Improved condensation on hierachically structured surfaces

微结构化表面上的液滴冷凝的受控生成增强了传热。为了实现这一点，我们将结合联合收割机带状表面结构与极低的接触角滞后与一组集成的微结构化的隔间开发的个别液滴的形成。当冷凝过程中的液滴尺寸超过阈值时，后者通过带状线被清除。通过在带状线旁边集成冷凝隔室，可以防止连续流体膜的产生。隔室的几何形状和尺寸需要优化，以产生小液滴，从而改善传热。液滴的大小和速度将通过在空气中略微降低的温度下操作的光学成像装置来确定。利用相同的设置来评估在冷凝期间在带状线上抬起的液滴的去湿过程，因为它们的直径超过给定表面结构的阈值。在传热过程的理论建模期间，这些液滴数量数据是必要的，以确定给定设置的热通量。液滴输送的动力学可能是由已经移动的液滴与仍然保留在结构上的液滴的聚结支持的，从而导致沿条带沿着的清扫效应。这些热交换板的总体效率将通过在真实的即工业条件下操作的第二个实验装置进行研究。所有研究将首先使用硅作为基础材料开始，因为微结构化工艺已经在TUK的洁净室设施中可用。优化后的表面结构由于其工业相关性将以共同的作用转移到高温聚合物的表面上。为此，制备负表面结构的硅母版，并用于将所需结构嵌入聚合物表面。这些过程需要优化的化学性质方面所涉及的表面转移纳米结构的压花和促进分离的主和底层polymer.The最后一个项目的一部分是专门的问题是否分层的表面结构提高热交换板的效率，通过将它们与超疏水和-或超亲水纳米结构。用于产生所需纳米结构的技术需要被采用到所使用的材料，并且可以从在聚合物纳米结构的直接激光写入上的黑硅的等离子体蚀刻到在等离子体蚀刻期间使用旋涂的纳米级材料作为硬掩模的聚合物的干法蚀刻。总的来说，新开发的混合结构在其他技术应用中具有广泛的潜力，这些技术应用需要非润湿（从管流出-奶油、番茄酱等）。

Controlled generation of droplet condensation on microstructured surfaces enhances heat transfer. To achieve this we will combine strip-like surface structures with exceedingly low contact angle hysteresis with a set of integrated microstructured compartments exploited for individual droplet formation. The latter are cleared via the strip lines when the droplet dimension during the condensation process exceeds a threshold value. Through the integration of the condensation compartments besides the strip lines the generation of a continuous fluid film is prevented.The geometry and dimensions of the compartments need to be optimized to generate small droplets to improve heat transfer. The droplet size and velocity will be determined by an optical imaging set-up operated at slightly reduced temperatures in air. The same set-up is exploited to evaluate the dewetting process of droplets that are lifted up on the strip lines during condensation because their diameter exceeds the threshold value of the given surface structure. These droplet population data are necessary during the theoretical modelling of the heat transfer process to determine the thermal throughput of the given set-up. The dynamics of droplet transport is presumably supported by coalescence of already moving droplets with those still retained on the structure, leading to a sweeping effect along the strips. The overall efficiency of these heat exchange plates will be investigated with a second experimental set-up that is operated under real i.e. industrial conditions.All investigations will be first started using silicon as base material because the microstructuring processes are already available at the clean room facility of TUK. The optimized surface structures will then be transferred in a common action onto the surface of high-temperature polymers due to their industrial relevance. For this purpose, silicon masters of the negative surface structures are prepared and used to emboss the desired structure into the polymer surface. These processes need to be optimized with respect to the chemical nature of the involved surfaces to transfer nanostructures by embossing and facilitate the separation of the master and underlying polymer.The last project part is devoted to the question whether hierarchical surface structures improve the efficiency of the heat exchange plate by combining them with superhydrophobic and - or superhydrophilic nanostructures. The techniques used to generate the desired nanostructures need to be adopted to the material in use and may range from plasma etching of black silicon over direct laser writing of polymeric nanostructures to dry etching of the polymer using spincoated nanoscopic materials as a hard mask during plasma etching. Overall, the newly developed hybrid structures have a wide potential in other technical applications were non-wetting is desired (efflux from tubes - creams, ketchup, etc.).