| dc.description.abstract | In this study, the improved “solar rotors” can be operated with ＂direct sunlight＂ by manufacturing without previous mistakes. This advancement implies a more effective conversion of energy, and will facilitate their popularization. The approach in this thesis is two-folded: simulation and experiment.
In the part of computer simulation, the finite element analysis is used to simulate the effects of actual experimental environment on the rotation of rotors. In the experimental part, the sunlight and a high-power electrical torch are used as the light source. The former is used to verify that the “solar rotor” can be operated without using a convex lens, followed by the latter to study the dependence of the rotors’ speed upon various parameters.
It is found that a higher light intensity results in a faster rotor as expected. However, the depth of water affects the rotation in different ways depending on the size of the container. In the case of a small container such as a beaker, a lower water level results in a faster rotation, which is contradict to the simulated result. This surprising result is attributed to a possible focusing effect by reflection of light from the beaker’s wall. On the other hand, hotter water is found to slow down the rotors due to a reduced temperature difference between water and the copper foil. As for the size effect of the rotors, our data reveal that a larger rotor has a slower rotation (which implies a great effect of viscous resistance over that of light absorption) but a higher efficiency of energy conversion. Also, there appears to be an optimized contact width of copper foil with water for each rotor size, unlike the result of simulation that predicts a faster rotor corresponds to a larger contact width. As for the effect of the foil’s thickness, it is found that a thicker copper foil results in a faster rotor, which can be attributed to a greater effective thermal conductance. Finally, the rotation will be slowed down when the area of water surface is reduced, which is presumably caused by the viscous force of water between the rotor and the wall of container. However, a maximum speed of rotation will be reached as the area of water surface is increased. Both of these observations are consistent with the results of simulation. | en_US |