Investigation of frosting on vertical surfaces exposed to humid air flow

Frost formation on surfaces exposed to humid air presents significant challenges across various industrial applications, including HVAC systems and renewable energy technologies, as it hinders system performances. Despite its relevance, comprehensive studies on the frosting phenomenon remain limited. This thesis aims to investigate frost formation on low-wettable surfaces, emphasizing the effects of various operating conditions. The study is organized into four chapters: a thorough literature review on surface wettability and frost formation; detailed descriptions of the experimental apparatus and the characteristics of the surfaces used; an in-depth analysis of frost growth and key parameters; and a comparative evaluation of experimental results against theoretical models. Insights gained from time-lapse videos and heat flux measurements reveal critical trends in frost dynamics, indicating that low-wettability coatings delay frost onset and reduce ice adhesion. Additionally, the literature review examines existing predictive models for frost dynamics and growth, identifying key areas for future research to enhance frost management strategies. Experiments were conducted in a controlled environment within the two-phase heat transfer laboratory at the University of Padua. The experimental setup includes an environmental chamber and a test section, where air conditions are meticulously regulated using humidifiers, fans, a finned coil, and a thermoelectric cooler. Tests on both bare aluminum and sol-gel coated surfaces demonstrated that, at a constant air temperature of 13ºC, increasing relative humidity from 70% to 90% significantly enhances frost mass and density, while surface wettability plays a crucial role in influencing frosting propagation rates. These findings provide valuable insights into the complex dynamics of frost formation and inform effective strategies for frost management in industrial applications.