Executive Summary : | Condensation and water freezing on solid surfaces are ubiquitous in nature. It is well-established fact that the condensation efficiency in a pure steam environment is way better in dropwise condensation (DWC) than the filmwise condensation (FWC). However, even the presence of a small quantity (around 0.5%) of non-condensable gases (NCG) could reduce the heat transfer efficiency by 50% compared to a pure steam environment due to the formation of a thin NCG diffusion layer. Achieving efficient and stable DWC in presence of NCG is quite difficult as the interplay among several factors, specifically, surface texture and its chemistry; vapour diffusion flux within the NCG layer; condensate drop mobility, and moreover surface durability ultimately governs the fate of this phenomenon. Further, at very low surface temperature, condensate drop will start to freeze either via heterogeneous or homogeneous nucleation depending on different atmospheric conditions and surface properties. Thus, the prediction of the onset of droplet freezing is quite difficult and at the same time intriguing. The nature-inspired (e.g. lotus leaves, butterfly wings) superhydrophobic surfaces have been widely used in the past for investigating both dropwise condensation as well as icing phenomena due to their excellent water repellency and low contact angle hysteresis. However, most of the studies used per-fluorinated synthetic chemicals (PFCs) for reducing surface energy and thereby achieving superhydrophobicity. These PFCs are, however, not environment friendly and hazardous to human health. Hence, the present work aims at the fabrication of a durable, scalable, water repellent surface in a green approach. Two different types of surfaces, namely, slippery hydrophobic surface (based on Metal Organic Framework) and superhydrophobic surface (based on fatty acids) will be fabricated to promote stable DWC in presence of NCG and freezing delay. The real-time experimental images will further be used to develop a ‘data-driven model’ with an expectation that the developed model could precisely predict the onset of droplet freezing under different environmental conditions. |