液滴撞击梯度润湿表面的运动特性及对摩擦发电影响机理研究

Droplet impact phenomena commonly happens in natural world and industrial process. There exists large amount of droplet kinetic energy in these processes. Triboelectric nanogenerator a kind of device for converting the kinetic energy of the falling droplets into electricity. However, the output performance of the triboelectric nanogenerator is limited when using the surfaces with uniform wettability (either hydrophilic, hydrophobic or superhydrophobic). Wettability gradient surface has the potential to break through the bottleneck, but in the current stage, the investigation of droplet impact onto wettability gradient surface is insufficient. In this proposal, experimental investigation, numerical simulation as well as theoretical analysis would be conducted to deeply explore the droplet dynamics when impacting onto a wettability gradient surface where the unbalanced Young’s force, gravitational force and inertial force all take effect. The droplet dynamics and output current would be recorded by a high speed camera and a high speed electrometer. A numerical model would be established by integrating the droplet impact dynamics with the triboelectric nanogenerators. With the results obtained by experimental test, numerical simulation and energy conservation theory, theoretical models for predicting the spread area and sliding speed of the droplet would be established. The droplet impact dynamics would be analysed based on the theoretical model. A model for estimating the output current of the droplet based triboelectric nanogenerator would be raised. The optimization criteria would be given as a theoretical basis for enhancing the output performance of the droplet based triboelectric nanogenerators. This would be helpful for efficiently harvesting the widely available kinetic energy of falling droplets.

液滴撞击固壁现象广泛存在于自然界和工业生产中，其中蕴含了丰富的液滴动能资源。摩擦纳米发电机是一种将液滴动能转化为摩擦电能的装置，然而现有均匀润湿表面限制了装置的输出功率。梯度润湿表面有望突破该功率瓶颈，但目前对液滴撞击梯度润湿表面的运动特性认识不足。本项目拟通过实验研究、理论分析、数值模拟的方法，深入探索液滴撞击梯度润湿表面时，在非平衡杨氏应力、重力、惯性力共同作用下的运动规律及对摩擦发电影响机理。通过高速摄像和高速电流测试实现对液滴运动特性和发电机输出电流的高速采集；建立包含液滴撞击固壁的多相流问题和摩擦引发的电荷转移问题的多物理场耦合数值模型；基于实验、数值模拟结果和能量平衡理论，建立液滴撞击梯度润湿表面的铺展面积和滑动速度模型，分析复杂受力条件下液滴能量转化与耗散的理论规律；基于该规律，建立详细液滴摩擦纳米发电机输出电流模型并获取优化准则，为高效利用储量丰富的液滴动能资源提供基础。

液滴撞击固壁现象广泛存在于自然界、工业生产和人类日常生活中。近年来随着微纳米技术的不断进步，将液滴撞击固壁时的动能通过纳米发电机进行电能化转换已成为可能。然而液滴撞击固壁过程的表面动力学复杂，现有液滴摩擦纳米发电机输出功率过低，这限制了液滴摩擦纳米发电机在能量收集和流动传感中的广泛应用。本研究提出基于梯度润湿表面的液滴摩擦纳米发电机性能强化技术，旨在通过梯度润湿表面提供的非平衡杨氏应力，解决液滴摩擦纳米发电机工作过程中液滴铺展面积和下落速度之间的共高制约关系。本研究通过实验、数值模拟和理论研究相结合的方法对液滴撞击固壁时的机械能向电能转化这一过程进行了深入研究，分析了润湿梯度对液滴滑动速度和铺展面积的强化作用，构建了液滴撞击固壁摩擦纳米发电机输出电流的理论表达式，揭示了梯度润湿表面强化液滴摩擦纳米发电机输出功率的根本原理。实验表明，液滴撞击5°/mm和7°/mm的梯度润湿表面时，润湿梯度的存在对滑落速度起到明显提升作用（14.5%），实验验证了本申请最初的设想，即液滴摩擦纳米发电机输出性能在梯度润湿表面上将得到强化。在此基础上，拓展了液滴摩擦纳米发电机在液滴撞击行为调控、水凝胶摩擦纳米发电机、玻璃表面雾滴移除和气液界面毛细波推进器领域的应用。项目执行期内，在Physics of Fluids、Nano Energy、ACS Nano等过期期刊共发表SCI检索论文9篇（第一标注）、授权中国发明专利2项，日本发明专利1项，获得会议优秀论文奖2项、全国大学生节能减排科技竞赛三等奖等1项，培养博士研究生2名，硕士研究生7名，参与国际学术会议并做口头报告3次，参与国内学术会议并做口头报告4次。本项目的实施为液滴能量收集、液体生物化学传感器的研发提供理论支撑。