ICMCTF2012 Session TS1-1: Surface Engineering for Thermal Transport, Storage and Harvesting

Wednesday, April 25, 2012 1:50 PM in Room Sunset

Wednesday Afternoon

Time Period WeA Sessions | Abstract Timeline | Topic TS1 Sessions | Time Periods | Topics | ICMCTF2012 Schedule

Start Invited? Item
1:50 PM TS1-1-1 Textured CrN Thin Coatings Enhancing Heat Transfer in Nucleate Boiling Processes
ElenaMaja Slomski, Matthias Oechsner, Sebastian Fischer, Peter Stephan, Herbert Scheerer, Torsten Troßmann (Technische Universitat Darmstadt, Germany)
Subsequent research work aims to investigate the potential of PVD thin coatings for new fields of application. The present study is based on measurements of electrical conductivity, light absorption and thermodynamic nucleate boiling tests of specific textured Cr/CrN-coatings with predominant (1 1 1), (3 1 1) or (2 0 0), (2 2 0) crystal lattice orientations. Those tests reveal promising results concerning thin film applications in the field of heat transfer enhancement during nucleate boiling. High Power Impulse Magnetron Sputtering (HiPIMS) in combination with Direct Current Magnetron Sputtering (DCMS) was applied to deposit CrN coatings of 3-4 µm thickness on different substrate materials. An ultrathin coating of pure Cr was used as adhesive interlayer between substrate and CrN coating. The crystallographic phases and orientations of the coatings were determined by X-ray analyses (XRD) using glancing-incidence and θ /2 θ mode and texture coefficients were calculated. High resolution scanning electron microscope (SEM) analyses visualize the different shapes, sizes and orientations of the grains. Finally selected Cr/CrN coatings were deposited on heater samples and boiling curves were measured in nucleate boiling experiments in order to determine heat transfer coefficients and critical heatflux (CHF) at dryout of the heater surface. Results show an up to 2.2 times higher CHF of the coated heater, compared to an uncoated pure copper heater.
2:10 PM TS1-1-2 Effects of strain on thermal conductivity in amorphous thin films
M. Alam, M. Manoharan (Penn State Unviersity, Mechanical & Nuclear Engineering Department); Sergei Shenogin (UES/Air Force Research Laboratory, Materials and Manufacturing Directorate, Thermal Sciences and Materials Branch, US); Andrey Voevodin, Ajit Roy, Christopher Muratore (Air Force Research Laboratory, Materials and Manufacturing Directorate, Thermal Sciences and Materials Branch, US); Aman (M.A.) Haque (Penn State University, Mechanical & Nuclear Engineering Department, US)

To investigate mechanisms of thermal conductivity in amorphous materials, we developed a technique for microfabricating freestanding ultrathin films with built-in strain actuation and instrumentation for thermal conductivity measurement. Using a combination of infrared thermal micrography, 3-omega analysis, and multi-physics simulations, we measured the thermal conductivity of amorphous silicon nitride and silicon oxide films under a range of tensile strains. The thermal conductivity of the silicon nitride film showed a remarkable decrease with tensile strain, dropping down by an order of magnitude at approximately 2% strain when compared to the unstrained film. Silicon oxide showed no change in thermal conductivity up to 1% tensile strain. The theoretical analysis was performed using classical molecular dynamics and lattice dynamics simulations, showing that amorphous silicon nitride has unusual vibrational properties resembling those of amorphous silicon and other chemically uniform glasses. The unusual relationship between strain and thermal conductivity in amorphous silicon nitride suggests that an additional mechanism such as long-range unharmonic coupling between oscillators plays an important role in heat conduction, as the conductivity agrees with harmonic theory predictions at large values of tensile strain (>2%). This work is supported by AFOSR Low Density Materials Program,Task #2306CR7P.

2:30 PM TS1-1-3 Surface engineering for improved thermal transport at metal/carbon interfaces
Sergei Shenogin (UES/Air Force Research Laboratory, Materials and Manufacturing Directorate, Thermal Sciences and Materials Branch, US); Jamie Gengler (Spectral Energies, LLC/Air Force Research Laboratory, Thermal Sciences and Materials Branch, US); Jianjun Hu, John Bultman (UDRI/Air Force Research Laboratory, Thermal Sciences and Materials Branch, US); Amber Reed, Andrey Voevodin, Ajit Roy, Christopher Muratore (Air Force Research Laboratory, Materials and Manufacturing Directorate, Thermal Sciences and Materials Branch, US)
Carbon nanotubes are appealing for diverse thermal management applications due to their high thermal conductivity (as high as 3,000 W m-1 K-1) coupled with interesting mechanical properties (super-strong, but also exhibiting foam-like deformation in CNT arrays). Unfortunately, CNT surfaces are generally non-reactive and demonstrate weak bonding to other materials, limiting thermal interfacial conduction. To better understand the nature of interfacial resistance in carbon nanotubes, modeling and experimental studies investigating engineered interfaces on highly oriented pyrolytic graphite (HOPG) substrates were conducted. This substrate was selected as a practical 2-dimensioinal analog for nanotube sidewalls to facilitate modeling and experimentation, however there are differences between HOPG and CNTs which are addressed in simulations to account for differences in metal-carbon interfaces. Measurements of thermal conductance at these interfaces were made by analysis of the two-color time domain thermoreflectance (TDTR) data from the samples. The TDTR analysis of the different metals on HOPG was made possible by having an optical parametric oscillator on the probe beam which allows for tuning the probe beam wavelength to match absorption bands for each metal studied. Metal films were selected to identify effects of atomic mass, chemical interactions (i.e., interfacial carbide formation) and electron configuration. Measurements of chemically “inert” metals at the carbon interface, including Al, Cu and Au demonstrated a strong dependence on Debye temperature, with conductance values differing by a factor of 3. For metals known to exhibit in situ formation of an interfacial carbide layer when in contact with a carbon substrate, such as titanium and boron, conductance values were roughly a factor of 4 higher than for inert metals. The effects of thermal formation of interfacial carbide layers with varied areal densities on HOPG surfaces on thermal conductance were also examined, in addition to metal interlayers specifically selected for acoustic matching to other materials, as in a composite structure. This work is supported by AFOSR Low Density Materials Program, Task #2306CR7P.
2:50 PM TS1-1-4 Heat flow across heterojunctions: Toward useful nanoscale thermal interface materials
Timothy Fisher, Stephen Hodson, Anurag Kumar (Purdue University, US); Andrey Voevodin (Air Force Research Laboratory, US)

Improved understanding of thermal energy transport at nanometer scales has enabled a broad range of technological advances in recent years. Today, new materials can be designed at the atomic level and are projected to improve the efficiency of information processing, heat transfer, and energy conversion, among other applications relevant to aerospace vehicles and systems. For the transfer of energy by phonons, approaches based on atomistic Green’s functions have been recently developed and offer the possibility of including atomic-scale detail at material interfaces, while mesoscopic scales can be modeled with the particle-based Boltzmann transport equation. This review will summarize a framework for the inclusion of such high-fidelity atomistic modeling within multi-scale modeling tools that are needed to understand complex interfacial transport processes and scaling principles in thermal interface materials enhanced with carbon nanotubes (CNTs). Experimental validation and refinement on model components is essential to this work, and includes highly localized techniques such as transient thermoreflectance techniqes, as well as traditional 1D reference bar approaches to assess overall performance. As an example of recent work, we briefly describe critical results related to contact resistance measurements with CNT arrays and other graphene-based structures. The talk will conclude with enumeration of important questions related to heterojunction bonding and materials processing for scaled-up manufacturing.

3:30 PM TS1-1-6 Factorial increases in interfacial thermal conductance using a monolayer
Peter O'Brien, Sergei Shenogin, Jianxiun Liu, Masashi Yamaguchi, Pawel Keblinski, Ganpati Ramanath (Rensselaer Polytechnic Institute, US)
Manipulating interfacial thermal transport is a compelling need for a number of technologies including nanoelectronics and biomedical devices, solid-state lighting, energy generation, nanocomposites, and device packaging. Here, we demonstrate that introducing a strongly-bonding organic nanomolecular monolayer (NML) at a metal-dielectric interface leads to a factor of four increase in the interfacial thermal conductance to values as high as 450 MW/m2-K. Molecular dynamics simulation and a vibrational analysis of NML-tailored interfaces verify that this remarkable interfacial conductance enhancement is due to strong NML-silica and NML-metal bonding. The strong overlap of broadband low-frequency vibrational states at the interface further facilitates efficient heat transfer through the molecules comprising the NML. These results provide a rational means of increasing heterointerfacial thermal conductance through molecular functionalization with adhesion-enhancing functional groups for a wide variety of material systems and applications.
3:50 PM TS1-1-7 Ruthenium organometallic complexes with photo-switchable wettability for boiling heat transfer applications
Chad (C.) Hunter (Air Force Research Laboratory, Materials and Manufacturing Directorate, Thermal Sciences and Materials Branch, US); David (D.) Turner (Universal Technology Corporation, US); Nicholas (N.) Glavin (Air Force Research Laboratory, Materials and Manufacturing Directorate, Thermal Sciences and Materials Branch, US); Michael Jespersen (University of Dayton Research Institute, US); Michael Check, Shawn Putnam (Universal Technology Corporation, US); Andrey Voevodin (Air Force Research Laboratory, Materials and Manufacturing Directorate, Thermal Sciences and Materials Branch, US)

Liquid to vapor phase change technology utilizing latent heat of vaporization, which can have heat transfer rates orders of magnitude higher than single phase liquid cooling, is necessary for advanced aircraft due to the onboard heat generated by high power (electrical and chemical) components. The wettability of engineered surfaces used in these cooling systems, in addition to other parameters such as surface roughness, is strongly correlated to the performance of the heat exchanger systems that use these materials. In addition to optimizing performance using passive means (e.g., surface texturing), it would also be advantageous to control heat transfer rates using applied stimuli (e.g., light or sound waves), which could result in weight savings and/or energy optimization. Oxide photocatalysts have been investigated to influence boiling performance on surfaces1, but time scales for switching between wettability states are on the order of tens of minutes to hours, much longer than for practical use to control boiling processes. In previous work, synthesis of [Ru(bpy)2(pox)]Cl2, an organometallic complex which undergoes reversible photo-isomerization that changes the inherent water affinity of the molecule, was achieved2. In the current research, new ruthenium-centered organometallic complexes with functionalized bipyridine (bpy) ligands are synthesized. The functionalization allows the Ru complexes to be covalently tethered to metallic substrates. Surface chemistry is investigated with XPS, indicating a character of the bonding linkage, which is then correlated with contact angle measurements of the surface energy modification with and without UV-VIS light irradiation. Water boiling heat transfer studies during UV-VIS light irradiation are conducted on these samples and correlated with the reversible switching of surface wetting.

1Takata, et al., International Journal of Chemistry Research, 2003.

2D.B. Turner, et al., Inorganic Chemistry, in preparation.
4:10 PM TS1-1-8 From hard coatings to thermoelectrics: effects of nanostructure on fundamental physical properties of transition metal nitride, oxide, and oxynitride thin film alloys
Brandon Howe (Air Force Research Laboratory, US)

Recent advances in aerospace and defense technologies have lead to an increasing need to develop novel materials with exotic physical properties for use in a variety of applications involving extreme, high-temperature, high mechanical stress, and oxidizing environments. Transition metal nitrides (TMN), oxides, and oxynitrides are well known to have remarkable range of unique physical properties including high hardness and mechanical strength, high melting temperatures (>>2000 °C), and tunable optical-electronic properties. One method to further enhance the physical properties of many binary transition metal nitrides is to alloy them with a second thermodynamically immiscible nitride to form metastable compounds with enhanced physical properties. Many of these properties are accompanied by the formation of nanoscale compositional modulations during film growth as well as post annealing experiments, however, very little has been reported on the ability to control this nanostructure, and as a result, the effects of these nanostructures on fundamental physical properties is relatively unknown.

Nanostructuring methods using these kinetically-limited growth techniques involving high-flux low-energy ion bombardment during film growth, lead to a unique independent control of both electric and thermal transport. The right materials system, combined with said growth techniques, would allow for the realization of hard, chemically inert, environmentally-friendly, and refractory thermal-to-electrical energy conversion thin films materials to tackle a variety of demanding defense applications.

I have used Hf1-xAlxN as a model system to study the nanostructures of interest. I begin by reporting on the effects of nanostructure on the optical, electronic, thermal transport and elastic constant properties of Hf1-xAlxN single crystal layers grown on MgO(001) by reactive unbalanced magnetron cosputtering using ellipsometry, temperature dependent hall effect, picosecond probe thermoreflectance and acoustic transport measurements, respectively. I will also present thermal transport studies of nanocrystallione SrTiO3 (a promising oxide thermoelectric) and SrTiO3/TiO2 systems, as a first step towards understanding thermal and electron transport in nanostructured oxide thin films.

4:30 PM TS1-1-9 Modified Lithium Alanate for High-Capacity Thermal Energy Storage
Placidus Amama (Air Force Research Laboratory, US); John Grant (UDRI/Air Force Research Laboratory, Thermal Sciences and Materials Branch, US); Patrick Shamberger, Andrey Voevodin (Air Force Research Laboratory, US); Timothy Fisher (Purdue University, US)

The development of novel and efficient thermal energy storage (TES) materials is a major challenge in addressing needs in a variety of applications, from intermittent solar energy harvesting to thermal management of transient, high-flux heat loads. Lithium alanate (LiAlH4) is a potential TES material that possesses extraordinarily high inherent thermal energy density, and the possibility of a system that is compact and lightweight. However, the high desorption temperature at atmospheric pressure and slow kinetics represent significant challenges to the use of this material for TES. In order to address these challenges, the present work focuses on the modification of LiAlH4 via high-energy ball milling with Ti-based catalysts, resulting in nanoscale features. The doping of LiAlH4 with Ti-based catalysts has resulted in improved thermal energy storage properties. Quasi in situ X-ray photoelectron (XPS) study of the dehydrogenation reaction of LiAlH4 has provided new insights into the role of the catalysts.

5:10 PM TS1-1-11 Heat reduction of concentrator photovoltaic module using high radiation coating
Kensuke Nishioka, Yasuyuki Ota (University of Miyazaki, Japan); Kazuyuki Tamura, Kenji Araki (Daido Steel Co., Ltd., Japan)

Light concentration is important for the development of advanced PV system using high efficiency solar cells. High efficiency multi-junction cells under high concentration operations have been investigated for terrestrial application. Also, low concentration operations with multi-junction cells have been investigated for space satellite. It is considered that the temperature of solar cells considerably rises under light concentrating operations.

It is very important for concentration photovoltaic (CPV) modules to decrease their temperature. A heat release from aluminum chassis of CPV module should be enhanced. In this study, a heat radiation layer was coated on the aluminum chassis of CPV module, and the effect of the layer on cell temperature was evaluated and discussed.

A CPV module consisted of 25 pairs of Fresnel lens (160 mm x 160 mm) and triple-junction solar cell (7 mm x 7mm), and an aluminum chassis was used. A heat radiation layer (PELNOX LTD., PELCOOL(R)) was coated on the aluminum chassis of CPV module. The triple-junction solar cells were arrayed on the aluminum chassis. In order to detect the cell temperature, a Pt100 was embedded just below the triple-junction solar cell. A CPV module was fabricated by connecting 25 lens-cell pairs in series.

The cell temperature of CPV module with heat release coating was about 15K lower than that without coating. The effect of the high radiation layer was remarkable, and the output powers of the CPV module with and without coating were 170.7 W and 162.4 W, respectively.

This study was carried out in Japan. Since the effect of the high radiation layer becomes remarkable, as the temperature of the heat source is higher, it can be expected that the high radiation coating for the CPV module works more effectively in more higher temperature area.

Time Period WeA Sessions | Abstract Timeline | Topic TS1 Sessions | Time Periods | Topics | ICMCTF2012 Schedule