Thermal Management of Downhole Oil and Gas Logging Sensors for HTHP Applications Using Nanoporous Materials

One of the main challenges in designing oil & gas downhole wireline logging tools for high temperature and high pressure (HTHP) environments is to put together the most efficient thermal packaging to enhance the tool’s temperature survival time. In general, not all electronic components and sensors can withstand severe downhole temperature (max 500 degrees Fahrenheit). For those heat sensitive components, their electrical response and performance either decay or in some cases they completely fail when their temperature exceeds 300° F. In oil & gas wireline logging applications, the heat sensitive components can be thermally protected inside a Dewar vacuum flask that includes one or two thermal isolators and heat sinks. Cooler electronic components results in longer logging times that lead to a much higher performance and profitability. This paper first discusses the development of a one-dimensional analytical model to determine the transient temperature of heat sensitive sensors and electronic components in wireline logging tools. Second, it introduces a new and improved thermal packaging scheme based on a newly developed and commercially available nanoporous material. This material has a very low thermal conductivity and is used as a thermal shield between the outside environment and the electronics inside the flask. The new packaging scheme also includes a new design for the heat sink which is made of several solid disks separated by this nanoporous material. Results from this new design have shown roughly a 30% improvement compared with the conventional design. Results from both analytical and laboratory tests are discussed in this paper.

The Science and Technology of Al-Ga Alloys as a Material for Energy Storage, Transport and Splitting Water

Currently, there is much public discussion about the realization of a hydrogen economy as a viable alternative for future large-scale energy sources. Hydrogen as an energy source has several compelling features. For example, its gravimetric energy density is three times that of oil, its combustion and fuel cell product is usually water and, hence, does not leave a carbon footprint, and its abundance, as water is plentiful.

Growth of Carbon Nanotubes on Carbon Toray Paper for Bio-Fuel Cell Applications

In recent years carbon nanotubes have emerged as excellent materials for applications in which high surface area is required e.g. gas sensing, hydrogen storage, solar cells etc. Ultra-high surface to volume ratio is also a desirable property in the applications requiring enhanced catalytic activity where these high surface area materials can act as catalyst supports. One of the fastest developing areas needing such materials is fuel-cell. Here we investigate the process through which carbon nanotubes can be manufactured specifically to be used to increase the surface area of a carbon paper (Toray™). This carbon support is used in bio-catalytic fuel cell as an electrode to support enzyme which catalyzes the redox reaction. Deposition of nanotubes on these carbon fibers can result in great enhancement in the overall surface area to support the enzyme, which increases the reaction rate inside the fuel cell. The present paper describes a method to achieve ultra-thick growth of multiwall carbon nanotubes (MWNT) on a carbon Toray™ paper using a joule heating process and gas-phase catalyst. Using this method, we are able to achieve rapid, high-density, and uniform MWNT growth. This method is also potentially scalable toward larger-scale production.

Nitride Metal/Semiconductor Superlattices for High Temperature Direct Thermal-to-Electrical Energy Conversion

We have identified TiN/GaN and ZrN/ScN as two possible pure rocksalt structured metal/semiconductor combinations for fabrication of solid-state thermionic energy converters for high operational temperatures. The selection of the materials was constrained by issues that are critical to the integration of heterogeneous materials such as crystallographic compatibility and thermodynamic stability of the metal/semiconductor combinations at high operating temperatures. The first nitride superlattice system consists of TiN as the metal layer and GaN, in its metastable rocksalt phase, as the semiconductor layer, grown on rocksalt MgO substrates. The metastable rocksalt GaN (rs-GaN) phase is stabilized by pseudomorphic epitaxy on a metallic rocksalt TiN underlayer, and its existence has been verified using high-resolution x-ray diffraction and transmission electron microscopy. The critical thickness for the rocksalt-to-wurtzite phase transition has been empirically determined to be between 1 and 2 nm, although much thicker rocksalt GaN films, up to approximately 6 nm, can be maintained for several superlattice periods. The second pure rocksalt-structured superlattice system analyzed consists of alternating layers of metallic ZrN and semiconducting ScN. These epitaxial superlattices were grown on rocksalt MgO substrates using dc magnetron sputtering in a nitrogen-argon ambient.

Heat Conduction in Metal Hydride Nano-Particles

Metal hydrides hold significant potential for use in solid-state hydrogen storage through reversible chemical reactions of metal constituents and hydrogen. Managing heat loads in the system is critical to controlling system performance because a substantial amount of the energy content in hydrogen gas is released during the exothermic hydrogen uptake process, and this process must occur in only a few minutes for vehicle applications. These materials often are used in a powder form in which the initial particle size is 50–100 micrometers. However, as the material is cycled by hydriding (M+H2→MH) and dehydriding (M+H2←MH), particle size can decrease by several orders of magnitude. For the solid metal hydride phase, relative contributions of the electronic and phononic thermal conductivities are quantified with varying composition and particle size. Particle size effects are approximated by a boundary scattering term in the phononic thermal conductivity formulation. Also, the electronic contribution to thermal conductivity is estimated as a function of hydrogen content. The results reveal that overall thermal conductivity is highly material-specific. Materials with large electronic contributions in the pure metal state are relatively unaffected by particle size, while those with lower electronic contributions exhibit a substantial decrease in thermal conductivity with particle size.

Bi2Te3 Nanowire Array/Epoxy Composites for Thermoelectric Power Generators and Microcoolers

The thermal conductivity of a nanowire array composite is controlled by the matrix thermal conductivity and volume fraction, thus the effective thermoelectric figure-of-merit (ZT) of the composite will be reduced relative to that of the thermoelectric nanowire material alone. In this report, we demonstrate a process for fabricating nanowire array /epoxy composite with high structural integrity and low effective thermal conductivity required for thermoelectric power generation applications. Using galvanostatic electrodeposition into sacrificial porous anodic alumina (PAA) templates of 50 micron thickness, we synthesized dense (∼75% volume fraction) self-supporting nanowire arrays of textured Bi2Te3. X-ray diffraction and transmission electron microscopy analysis showed that the nanowires have <11.0> texture, the orientation that yields the highest ZT in single crystals. The nanowire array was infiltrated with SU-8 epoxy resin, a low thermal conductivity material (0.2 W/m-K) with a thermal conductivity that is about an order of magnitude lower than that of PAA (1.7 W/m-K). Scanning electron micrographs of fractured composites confirm nearly complete infiltration of SU-8 epoxy in nanowire array with good adhesion and high structural integrity.

The Effects of Particle Size, Morphology, and Mass Loading on the Reactivity of Nanocatalytic Particles

Nanocatalytic particles of Gold (Au), Platinum (Pt), and Palladium (Pd) are highly reactive at room-temperature and can be used to generate heat in micro-scale devices for portable power generation. No pre-heating is required for light-off and high steady-state operating temperatures can be sustained with high density alcohol-air premixtures. Preliminary experiments conducted in our lab and those reported by Hu and co-workers at Oak Ridge National Lab have measured peak operating temperatures ∼ 300–500 degrees Celsius using near-stoichiometric methanol/air and ethanol/air premixtures at ambient initial temperature and atmospheric pressure. The effect of particle size, morphology, mass loading, and flow residence time are reported for different mixture stoichiometries. Temperature measurements and gas species analyses are also tabulated. Interestingly, smaller particles were observed to be less reactive than larger particles for the same mass loadings for select conditions. Materials characterization of the particles has also been conducted to characterize the specific surface area of the catalyst and evaluate the importance of particle sintering, morphology changes, and particle distribution.

Effect of the Excess Volume of Lattice Defects on the Enthalpy of Formation and Desorption Temperature of Metal Hydrides

Metal and complex hydrides offer very promising prospects for hydrogen storage that reach the DOE targets for 2015. However, slow sorption kinetics and high release temperature must be addressed to make automotive applications feasible. Reducing the enthalpy of formation by destabilizing the hydride reduces the heat released during the hydrogenation phase and conversely allows desorption at a lower temperature. High-energy ball milling has been shown to decrease the release temperature, increase reaction kinetics and lower the enthalpy of formation in certain cases. Increased surface and grain boundary energy could play a role in reducing the enthalpy of formation, but the predicted magnitude is too small to account for experimental observations. As the particle and grain sizes are reduced considerably under high-energy treatments, structural defects and deformations are introduced. These regions can be characterized by an excess volume due to deformations in the lattice structure, and have a significant effect on the material properties of the hydride. We propose a thermodynamic model that characterizes the excess energy present in the deformed regions to explain the change in physical properties of metal hydrides. An experimental investigation using the TEM to study the effect of lattice deformations and other nanostructures on the desorption process is underway.

Thermionic Emission From Alkali Potassium-Intercalated Carbon Nanotube Arrays for Direct Energy Conversion

Vacuum and solid-state thermionic electron emission are potentially efficient means for converting heat or solar energy directly into electrical power. However, low work function materials must be developed before reasonable efficiency can be realized with a power generation device based on thermionic emission. In this work, carbon nanotube (CNT) arrays have been doped with potassium atoms using a two-zone vapor method to lower their work functions to 2–4 eV. We have previously shown that carbon nanotube emitters prepared in this way are stable in atmospheric air although undesirable oxide compounds can form on the carbon nanotube surface. Using a hemispherical electron energy analyzer to obtain thermionic emission energy distributions, we show that low work function emitters can be prepared from potassium-intercalated CNT mats at temperatures as low as 400°C and that emitters prepared in this way can be stable at temperatures up to 620°C.

Performance of Nanoscale Quantum Well Thermoelectrics

Alternating 10 nm thermoelectric films of N-type Si/SiGe and P-type Si/SiGe and B4C/B9C have been fabricated on various substrates, electrically joined and thermoelectric properties measured from 40°K up to 700°K. These nanoscale thermoelectric films demonstrate excellent thermoelectric power factors significantly higher than current bulk thermoelectric materials. The implications of the measured thermoelectric Seebeck coefficient data and electrical resistivity data for alternating 10 nm films that are grown to thicknesses of one to 10 microns means efficiencies of 15% at 200°C temperature differences and efficiencies of 30% at 400°C temperature differences. Utilizing Seebeck and resistivity data obtained by Hi-Z and UCSD, along with published bulk thermal conductivity data, which is conservative, unique thermoelectric module and generator concept designs for both power generation and cooling are presented over wide temperature and power ranges.