# Design Limitations of Laboratory Solar Chimney for Engineering Education
## 5 Conclusions  
In this contribution, a small-scale solar chimney mock-up with a tower height of 50 cm is analyzed numerically and experimentally. The practical application of this study is the practical teaching of STEM. Specifically, to enable (under)graduate power engineering students to thoroughly comprehend the advanced concepts of thermodynamics and its real-world applications. Because the mock-up is intended to educate college-level engineers, the analysis was based on a simple mathematical model proposed by the [PERSON] group. The model suggests that the efficiency of the solar chimney power plant depends on the height of the tower. In such a model, the viscosity is negligible, and the heat conduction is natural. Therefore, the model can be derived from the Pascal principle. ANSYS software was used to perform numerical thermodynamic analysis. The results for the mass flow rate, the pressure difference, and the speed of air inside the tower were compared to the mathematical model of the [PERSON] prototype. The findings implied that the resultant upward force is overcome by boundary physics at a certain geometry limit. The physical dependence of the numerically obtained results for pressure inside the tower is identical to that of the analytical model, but the pressure difference is much smaller than what is needed to create spontaneous flow. Increasing the temperature typically results in an increase in pressure, as the mathematical model suggests, and the particles accelerate. However, because of the small geometry, particles of higher kinetic energy largely interact with boundaries, which prevents spontaneous development of the upward draft. The solar chimney power plant mock-up under study was constructed as part of the project, the requirements of which were ease of transport and a maximum volume of 50 cubic centimeters. In addition, the project funding was relatively small. Therefore, the materials used had to be cost-effective and light. Hence, the structure was 3D printed, the collector base was constructed of extruded polystyrene, the collector roof was constructed of glass, and the tower was constructed of PVC pipe. Furthermore, since the mock-up is primarily to be used for the education of engineering (under)graduates, the design was aimed to be simple. Experimental measurements were conducted on a physical model of the solar chimney power plant enhanced with fans to induce air flow. The Nyquist criterion was fulfilled. The initial design was modified with features suggested in the literature to increase efficiency: divergent shape tower, collector divided into partitions with a sloped roof, and a modified NACA 7407 airfoil turbine. The turbine did not rotate when two PC fans were used to induce airflow despite the air speed achieving 3.39 m/s per fan. Therefore, the two fans were modified to become a fan-generator pair via the LAB setup. For an air speed of 2.58 m/s, the resistance of the magnet was overcome, and the generator was started. The vacuum cleaner was then used to determine the minimal air flow for which the turbine rotates. However, the structure could not withstand that speed. In other words, if the Nyquist criterion is met to overcome the boundary physics and induce the flow, then the mechanical force is destructive. A possible solution is to use a smaller motor such as one that can be found in toothbrushes and vibrators for mobile phones and tactile devices. However, such engines have significant technical limitations regarding the connection to the turbine due to the dimensions of the shaft; therefore, future work will focus on research and construction of a specialized generator without permanent magnets and with variable excitation to overcome the geometric limitations presented in this paper. **Author Contributions:** Conceptualization, H.G. and D.J. ; methodology, H.G. and D.J. ; software, D.J. and L.S. ; validation, D.J., T.B. and L.S. ; formal analysis, D.J. and T.B. ; investigation, D.J. ; resources, H.G., D.J. and T.B. ; data curation, D.J.