Frosting on CNT-based superhydrophobic surface

• Main Author: Teo, Ming Kai.
• Other Authors: Yang Chun, Charles
• Format: Final Year Project
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering::Mechanical engineering
• Online Access: http://hdl.handle.net/10356/54047
• Institution: Nanyang Technological University

Surface superhdrophobicity possesses the ability of self-cleaning due to its water repellency. Many methods of fabricating superhydrophobic surfaces have been developed over the years. In this present study, a simple method of developing such surfaces with Multi-walled Carbon nanotubes is proposed. The surface fabricated exhibits the two level roughness of micro-nanoscale hierarchical structures that resembles the bio-inspired lotus leaves, as can be seen from the scanning electron microscopy analysis. Contact angle measurements were carried out to characterize the various surfaces fabricated. Surface superhydrophobicity is also an important factor that influences the frost formation. However, it is evident that the influence of this effect is still not well understood as there are numerous controversies over it. To study this effect, observations of the initial frost growth and frost growth thickness for a prolong period of time were made under free convection conditions. The formation, geometrical shape of initial frost crystals and the frost thickness growth over time comparing both superhydrophobic and plain aluminum surfaces were presented. The heat transfer performance of the two surfaces with different structures and surface energy were discussed. This revealed that superhydrophobic surfaces with micro-nano hierarchical structures and low surface energy can degrade the heat transfer performance of dropwise condensation and delay initial frost growth. The experimental results showed that the condensate droplets formed on the superhydrophobic surface are smaller, more spherical and remained in its liquid state longer as compared to the plain aluminum surface. The characteristics of the superhydrophobic surfaces are not limited to the initial frost growth period but they also influences the later stages of frost formation over time. With an increase of contact angle, the potential barrier for frost nucleation and growth is increased. It was observed that the frost growth thickness is lower on the superhydrophobic surface having a higher contact angle than on the plain aluminum surface. However, this effect only extends to a certain degree, as substrate temperature approaches -20 degrees celsius such effect is observed to be less significant with lower temperatures.