Donald A. Jordan

Reducing thermal conductivity of binary alloys below the alloy limit via chemical ordering

Substitutional solid solutions that exist in both ordered and disordered states will exhibit markedly different physical properties depending on their exact crystallographic configuration. Many random substitutional solid solutions (alloys) will display a tendency to order given the appropriate kinetic and thermodynamic conditions. Such order-disorder transitions will result in major crystallographic reconfigurations, where the atomic basis, symmetry, and periodicity of the alloy change dramatically. Consequently, the dominant scattering mechanism in ordered alloys will be different than that in disordered alloys. In this study, we present a hypothesis that ordered alloys can exhibit lower thermal conductivities than their disordered counterparts at elevated temperatures. To validate this hypothesis, we investigate the phononic transport properties of disordered and ordered AB Lennard-Jones alloys via non-equilibrium molecular dynamics and harmonic lattice dynamics calculations. It is shown that the thermal conductivity of an ordered alloy is the same as the thermal conductivity of the disordered alloy at ≈0.6T(melt) and lower than that of the disordered alloy above 0.8T(melt).

The Effect of Fill Volume on Heat Transfer From Air-Cooled Thermosyphons

The effect of fill volume on the heat transfer performance of a cylindrical thermosyphon with an aspect ratio (ratio of the length of the evaporator section to the inner diameter) of 2.33 immersed in a cooling air flow is investigated. The fill volume was systematically varied from 0% to 70.3% of the volume of the evaporator section in a copper-water thermosyphon having an inner diameter of 19 mm. The condenser section was immersed in a uniform air flow in the test section of an open return wind tunnel. The heat transfer rate was measured as a function of evaporator temperature and fill volume, and these results were characterized by three distinct regions. From 0% to roughly 16% fill volume (Region I), the low rate of heat transfer, which is insensitive to fill volume, suggests that dry out may be occurring. In Region II (extending to approximately 58% fill volume), the heat transfer rate increases approximately linearly with fill volume, and increasing evaporator temperature results in decreased rate of heat transfer. Finally, in Region III (from roughly 58–70.3%), the rate of heat transfer increases more rapidly, though still linearly, with fill volume, and increasing evaporator temperature results in increased rate of heat transfer. The thermosyphon rate of heat transfer is greatest at 70.3% fill volume for every evaporator temperature. [DOI: 10.1115/1.4023039]

Controlling Thermal Conductivity of Alloys via Atomic Ordering

Many random substitutional solid solutions (alloys) will display a tendency to atomically order given the appropriate kinetic and thermodynamic conditions. Such order–disorder transitions will result in major crystallographic reconfigurations, where the atomic basis, symmetry, and periodicity of the alloy change dramatically. Consequently, phonon behavior in these alloys will vary greatly depending on the type and degree of ordering achieved. To investigate these phenomena, the role of the order–disorder transition on phononic transport properties of Lennard–Jones type binary alloys is explored via nonequilibrium molecular dynamics simulations. Particular attention is paid to regimes in which the alloy is only partially ordered. It is shown that by varying the degree of ordering, the thermal conductivity of a binary alloy of fixed composition can be tuned across an order of magnitude at 10% of the melt temperature, and by a factor of three at 40% of the melt temperature.

Parameter estimation of spiral waves from atrial electrograms

The problem of retrieving spiral wave parameters (frequency, radial velocity, and center location) using a minimal number (4) of spatial sensors is considered. The problem has the important application of localization of spiral wave sources of atrial fibrillation from basket catheter electrograms. Numerical simulations demonstrate that our algorithm works effectively for a wide range of parameters, and for spiral waves generated by a cellular automaton model of cardiac wave propagation.

Experimental Investigation of the Heat Transfer Performance of a Hybrid Cooling Fin Thermosyphon

The effect of fill volume on the heat transfer performance of a hybrid cooling fin thermosyphon, characterized by an airfoil cross-sectional shape and a slot-shaped cavity, is investigated. The performance was examined at three fill volumes, expressed as a percentage of the evaporator section: 0%, 60%, and 240%. These were chosen to represent three distinct regimes: unfilled, filled, and overfilled evaporator sections, respectively. The cross section of this copper–water thermosyphon has a NACA0010 shape with a chord length of 63.5 mm and an aspect ratio (ratio of the length of the evaporator section to the cavity width) of 1.109. The evaporator length comprises 8.3% of the total thermosyphon length. The air-cooled condenser section was placed in a uniform air flow in the test section of an open return wind tunnel. The rate of heat transfer, or performance, was measured as a function of fill volume and evaporator temperature. The heat transfer performance increased by 100–170% by adding 0.86 ml of working fluid (de-ionized water), i.e., when the fill volume increased from 0% to 60%, which illustrates the improvement of a cooling fin’s heat transfer rate by converting it to a hybrid cooling fin thermosyphon. Of the fill volumes investigated, the thermosyphon achieves a maximum heat transfer rate and highest average surface temperature at the 60% fill volume. Overfilling the evaporator section at 240% fill results in a slight decrease in performance from the 60% fill volume. The results of this study demonstrate the feasibility of hybridizing a cooling fin to act both as a cooling fin and a thermosyphon. [DOI: 10.1115/1.4028000]

Deposition of Polypyrrole Onto Bucky Gel for Use in a Biomimetic Artificial Excitable Cell Membrane

A novel and inexpensive bucky gel electrode was investigated for use as the electrode substrate for polypyrrole deposition. Potentiostatic deposition of polypyrrole onto gold and bucky gel electrodes was carried out at +1.2 V vs. saturated calomel electrode for 1 hour in a standard 3-electrode electrochemical cell. The electroactive polypyrrole membrane was successfully deposited onto bucky gel, and its surface morphology studied using scanning electron microscopy. Given the bucky gel’s dual ability to both conduct electricity and ions, this work establishes the first step towards a semi-solid ion-gating system to be used in further applications.

Role of Chemical Ordering on Phononic Transport in Binary Alloys

Many random substitutional solid solutions (alloys) will display a tendency to chemically order given the appropriate kinetic and thermodynamic conditions. Such order-disorder transitions will result in major crystallographic reconfigurations, where the atomic basis, symmetry, and periodicity of the alloy change dramatically. Consequently, phonon behavior in these alloys will vary greatly depending on the type and degree of ordering achieved. To investigate these phenomena, the role of the order-disorder transition on phononic transport properties of Lennard-Jones type binary alloys is explored via non-equilibrium molecular dynamics simulations. Particular attention is paid to regimes in which the alloy is only partially ordered. It is shown that, through exploitation of the long-range order parameter, thermal conductivity of binary alloys can be effectively tuned across half an order of magnitude at low-to-moderate temperatures.Copyright

DEPOSITION OF POLYPYRROLE ONTO A NOVEL POLYMER ELECTRODE FOR USE IN A BIOMIMETIC ARTIFICIAL EXCITABLE CELL MEMBRANE

A novel and inexpensive bucky gel electrode has been investigated for use as the electrode substrate for deposition of polypyrrole. The electroactive polymer membrane was successfully deposited and the surface morphology studied using scanning electron microscopy. Given the properties of the bucky gel electrode and its ability to conduct ions, this work establishes the first step towards a semi-solid ion-gating system to be used in further applications.Copyright

THE EFFECT OF INTERSTITIAL LAYERS ON THERMAL BOUNDARY CONDUCTANCE BETWEEN LENNARD-JONES CRYSTALS

Thermal transport at the interface between Lennard-Jones crystals is explored via non-equilibrium molecular dynamics simulations. The vibrational properties of each crystal are varied by changing the atomic mass of the crystal. By applying a constant thermal flux across the two-crystal composite system, a steady-state temperature gradient is established and thermal boundary conductance at the interface between the crystals is calculated via Fourier’s law. With the material properties of the two crystals fixed, thermal boundary conductance can be affected by an intermediate layer inserted between the two crystals. It is found that when the interstitial layer atomic mass is between those values of the crystals comprising the interface, interfacial transport is enhanced. This layer helps bridge the gap between the different vibrational spectra of the two materials, thus enhancing thermal transport, which is maximized when the interstitial layer atomic mass approaches the average mass of the two fixed crystals. The degree of enhancement depends on the vibrational mismatch between the interstitial layer and the crystals comprising the interface, and we report an increase in thermal boundary conductance of up to 50 %. NOMENCLATURE

Innovative Configurations of Large Scale Heat Pipes

A large-scale heat pipe is one of many possible solutions to the modern day problem of quickly dissipating high amounts of concentrated heat. While heat pipes are a proven technology, little research has been directed at large-scale heat pipe systems. Two configurations of large-scale heat pipes are investigated in this study. The two configurations examined were a 2’ × 2’ heat spreader plate (a type of heat pipe) and an innovative heat pipe system that combines traditional heat pipes and heat spreader plates. The heat spreader plate, when tested, quickly becomes isothermal and works as a traditional heat pipe. This demonstrates the ability of this large-scale heat pipe configuration to work effectively to spread out high amounts of deposited heat. The experimentation on the innovative heat pipe system gave similar results, showing that the configuration works as a traditional heat pipe.Copyright