Abstract
Self-oscillating systems based on thermally responsive polymer materials can realize heat-mechanical transduction in a steady ambient temperature field and have huge application potential in the field of micro-active machines, micro-robotics and energy harvesters. Recently, experiments have found that a torus on a hot surface can rotate autonomously and continuously, and its rotating velocity is determined by the competition between the thermally induced driving moment and the sliding friction moment. In this article, we theoretically study the self-sustained rotation of a hollow torus on a hot surface and explore the effect of the radius ratio on its rotational angular velocity and energy efficiency. By establishing a theoretical model of heat-driven self-sustained rotation, its analytical driving moment is derived, and the equilibrium equation for its steady rotation is obtained. Numerical calculation shows that with the increase in the radius ratio, the angular velocity of its rotation monotonously increases, while the energy efficiency of the self-rotating hollow torus motor first increases and then decreases. In addition, the effects of several system parameters on the angular velocity of it are also extensively investigated. The results in this paper have a guiding role in the application of hollow torus motor in the fields of micro-active machines, thermally driven motors and waste heat harvesters.
Highlights
Self-excited oscillation is a kind of periodic motion fueled by a constant external stimulation [1–4] and has potential applications in the areas of motors [5–7], micro-active machines [8–12], energy harvester [13–15] and micro-robotics [16–19]
The inhomogeneity of the steady-state temperature field in the cross section of the hollow torus decreases with the increase in rotation angular velocity ω, which causes the reduction of the driving moment Mdrive
Self-oscillating systems based on thermally responsive polymer materials have the advantages of simple structure, strong practicability and sustainability, and can realize heat-mechanical transduction in a steady ambient temperature field, which have huge application potential in the field of micro-active machines, micro-robotics and energy harvesters
Summary
Self-excited oscillation is a kind of periodic motion fueled by a constant external stimulation [1–4] and has potential applications in the areas of motors [5–7], micro-active machines [8–12], energy harvester [13–15] and micro-robotics [16–19]. Similar to biological active feeding, self-oscillation can directly harvest energy from a constant environment to maintain its periodic motion [20,21]. This feature makes the self-oscillating system has no requirement of complex controllers or heavy batteries, and is simple and portable [22,23]. The Nylon/PDMS torus continuously converts thermal energy to mechanical work, we can use it as a heat-driven motor or use it to harvest low-grade waste heat. The effects of the thermal expansion coefficient, heat flux, contact angle, curvature of the hollow torus, heat transfer coefficient and sliding friction coefficient on the rotation angular velocity of the hollow torus are studied in detail, and the dependence of the energy efficiency on the radius ratio and dimensionless heat flux is investigated.
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