| 1. |
- Brown, D. R., et al.
(författare)
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Relating phase transition heat capacity to thermal conductivity and effusivity in Cu2Se
- 2016
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Ingår i: Physica Status Solidi - Rapid Research Letetrs. - : Wiley. - 1862-6254 .- 1862-6270. ; 10:8, s. 618-621
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Tidskriftsartikel (refereegranskat)abstract
- Accurate measurement of thermal conductivity is essential to determine the thermoelectric figure-of-merit, zT. Near the phase transition of Cu2Se at 410 K, the transport properties change rapidly with temperature, and there is a concurrent peak in measured heat capacity from differential scanning calorimetry (DSC). Interpreting the origin as a broad increase in heat capacity or as a transient resulted in a three-fold difference in the reported zT in two recent publications. To resolve this discrepancy, thermal effusivity was deduced from thermal conductivity and diffusivity measurements via the transient plane source (TPS) method and compared with that calculated from thermal diffusivity and the two interpretations of the DSC data for heat capacity. The comparison shows that the DSC measurement gave the heat capacity relevant for calculation of the thermal conductivity of Cu2Se. The thermal conductivity calculated this way follows the electronic contribution to thermal conductivity closely, and hence the main cause of the zT peak is concluded to be the enhanced Seebeck coefficient.
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| 2. |
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| 3. |
- DAWODY, JAZAER, 1959, et al.
(författare)
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An integrated system for energy-efficient exhaust aftertreatment for heavy-duty vehicles
- 2015
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Ingår i: Renewable Energy in the Service of Mankind. - Cham : Springer International Publishing. - 9783319177779 - 9783319177762 ; , s. 133-143
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- © Springer International Publishing Switzerland 2015. This chapter presents a unique system approach applied in a joint academic- industrial research programme, E4 Mistra, to attain the goals of high energy efficiency and low emissions in an exhaust aftertreatment system for heavy-duty vehicles. The high energy efficiency is achieved by heat recuperation, onboard hydrogen production for NOx reduction, and by finding new solutions for making the aftertreatment system active at low exhaust temperatures. To reach low particulate emissions, a mechanical filter using a sintered metal powder is developed and coated with catalytic material to improve the soot oxidation efficiency. Low NOx emissions are achieved by an efficient NOx reduction catalyst. The integrated E4 Mistra system comprises four technological advances: thermoelectric (TE) materials for heat recuperation, catalytic reduction of NOx over innovative catalyst substrates using either the onboard diesel or biodiesel, H2 from a high-efficiency fuel reformer, and particulate filtration over a porous metal filter. The TE materials are used in a TE generator (TEG) which converts thermal energy into electricity. The TEG is used to recuperate heat from the exhaust-gas recirculation (EGR) circuit of heavy-duty trucks and is expected to generate ~1 kW electric power from 20 kW heat in the exhaust gas. The TEG is integrated in a plate heat exchanger (HEX) designed particularly for this application. Apart from the knowledge and experiences in TEG and heat exchange technologies, a thorough fluid dynamics and TE analysis are performed in this project to understand the governing processes and optimize the system accordingly. The components of the E4 Mistra system are explained in the chapter in addition to test results, which show the system's capacity for H2 production, NOx conversion, particulate matter filtration and soot oxidation, and finally electric power generation via heat recuperation from the exhaust gas using the developed TEG-HEX system.
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| 4. |
- DAWODY, JAZAER, 1959, et al.
(författare)
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E4-Mistra, a research program for the development of an energy efficient low emission exhaust aftertreatment system for heavy duty vehicles
- 2012
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Ingår i: World Renewable Energy Forum, WREF 2012, Including World Renewable Energy Congress XII and Colorado Renewable Energy Society (CRES) Annual Conference. - : American Solar Energy Society. - 9781622760923 ; , s. 4530-4536
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Konferensbidrag (refereegranskat)abstract
- This paper presents a unique system approach applied in a joint academic - industrial research program, E4 Mistra, to reach the goals of energy efficiency and low emissions exhaust aftertreatment system for heavy duty vehicles. The high energy efficiency is achieved by heat recuperation, on-board hydrogen production for use in both an auxiliary power unit and for NOx reduction and by finding new solutions for making the after-treatment system active at low exhaust temperatures. To reach low particulate emissions a mechanical filter using a sintered metal filter is developed. Low NOx emissions are achieved by an efficient NOx reduction catalyst. The system is based on four technological advances: Thermoelectric material s for heat recuperation, catalytic reduction of NOx over innovative catalyst substrates using hydrocarbons from the fuel and H2 from a high efficiency fuel reformer, and particulate filtration over a porous metal filter.
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| 5. |
- Heijl, Richard, 1984
(författare)
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Synthesis and Characterization of Composite Materials for Thermoelectric Power Generation
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In a thermoelectric material, a temperature difference will give rise to an electric potential that is proportional to the temperature gradient. In a closed circuit, this potential can keep a current flowing as long as the temperature gradient is maintained. This is a type of power conversion that has received increasingly more attention in science over the past two decades because of the world-wide growing concern for the environment and the depletion of fossil fuel resources. With thermoelectric materials it is possible to build electric power generators that run on heat. The generators can be adapted to the temperature the heat is supplied at by engineering of the thermoelectric materials used in the generator. Thermoelectric generators are therefore interesting for applications in waste heat recovery.A challenge with thermoelectric materials for power conversion is the relatively low conversion efficiency compared to their cost of fabrication. Since the mid 1990’s a number of new concepts have been introduced for the development of more efficient materials. Many of these are based on nanostructuring.Thermoelectric materials are usually semiconductors with relatively high charge carrier concentrations. The main focus of this thesis has been to explore different synthesis methods for making nanostructured composite thermoelectric materials and to analyze the effect of the obtained structures on the thermoelectric properties.Most of this thesis has been devoted to improving the clathrate Ba8Ga16Ge30 system by employing several approaches to engineering its nano- and microstructure. Different types of nanoparticles have been introduced to the clathrate matrix but also phase separation has been evaluated. It was seen that even very small amounts of nanoparticles can have dramatic effects on the thermoelectric properties. By adding TiO2 nanoparticles to Ba8Ga16Ge30 it was possible to enhance the material figure-of-merit, zT, through a reduction of the thermal conductivity as well as through a complex doping effect. For a mixed guest clathrate system with part substitution of Sr for Ba on the guest position in Ba8Ga16Ge30 it was possible to achieve a system that phase separates into Sr8Ga16Ge30 and Ba8Ga16Ge30 during cooling after heat treatment, resulting in a composite material. However, sintering of this material proved challenging and the final material had low thermoelectric performance due to high electrical resistivity and structural changes. The Mg2Si system was modified by employing different quenching procedures after heat treatment of Mg2Si0.94Sn0.06 resulting either in a solid solution or a material with a novel compositional microstructure. The microstructured material had lower thermal conductivity as well as enhanced Seebeck coefficient, resulting in improved zT.Finally, a thermoelectric module has been constructed and evaluated. The module uses Ba8Ga16Ge30 as n-type material and La-doped Yb14MnSb11 as p-type material. The tested module performed well over the whole temperature range for which it was designed, from room temperature to 800°C. However, challenges were identified in achieving good electrical contacts as well as in protecting the sensitive Yb14MnSb11 compound from oxidization and sublimation.
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| 6. |
- Heijl, Richard, 1984, et al.
(författare)
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Thermoelectric properties of Ba8Ga16Ge30 with TiO2 nanoinclusions
- 2012
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 112:4
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Tidskriftsartikel (refereegranskat)abstract
- The effects on thermal and electrical properties of adding small amounts of TiO2 nanoinclusions to bulk Ba8Ga16Ge30 clathrate have been investigated. The thermal properties were analysed using the transient plane source technique and the analysis showed a significant decrease in thermal conductivity as the volume fraction of TiO2 increased from 0 vol. % to 1.2 vol. %. The introduction of TiO2 nanoparticles caused a shift in the peak value of the Seebeck coefficient towards lower temperatures. The maximum value of the Seebeck coefficient was, however, only little affected. The introduction of TiO2 nanoparticles into the bulk Ba8Ga16Ge30 resulted in an increased electrical resistivity of the sample, thus simultaneously reducing the charge carrier contribution to the thermal conductivity, partly explaining the decrease in total thermal conductivity. Due to the large increase in resistivity of the samples, ZT was only somewhat improved for the material with 0.4 vol. % TiO2 while the ZT values of the other materials were lower than for the reference Ba8Ga16Ge30 material without TiO2 nanoparticles. The combined results are consistent with a scenario where the nanoparticle introduction causes a light doping of the semiconductor matrix and an increased concentration of phonon scattering centres.
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| 7. |
- Köhler, Elof, 1980, et al.
(författare)
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Fabrication of High Temperature Thermoelectric Energy Harvesters for Wireless Sensors
- 2013
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 476:1, s. Art. no. 012036-
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Konferensbidrag (refereegranskat)abstract
- Implementing energy harvesters and wireless sensors in jet engines could simplify development and decrease costs. A thermoelectric energy harvester could be placed in the cooling channels where the temperature is between 500–900°C. This paper covers the synthesis of suitable materials and the design and fabrication of a thermoelectric module. The material choices and other design variables were done from an analytic model by numerical analysis. The module was optimized for 600–800°C with the materials Ba8Ga16Ge30 and La-doped Yb14MnSb11, both having the highest measured zT value in this region. The design goal was to be able to maintain a temperature gradient of at least 200°C with high power output. The La-doped Yb14MnSb11 was synthesized and its structure confirmed by x-ray diffraction. Measurement of properties of this material was not possible due to insufficient size of the crystals. Ba8Ga16Ge30 was synthesized and resulted in an approximated zT value of 0.83 at 700°C. Calculations based on a module with 17 couples gave a power output of 1100mW/g or 600mW/cm2 with a temperature gradient of 200K.
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| 8. |
- Köhler, Elof, 1980, et al.
(författare)
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High temperature energy harvester for wireless sensors
- 2014
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Ingår i: Smart Materials and Structures. - : IOP Publishing. - 0964-1726 .- 1361-665X. ; 23:9, s. Art. no. 095042-
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Tidskriftsartikel (refereegranskat)abstract
- Implementing energy harvesters and wireless sensors in jet engines will simplify development and decrease costs by reducing the need for cables. Such a device could include a small thermoelectric generator placed in the cooling channels of the jet engine where the temperature is between 500-900 degrees C. This paper covers the synthesis of suitable thermoelectric materials, design of module and proof of concept tests of a thermoelectric module. The materials and other design variables were chosen based on an analytic model and numerical analysis. The module was optimized for 600-800 degrees C with the thermoelectric materials n-type Ba8Ga16Ge30 and p-type La-doped Yb14MnSb11, both with among the highest reported figure-of-merit values, zT, for bulk materials in this region. The materials were synthesized and their structures confirmed by x-ray diffraction. Proof of concept modules containing only two thermoelectric legs were built and tested at high temperatures and under high temperature gradients. The modules were designed to survive an ambient temperature gradient of up to 200 degrees C. The first measurements at low temperature showed that the thermoelectric legs could withstand a temperature gradient of 123 degrees C and still be functional. The high temperature measurement with 800 degrees C on the hot side showed that the module remained functional at this temperature.
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| 9. |
- Ma, Yi, 1982, et al.
(författare)
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Composite thermoelectric materials with embedded nanoparticles
- 2013
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Ingår i: Journal of Materials Science. - : Springer Science and Business Media LLC. - 0022-2461 .- 1573-4803. ; 48:7, s. 2767-2778
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Tidskriftsartikel (refereegranskat)abstract
- The current status of the development of composite thermoelectric materials with embedded nanoparticles is reviewed. An introduction is given to the suggested mechanisms of improving thermoelectric properties by inclusions of nanoparticles and to experimental methods used to prepare such composites. The progress made in the development of thermoelectric materials with embedded nanoparticles is then covered, grouping the studies according to the optimal temperature range of operation of the materials investigated. Most studies have been devoted to materials within the medium temperature range, followed by low temperature materials, whereas high temperature materials have not yet received much attention within this area. In the majority of the materials systems studied, reports of improved thermoelectric performance upon introduction of nanoparticles in bulk thermoelectrics are found. However, for continued progress in this area, there is a need for systematic experimental studies that unambiguously correlate the resulting physical effects of the nanoinclusions to the measured materials properties.
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