Pixel International Conferences

The p,v,T-phase diagram shows the correlation between the three thermal state variables pressure p, specific volume v and temperature T of a certain substance in a three-dimensional plot. Experience showed that many students have difficulties to recognize the derivation and meaning of the three-dimensional phase diagram and its projections. At the moment there is no realistic 3D-model of the p,v,T-phase diagram available. For explaining these phase diagram to the students in a more illustrative and clear way, a special 3D- model for teaching purposes was developed and manufactured. The main objective was to improve the students understanding of complex basics in thermodynamics. Therefore, literature research was done about relevant thermodynamic information of the phase diagram and also topics of physics didactics for getting a better understanding about the effect and arrangement of media in teaching sessions. Creativity techniques were used to develop a concept for the construction and design of the model. Important requirements like portability, durability and clearness were taken care of during this process. By using a computer-aided design (CAD) software a digital reproduction of the p,v,T-phase diagram of carbon dioxide was constructed as a basis for the following production process. Inserting several working screens into the model allowed a division in smaller segments. Attention was paid to set these slices in every striking area of the model like for instance around the critical point. The model was divided into 94 segments by using four isobars, five isotherms and five isochors as screen cuts. These segments were printed as hollow bodies by a 3D printer using polylactic acids (PLA). Small magnets were used for the cohesion between the segments. The main advantage is the possibility to separate and assembly the segments again and again like a puzzle very easily. In addition, a casing was built of plywood panels and acrylic glass for transportation on the one hand and, more important, as an area for the tree different projections of two-dimensional diagrams on the other hand. The projected curves were highlighted by cables fixed onto the acrylic glass allowing to switch illumination of each single line. In case the projection areas would be removed the tree-dimensional phase diagram with its different phase regions and binodals are visible directly. The model can easily be cut open in several levels or certain areas can be taken out for presentation. In the opened model the isolines can be seen as well. The different binodals in each projection can be illuminated independently, in different colours. The designed model was resulting in a significantly better understanding of thermodynamic lectures and also turned out to be very useful in an educational film.

Keywords: phase diagram, thermodynamics, teaching sessions, 3D printing.