Beyond Leidenfrost levitation: A thin-film boiling engine for controlled power generation
Beyond Leidenfrost levitation: A thin-film boiling engine for controlled power generation
复制标题
DOI：
10.1016/j.apenergy.2021.116556
复制
发表时间：
2021-02-13
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
克服运动部件之间的摩擦对于减少能量损失和部件磨损是重要的。通过薄膜沸腾的流体动力润滑提供了减少摩擦能量和质量传输的机会。这种润滑的一个常见例子是莱顿弗罗斯特效应，其中液滴悬浮在加热到液体沸点以上的表面上的其自身蒸汽的垫上。这种蒸气流的不对称性会由于粘性阻力而在表面上自推进液滴，将热能转化为机械运动，就像热力发动机一样。虽然悬浮显着减少摩擦，诱导自推进取决于基板的几何形状和材料特性，这限制了动态推进控制。因此，控制功率输出的能力是实现可操作的毫米级和亚毫米级几乎无摩擦发动机的重大挑战。在这里，我们提出了一个薄膜沸腾发动机，我们控制的功率输出机械。转子包括耦合到非挥发性固体的工作液体，该转子被手动定位在处于薄膜沸腾状态的加热的涡轮机激发的定子上方。我们表明，通过控制转子在基板上的位置，从旋转输出的功率可以控制在莱顿弗罗斯特温度（类似于250摄氏度）以上和以下。我们解释这些实验观察使用流体动力学分析模型。此外，我们实现的推进输出几乎是基于悬浮的推进系统的4倍。控制这种几乎无摩擦发动机的旋转特性的能力允许在极端环境中的潜在应用，例如在微尺度或用于空间和行星探索。
Overcoming friction between moving components is important for reducing energy losses and component wear. Hydrodynamic lubrication via thin-film boiling provides an opportunity for reduced friction energy and mass transport. A common example of such lubrication is the Leidenfrost effect, where a liquid droplet levitates on a cushion of its own vapor on a surface heated to temperatures above the liquid's boiling point. An asymmetry in this vapor flow, self-propels the droplet on the surface due to viscous drag, converting thermal energy to mechanical motion, like a heat engine. Although levitation significantly reduces friction, the induced self-propulsion depends on substrate geometry and material properties, which limits dynamic propulsion control. Therefore, the ability to control the power output is a significant challenge in realizing operational mm and sub-mm scale virtually frictionless engines. Here, we present a thin-film boiling engine where we control the power output mechanically. The rotor, which comprises of a working liquid coupled to a non-volatile solid, is manually positioned over a heated turbine-inspired stator in a thin-film boiling state. We show that by controlling the position of the rotor over the substrate the power output from the rotation can be controlled above and below the Leidenfrost temperature (similar to 250 degrees C). We explain these experimental observations using a hydrodynamic analytical model. Additionally, we achieve propulsion outputs almost 4 times higher than levitation-based propulsion systems. The ability to control the rotation characteristics of such virtually frictionless engines allows potential applications in extreme environments such as at microscales or for space and planetary exploration.