Developing methodology for searching efficient thermoelectric materials and their utilization in designing thermoelectric generators (MS)

Abstract

In this thesis, we discuss the methodology for accurate measurement of efficiency for thermoelectric generator (TEG), which is of great importance for materials research and development. Approximately all the parameters of a thermoelectric material (TEM) are temperature dependent, so we can't directly apply the max formula for e ciency calculation in the large temperature range. We have calculated the TEG e ciency and studied the suitability of di erent TEM like Bi2Te3, Sb2Te3, PbT e, TAGS, CeF e4Sb12, SiGe and TiO1:1 in the estimation of TEG e ciency. The e ciency of TEG made up of Bi2Te3 or Sb2Te3 gives 7% in temperature range of 310 K - 500 K. PbT e or TAGS or CeF e4Sb12 generates 6% in temperature range of 500 K - 900 K and SiGe or TiO1:1 also have remark-able e ciency in higher temperature range i.e 1200 K. The e ciency obtained is close to experimental results. Here, we report the enhancement of efficiency by using the segmented technique for di erent combinations of above-mentioned materials. To this end, the proposed values of overall e ciency of TEG by segmenting Bi2Te3 and PbT e; Bi2Te3 and TAGS; Bi2Te3 and CeF e4Sb12 are 12%, 14%, and 11.88%, respectively, for the temperature range of 310 K to 900 K. For automobile, the e ciency of TEG having xed exhaust temperature with varying sink temperature is also discussed. For steel industry and spacecraft application ( 1200 K), either segmentation is done by comprising Bi2Te3, PbT e and SiGe or Bi2Te3 and TiO1:1, which shows e ciency of 15.2% and 17.2%, respectively. The relative change in e ciency by considering loss at interface surface is found out to be 10.5%. In this work, we are developing the theoretical prototype and improving the technique for installing the TEG set up in automobiles. We have used methodology for enhancing the e ciency of TEG and make it economical and user friendly. We have considered a linear curve fit from a zigzag curve of reported mass flow rate and temperature variation at the hot gas inlet. Accordingly, the temperature of the coolant is also varied linearly at inlet from 300 K to 320 K and accordingly the mass flow rate of coolant. Circular n is installed around each circular layer of TEM after the water jacket. The calculated heat loss through each n is 24 W. Energy balance was done at each and every TEM and correspondingly calculated the amount of power transferred through each segment of TEG as 32 W. We have calculated the length of TEM sample for attaining the respective temperature range for the hybrid of Bi2Te3 and TiO1:1. This calculation is done by considering the compatibility factor derived as s = p1+ZTð€€€1 T which is a function of only intrinsic material properties and temperature and is represented by a ratio of current to conduction heat ux. The length obtained for this particular combination is 8 mm. To this end, we have reported the e ciency with respect to mass flow rate of hot ue gas from automobile for di erent layers of TEG for the above mentioned combination. Here, we have explored the possibility of installing a number of di erent layers TEG module which can be installed throughout the lateral surface area of exhaust chamber. Thermal mismatching criteria is also discussed at the adjoining surface of TEM because of high temperature. To maintain the thermal expansion or contraction of TEM, spring and bolt arrangement is provided, which is fixed over the aluminium oxide ceramic substrate. The proposed methodology and results can be treated as a viable option for engineers, who are looking for fabricating TEG in real life by using the temperature-dependent material's parameters like thermal conductivity, electrical conductivity, and Seebeck coe cient on which z T depends.