Thermoelectric generators (TEGs) are solid state devices that convert thermal energy into electrical energy using the Seebeck effect. They can be used for energy harvesting in trucks and passenger vehicles by taking advantage of the temperature difference between the exhaust pipes and ambient environment. The key issue with thermoelectric devices today is the demand for increased operating temperatures while maintaining adequate reliability and low cost. Since, TEGs are subjected to sub-critical thermal cyclic loading, ensuring satisfactory reliability is important for commercially viable products. TEGs used in passenger vehicles should be able to withstand extreme environmental conditions such as high temperature, shock and mechanical vibration [1]. Since the operating temperatures of TEGs can reach temperatures higher than 500 °C, aluminum brazes offer a good high temperature solution for die attach applications. The thermoelectric materials of TEGs are prone to oxidation and sublimation. A solution to minimize these phenomena is to enclose the TEG device in a hermetic package. This paper analyzes the reliability of aluminum alloy braze Al 718 (12% Si, 88% Al) used in TEG packages under fatigue loading. A power cycling temperature fluctuation method was employed to simulate the operating conditions of the TEGs for passenger vehicle. Low cycle fatigue simulations were performed using the direct cyclic approach embedded in the finite element software ABAQUS. Direct cyclic approach uses an extrapolation technique, which allows for efficient and computationally inexpensive simulations. The numerical model was validated using experimental test data. A validated damage model was used to analyze the cyclic damage evolution in the aluminum alloy braze for the hermetic TEG packages.
Abstract. This paper describes the computational simulation of contact zones between pebbles in a pebble bed reactor. In this type of reactor, the potential for graphite dust generation from frictional contact of graphite pebbles and the subsequent transport of dust and fission products can cause significant safety issues at very high temperatures around 900• C in HTRs. The present simulation is an initial attempt to quantify the amount of nuclear grade graphite dust produced within a very high temperature reactor.
Ceramic substrates with thin film and thick film conductor traces are widely used in microelectronic packages for high temperature operation. In high power applications where the maximum current in the package may be hundreds of amperes, much thicker conductive traces are normally required. For such applications, Direct Bonded Copper (DBC), Direct Bonded Aluminum (DBA) or Active Metal Bonded (AMB) substrates are good candidates. These substrates provide low electrical resistance and high ampacity, thereby enable the design of high power circuits for high temperature operation. The most commonly observed failure mode in these substrates is the delamination of metal layer from the ceramic. The lifetime of a ceramic substrate can be significantly reduced by the processing conditions such as maximum process temperature, and the process gases that the substrates are exposed to. It has also been shown that the propagation of cracks in the ceramic can be abated by dimpling the metal layers along edges and corners. In order to evaluate the effectiveness of these types of substrates for power applications, substrates with various combinations of metal thicknesses and ceramic composition (Al2O3 and AlN) were evaluated for delamination as a function of thermal shock cycles. These samples included both dimpled and non-dimpled metallization. The samples were thermally cycled between −40 °C and 200 °C. A few of these substrates were exposed to forming gas at 340 °C prior to thermal cycling to imitate process conditions. Sample randomization was performed to provide statistically significant data. After a certain number of thermal cycles, delamination cracks were observed to nucleate and propagate in the substrates. Data regarding the reliability of these substrates as a function of thermal shock cycles is presented in this paper, along with failure mechanisms that are commonly observed. Computer simulations were performed to understand the conditions that lead to delamination cracks, and to estimate the crack growth rates in these substrates.
The objective of this work is to design a commercially viable thermoelectric generator (TEG) assembly that can be used in passenger vehicles to be able to withstand extreme environmental conditions. Since the operating temperatures of the TEGs can reach temperature levels higher than 500 °C, aluminum braze alloys offer a good high temperature solution for die attach. However, the evolution of fatigue damage in the aluminum braze must be understood in order to ensure an acceptable reliability of the TEG. In this paper, the proposed design of TEG package assembly was evaluated under extreme temperature conditions. Three-dimensional models of full scale TEG were analyzed using finite element analysis (FEA). The failures of aluminum alloy based braze (high temperature form of solder) material in the TEG application was investigated. Low cycle fatigue using direct cyclic approach was considered for the reliability analysis. Continuum damage mechanics approach was used to study the fatigue failure due to power cycling. Different TEG assembly designs were investigated and compared to determine the best possible solution for the extreme environment application.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.