Aluminum Nitride (AlN) Ceramic Surfaces for Enhanced Dropwise Condensation

Condensation is ubiquitous in a wide variety of industrial applications ranging from heating, ventilation and air conditioning (HVAC), to harvesting water from the atmosphere and thermal management of many devices. Dropwise (DwC) and filmwise (FwC) condensation are the two primary modes of condensation, and their dominance is governed by the wettability of the cooled surface. In DwC, the condensate forms droplets, which eventually coalesce with each other and leave the surface by gravity (if the surface is inclined). In FwC, a film of liquid is formed on the surface. From well-known theories of wetting and condensation, it has been established that DwC is more efficient than FwC. Therefore, surface engineering is warranted to enhance condensation heat transfer by promoting DwC. While numerous studies, including our own, have explored the role of wettability in condensation, creation of hydrophobic ceramic surfaces presents an interesting challenge. Ceramics, like Aluminum Nitride (AIN) (which are attractive due to their high thermal conductivity and combined high electrical resistance), are hard, brittle and chemically resistant, which presents difficulties in creating micro or nano scale roughness necessary to impart specific surface properties. In this study, the wettability (hy-drophobic/superhydrophilic) characteristics of AlN are modified with ultimate goal to obtain the desired mode of condensation and increase the heat transfer from the surface. An environmental chamber is used to investigate the condensation performance of wettability-altered AIN plates over a range of wettability and environmental conditions. The temperature and relative humidity of the chamber are set at desired levels and the condensation heat transfer coefficients are estimated using the Inverse Heat Transfer (IHT) methodology. The study provides a step towards efficient and reliable wettability engineering of ceramic surfaces, which can be used in numerous scenarios that require thermally conductive, chemically resistant or hard surfaces that do not wear over extended periods of operation.