Raphael Raab

• Heat exchangers play a crucial role in the chemical industry, where efficient heat management is essential for maintaining process control, reducing operational costs, and conserving energy. A considerable portion of the energy used in chemical production is associated with the heating and cooling of process fluids. Traditionally, metals such as stainless steel have been employed in heat exchanger construction due to their high thermal conductivity and mechanical robustness. However, their application is often limited by disadvantages such as high weight, high material cost, and susceptibility to corrosion in aggressive chemical environments. Polymers have emerged as a promising alternative, particularly when reinforced with thermally conductive fillers. These materials combine chemical resistance, low weight, and ease of manufacturing. In this thesis, thermally conductive graphite-filled polymer composites were modified to create superhydrophobic surfaces. This was achieved through a combination of microscale structuring via thermal imprinting, nanostructuring using metal oxide nanostructures (MONSTRs), and subsequent functionalization with fatty acid coatings such as stearic and lauric acid. The resulting surfaces were systematically characterized to evaluate their wetting behavior, condensation dynamics, and heat transfer performance under varying relative humidity conditions. Experimental results showed that the surface-modified composites achieved contact angles exceeding 170◦ with contact angle hysteresis below 5◦, demonstrating effective superhydrophobicity. Condensation experiments revealed enhanced droplet shedding and significantly higher heat transfer coefficients compared to stainless steel and its filmwise condensation. Furthermore, droplet size distributions were determined from high-resolution imaging and compared with predictions from a population balance model based on the frameworks of Wang et al. [1] and Tancon et al. [2]. While good agreement was found in droplet size distribution, discrepancies in predicted heat fluxes were observed, primarily due to the presence of non-condensable gases (NCGs) in humid air, which are not fully captured by existing models. These findings underscore the potential of surface-engineered polymer composites to enhance condensation-driven heat transfer and highlight the need for advanced modeling approaches that incorporate the effects of NCGs. The results provide valuable insights into the potential of surface-engineered polymer composites for condensation-based heat transfer enhancement.