TY - JOUR A1 - Schäfle, Claudia A1 - Kautz, Christian T1 - Student reasoning in hydrodynamics: Bernoulli’s principle versus the continuity equation JF - Physical Review Physics Education Research N2 - We report on an investigation of student thinking about steady-state pipe flow of an incompressible fluid. About 250 undergraduate engineering students were given a test consisting of two hydrodynamics questions, combining multiple-choice format with subsequent open-ended explanations. There is substantial evidence that students have difficulty applying and prioritizing the two basic principles of mass conservation (expressed in the continuity equation) and energy conservation (i.e., Bernoulli’s equation). When faced with questions that involve gravity, dissipative effects (“friction”), or a visible pressure drop, a considerable number of students did not invoke the continuity equation in situations where applying it is a necessary step for arriving at the correct answer. Instead, even after lecture instruction on this topic, many of the first-year students based their answers on ill-supported assumptions about local pressures. Some of them used formal arguments from a simplified Bernoulli equation (“lower pressure means higher velocity”), while others based their answer on intuitive arguments (“higher pressure leads to higher velocity”). We also found reasoning based on analogies to single-particle motion (“flow velocity decreases when flowing upwards or friction is present”). Contrary to other researchers, we did not see any evidence for the hypothesis that students think of water as a compressible fluid. Instead, students’ answers often indicate a lack of understanding of the conservation of mass or its implications for incompressible fluids or of the role that this principle plays in the context of fluid flow. In addition, our data indicate that some students have more general difficulties in describing and reasoning about technical situations, such as applying equations containing multiple variables, distinguishing spatial differences in a quantity from its changes with respect to time, or realizing the meaning of idealizations. We also present some evidence that different levels of activation of students during instruction influence the prevalence of these difficulties and discuss some implications for instruction. KW - Physics Education research KW - Concepts& Principles KW - Instructional strategies KW - Instructional materials development KW - Strömungsmechanik Y1 - 2021 UR - https://doi.org/10.1103/PhysRevPhysEducRes.17.010147 VL - 17 IS - 1 SP - 010147 PB - American Physical Society ER - TY - JOUR A1 - Schäfle, Claudia A1 - Lux, Christine A1 - Feldmeier, Franz T1 - Untersuchung des Gesamtenergiedurchlassgrades an gebäudeintegrierbaren, teiltransparenten Photovoltaik- Modulen bei elektrischer Leistungsentnahme JF - Bauphysik N2 - Der Gesamtenergiedurchlassgrad (g-Wert) verschiedener teiltransparenter, gebäudeintegrierbarer Photovoltaik-Module wurde mit und ohne Entnahme elektrischer Leistung kalorimetrisch gemessen. Durch die Leistungsentnahme sinkt die Oberflächentemperatur des Moduls um bis zu 4 K. Gleichzeitig reduziert sich der g-Wert aufgrund der geringeren sekundären Wärmeabgabe. Die Größe der Abnahme hängt von der entnommenen Leistung ab und stimmt sehr gut mit einem einfachen, auf dem Energiesatz basierenden Rechenmodell überein. N2 - Investigation of the total solar energy transmittance on buildingintegrated, semitransparent photovoltaic modules with and without extraction of electrical power. The total solar energy transmittance (g-value) of different building-integrated PV-elements has been measured with and without extracting electrical power from the module. When extracting energy, a reduction in the gvalue has been measured. Moreover, a reduction in temperature up to 4 K on the inner surface is observed. The experimental results are in very good agreement with a physical model based on energy conservation. KW - g-Wert KW - Photovoltaik KW - Building-integrated PV-modules KW - total solar energy transmittance KW - building physics Y1 - 2012 UR - https://doi.org/10.1002/bapi.201200019 VL - 34 IS - 4 SP - 153 EP - 165 ER -