Marlis Morschel holds a degree in Energy and Process Engineering and is currently working on her PhD in the field of thermoelectrics as part of the EcoTEG research project at Rhine-Waal University of Applied Sciences. In October, she will present her latest findings at the ‘Materials Science and Technology’ conference in Montréal, Canada.
Kleve/Kamp-Lintfort, 22 August 2013: Since early 2011, the Faculty of Technology and Bionics at Rhine-Waal University of Applied Sciences, under the leadership of Prof. Dr Georg Bastian, has been working on the EcoTEG research and development project. The name refers to an industrialisation concept for high-temperature-resistant thermoelectric generators (TEGs) designed to utilise exhaust heat in motor vehicles, based on innovative materials. The aim is to convert the unused waste heat generated by internal combustion engines into usable electrical energy with the aid of thermoelectric generators.
In collaboration with the University of Duisburg-Essen, Ms Morschel is now investigating the deformations that occur in the thermoelectric generator as part of her PhD at Rhine-Waal University of Applied Sciences.
To generate electrical energy using a thermoelectric generator, a heat source (in this case, the exhaust gases from a car) and a heat sink (the vehicle’s cooling circuit) are required. These two components provide the temperature difference necessary for the thermoelectric generator to operate. The generator is connected to both the heat source and the heat sink via a heat exchanger. Much like a sandwich, the thermoelectric generator is sandwiched between the heat source and the heat sink. In this way, the hot and cold air flows past it. Good thermal coupling to these airflows is very important in order to transfer the energy from the exhaust gases into the thermoelectric generator.
Stresses and surface deformations
However, one consequence of this arrangement is that the hot side of the thermoelectric generator tends to expand, whilst the cold side tends to contract. These opposing processes lead to stresses and deformations, which can result in material failure of the module. To prevent this, research is being carried out at Rhine-Waal University of Applied Sciences using an optical measurement system and a thermal imaging camera. The optical measurement system uses a laser beam to detect even the smallest surface deformations. The thermal imaging camera can be used to measure surface temperatures, which is an important analytical method for the investigation. This reveals how successfully and evenly the heat from the exhaust gas is conducted into the thermoelectric generator.
Simulation of real-world conditions
In addition, the thermoelectric generator is subjected to realistic temperature differentials. To this end, the PhD student uses a test bench that replicates the temperatures found in a vehicle’s exhaust system. This is based on the New European Driving Cycle (NEDC), which car manufacturers use to simulate a standardised journey in a car through the city, along country roads and on the motorway. At the same time, a simulation based on the finite element method (FEM) is fed with the same temperature data. This computer simulation is designed to represent reality in a model. Simulations are extremely useful in cases involving highly complex scenarios, costly tests or prototypes that do not yet exist. This simulation of long-term, real-world stress on the thermoelectric generator is intended to provide an indication of how promising the use of thermoelectric generators in vehicles is. If it can withstand real-world stresses (temperature differences of around 350°C), fuel savings can be achieved through the additional supply of electrical energy to the vehicle’s electrical system.
‘Materials Science and Technology’ Conference
Under the title ‘Analysis of Thermal and Mechanical Stress in a Thermoelectric Generator under Realistic Load’, Ms Morschel will present the results of the FEM simulation carried out at the prestigious ‘Materials Science and Technology’ conference in Montréal, Canada, in October. The conference focuses on various materials, their properties and applications. Particular emphasis is placed on biomaterials, ceramics, nanomaterials and their sustainable use. The DAAD supports the active participation of German researchers in international events.
The partners in the EcoTEG research and development project are Daimler AG, Robert Bosch GmbH, J. Eberspächer GmbH & Co. KG and the German Aerospace Centre (DLR). The project is funded by the Federal Ministry of Education and Research (BMBF).
