Leidenfrost heat engine: Sustained rotation of levitating rotors on turbine-inspired substrates
Leidenfrost heat engine: Sustained rotation of levitating rotors on turbine-inspired substrates
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DOI：
10.1016/j.apenergy.2019.02.034
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发表时间：
2019-04-15
期刊：
影响因子：
11.2
通讯作者：
Sefiane, Khellil
中科院分区：
文献类型：
--
作者：
Agrawal, Prashant;Wells, Gary G.;Sefiane, Khellil
在空间或微观尺度等极端环境中收集热能的前景为开发替代能源转换技术提供了独特的机遇和挑战。在微观尺度上，机械摩擦以能量损失和磨损的形式提出了挑战，而高温差异的存在和当地可用的资源激发了用于空间和行星探索的新型热机的开发。最近，利用薄膜沸腾的悬浮，通过莱顿弗罗斯特效应，将热能转化为机械运动，为新型减摩擦热机奠定了基础。在莱顿弗罗斯特效应中，液滴和受热表面之间发生瞬时薄膜沸腾，从而使液滴悬浮在其自身的蒸气上。这种液滴状态提供了几乎无摩擦的运动和自我推进，其方向可以通过不对称的基板纹理设计到系统中。然而，维持这种热能到机械能的转换是具有挑战性的，因为水在光滑金属表面的莱顿弗罗斯特转变温度接近220摄氏度，尽管蒸汽层的导热性很低，但液滴会不断蒸发。进一步的挑战包括有效地将热能转化为旋转运动，而不是线性运动，以及驱动固体部件，而不仅仅是液滴。在这里，我们提出了一个莱顿弗罗斯特转子，其中一个固体组件是耦合到一个旋转的液体体积使用表面张力和悬浮在一个涡轮机启发的衬底上连续运行。我们解决了两个关键挑战：我们展示了如何补充液体以实现设备的连续运行；我们展示了在基材上涂上一层超疏水涂层是如何扩大转子的工作温度范围和稳定性的。由于液体作为一种工作物质，通过从基片中提取热量，以耦合固体部件的旋转形式产生有用的功，我们的结果表明，莱顿弗罗斯特发动机在封闭的热力学循环中运行是可能的。
The prospect of thermal energy harvesting in extreme environments, such as in space or at microscales, offers unique opportunities and challenges for the development of alternate energy conversion technologies. At microscales mechanical friction presents a challenge in the form of energy losses and wear, while presence of high temperature differences and locally available resources inspire the development of new types of heat engines for space and planetary exploration. Recently, levitation using thin-film boiling, via the Leidenfrost effect, has been explored to convert thermal energy to mechanical motion, establishing the basis for novel reduced-friction heat engines. In the Leidenfrost effect, instantaneous thin-film boiling occurs between a droplet and a heated surface, thereby levitating the droplet on its own vapor. This droplet state provides virtually frictionless motion and self propulsion, whose direction can be designed into the system by asymmetrically texturing the substrate. However, sustaining such thermal to mechanical energy conversion is challenging because the Leidenfrost transition temperature for water on a smooth metal surface is similar to 220 degrees C and, despite the low thermal conductivity of the vapor layer, the droplet continuously evaporates. Further challenges include effective transfer of thermal energy into rotational, rather than linear motion, and driving solid components and not simply droplets.Here we present a Leidenfrost rotor, where a solid component is coupled to a rotating liquid volume using surface tension and levitated in continuous operation over a turbine-inspired substrate. We address two key challenges: we show how the liquid can be replenished to achieve the continuous operation of the device; and we show how a superhydrophobic coating to the substrate can broaden the temperature range of operation and the stability of the rotor. Because the liquid acts as a working substance by extracting heat from the substrate to produce useful work in the form of rotation of the coupled solid component, our results demonstrate that a Leidenfrost engine operating in a closed thermodynamic cycle is possible.