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fbtwitterlinkedinvimeoflicker grey 14rssslideshare1
Languages: English
Types: Doctoral thesis
Subjects: TK
Many researchers have tried to exploit waste heat to generate electrical power.\ud There are two phenomena that are related to the conversion of heat into electrical\ud power: thermoelectric (TE) and thermomagnetic (TM) phenomena. In this work the\ud latter (TM phenomenon) deals with the conversion of waste heat to generate electrical\ud power. TM effect began in the 1960s due to the difficulties in induction of a strong\ud magnetic field in the past.\ud The work presented in this thesis focuses on the preparation of polycrystalline\ud indium antimonide (InSb) bulk materials and investigation of their TM properties. The\ud research was motivated by their anticipated application in technologically important\ud regions of reducing energy losses and in operating conditions of electro-magnetic\ud machines, such as motors, generators and transformers, by incorporating such energy\ud conversion devices into the machines at carefully chosen locations.\ud When a thermomagnetic sample is subjected to both temperature gradient and\ud magnetic flux density concurrently, it will produce electrical output. A high electrical\ud power output will be produced when the sample has similar numbers of both charge\ud carriers, and, in addition, when the sample is subject to high temperature difference and\ud high magnetic flux density across it.\ud A new technique has been developed in this work to make undoped and doped\ud InSb polycrystalline bulk materials with tellurium Te, based on open quartz tube instead\ud of the traditional method requiring sealing of the quartz tube. A modification in the raw\ud materials ratio was adjusted to obtain pure InSb sample. The X-ray diffraction (XRD) and\ud the inter-planar spacing analysis were carried out to check the structure of the samples\ud and the result confirmed that the material was pure InSb.\ud Measurements were taken under direct magnetic field, which was produced\ud from direct current (DC) supply, and alternative magnetic field, which was induced from\ud alternative current (AC). The design procedure involved determining the longitudinal,\ud transverse and hybrid transverse voltages. Modifications in design of the measurement\ud IV\ud system have been made to minimise the effect of AC magnetic field on these parts, such\ud as the heat sink being made of copper plate and K-type thermocouples. In addition,\ud magnetic shielding was used for wires in the vicinity to minimise the induced voltage\ud that affects measurements of transverse voltage. The induced voltage was still higher\ud than the transverse voltage, even with the use of magnetic shielding. For this reason,\ud the research performed in this work relating to the thermomagnetic parameters under\ud AC magnetic field did not obtain appropriately good results.\ud The thermomagnetic parameters of samples under DC magnetic field have been\ud improved by doping them with Te at different levels of 0.1% and 0.25%. The resistivity\ud and Seebeck coefficient of the doped InSb with 0.25% Te was lower than those for\ud undoped InSb single crystalline, which was used as a reference sample. The resistivity\ud was lower, around 24% and 38% at the magnetic flux density 0 T and 1 T respectively,\ud and the Seebeck coefficient was about 8% lower for various magnetic flux densities. In\ud contrast, the Nernst, Righi-Leduc voltages and thermomagnetic power of the doped InSb\ud with 0.25% Te were higher than those for undoped InSb single crystalline. The Nernst\ud voltage was around 2% and 0.5% for the magnetic flux density of 1 T and temperature\ud difference 30 °C and 80 °C respectively, while the Righi-Leduc voltage was higher, around\ud 2.6% and 0.9%, and thermomagnetic power was higher around, 2.9% and 1%\ud respectively for the same magnetic field and temperature differences.
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    • B=-0.4 T B=-0.1 T B=-0.7 T B=-1 T 0 B=1 T B=0.7 T B=0.4 T B=0.1 T B=-0.2 T B=-0.5 T B=-0.8 T
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