Mahder Tewolde

Fabrication of Thermoelectric Devices Using Thermal Spray: Application to Vehicle Exhaust Systems

Thermoelectric devices produce electricity directly from heat; they are small, have no moving parts, and are quiet. Commercially available thermoelectric devices, however, are expensive and labor intensive to produce, and come in very limited form factors. This article presents initial results for the use of thermal spray to directly fabricate thermoelectric devices. The target application is automotive exhaust systems and other high-volume heat sources. In this work, FeSi2 and Mg2Si metal silicides were sprayed. Characterization of the Mg2Si deposits indicates that both the thermal conductivity and the Seebeck coefficient are roughly one half the values of bulk Mg2Si. The electrical conductivity, however, is several orders of magnitude lower than bulk measurements in the literature, with likely reasons including impurities in the starting powder, oxidation during spraying, and using an undoped material. FexCo4−xSb12 skutterudite material has also been sprayed; however, not enough powder was available to fabricate samples large enough for characterization. The steps required to fabricate a thermoelectric device are presented, including the formation of the bottom and top metallic layers and the thermoelectric legs using thermal spray and laser micromachining. A technique for bridging the air gap between adjacent thermoelectric elements for the top layer based on a sacrificial filler material has also been demonstrated.

Sensors for Small Modular Reactors Powered by Thermoelectric Generators

The aim of this work is to develop thermoelectrically powered sensing and actuating devices for normal and off-normal conditions in Small Modular Reactors (SMRs). This is realized using thermoelectric generators (TEGs) placed on key reactor components such as pipes, pump housings, heat exchangers or reactor vessels to capture waste heat and produce usable electric power. The electrical power generated is used to drive sensors, signal conditioning, and wireless communication to relay critical plant information to operators and emergency crew. Surplus power can be stored in batteries and/or super capacitors for actuation and other high-current, short-duration power needs. A review of key SMR reactor types and candidate locations for installing these devices is presented. The design and manufacturing process of an integrated TEG assembly that attaches to a schedule 40 steam pipe and preliminary test data of the system from an installation performed on a conventionally-fueled cogeneration power plant located on site are presented. The nominal pipe temperature is 350°C, and the assembly is designed to reduce the temperature to 230°C on the hot side of the TEG. A cold side temperature of 70°C was obtained using a large heat sink cooled by natural convection to the ambient. Designs for an enclosure system are also presented to protect the electrical components from fire and radiation.Copyright

High-resolution meter reading system for gas utility meter

This paper presents the design and implementation of a high-resolution automated metering system for a residential natural gas meter. This new high resolution sensing technique can non-intrusively monitor the gas consumption of individual appliances in a home by resolving small amounts of gas usage. It relies on utilizing an existing meter that will be retrofitted with a module that includes a high-resolution encoder to collect gas flow data and a microprocessor to analyze and identify ap-pliance load profiles. Additional benefits of the system include the ability to detect very small leaks and theft, efficiency analysis, and real time customer feedback of gas usage. The system has the potential for wide scale market adoption.

Thermoelectric Properties of Magnesium Silicide Depositedby Use of an Atmospheric Plasma Thermal Spray

The thermoelectric properties of magnesium silicide (Mg2Si) samples prepared by use of an atmospheric plasma spray (APS) were compared with those of samples prepared from the same feedstock powder by use of the conventional hot-pressing method. The characterization performed included measurement of thermal conductivity, electrical conductivity, Seebeck coefficient, and figure of merit, ZT. X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive x-ray spectroscopy (EDX) were used to assess how phase and microstructure affected the thermoelectric properties of the samples. Hall effect measurements furnished carrier concentration, and measurement of Hall mobility provided further insight into electrical conductivity and Seebeck coefficient. Low temperature and high velocity APS using an internal-powder distribution system achieved a phase of composition similar to that of the feedstock powder. Thermal spraying was demonstrated in this work to be an effective means of reducing the thermal conductivity of Mg2Si; this may be because of pores and cracks in the sprayed sample. Vacuum-annealed APS samples were found to have very high Seebeck coefficients. To further improve the figure of merit, carrier concentration must be adjusted and carrier mobility must be enhanced.

High-resolution meter reading technique for appliance gas usage monitoring for the smart grid

The smart grid is a rapidly emerging field that aims to modernize the distribution and delivery of electricity, water and gas utilities. A key component in the smart grid is the smart meter, which is installed at utility endpoints for usage monitoring and billing. Currently electric meters have received the majority of research attention and focus. However, smart gas meters will also play an important role in the emerging smart grid. This paper presents a high-resolution automated gas meter reading system for residential households. The system can be used to non-intrusively monitor the natural gas consumption of individual appliances in a home. It is implemented by utilizing an existing gas meter retrofitted with a module that includes a high-resolution encoder to collect gas flow data and a microprocessor to analyze and identify appliance load profiles. Additional benefits of the system include the ability to detect very small leaks and theft, perform efficiency analyses, and provide real time customer feedback on gas usage.

Laser Processing of Thermal Sprayed Coatings for Thermoelectric Generators

Recent research has shown that thermal spray has the potential to fabricate thermoelectric devices at low cost and high volumes. An integral aspect of the device fabrication is laser processing of the various thermal sprayed layers, which is used to form electrically isolated regions and minimize heat loss to adjacent structures. In this article, experimental results are presented for the laser patterning of thermal spray samples ranging from 50μm to 2mm in thickness. The optimization of process parameters is important for successful electrical isolation and high-quality features. In this study results are presented several short-pulse lasers (nanosecond and picosecond) in which laser power, laser wavelength, type of focusing lens, processing speed, repetition rate, and pressure and flow of purge gas were varied. The optimum laser parameters were those that minimize the heat affected zone and delamination due to thermal damage while providing maximum material removal. The resulting laser patterns were characterized using both optical and scanning electron (SEM) microscopy, and by verifying electrical isolation between patterned regions using contact resistance measurements. Cut quality attributes including kerf width and edge profile were also studied, and their dependence on process parameters reported.Copyright

Laser Processing of Multilayered Thermal Spray Coatings: Optimal Processing Parameters

Laser processing offers an innovative approach for the fabrication and transformation of a wide range of materials. As a rapid, non-contact, and precision material removal technology, lasers are natural tools to process thermal spray coatings. Recently, a thermoelectric generator (TEG) was fabricated using thermal spray and laser processing. The TEG device represents a multilayer, multimaterial functional thermal spray structure, with laser processing serving an essential role in its fabrication. Several unique challenges are presented when processing such multilayer coatings, and the focus of this work is on the selection of laser processing parameters for optimal feature quality and device performance. A parametric study is carried out using three short-pulse lasers, where laser power, repetition rate and processing speed are varied to determine the laser parameters that result in high-quality features. The resulting laser patterns are characterized using optical and scanning electron microscopy, energy-dispersive x-ray spectroscopy, and electrical isolation tests between patterned regions. The underlying laser interaction and material removal mechanisms that affect the feature quality are discussed. Feature quality was found to improve both by using a multiscanning approach and an optional assist gas of air or nitrogen. Electrically isolated regions were also patterned in a cylindrical test specimen.

Laser-assisted manufacturing of thermal energy devices

In this study, we will present recent progress in the laser-assisted manufacturing of thermal energy devices that require suppressed thermal transport characteristics yet maintaining other functionalities such as electronic transport or mechanical strength. Examples of such devices to be demonstrated include thermoelectric generator or insulating materials. To this end, it will be shown that an additive manufacturing approaches can be facilitated and improved by unique processing capabilities of lasers in composite level. In order to tailor thermal characteristics in thermal devices, we will mainly investigate the potential of laser heating, curing, selective removal and sintering processes of material systems in the composite level.

Multifunctional magneto-plasmonic nanotransducers for advanced theranostics: synthesis, modeling and experiment

In this work, nano-transducers with a superparamagnetic iron oxide (SPIO) core have been synthesized by preparation of precursor gold nanoseeds loaded on SPIO-embedded silica to form a gold nanoshell. The goal is for such nanotansducers to be used in theranostics to detect brain tumors by using MRI imaging and then assist in their treatment by using photothermal ablation. The iron oxide core provides for the use of a magnetic-field to guide the particles to the target (tumor) site. The gold nanoshell can be then readily heated using incident light and/or an alternating magneticfield. After synthesis of nano-transducer samples, Transmission Electron Microscopy was employed to analyze the formation of each layer. Then UV spectroscopy experiments were conducted to examine the light absorbance of the synthesized samples. The UV-visible absorption spectra shows a clear surface plasmon resonance (SPR) band around 530 nm, verifying the presence of gold coating nanoshells. Finally photothermal experiments using a high-power laser beam with a wavelength of 527 nm were performed to heat the samples. It was found that the temperature reaches 45° C in 12 minutes.

Thermoelectrically Powered Sensing for Small Modular Reactors

This project aims to develop thermoelectric generator (TEG)-based devices for sensing during normal and off-normal conditions in Small Modular Reactors (SMRs). TEGs will be placed on key reactor components including pipes, pump housings, heat exchangers and reactor vessels. The heat is conducted by heat pipes to the TEGs and removed by a heat sink in natural convection. The electrical power generated by is then used to drive sensors and wireless communications. The estimated power generated by one TEG is 19 W, and sensors with related circuit only require less than 7 W. Extra power can be stored into batteries and used for actuation and similar high-current, short duration power needs. Initial enclosure designs are also presented to protect the electrical devices from fire, force, water, and radiation. Preliminary experiments have been set up for testing TEGs. An experimental test stand design has been simulated, and is now being built. Radiation dosage at different locations and its effects on electrical devices and TEGs are also investigated. A fin analysis of the cooling side of the TEG is also presented. According to the results, the annular finned-tube with an inner pipe diameter of 58 cm can provide a maximum heat dissipation of 1,700 W.Copyright