Physik | Technik
Tobias Reber, 2002 | Therwil, BL
In search of alternative means of generating green energy, this study explored the potential of the forgotten nitinol heat engine. The central question asked was how a solar-powered variation of such a heat engine could be built and how efficient it would be. It was expected for the heat engine to run, however with a low efficiency. The heat engine took advantage of the unique shape-memory effect of nitinol, a property which allows the alloy to return to an original shape when heated up. In the end the heat engine did not run due to a lack of energy being input as well as imprecise technical considerations. However, the study did discover some potential in the design and sees many possible improvements to further use the heat engine’s potential as means of generating green energy.
This study sought to revisit the nitinol heat engine by designing and constructing one from scratch. The heat source was based on solar energy using a parabolic mirror in order to make the heat engine solar-powered; the aim was to see whether a solar-powered nitinol heat engine would be a viable source of renewable energy. The central question hence was: What is the practical efficiency of a self-designed nitinol heat engine powered by solar heating using mirrors? It was expected that the heat engine would end up running, however with a low efficiency. This assumption was based on the fact that there were many spots where energy could be lost as well as a lack of optimization that could improve the efficiency.
A nitinol heat engine consists of a thin nitinol wire wrapped around two wheels. In theory, local heating at one of the wheels straightens the nitinol, putting tension on the whole nitinol loop and setting the heat engine into motion. In this study the heat engine was supposed to be solar-powered which was done by redirecting light via a parabolic mirror onto one of the wheels. This wheel was coated in black paint and made of stainless steel to improve the light absorption. It was placed in a basin, heating up water around it which in turn heated up the nitinol. The other wheel was larger and made of plastic, as its primary purpose was to create larger amounts of torque to bend the nitinol wire. Due to the increased reliance on weather conditions, the study had to be broken up into two experiments: The first experiment determined the temperature at which the heat engine would engage at, the second experiment then monitored what temperatures could be achieved via solar heating. The data was then extrapolated to see whether the heat engine could have run at any point in the year in order to make a qualitative statement about the heat engine’s efficiency.
The solar-powered nitinol heat engine did not end up working, due to the energy input being too low. It was discovered that the actual heat engine does not engage at the transformation temperature of the nitinol as expected; due to a lack of torque generated at the wheels, it takes higher temperatures to actually engage the heat engine, which results in a separate engaging temperature.
The findings differed a lot from what was expected: Not only did the results suggest a very low efficiency, the heat engine did not even end up running. The problem were traced back to mainly imprecise technical considerations: Not enough torque was generated at one of the wheels which resulted in an engaging temperature that differed from the nitinol’s transformation temperature. Additionally, the heat engine suffered from too little energy being input. However, many possible ways of improving the heat engine were shown to exist: The wheels could be enlarged to create more torque and thinner nitinol could be chosen to reduce the needed amount of torque, among other possible improvements.
The study showed a lot of the potential that lies in the nitinol heat engine. The actual idea behind a solar-powered nitinol heat engine as discussed in the study definitely works in theory; the problems arose in the implementation, meaning they could be worked out with small adjustments. It was concluded that whilst the solar-powered nitinol heat engine may not be the most efficient way of generating green energy, it could definitely serve as valid means to do so, at least in warm or temperate climates; a solar-powered nitinol heat engine has its advantages in its simplicity and could thus find use in combination with traditional solar energy sources.
Würdigung durch die Expertin
Dr. Esther Linder
Tobias Reber baut seine Arbeit auf einer bekannten, vergessenen Methode zur Energiegewinnung auf. Dabei bettet er das Thema der Energiegewinnung in den Klimawandel ein. Geschickt werden die zur Verfügung stehenden Ressourcen genutzt, um die Wärmemaschine zu bauen und Experimente durchzuführen. Die auftauchenden Probleme werden kreativ und umsichtig gelöst, bis ein funktionierender Experimentalaufbau vorhanden ist. Die selbstkritische Reflexion der Arbeit weist auf eine reife Haltung hin. Die Arbeit überzeugt durch die Kombination von intellektueller und handwerklicher Leistung.
Lehrer: Bernhard Walz