亲疏水异质表面可控滴状冷凝传热机理及实现方法

During dropwise condensation on superhydrophobic nanostructure surface, the drop size distribution is random and the wetting states change with operating conditions. As a result, coalescence-induced droplet jumping is just a possible event. However, the dropwise condensation may be controllable with uniform droplet sizes, yielding multi-droplets coalescence and large area droplet jumping on hybrid surface with patterned hydrophilic dots among superhydrophobic nanostructure. The structure parameters of hybrid surface are the key factor to obtain controllable dropwise condensation and heat transfer enhancement. Thus, the scientific issue is proposed as the influence mechanism of structure parameters on dropwise condensation heat transfer on patterned hydrophilic/superhydrophobic surface. Three main research aspects will be performed. (1) Based on theoretical study of dropwise condensation on patterned hydrophilic/superhydrophobic surface, critical criterion of mode selection for droplet growth and departure will be proposed. The range of structure parameter for controllable condensation will be suggested step by step. The maximal heat transfer enhancement factor is expected to be calculated theoretically. (2) To develop fabrication method of hybrid surface, the characteristics of the nanofluids evaporation and particle deposition in confined space will be obtained first. Base on particle self-assembly, sintering and selective corrosion, a increasing material method to fabricate hybrid surface on metal substrate will be developed. (3) Among experimental researches on controllable dropwise condensation, the influence mechanism of the size and spacing of hydrophobic structures on the nucleation, growth, jumping and distribution of condensate droplet will be focused on. The operating conditions for controllable dropwise condensation are also interested in. Obtaining controllable dropwise condensation and heat transfer enhancement by matching of microstructure parameters is the characteristic of this project.

超疏水纳米表面冷凝液滴尺寸随机分布、浸润状态随运行条件改变，影响液滴聚合弹跳概率。具有阵列化亲水点的亲疏水异质表面有望实现可控冷凝：冷凝液滴同步生长、多滴聚合、大规模弹跳，从而强化传热，其关键在于表面结构参数的匹配。因此，申请人提出“亲疏水表面结构参数对滴状冷凝传热影响机理”的科学问题，安排3个研究内容：(1)亲疏水表面滴状冷凝理论研究，提出液滴生长模式、脱落模式转变临界准则，逐级限定亲疏水表面可控冷凝的结构参数范围，探究表面冷凝传热强化极限；(2)亲疏水表面制备方法研究，获得受限空间纳米流体蒸发、颗粒沉积规律，基于颗粒自组装、烧结与选择性腐蚀，发展一种结构参数可控的金属基亲疏水表面增材加工方法；(3)可控滴状冷凝实验研究，揭示亲疏水表面亲水环尺寸及间距对液滴生长、弹跳及时空分布的影响机理，获得可控滴状冷凝的运行条件。项目特色在于：调控微观结构参数，实现可控滴状冷凝，大幅提升传热性能。

项目围绕“亲疏水表面结构参数对滴状冷凝传热影响机理”这一关键科学问题，开展亲疏水异质表面冷凝传热理论模型、表面制备方法、冷凝传热实验三方面研究。理论研究方面，建立了条纹状与点阵状两类亲疏水异质表面冷凝传热模型，获得了基于表面结构参数的传热分区图，明晰了传热强化必备条件与最佳条件：存在最优亲水区间距，使得表面总传热性能最优；当亲水区域尺寸小于一定值、亲水区域间距大于一定值时，异质表面才能强化传热。表面制备方面，结合热扩散焊、受限空间纳米流体蒸发与自组装、化学/电化学腐蚀等方法，研发了多种亲疏水异质表面并掌握了其结构参数调控方法。冷凝传热实验方面，警示了冷凝环境下浸润性功能表面稳定性问题，揭示了杆状纳米结构伏倒、疏水高分子团聚两种表面破坏机制。具有纳米颗粒结构的亲疏水异质表面稳定性更好，将其引入微通道对流冷凝传热，与全疏水表面相比，冷凝传热系数最大强化89%，在电子散热、海水淡化等领域具有应用前景。.项目发表期刊论文6篇、会议论文5篇，授权发明专利4项。项目成员参加学术会议13人次，作大会报告/特邀报告报告4次，获IAAM Award国际学术奖；协助培养毕业生3人，获博士国家奖学金及校长奖学金、北京市大学生节能减排竞赛三等奖等。研究成果得到了同行认可和企业关注，冷凝传热理论模型被评价为：为异质冷凝表面设计建立了通用框架(“establishes a general framework”)；与中兴通讯股份有限公司等企业合作，将研发的冷凝功能表面应用于5G基站散热热管研制等。另外，项目启发了将口罩表面制备成浸润性功能表面，应对寒冷季节人体呼出温湿气体冷凝引起的口罩防护漏洞，为疫情科学防控提供了建议。为解决项目执行中发现的冷凝功能表面稳定性问题，提出超疏水软表面，获得国家自然科学基金面上项目后续资助。

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