| 1. |
- 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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| 2. |
- Cederkrantz, Daniel, 1979, et al.
(författare)
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Enhanced thermoelectric properties of Mg2Si by addition of TiO2 nanoparticles
- 2012
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 111:2
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Tidskriftsartikel (refereegranskat)abstract
- The effects on the thermoelectric properties of Mg2Si when adding TiO2 nanoparticles have been evaluated experimentally. A batch of Mg2Si was prepared through direct solid state reaction and divided into portions which were mechanically mixed with different amounts of TiO2 nanoparticles ranging from 0.5 to 3 vol% and subsequently sintered to disks. All materials showed n-type conduction and the absolute value of the Seebeck coefficient was reduced with increasing amount of TiO2 added, while the electrical resistivity was greatly reduced. The thermal conductivity was surprisingly little affected by the addition of the nanoparticles. An optimum value of the thermoelectric figure-of-merit ZT = TS2 sigma/k was found for the addition of 1 vol% TiO2, showing almost three times higher ZT value than that of the pure Mg2Si. Larger TiO2 additions resulted in lower ZT values and with 3 vol% added TiO2 the ZT was comparable to the pure Mg2Si. The sintering process resulted in reduction or chemical reaction of all TiO2 to TiSi2 and possibly elemental titanium as well as reduced TiOx. The increased electrical conductivity and the decreased Seebeck coefficient were found due to an increased charge carrier concentration, likely caused by the included compounds or titanium-doping of the Mg2Si matrix. The low observed effect on the thermal conductivity of the composites may be explained by the relatively higher thermal conductivity of the included compounds, counter-balancing the expected increased grain boundary scattering. Alternatively, the introduction of compounds does not significantly increase the concentration of scattering grain boundaries.
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| 3. |
- Cederkrantz, Daniel, 1979
(författare)
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Synthesis and Characterization of New Inorganic Thermoelectric Materials
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- With thermoelectric materials it is possible to convert a difference in temperature into electrical energy. This can be utilized for a more efficient use of available energy, eg. by converting waste heat from a combustion process. Based on recent theoretical predictions, there is a renewed interest to find and develop new and more efficient thermoelectric materials, improving this potential even further. To do this the thermoelectric properties, thermopower, electrical and thermal conductivity, must be optimized. There are a number of possible ways to achieve this, among them nanostructuring to reduce thermal conductivity, doping to improve electrical properties and crystal structure optimization to potentially improve all properties. For this, it is essential to have the appropriate tools for accurate characterization of these material properties. Thermoelectric properties may be determined using different analytic techniques and it is therefore important that these are compared to assess their level of agreement.Synthesis and characterization of new thermoelectric materials have been the aim of this thesis. Work to improve the thermoelectric properties of Ba8Ga16Ge30 and Mg2Si through substitution and nanoinclusions have been performed as well as studies of the thermal stability of p-type Ba8Ga16Ge30. It is shown that p-type Ba8Ga16Ge30 is not stable above 400°C, in fact it is possible to change the doping from p- to n-type through thermal treatment of the material. Substituting Ge with Zn in n-type Ba8Ga16Ge30 results in slight improvement of ZT in the low to intermediate temperature range, which likely could be further improved with optimization of the system. With TiO2 nanoparticles added to Ba8Ga16Ge30 some improvements of ZT were recorded and a complex effect on the charge carrier concentration in the material was observed. The thermoelectric properties of Mg2Si were improved after addition of TiO2 nanoparticles, even though TiO2 was completely reduced or reacted to metallic Ti and TiSi2. The charge carrier concentration of the titanium-containing Mg2Si material was improved, likely through doping of the material. The Laser Flash (LFA) and Transient Plane Source (TPS) techniques for thermal conductivity measurements have been evaluated and compared. The methods were concluded to be comparable, with the TPS technique requiring larger sample specimens for materials with high thermal conductivity and the LFA method sometimes suffers from with compromised surface coating and only indirectly measuring thermal conductivity.
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| 4. |
- Cederkrantz, Daniel, 1979, et al.
(författare)
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Thermal stability and thermoelectric properties of p-type Ba8Ga16Ge30 clathrates
- 2009
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 106:7, s. 074509 (artno)-
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Tidskriftsartikel (refereegranskat)abstract
- The thermal stability of p-type Ba(8)Ga(16)Ge(3)0 clathrates grown from gallium flux has been tested by heat treatment in low pressure Ar atmosphere at 400, 600, and 800 degrees C. Significant gallium loss was observed for all samples during heat treatment. The treatment at 400 degrees C does not significantly change the sample properties, and the samples remain p-type and comparable to the untreated, as-prepared, sample. At 600 degrees C the sample switches from extrinsic p-type to extrinsic n-type, presumably due to significant loss of Ga, and shows a high thermopower but a reduced electrical conductivity compared to as-made n-type samples. Surprisingly, after a thermal treatment at 800 degrees C, the crystal structure seemingly loses less Ga, only reducing the hole concentration to near intrinsic levels and thus has a negative impact on ZT. Regardless of the heat treatment temperature of the p-type samples the thermal conductivity remained exceptionally low, for some samples 0.9 W/m K. Heat treatment can thus greatly affect the thermoelectric properties of p-type Ba(8)Ga(16)Ge(3)0, but the crystal structure remains intact. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3236635]
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| 5. |
- Cederkrantz, Daniel, 1979
(författare)
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Thermoelectric Ba8Ga16Ge30 clathrates for waste heat recovery
- 2010
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The modern, highly industrialized, society of today requires huge amounts of energy to function. This has resulted in a heavy dependence on the very energy efficient fossil fuels, a source of energy which of course is not infinite and we are slowly approaching the day when oil runs out. As a result of this dependence on fossil fuels we see steadily increasing energy prizes and environmental problems related to the combustion of these fuels. One way of improving fuel economy is to recycle the waste heat produced in all combustion processes. In a normal combustion engine only about one third of the energy released is transformed into usable energy while two thirds are lost as waste heat. To reduce these losses thermoelectric materials can be used to transform some of this waste heat to electrical energy, which can be stored in batteries or used directly.In this thesis the thermoelectric material Ba8Ga16Ge30 is studied with the aim of using it for waste heat recovery in heavy trucks. The materials has been synthesised with direct solid state reaction of pure elements and the phase purity has been investigated with powder XRD analysis. The thermoelectric properties which determine the efficiency of the material have been carefully studied using several methods. Seebeck coefficient and electrical resistivity have been measured with both commercial equipment and laboratory setups, the former utilizing a small ΔT differential method and the four-point-probe while the latter using a light-pipe system and the van der Pauw technique. The thermal conductivity was investigated with two different techniques, the laser flash method and the transient plane source technique. With the help of these techniques the thermal stability of the p-doped version of Ba8Ga16Ge30 has been mapped out, revealing irreversible material property transformations at temperatures above 400°C. At 600°C a transformation from p- to n-type was observed while treatment at 800°C resulted in a close to intrinsic material. Also the effects of partially substituting Ga or Ge in the n-type Ba8Ga16Ge30 with Sb or Zn have been studied. Here it was seen that partially substituting Ge with Zn results in enhanced thermopower and reduced thermal conduction, improving the materials thermoelectric potential up to around 400°C. Partially substituting Ga with either Sb or Zn results, however, in an unexpected deterioration of all thermoelectric properties, including a curious simultaneous increase in both thermal conduction and electrical resistance. Keywords: Clathrates, Ba8Ga16Ge30, waste heat recovery, thermal stability, semiconductors, substitution, Seebeck coefficient, electrical resistance, thermal conductivity
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| 6. |
- Cederkrantz, Daniel, 1979, et al.
(författare)
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Thermoelectric properties of partly Sb- and Zn-substituted Ba8Ga16Ge30 clathrates
- 2010
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 108:11, s. 113711-
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Tidskriftsartikel (refereegranskat)abstract
- The effects on the thermoelectric properties of n-Ba8Ga16Ge30 when substituting small amounts of the Ga or Ge with Sb or Zn have been investigated. A number of syntheses were prepared in quaternary systems of Ba8Ga16Ge30 substituted with either Sb or Zn but only three samples were found to yield single phase products with nominal compositions of Ba8Ga15Sb1Ge30, Ba8Ga15Zn1Ge30 and Ba8Ga16Ge28Zn2, respectively. When Ge was substituted for Zn the resulting sample remained n-type and an increase in thermopower and a decrease in thermal conductivity were achieved. These positive effects were accompanied with an increased electrical resistivity and thus the ZT was only somewhat improved up to about 400 °C. When substituting Ga with either Sb or Zn samples remained n-type but showed decreased thermopower and increased electrical resistivity and thermal conductivity. It is thus concluded that substitution of Ga with Zn or Sb is detrimental for the thermoelectric properties of Ba8Ga16Ge30, whereas substitution of Ge with Zn appears a potent method for improving its performance.
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| 7. |
- Hanstorp, Karl, et al.
(författare)
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Numerical Simulation and Experimental Scheme for Monitoring Hoof Wall Structure and Health in Sport Horses
- 2016
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Ingår i: Proceedings of the 4th International Congress on Sport Sciences Research and Technology Support. - : SCITEPRESS - Science and Technology Publications. - 9789897582059 ; , s. 171-175
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Konferensbidrag (refereegranskat)abstract
- This study provides a computational model developed to demonstrate the possibility of monitoring hoof structure and health in equestrian sport. This is achieved by employing finite element simulation of threedimensional heat flow from a surface heat source into a hoof structure while simultaneously sensing the surface temperature. The time evolution of the recorded surface temperature, transient curve, is used to investigate hoof structure and predict its intactness by comparing these curves for three different models. We have observed differences between the transient curves obtained from a normal hoof structure, a hoof structure containing a foreign material and hoof capsule subjected to wall separation. An experimental method for probing hoof profile was briefly discussed. It uses temperature sensor/heat source. The method can determine the thermal conductivity of the hoof along the hoof structure from the recorded transient curve. Thus, it displays the hoof structure by utilizing the thermal conductivity variation between the hoof parts.
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| 8. |
- 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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| 9. |
- Mekonnen Mihiretie, Besira, 1983, et al.
(författare)
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Finite element modeling of the Hot Disc method
- 2017
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Ingår i: International Journal of Heat and Mass Transfer. - : Elsevier BV. - 0017-9310. ; 115, s. 216-223
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Tidskriftsartikel (refereegranskat)abstract
- The Hot Disc method, also known as the transient plane source (TPS) technique, is an experimental approach to determine the thermal transport properties of materials. The core of the method is the Hot Disc sensor, an electrically conducting metallic strip, shaped as a double spiral clad with a protective polymer film. The mean temperature increase in the sensor has been approximated from various analytical approaches such as: the concentric ring sources model, the thermal quadrupoles formalism, and concentric circular strips structure approach. However, full numerical simulation of the sensor has not been addressed so far. Here we develop a 3D model of Hot Disc sensors and compare simulated mean temperature increase to experimental recordings. Joule heating coupled with heat transfer of solids (of COMSOL Multiphysics software) is used to simulate the working principle of the sensor. The volume mean temperature increase in the sensor from the simulations proves to be in a good agreement with the corresponding experimental recordings. The temperature distributions of the metallic strip are also evaluated and discussed with respect to the previous experimental findings. Furthermore, the current distribution across the strip is obtained. Such simulation can potentially be used in further optimizing geometry and parameter estimation.
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| 10. |
- Mekonnen Mihiretie, Besira, 1983, et al.
(författare)
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SIMULATION OF THE HOT DISK SENSOR: TEMPERATURE AND ELECTRIC CURRENT DISTRIBUTION
- 2017
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Ingår i: Proceedings of the Asian Conference on Thermal Sciences 2017.
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Konferensbidrag (refereegranskat)abstract
- The Hot Disk method, also known as the transient plane source (TPS) technique, is an experimental approach for determining the thermal transport properties of materials. The core of the method is the Hot Disk sensor, an electrically conducting metallic foil (typically nickel), shaped as a double spiral, clad with a protective polymer film or mica. The double spiral serves simultaneously as heat source and temperature probe. The mean temperature increase of the TPS- sensor has been formulated from various analytical approaches such as: the concentric ring sources model, the thermal quadrupoles formalism, and concentric circular strips structure approach. However, full numerical simulation of the sensor has not been addressed so far. Here we develop 3D model of a Hot Disk sensor. The simulation provides information such as temperature and current distribution along each spiral which is not accessible from the experiment. Modeling feature, Joule heating coupled with heat transfer in solids of COMSOL Multiphysics software is used to simulate the sensor. The temperature and current distributions along the nickel wire is obtained. This can potentially be used in further optimizing geometry and estimating better parameters.
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| 11. |
- Mekonnen Mihiretie, Besira, 1983, et al.
(författare)
-
Thermal depth profiling of materials for defect detection using hot disk technique
- 2016
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Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 6:8
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Tidskriftsartikel (refereegranskat)abstract
- A novel application of the hot disk transient plane source technique is described. The new application yields the thermal conductivity of materials as a function of the thermal penetration depth which opens up opportunities in nondestructive testing of inhomogeneous materials. The system uses the hot disk sensor placed on the material surface to create a time varying temperature field. The thermal conductivity is then deduced from temperature evolution of the sensor, whereas the probing depth (the distance the heat front advanced away from the source) is related to the product of measurement time and thermal diffusivity. The presence of inhomogeneity in the structure is manifested in thermal conductivity versus probing depth plot. Such a plot for homogeneous materials provides fairly constant value. The deviation from the homogeneous curve caused by defects in the structure is used for inhomogeneity detection. The size and location of the defect in the structure determines the sensitivity and possibility of detection. In addition, a complementary finite element numerical simulation through COMSOL Multiphysics is employed to solve the heat transfer equation. Temperature field profile of a model material is obtained from these simulations. The average rise in temperature of the heat source is calculated and used to demonstrate the effect of the presence of inhomogeneity in the system.
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| 12. |
- Sizov, Andrey, 1989, et al.
(författare)
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Thermal conductivity versus depth profiling of inhomogeneous materials using the hot disc technique
- 2016
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 87:7, s. 074901-
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Tidskriftsartikel (refereegranskat)abstract
- Transient measurements of thermal conductivity are performed with hot disc sensors on samples having a thermal conductivity variation adjacent to the sample surface. A modified computational approach is introduced, which provides a method of connecting the time-variable to a corresponding depth-position. This allows highly approximate—yet reproducible—estimations of the thermal conductivity vs. depth. Tests are made on samples incorporating different degrees of sharp structural defects at a certain depth position inside a sample. The proposed methodology opens up new possibilities to perform non-destructive testing; for instance, verifying thermal conductivity homogeneity in a sample, or estimating the thickness of a deviating zone near the sample surface (such as a skin tumor), or testing for presence of other defects
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