(5), 051301-051301-11 (2018). doi: 10.1115/1.4038554.
J. Harter, P. A. Greaney, and T. Palmer, “Quantifying the Uncertainty in Deterministic Phonon Transport Calculations of Thermal Conductivity using Polynomial Chaos Expansions”, Trans. Am. Nucl. Soc, 115, 611-614 (2016).
J. Harter, P. A. Greaney, and T. Palmer, “Characterization of Thermal Conductivity using Deterministic Phonon Transport in Rattlesnake,” Trans. Am. Nucl. Soc, 112, 829–832 (2015).
J. Harter, “Predicting Thermal Conductivity in Nuclear Fuels using Rattlesnake-Based Deterministic Phonon Transport Simulations”, Master’s Thesis. (2015).
J. Harter, N. Whitman, T. Palmer, and P.A. Greaney, “Deterministic phonon transport as a verification tool for spent nuclear fuel”, Institute of Nuclear Materials Management Discovery Workshop, Pacific Northwest National Laboratory, Richland, WA, May 2018.
J. Harter, T. Palmer, and P.A. Greaney, “Deterministic phonon transport and applications in nanoscale heat transfer”, University of Arizona, Tuscon, AZ, Apr 2018.
J. Harter, T. Palmer, and P.A. Greaney, “Frequency dependence in deterministic phonon transport simulations”, Applied Mathematics and Computation Seminar, Corvallis, OR, Mar 2018.
J. Harter, T. Palmer, and P.A. Greaney, “Frequency dependence in deterministic phonon transport simulations”, International Conference on Transport Theory, Monterey, CA, Oct 2017.
J. Harter, S. Hosseini, T. Palmer, and P.A. Greaney, “Deterministic Simulation of Frequency Dependent Phonon Transport in Nuclear Materials”, Materials Research Society Spring Meeting, Phoenix, AZ, Apr 2017.
I love Oregon and the west coast. I’m into fly fishing, yoga, shooting guns, cooking, H.P. Lovecraft, old science fiction, rare cooking/science books, computer games, board games, and much more.
Assistant Professor, Department of Mechanical Engineering and MS&E Program, University of California - Riverside ↩︎