||In this thesis, we study what we call the “solar rotors” for their materials, structures and influence of different parameters. The “solar rotor” in this case is an application of surface tension as a function of temperature. Our solar rotor is a tri-layer design – a light absorptive material, a thermally conducting material, and a thermally insulating substrate. All materials are cheap and easy to obtain. |
The structure of our rotors is formed by coating absorptive material onto the thermal conductor, which is then fixed on the substrate. The most important thing is that the shape of thermal conductor should be asymmetrical for small-area contacts with water. We use focused sunlight to irradiate the rotor to raise temperature of the rotor, which in term heats the local water via small-area contacts. The local heating induces the gradients of surface tension. The different value of surface tension on different sides add up to produce a net torque on the rotor. That is the reason why rotor can rotate.
After testing various materials, we decide to use graphite as the absorptive material, copper foil as the thermally conducting material, and glass coverslips as the thermally insulating substrate. The parameters studied in this thesis include rotating directions, solar irradiation, water temperature, and the contact length of copper foil with water. We find that different rotating directions make no difference in our experiment. However, the stronger solar irradiance faster rotating speed. The rotating speed is found to be linearly related to the solar irradiation. Furthermore, the lower water temperature, the faster rotating speed. The latter is a square function of the former. On the other hand, contact length in this thesis is complicate coefficient, there is a maximum value of rotating speed as a function of contact length.
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